INTRODUCTION

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1. INTRODUCTION

1.1 History :-

The primordial Greek mathematician Archimedes invented a type of an elevator

before 230 B.C. It uses ropes and pulleys and it could lift one person. The elevators were

in use in the early 1800’s. By 1840 hydraulic and steam powered elevators which were

ropes very slow and the carrying them often broke.

The first elevator with a safety device was invented by Elisha G. Otis in 1854,

which was having an automatic safety device, which prevent the elevator from falling in

case of the rope breaks. The world’s first electric lift started working in 1889. Automatic

elevators were introduced in the residential buildings in 1890’s.

1.2 Importance of Elevator System :-

In the 1800s, new iron and steel production processes revolutionized the world of

construction. With sturdy metal beams as their building blocks, architects and engineers

could erect monumental skyscrapers hundreds of feet in the air.

These towers would have been basically unusable if it weren't for another technological innovation that came along around the same time. Modern elevators are the crucial element that makes it practical to live and work dozens of stories above ground. High-rise cities like New York absolutely depend on elevators. Even in smaller multi-story buildings, elevators are essential for making offices and apartments accessible to handicapped people. An elevator (lift in British English) is a type of vertical transport equipment that efficiently moves people or goods between floors (levels, decks) of a building, vessel, or other structure. Elevators are generally powered by electric motors that either drive traction cables or counterweight systems like a hoist, or pump hydraulic fluid to raise a cylindrical piston like a jack.

In agriculture and manufacturing, an elevator is any type of conveyor device used to lift materials in a continuous stream into bins or silos. Several types exist, such as the chain and bucket bucket elevator, grain auger screw conveyor using the principle of Archimedes' screw, or the chain and paddles or forks of hay elevators. Whether it be a residential or commercial application, every day many people depend on the safe and reliable operations of vertical transportation systems. It is of critical importance to the

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owners and ultimately to the tenants, guests or visitors who travel throughout residences and buildings each day. Deciding on a competent maintenance company is a complicated decision. Elevator maintenance can be provided by manufacturers, installation companies or Independents.

Today, many new elevators run on proprietary computer-based software that requires specialized tools for proper maintenance that only the manufacturer or company that installed the lift can provide. If your home or building has proprietary equipment you will have limited maintenance service options and generally will have to pay a premium for elevator maintenance. One advantage of using OEM (Original Equipment Manufacturer) maintenance is the ability to provide spare parts quickly and reduce overall downtime for repairs. In addition, with OEM manufacturer maintenance you deal with the organization that designed the equipment and know it operating systems the best. Usually, manufacturer's maintenance contracts are the most risk-free choice but you may pay a premium.

Elevator manufacturing companies actively pursue maintenance contracts for elevator equipment they did not manufacture. The service contracts they offer are comparable to service contracts you would consider with the actual OEM manufacturer of equipment in your home or building. An advantage of using another manufacturer may be to save money or obtain better service in a specific geographic area. Most companies and manufacturers also offer a variety of discounts for contracts covering multiple buildings with the same owner or property manager.

Independent elevator maintenance companies are located in most areas of the country. Independents often charge less for their maintenance programs than manufacturers. When considering an independent you will want to investigate the company's level of technical expertise of your specific equipment and ability to provide spare parts to avoid extended downtimes.

Large facilities such as universities and medical facilities provide in-house maintenance for elevator equipment to reduce overall maintenance costs. The decision to self maintain elevator equipment should be based on local code requirements, economics and the availability of skilled labor. Other factors to consider include the ability to obtain spare parts and manage major components repairs. Due to the increased liability exposure and technical expertise needed to maintain the elevator equipment properly, using other maintenance options is recommended for most customers. Many elevator companies will not service elevator equipment that is being maintained by non-certified elevator mechanics without conducting a complete inspection and bringing it up to a maintainable level. Sometimes, it may be impossible to take on a service contract due to increased exposure to lawsuits.

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Knowing the different types of elevator contract options can greatly increase the chances of saving money and finding a maintenance agreement that meets your home or building's requirements. The more risk you are willing to assume, the lower the cost of services will be. Most elevator companies offer different types of elevator maintenance contracts. These contracts offer you a range of coverage options and discount opportunities.

Survey and Report Contract :-

Coverage under a survey and report contract consists of quarterly, semi-annual or annual inspection of all major equipment components. The inspection does not include maintenance, repair work or dismantling equipment that necessitate elevator mechanics. Maintenance or replacement recommendations may be completed by the owner or by selected contractors under the property manager's coordination. Most jurisdictions require regular basic servicing so this type of contract is not an option. This type of contract also makes it extremely difficult for a building owner to avoid liability if an accident should occur.

Oil and Grease (O & G) or Examination & Lubrication Contract :-

O & G contracts include lubrication of moving parts and minor adjustment on a regularly scheduled basis. When additional services are needed, the service company reports potential problems to the customer with an estimated cost to then schedule all repairs, once approved, to be paid by the home or building owner. The cost for the O & G contract is relatively low but when you include repairs, the entire yearly cost is usually much higher and more complicated to budget. O & G agreements also generate additional paper work, as the customer must coordinate with the service company on all repairs. Liability exposure to claims in the event of shut downs, accidents or injuries are even greater because the owner is responsible for the approval of having parts repaired and replaced. Customer satisfaction with this type of agreement is usually very low.

A variation of an O & G contract lists specific items of equipment that are covered and not covered in the contract, such as controllers, elevator machines, motor-generator sets, and cables, etc. This type of contract will only have value if the contract clearly stipulates the work to be covered and the parts to be supplied including frequency of examinations and trouble calls to be answered. These service agreements also generate additional paperwork and the customer must coordinate with the service company on what is covered in the contract and what will be done under repair orders at a later date. It is important to know what is and what is not covered in this variation of service contract.

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Full Maintenance Contract or Agreement (FMC or FMA) :-

A full maintenance contract or agreement is written to allow the elevator service company to take total care of the elevator equipment identified in the maintenance agreement. This contract acts like an insurance policy and allows the home or building owner to budget total yearly costs and eliminate concerns relating to elevator repairs as they become necessary. Shut downs are limited because the maintenance contractor assumes all responsibility and determines the amount of service visits required to keep the elevator system operating safely. If an accident should occur, the elevator maintenance company may be responsible for defending itself against accident claims and will exhaust every effort to ensure safe operating condition.

Once a maintenance contract has been chosen that will work best for your elevator you will need to find an elevator company. The company you select will then perform maintenance services under the type of contract you have specified. But here's where your troubles can begin. You must understand what is not covered and how those services will be billed and what steps can be taken to control overall maintenance costs.

1.3 Construction of Elevator System :-

Most of the elevators operate automatically. A person brings an elevator to a

certain floor by pushing a button that has been installed on the wall outside the shaft or

inside the cabin. Most of the elevators in buildings of 5 or more floors are lifted by steel

cables. There are two types of traction elevators, gearless and geared traction.

Gearless traction systems are employed in the buildings of more than 10 floors. They

travel at 120 to 600 meters per minute. The hoisting ropes lift the cage, fit around a sheave

(pulley) that is connected to the driving motor.

Geared traction elevators travel at a speed of 140 meters per minute. The operation is

similar to that of a gearless traction system. However, the motor of geared traction

elevator operates a reduction gear, which turns the sheave. This gear decreases the speed

at which the sheave would otherwise turn. Fig. (1.1) shows typical elevator system

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ELEVATORS AND CONVEYING SYSTEMS GENERAL :-

This chapter establishes the minimum safety requirements for, and governs the

design, construction, installation, alteration, maintenance, inspection, test and operation

of,elevators, dumbwaiters, escalators, moving walks, industrial lifts and loading ramps,

mechanical

parking equipment, console or stage lifts, power operated scaffolds, amusement

devices, and special hoisting and conveying equipment. This chapter and all the

provisions of this code for new installations shall also apply to elevators in existing

buildings moved to new hoistways. High-rise buildings elevators shall also conform to the

provisions of Section 403 of this code.

Exception: Personnel and material hoists used for construction operations subject

to the Except as otherwise provided for in this code, the design, construction, installation,

alteration, repair and maintenance of elevators and other conveying systems and their

components shall conform .

A change in use of an elevator from freight to passenger, passenger to freight, or

from one freight class to another freight class shall comply No piping or ductwork of any

kind shall be permitted within hoistway or elevator enclosures except:

1. As required for the elevator installation; and

2. Low voltage wiring less than 50 volts required for fire alarm systems required

by this code. A mirror shall be installed in each self-service passenger elevator in multiple

dwellings. Such mirror shall be affixed and maintained in a manner sufficient to enable

persons entering such elevator to view the inside thereof prior to entry to determine

whether any person is in the elevator Car switch operation. Elevators with car

switch operation (manual operation) shall be provided with a signal system by means of

which signals can be given from any landing whenever the elevator is desired at that

landing.

The following devices shall be prohibited

1.The installation of manlifts is prohibited.

2.The installation of sidewalk elevators located outside the street line is prohibited

Approved equipment Buffers, PA interlocks, elevator entrances, wedge shackles, and

elevator governors shall be approved by the commissioner. 6

Construction documents. Applications for elevator, escalator, moving walkway

and stairway, dumbwaiter, and similar equipment shall contain construction documents

that include the following:

1. The location of all machinery, switchboards, junction boxes, and reaction

points, with loads indicated;

2. The details of all hoistway conditions including bracket spacing;

3. The estimated maximum vertical forces on the guide rails on application of the

safety device;

4. In the case of freight elevators for class B or C loading, the horizontal forces on

the guide-rail faces during loading and unloading; and the estimated maximum

horizontal forces in a postwise direction on the guide-rail faces on application

of the safety device;

5. The size and weight per foot of any rail reinforcements where provided;

6. Compliance with the accessibility features of this code;

7. The details of capability of the withstanding forces (impact) on door entrance

assembly and retaining devices;

8. The withstanding hourly fire rating of the hoistway and the hoistway door

assembly;

9. The impact loads imposed on machinery and sheave beams, supports and floors

or foundations;

10. The impact load on buffer supports due to buffer engagement at the maximum

permissible speed and load;11. Where compensation tie down is applied, the

load on the compensation tie down supports; and

12. The total static and dynamic loads from the governor, ruper and tension

system.

HOISTWAY ENCLOSURES :-

Hoistway enclosure protection. Elevator, dumbwaiter and other hoistway

enclosures shall have a fire-resistance rating not less than that specified shall be

constructed in accordance. Openings in hoistway enclosures shall be protected as 7

Hardware on opening protectives shall be of an approved type installed as tested, except

that approved interlocks, mechanical locks and electric contacts, door and gate electric

contacts and door-operating mechanisms shall be exempt from the fire test requirements.

Number of elevator cars in a hoistway. Where four or more elevator cars serve all

or the same portion of a building, the elevators shall be located in at least two separate

hoistways. Not more than four elevator cars shall be located in any single hoistway

enclosure. Elevators that service different risers shall be located in separate hoistways.

An approved pictorial sign of a standardized design shall be posted adjacent to

each elevator call station on all floors instructing occupants to use the exit stairways and

not to use the elevators in case of fire. The sign shall read: in fire emergency, do not use

elevator. use exit stairs. The emergency sign shall not be required for elevators that are

part of an accessible means of egress complying. Elevator car to accommodate ambulance

stretcher. In buildings five stories in height or more, at least one elevator shall be provided

for Fire Department emergency access to all floors. Emergency power shall be provided in

accordance. Such elevator car shall be of such a size and arrangement to accommodate a

24-inch by 76-inch (610 mm by 1930 mm) ambulance stretcher in the horizontal, open

position and shall be identified by the international symbol for emergency medical

services (star of life). The symbol shall not be less than 3 inches (76 mm) high and shall

be placed on both jambs of the hoistway entrances on each floor.

Emergency doors. Where an elevator is installed in a single blind hoistway or on

the outside of a building, there shall be installed in the blind portion of the hoistway or

blank face of the building, an emergency door in accordance. Common enclosure with

stairway. Elevators shall not be in a common shaft enclosure with a stairway.

ELEVATOR EMERGENCY OPERATIONS :-

Emergency power. In buildings and structures where emergency power is required

or furnished to operate an elevator, the operation shall be in accordance.

Manual transfer. Emergency power shall be manually transferable to all elevators in each

bank.

One elevator. Where only one elevator is installed, the elevator shall automatically

transfer to emergency power within 60 seconds after failure of normal power. 8

Two or more elevators. Where two or more elevators are controlled by a common

operating system, all elevators shall automatically transfer to emergency power within 60

seconds after failure of normal power where the emergency power source is of sufficient

capacity to operate all elevators at the same time. Where the emergency power source is

not of sufficient capacity to operate all elevators at the same time, all elevators shall

transfer to emergency power in sequence, return to the designated landing and disconnect

from the emergency power source. After all elevators have been returned to the designated

level, at least three elevators shall remain operable from the emergency power source.

Where emergency power is connected to elevators, the machine room ventilation

or air conditioning shall be connected to the emergency power source. Fire fighters’

emergency operation. Elevators shall be provided with Phase I emergency recall operation

and Phase II emergency in-car operation in accordance. Elevator in readiness.

Requirements for elevator in readiness shall be as defined in High-rise buildings. Except

as provided in high-rise buildings as defined . all floors shall be served by at least one

elevator that shall be kept available for immediate use by the Fire Department during all

hours of the night and day, including holidays, Saturdays and Sundays. There shall be

available at all times a person competent to operate the elevator. However, an attendant

shall not be required for buildings with occupied floors of 150 feet (45 720 mm) or less

above the lowest level of the fire department vehicle access that have elevators with

automatic or continuous pressure operation with keyed switches meeting the requirements

as modified by so as to permit sole use of the elevators by the Fire Department. Number

of Elevators. A number of elevators shall be kept available at every floor for the sole use

of the Fire Department as required This requirement shall apply to the following types of

buildings:

1. High-rise buildings with occupancies classified in Groups A, B, E, I, F, H, M

and S;

2. Buildings with Group B occupancies with a gross area of 200, 000 square feet

( 18581 m2 );

3. Buildings with a main use or dominant occupancy in Group R-1 or R-2.

Three or fewer elevators. Where a floor is serviced by three or fewer elevator

cars, every car shall be kept available for sole use by the Fire

Department.3003.3.2.2 More than three elevators. Where a floor is serviced by9

more than three elevator cars, at least three elevator cars with a total rated

load capacity of not less than 6,000 pounds (2722 kg) shall be kept available for sole

use by the Fire Department. Such cars shall include not more than two cars that

service all floors and at least one other car in another bank servicing that floor. If

the total load capacity of all cars servicing the floor is less than 6,000 pounds (2722 kg),

all such cars shall be kept available for sole use by the Fire Department. Operation and

control. Elevators that are kept for the sole use of the Fire Department and that have

automatic or continuous pressure operation shall be controlled by keyed switches meeting.

Other elevator cars. In high rise buildings classified in occupancy groups A, B, E, F, H, I,

M and S, in low-rise buildings classified in occupancy group B with a gross area of

200,000 square feet (18 581 m2) or more and in buildings classified in occupancy group

R-1or R-2, all other automatically operated cars shall have manual operation capability.

HOISTWAY VENTING :-

Plumbing and mechanical systems. Plumbing and mechanical systems shall not be

located in an elevator shaft.Exception: Floor drains sumps and sump pumps shall be

permitted at the base of the shaft provided they are indirectly connected to the plumbing

system.

Control of smoke and hot gases. Hoistways of elevators shall be provided with any one of

the following means to prevent the accumulation of smoke and hot gases in case of fire in

Accordance.Vents in the hoistway enclosures. Hoistway enclosures may be vented in

accordance with the following:

1. Location of vents:

1.1. The vents in the side of the hoistway enclosure below the elevator machine

room floor or in the roof of the hoistway shall open either directly to the outer

air or through non-combustible ducts to the outer air.

1.2. The vents in the wall or roof of an overhead elevator machine room through

the smoke hole in the top of the elevator hoistway shall be vented to the outer

air through non-combustible ducts.10

2. Area of vents. The area of vents in the hoistway or the elevator machine room

and the smoke hole shall be not less than 3½ percent of the area of the hoistway

nor less than square feet (0.28 m2) for each elevator car, whichever is greater.

Such vents Shall comply with the following requirements:

2.1. Open Vents. Of the total required vent area, not less than one-third shall be

permanently open or equipped with an openable hinged damper. The smoke

hole shall be permanently open.

2.2. Closed Vents. The two-thirds closed portion of the required vent area either in

the hoistway enclosure or in the elevator machine room may consist of windows

or skylights glazed with annealed glass not more than ⅛-inch (3.2 mm) thick.

A closed damper that opens upon the activation of a smoke detector placed at the

top of the hoistway shall be considered closed.

Mechanical ventilation of the hoistway enclosure. Hoistway enclosures may be

mechanically vented. The system of mechanical ventilation shall be of sufficient capacity

to exhaust at least 12 air changes per hour of the volume of such hoistways through a roof

or an approved location on an exterior wall other than the lot line wall. Such system shall

comply with the following requirements:

1. The smoke detector shall be placed at the top of the hoistway and shall activate

the mechanical ventilation system.

2. Such mechanical ventilation system shall not pass through the overnight

sleeping areas of a hotel, multiple dwelling, hospital, or similar buildings.

3. Such mechanical ventilation system shall be equipped with a manual shut-off in

or near the elevator control panel at the designated level.

Air pressurization of hoistway enclosure. Hoistways may be air pressurized.Where

such system is utilized, the air shall not cause erratic operation of the landing or car door

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equipment, traveling cables, selector tapes, governor ropes, compensating ropes, or any

other components sensitive to excess movement or deflection.

Alternate means. The commissioner may accept alternate means to prevent the

accumulation of smoke and hot gases in the hoistways and machine rooms in case of fire.

CONVEYING SYSTEMS :-

Conveying systems shall comply with the provisions of this section.Escalators and

moving walks. Escalators and moving walks shall be constructed of approved

noncombustible and fire-retardant materials. This requirement shall not apply to electrical

equipment, wiring, wheels, handrails and the use of 1/28-inch (0.9 mm) wood veneers on

balustrades backed up with noncombustible materials.

Enclosure. Escalator floor openings shall be enclosed except where Exception 2 is

satisfied. Where provided in below-grade transportation stations, escalators shall have a

clear width of 32 inches (813 mm) minimum. Exception: The clear width is not required

in existing facilities undergoing alterations.Conveyors and related equipment shall comply

Conveyors and related equipment connecting successive floors or levels shall be enclosed

with fire barrier walls and approved opening protectives complying Conveyor safeties.

Power-operated conveyors, belts, and other material-moving devices shall be equipped

with automatic limit switches, which will shut off the power in an emergency and

automatically stop all operation of the device.Amusement devices shall also comply with

rules of the department.

MACHINE ROOMS :-

An approved means of access shall be provided to elevator machine rooms and

overhead machinery spaces. Elevator machine rooms that contain solid-state equipment

for elevator operation shall be provided with an independent ventilation or air-

conditioning system to protect against the overheating of the electrical equipment. The

system shall be capable of maintaining temperatures within the range established for the

elevator equipment. The elevator machine room serving a pressurized elevator hoistway

shall be pressurized upon activation of a heat or smoke detector located in the elevator 12

machine room. Machine rooms and machinery spaces. Elevator machine rooms and

machinery spaces shall be enclosed with construction having a fire-resistance rating not

less than the required rating of the hoistway enclosure served by the machinery. Openings

shall be protected with assemblies having a fire-resistance rating not less than that

required for the hoistway enclosure doors.

Sprinklers are not permitted in elevator machine rooms. Plumbing systems not

related to elevator machinery shall not be located in elevator equipment rooms. Elevator

machinery noise control in multiple dwellings. Gear-driven machinery, gearless

machinery, and motor generators located in an elevator machinery room or shaft on a roof,

or on a floor other than a floor on grade, shall be supported on vibration isolator pads

having a minimum thickness of ½ inch (12.7 mm).

SERVICE EQUIPMENT CERTIFICATES :-

No service equipment shall be placed in operation until a service equipment

certificate of compliance has been obtained in accordance with the provisions of this code.

Posting of inspection certificate. At the time a service equipment certificate of compliance

is issued, an inspection certificate issued by the commissioner shall be posted. No such

inspection certificate shall be issued for elevators that are not subject to periodic

inspections pursuant to this code. The inspection certificate shall be in such form as the

commissioner shall determine by rule and shall be posted in a frame with a transparent

cover in the car of every passenger and freight elevator and on or near every escalator and

moving walk and power operated scaffold.

Alternate posting locations. In lieu of posting the inspection certificate in those

locations specified in this section, the inspection certificate may be kept in the on-site

building manager’s office. In such case, the building manager’s office must be open

during normal business hours. In addition, notice must be posted in each location and kept

in a frame with a transparent cover, or a plaque with an indelible inscription, stating that

the inspection certificate is located in the building manager’s office and identifying the

location of such office.

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Temporary use certificates. The commissioner may issue temporary use

certificates for any equipment or device regulated by this code, except power-operated

scaffolds, provided that such partial use and operation may be made safely and without

endangering public health, safety, and welfare and provided further that such temporary

use certificate shall not be issued for a period of more than thirty calendar days, subject to

renewal for additional thirty-day periods at the discretion of the commissioner. Temporary

use certificates for elevators shall also be conditioned upon compliance with the

following:

1. The class of service to be permitted shall be designated on the temporary use

certificate.

2. The hoistway shall be enclosed throughout in an enclosure complying or with a

temporary enclosure in accordance with the requirements for workers'

elevators (temporary elevators) of the Industrial Code of the State of New

York, No.23.Posting of temporary use certificate. The temporary use certificate

shall be posted in a conspicuous location on, or adjacent to, the device covered

by the certificate and shall state that the device has not been finally approved

by the commissioner.

ELEVATOR, AMUSEMENT, AND OTHER DEVICE OPERATORS :-

With the exception of automatic operation, continuous pressure elevators and

sidewalk elevators, every passenger and freight elevator with a rise of more than one story

shall be in the charge of a designated competent operator, who shall be at least 18 years

old, free from serious physical or mental defects, and selected with consideration of his or

her abilities to perform his or her duties in a careful and competent manner. Such

designated competent operator shall be instructed in accordance with requirements of

department rules.

Operators of amusement devices shall meet the requirements of rules of the

department. Other devices regulated by this code shall, when deemed necessary by the

commissioner to protect public safety, be in the charge of a designated competent operator 14

conforming to such qualifications as the commissioner may prescribe, except that

operators for workers' hoists shall be assigned as required by the applicable provisions. If

the commissioner finds that any person engaged in operating an elevator, amusement, or

other device is not competent to operate the elevator, amusement or other device, the

owner, agent or lessee of such elevator, amusement, or other device shall, upon notice

from the commissioner, discontinue the operation of such device by such operator.

ELEVATOR BEING SERVICED :-

When an existing or new automatic passenger elevator in any building or structure

is being serviced by an elevator maintenance company, elevator maintenance personnel,

or other person and there are no maintenance personnel available to remain in the elevator

car, “CAUTION” sign tapes shall be placed across the car door jamb. One strip of

“CAUTION” sign tape shall be placed at a height of 18 inches (457 mm) above the car

floor and another strip of “CAUTION” sign tape shall be placed at a height of 54 inches

(1372 mm) above the car floor.The “CAUTION” sign tape shall be 3 inches (76 mm) in

width with the words “CAUTION – DO NOT ENTER” repeated every 6 inches (152

mm). The lettering shall be black on yellow background. The letters shall be at least 2

inches (51 mm) high.

ACCIDENTS :-

The owner of any device regulated by this chapter shall promptly notify the

commissioner of every accident involving injury to any person requiring the services of a

physician or damage to property or to apparatus exceeding one thousand dollars on, about,

or in connection with such equipment, before commencing any repairs and shall afford the

commissioner every facility for investigating such accident or damage. The commissioner

shall make an investigation immediately thereafter, and shall prepare a full and complete

report of such investigation. Such report shall give in detail all material facts and

information available and the cause or causes as far as they can be determined. Such

report shall be a public record. When an accident involves the failure or destruction of any 15

part of the construction or operating mechanism of such equipment, no such equipment

shall be used until it has been made safe, and re-inspected by the commissioner; and the

commissioner may order the discontinuance of such equipment until a new service

equipment certificate has been issued by him or her for its use. No part shall be removed

from the premises of the damaged construction or operating mechanism until permission

to do so has been granted by the commissioner.

EXISTING INSTALLATIONS :-

Existing installations shall be modified in accordance with department rules.

inspection and testing elevators and Conveying Systems. Inspection and testing of

elevators and conveying systems shall be in accordance. Amusement devices. Inspection

and testing of amusement devices shall comply with rules of the department.

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The main parts of the elevator system are as follows:

Fig.(1.1): Elevator System

1) Control system : -

It gives smooth and fast operation of elevator system. It is the heart of the elevator

system. This system isolates the PLC from power supply of driving motor. Any faults in

the power supply side are prevented to appear on the PLC as the power levels at which

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both circuits work is very much different. Also it controls the UP and DOWN motion of

the elevator.

2) The driving motor : -

It gives the power to the cage for UP and DOWN motion of the elevator. This

motor is usually an induction motor with the gear reduction arrangement.

3) Sheave : - It is just a pulley with grooves around the circumference. The sheave grips the

hoist ropes, so when you rotate the sheave, the ropes move too. The sheave is connected to

an electric motor. When the motor turns one way, thesheave raises the elevator; when the

motor turns the other way, the sheave lowers the elevator.

4) The Counter Weight :-

The counter weight is nearly equal to the weight of the cage and about half of its

maximum passenger load. This decreases the load to be driven by the motor.

5) The Guiding Rails :-

These rails help the elevator move easily throughout. These rails are usually

applied grease in order to reduce the friction between the rails and the cage.

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19

LITERATURE

SURVEY

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2. LITERATURE SURVEY

2.1 Literature Review :-

Study project on Microcontroller Based digital display of time table

Being related to the syllabus of microcontroller, microcontroller based was

the first choice. We contacted different people having knowledge about

microcontroller. After gathering the information we came to know that there was

little application of Electrical engineering. So the project was rejected.

Study project on Load flow analysis in MSEB

The entire load flow analysis was carried out in this topic. The project was

rejected as the permission was not granted by MSEB.

Project on distance protection of transmission line

We decided to do project on this topic but we came to know that this project

was already done by our previous batch so the project was rejected.

2.2 Finalization of the project :-

The technologies like PLC are emerging these days, which necessitates us to improve

the current equipment into more sophisticated and technically advanced form. The

elevator is one of such commodity. Thus we finalized project on PLC Based Elevator

Control.

2.3 Market Survey :-

The market survey includes gathering information about following devices which are

going to be used in the project

1) DC Motor2) Limit switches3) Push buttons4) Toggle switches5)

The output of PLC is 24 V DC; the motor of proper rating was not available.

So as per the requirement of PLC the design of motor was done.

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PROBLEM DEFINATION

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3.PROBLEM DEFINATION

3.1 Objective of System :-

The objective of the project is the design and implementation of a three-level

elevator system controlled by a PLC.

3.2 Specification of System :-

Sr.No. Component Rating Quantity

1 Allen Bradley Micrologix 1400 DI -20, DO-12, 24V DC 1

2 DC Motor 24V DC, 30 rpm 1

3 Relay 24V DC , 2 C/O 2

3 Limit Switch 24V DC, 1NO,1NC 3

4 Push Button 24V DC, NO 3

5 Toggle Switch 24V DC 3

6 Pulley V-Grooved Diameter

6.5cm

2

7 Rope 8 Ft. 1

8 Iron Frame 1.5*2*4

Table 3.1 System Specifications

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DESIGN OF SYSTEM

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4. DESIGN OF SYSTEM

4.1 Hardware Design :-

4.1.1 Block Diagram :-

Working of elevator system is based on co-ordination of PLC with Hardware of

the elevator system. Fig (4.1) shows schematic block diagram of elevator system.

Hardware of Elevator system consists three main parts namely,

i) Micrologix 1400.

ii) Elevator.

iii) Control Panel.

.

Fig.(4.1)Schematic Block Diagram of Elevator System

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4.1.2 Elevator model :-

The basic aim in fabricating the elevator model is that it should be strong, sturdy

and overall cost effective. Sticking to this, we have decided to use mild steel (MS.),

instead of aluminum or wood. Aluminum structure is difficult to weld and is costly.

Experts are needed for welding aluminum materials. Also it is very hard to maintain the

sturdiness if nuts and bolts are used instead of weld. Wooden structure s flimsy and hence

it is not worthy. The only choice for us is to use MS, which can be easily fabricated,

welded; never the less the structure thus obtained will be a bit heavy.

1) Main Frame :-

To attain overall sturdiness the main frame is made up of L shape MS bars. The

frame measures about 1.5(L)x2(W)x4(H) ft.

2) The Elevator Cage :-

It is also made up of Wooden and measures about 15 x15x 20 cm. The elevator

cage moves in the main frame with the help of fiber clips and the fiber bars acting as

guidelines.

3) Counter Weight :-

It approximately balances the weight of cage. The counter weight is chosen in such

a way that the load on motor be minimized and thus motors function is only to transfer

load from one side to another. If counter weight is not taken into account, then winding

pulley arrangement is to be implemented. These will increase the load on motor and there

is possibility of misalignment of motor shaft.

4) Driving Motor :-

The motor used is permanent magnet direct current motor (PMDC), rated

for 24 volts. The rated speed of motor is approximately 30 rpm.

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4.1.3 Fabrication detail

Frame :-

Dimensions :- Height: 4 ft.

Width: 1.5 ft.

Depth: 2 ft.

Weight :- 12 kg

Material :- M.S.Angle Bars: 2 x 2x 2 cm.

Plywood: 1) Top Side: 2 x 1.5 ft

2) Bottom Side: 2 x 1.5 ft

3) Front Side: 1.5 x 4 ft

Plywood thickness : -12 mm

Elevator cage :- Height: 20cm

Width: 15cm

Depth: 15cm

Weight: 1 kg

Material:Plywood

Counter weight :- Weight: 1.2 kg.

Pulleys:- Motor shaft pulley: V - grooved diameter 6.5cm

Counter weight pulley: V- grooved diameter 6.5cm.

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4.1.4 Photographs of System :-

Fig (4.2)Front View

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Fig (4.3)Side View

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Fig(4.4)Top View

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4.1.5 Control circuit :-

The whole design of the elevator depends on the control circuit. It consists mainly;

Limit Switches

Push Buttons (Call Buttons).

Toggle Switches (Door Switches).

+

1) Limit Switches :-

To sense the position of the elevator, that is the status on which floor it is situated

limit switches are mounted on every floor.

Fig. (4.5): Limit Switches Circuit

Fig. (4.5) shows how all limit switches are interfaced with PLC. The construction

of the limit is very simple. The limit switches have the roller contacts on their tips.

These can comfortably operate during the motion of the elevator in both the

directions i.e. up and down. When the elevator starts moving, on every floor it will operate

the limit switch. This will give a signal out to the PLC, with which the status check will be

done by the PLC. This will give the exact position of the elevator.

When the destination to the elevator is given by the PLC, it will make the appropriate limit switch ON i.e. it will only sense the limit switch on that floor only. This will make the elevator to move on to the destination correctly. The logic of up- collecting

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and down collecting is also incorporated in the programming of the PLC. This will enable the PLC to take input signals in between current operation. In electrical engineering a limit switch is a switch operated by the motion of a machine part or presence of an object.

They are used for control of a machine, as safety interlocks, or to count objects passing a point. A limit switch is an electromechanical device that consists of an actuator mechanically linked to a set of contacts. When an object comes into contact with the actuator, the device operates the contacts to make or break an electrical connection.

Limit switches are used in a variety of applications and environments because of their ruggedness, ease of installation, and reliability of operation. They can determine the presence or absence, passing, positioning, and end of travel of an object. They were first used to define the limit of travel of an object; hence the name "Limit Switch".

A limit switch with a roller-lever operator; this is installed on a gate on acanal lock, and indicates the position of a gate to a control system.

Standardized limit switches are industrial control components manufactured with a variety of operator types, including lever, roller plunger, and whisker type. Limit switches may be directly mechanically operated by the motion of the operating lever. A reed switch may be used to indicate proximity of a magnet mounted on some moving part. Proximity switches operate by the disturbance of an electromagnetic field, by capacitance, or by sensing a magnetic field.

Rarely, a final operating device such as a lamp or solenoid valve will be directly controlled by the contacts of an industrial limit switch, but more typically the limit switch will be wired through a control relay, a motor contactor control circuit, or as an input to a programmable logic controller.

Miniature snap-action switch may be used for example as components of such devices as photocopiers, computer printers, convertibletops or microwave ovens to ensure internal

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components are in the correct position for operation and to prevent operation when access doors are opened. A set of adjustable limit switches are installed on a garage door opener to shut off the motor when the door has reached the fully raised or fully lowered position. A numerical control machine such as a lathe will have limit switches to identify maximum limits for machine parts or to provide a known reference point for incremental motions.

2) Push Button :-

Push Buttons are used as Call Buttons. There are total 3 call buttons are provided.

On each floor one call switch is provided. Fig.(4.6) shows interfacing of inner and outer

call switches panel with PLC.

While moving from 1 st floor to 3rd floor if we press the call button on 2ndfloor

and if lift is still to come to 2nd floor, then it will not stop on the 2nd floor, it will go to

3rdfloor and then come back to 2nd floor. For the simplicity we have not employed first

come first serve method.

Before proceeding to the next floor the elevator will stop for a given predetermined delay. These anti-co operations are done with help of limit switches. A push-button (also spelled pushbutton) or simply button is a simple switch mechanism for controlling some aspect of a machine or aprocess. Buttons are typically made out of hard material, usually plastic or metal. The surface is usually flat or shaped to accommodate the human finger or hand, so as to be easily depressed or pushed. Buttons are most often biased switches, though even many un-biased buttons (due to their physical nature) require a spring to return to their un-pushed state. Different people use different terms for the "pushing" of the button, such as press, depress, mash, and punch.

Uses :-

The "push-button" has been utilized in calculators, push-button telephones, kitchen appliances, and various other mechanical and electronic devices, home and commercial.

In industrial and commercial applications, push buttons can be connected together by a mechanical linkage so that the act of pushing one button causes the other button to be released. In this way, a stop button can "force" a start button to be released. This method of linkage is used in simple manual operations in which the machine or process have no electrical circuits for control.

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Pushbuttons are often color-coded to associate them with their function so that the operator will not push the wrong button in error. Commonly used colors are red for stopping the machine or process and green for starting the machine or process.

Red pushbuttons can also have large heads (called mushroom heads) for easy operation and to facilitate the stopping of a machine. These pushbuttons are called emergency stop buttons and are mandated by the electrical code in many jurisdictions for increased safety. This large mushroom shape can also be found in buttons for use with operators who need to wear gloves for their work and could not actuate a regular flush-mounted push button. As an aid for operators and users in industrial or commercial applications, a pilot light is commonly added to draw the attention of the user and to provide feedback if the button is pushed. Typically this light is included into the center of the pushbutton and a lens replaces the pushbutton hard center disk. The source of the energy to illuminate the light is not directly tied to the contacts on the back of the pushbutton but to the action the pushbutton controls. In this way a start button when pushed will cause the process or machine operation to be started and a secondary contact designed into the operation or process will close to turn on the pilot light and signify the action of pushing the button caused the resultant process or action to start.

In popular culture, the phrase the button (sometimes capitalized) refers to a (usually fictional) button that a military or government leader could press to launch nuclear weapons.

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.

Fig. (4.6) Call Switches Circuit

3) Toggle Switches :-

Instead of providing doors on each floor we have provided toggle switch on each

floor for simplicity. When all toggle switches are ON indicates that all doors are closed

while any toggle switch is OFF indicates that door on that respective floor is open. Fig.

(4.7) shows indicate that how door simulated switches are connected to the PLC.

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Fig. (4.7): Door Switch Circuit

The door switches are simulated with help of the toggle switches, connected in series so that it will give out a signal if any door of the elevator is open. If any of the doors is open then the elevator will not operate, until and unless that door is closed. This gives an additional safety feature that if anybody opens the door during elevator operation the lift will stall and after closing the door it run again. Electrical switches. Top, left to right: circuit breaker,mercury switch, wafer switch, DIP switch, surface mount switch, reed switch. Bottom, left to right: wall switch (U.S. style), miniature toggle switch, in-line switch, push-button switch, rocker switch, microswitch.

In electrical engineering, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another.

Description :-

The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts, which are connected to external circuits. Each set of contacts can be in one of two states: either "closed" meaning the contacts are touching and electricity can flow between them, or "open", meaning the contacts are separated and the switch is nonconducting. The mechanism actuating the transition between these two states (open or closed) can be either a "toggle" (flip switch for continuous "on" or "off") or "momentary" (push-for "on" or push-for "off") type.

A switch may be directly manipulated by a human as a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a light switch. Automatically operated switches can be used to control the motions of machines, for example, to indicate that a garage door has reached its full open position or that a machine tool is in a position to accept another workpiece. Switches may be operated by process variables such as pressure, temperature, flow, current, voltage, and force, acting assensors in a process and used to automatically control a system. For example, a thermostat is a temperature-operated switch used to control a heating process. A switch that is operated by another electrical circuit is called a relay. Large switches may be remotely operated by a motor drive mechanism. Some switches are used to isolate electric power from a system, providing a visible point of isolation that can be padlocked if necessary to prevent accidental operation of a machine during maintenance, or to prevent electric shock.

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An ideal switch would have no voltage drop when closed, and would have no limits on voltage or current rating. It would have zero rise time and fall time during state changes, and would change state without "bouncing" between on and off positions.

Practical switches fall short of this ideal; they have resistance, limits on the current and voltage they can handle, finite switching time, etc. The ideal switch is often used in circuit analysis as it greatly simplifies the system of equations to be solved, but this can lead to a less accurate solution. Theoretical treatment of the effects of non-ideal properties is required in the design of large networks of switches, as for example used in telephone exchanges.

Contacts :-

A toggle switch in the "on" position.

In the simplest case, a switch has two conductive pieces, often metal, called contacts, connected to an external circuit, that touch to complete (make) the circuit, and separate to open (break) the circuit. The contact material is chosen for its resistance to corrosion, because most metals form insulating oxidesthat would prevent the switch from working. Contact materials are also chosen on the basis of electrical conductivity, hardness (resistance to abrasive wear),mechanical strength, low cost and low toxicity.

Sometimes the contacts are plated with noble metals. They may be designed to wipe against each other to clean off any contamination. Nonmetallicconductors, such as conductive plastic, are sometimes used. To prevent the formation of insulating oxides, a minimum wetting current may be specified for a given switch design.

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Toggle switch :-

Large toggle switch, depicted in circuit "open" position, electrical contacts to left; background is 1/4" square graph paper

Bank of toggle switches on a Data General Nova minicomputer front panel.

Toggle switches with the shared cover preventing certain forbidden combinations

A toggle switch is a class of electrical switches that are manually actuated by a mechanical lever, handle, or rocking mechanism.

Toggle switches are available in many different styles and sizes, and are used in numerous applications. Many are designed to provide the simultaneous actuation of multiple sets of electrical contacts, or the control of large amounts of electric current or mains voltages.

The word "toggle" is a reference to a kind of mechanism or joint consisting of two arms, which are almost in line with each other, connected with an elbow-like pivot. However, the phrase "toggle switch" is applied to a switch with a short handle and a positive snap-

38

action, whether it actually contains a toggle mechanism or not. Similarly, a switch where a definitive click is heard, is called a "positive on-off switch".

Multiple toggle switches may be mechanically interlocked to prevent forbidden combinations.

Electronic switches :-

Three push button switches (Tactile Switches). Major scale is inches.

A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching—often a silicon-controlled rectifier or triac.

The analogue switch uses two MOSFET transistors in a transmission gate arrangement as a switch that works much like a relay, with some advantages and several limitations compared to an electromechanical relay.

The power transistor(s) in a switching voltage regulator, such as a power supply unit, are used like a switch to alternately let power flow and block power from flowing.

Many people use metonymy to call a variety of devices "switches" that conceptually connect or disconnect signals and communication paths between electrical devices, analogous to the way mechanical switches connect and disconnect paths for electrons to flow between two conductors. Early telephone systems used an automatically operated Strowger switch to connect telephone callers; telephone exchanges contain one or more crossbar switches today.

Since the advent of digital logic in the 1950s, the term switch has spread to a variety of digital active devices such as transistors and logic gates whose function is to change their output state between two logic levels or connect different signal lines, and even computers, network switches, whose function is to provide connections between different ports in a computer network. The term 'switched' is also applied to telecommunications networks, and signifies a network that is circuit switched,

39

providing dedicated circuits for communication between end nodes, such as the public switched telephone network. The common feature of all these usages is they refer to devices that control a binary state they are either on or off, closed or open, connected or not connected.

4) Emergency Stop Switch :-

This switch is very important concern with security of an elevator as well as of

user. When any fault is occurred, person can stop the elevator by pushing this emergency

stop switch. As soon as person realize the fault is occurred in the elevator system and he

press this emergency stop switch, which gives signal to PLC so as it cuts the supply to the

driving motor immediately. Fig. (4.8) shows connection of emergency switch with PLC.

Fig. (4.8): Emergency Stop Switch Circuit

The other use of this switch is that if person wants to land on the floor rather than floor destination is given by him previously, he can press this switch. As soon as the floor reaches in front of cage where he wants to land, he can push this button which cuts supply to the driving motor so as the cage stops immediately in front of that floor.

A kill switch, also known as an emergency stop or e-stop, is a safety mechanism used to shut off a device in an emergency situation in which it cannot be shut down in the usual manner. Unlike a normal shut-down switch/procedure, which shuts down all systems in an orderly fashion and turns the machine off without damaging it, a kill switch is designed and configured to a) completely and as quickly as possible abort the operation, even if this damages equipment and b) be operable in a manner that is quick, simple (so that even a panicking operator with impaired executive function can activate it), and, usually, c) be obvious even to an untrained operator or a bystander. Many kill switches feature a removable barrier or other protection against accidental activation (e.g., a plastic cover that must be lifted or glass that must be broken).

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PLC+ -

EMERGENCY SWITCH

Kill switches are featured especially often as part of mechanisms whose normal operation or foreseeable misuse may cause injury or death; designers who include such switches consider damage to or destruction of the mechanism to be an acceptable cost of preventing that injury or death.

Applications :-

A similar system, usually called a dead man's switch (for other names, see alternative names), as its name suggests, is a device intended to stop a machine in case the human operator becomes incapacitated, and is a form of fail-safe. They are commonly used in locomotives, tower cranes, freight elevators, lawn mowers, tractors, jet skis, outboard motors, snowblowers and snowmobiles. The switch in these cases is held by the user, and turns off the machine if they let go.

Vehicles :-

On railways, an emergency stop is a full application of the brakes in order to bring a train to a stop as quickly as possible, much like anemergency brake on a train.[1] This occurs either by a manual emergency stop activation, such as a button being pushed on the train to start the emergency stop, or on some trains automatically, when the train has passed a red signal or the driver has failed to respond to warnings to check that he/she is still alert, which is known as a dead man's switch.

In large ships, an emergency stop button pulls the countershaft for the fuel pumps to the stop position, cutting off the fuel supply and stopping the engines. With a controllable pitch propeller, the stop button may declutch the engine from the propeller.

NASCAR (National Association for Stock Car Auto Racing) requires all their stock cars to be equipped with a steering wheel-mounted kill switch, in case the accelerator pedal sticks and the driver needs to shut down the engine.

Kill switches are also used on land vehicles as an anti-theft system and as an emergency power off. Such devices are often placed in bait cars and configured so that observing police can trigger the switch remotely.

A related concept is the dead man's switch, where the operator must be holding a button or lever any time the vehicle is operating. A common example of this would be the kill switches used by boaters wherein a cord connects the kill switch to the operator (usually by the operator's life jacket), and if the operator is thrown overboard in an accident, the cord will pull the switch and immediately shut down the vessel's engine. This prevents it from becoming a run-away vessel that could impose a danger to other vessels or swimmers at sea, and allows the operator to swim back to the vessel and re-board it.

Machinery :-

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The arrows indicate that the stop button must be turned to reset the switch before the equipment can be restarted.On large industrial machines, an emergency stop button is typically located on the panel, and possibly in several other areas of the machine. This provides a rapid means to disconnect the energy source of the device to protect workers.[2] For fail-safe operation, the emergency stop is button is a normally closed switch which ensures that a broken wire will neither accidentally activate the emergency stop nor prevent it from being activated. On machinery controlled by a Programmable Logic Controller, the emergency stop is designed in a way that it overrides the output of the controller.In some contexts, such as nuclear reactors or data centers, the emergency stop is known as a scram switch.

In the European Union, most types of machinery are required to be equipped with an emergency stop according to the Directive 2006/42/EC. Exceptions apply for machinery in which an emergency stop would not lessen the risk as well as for portable hand-held/hand-guided machinery.

A kill switch is also used for gasoline pumps or any other device that pumps large amounts of explosive or flammable chemicals. Most vehicles nowadays also have a kill switch that cuts power to the fuel pump if the vehicle is overturned. There is commonly a single kill switch for all pumps at a pumping station. The kill switch is also used on such things as industrial band saws and belt sanders. Kill switches are also found on school-use electric powered tools such as drills and wood/metal lathes.

Forward and Reverse Operation Of Motor:

4.2 Software Design :-

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4.2.1: Introduction :-

A PLC is a digitally operated electronic system, designed for use in an Industrial

Environment, which uses a Programmable Memory for the internal storage of user-

oriented instructions for implementing specific functions such as Logic, Sequencing,

Timing, Counting, and Arithmetic, to control, through Digital or Analog Inputs and

Outputs, various types of machines or Processes. Both the PLC and its peripherals are

designed so that they can be easily integrated into an industrial control system and easily

used in all their intended functions.

PLCs are used in many “real world” applications. If there is industry present,

chances are good that there is a PLC present. Most of the applications involving

machining, packaging, material handling, automated assembly or countless other

industries are probably already using them. Almost any application that needs some type

of electrical control has a need for a PLC. A programmable logic

controller, PLC or programmable controller is a digital computer used for automation of

typically industrialelectromechanical processes, such as control of machinery on

factory assembly lines, amusement rides, or light fixtures. PLCs are used in many

industries and machines. PLCs are designed for multiple analogue and digital inputs and

output arrangements, extended temperature ranges, immunity to electrical noise, and

resistance to vibration and impact. Programs to control machine operation are typically

stored in battery-backed-up or non-volatile memory. A PLC is an example of a

"hard" real-time system since output results must be produced in response to input

conditions within a limited time, otherwise unintended operation will result.

4.2.2: History:-43

In the late 1960s PLCs were first introduced. The primary reason for designing such a device was eliminating the large cost involved in replacing the complicated relay based machine control systems. Bedford Associates (Bedford, MA) proposed something called a Modular Digital Controller (MODICON) to a major US car manufacturer. Other companies at the time proposed computer based schemes. The MODICON brought the world’s first PLC into commercial production. When production requirements changed so did the control system. This becomes very expensive when the change is frequent. Since relays are mechanical devices they also have a limited lifetime, which required strict adhesion to maintenance schedules. Troubleshooting was also quite tedious when so many relays are involved. Now picture a machine control panel that included many, possibly hundreds or thousands, of individual relays. The size could be mind-boggling and these relays would be individually wired together in a manner that would yield the desired outcome which is very tedious.

These new controllers also had to be easily programmed by maintenance and plant engineers. The lifetime had to be long and programming changes easily performed. They also had to survive the harsh industrial environment. The answers were to use a programming technique most people were already familiar with and replace mechanical parts with solid-state ones. Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was mainly composed of relays, cam timers, drum sequencers, and dedicated closed-loop controllers. Since these could number in the hundreds or even thousands, the process for updating such facilities for the yearly model change-over was very time consuming and expensive, as electricians needed to individually rewire the relays to change their operational characteristics.

Digital computers, being general-purpose programmable devices, were soon applied to control of industrial processes. Early computers required specialist programmers, and stringent operating environmental control for temperature, cleanliness, and power quality. Using a general-purpose computer for process control required protecting the computer from the plant floor conditions. An industrial control computer would have several attributes: it would tolerate the shop-floor environment, it would support discrete (bit-form) input and output in an easily extensible manner, it would not require years of training to use, and it would permit its operation to be monitored. The response time of any computer system must be fast enough to be useful for control; the required speed varying according to the nature of the process.Since many industrial processes have timescales easily addressed by millisecond response times, modern (fast, small, reliable) electronics greatly facilitate building reliable controllers, especially because performance can be traded off for reliability.

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In 1968 GM Hydra-Matic (the automatic transmission division of General Motors) issued a request for proposals for an electronic replacement for hard-wired relay systems based on a white paper written by engineer Edward R. Clark. The winning proposal came from Bedford Associates of Bedford, Massachusetts. The first PLC, designated the 084 because it was Bedford Associates' eighty-fourth project, was the result. Bedford Associates started a new company dedicated to developing, manufacturing, selling, and servicing this new product: Modicon, which stood for MOdular DIgital CONtroller. One of the people who worked on that project was Dick Morley, who is considered to be the "father" of the PLC The Modicon brand was sold in 1977 to Gould Electronics, and later acquired by German Company AEG and then by French Schneider Electric, the current owner.One of the very first 084 models built is now on display at Modicon's headquarters in North Andover, Massachusetts. It was presented to Modicon by GM, when the unit was retired after nearly twenty years of uninterrupted service. Modicon used the 84 moniker at the end of its product range until the 984 made its appearance.

The automotive industry is still one of the largest users of PLCs.

4.2.3: Importance of PLC :-

A PLC monitors inputs, makes decisions based on its program, and controls

outputs to automate a process or machine. The mass manufacture of automobiles involves

many machines, all of which must be controlled. Earlier the control function of these

machines was performed by control relays.

Control relays were effective but suffered from several disadvantages. Relays are capable

of on off control, so many relays are needed to design complicated control systems,

making the relay control scheme so expensive. Control systems can be bulky, so a control

system requiring lots of relays takes lots of space. They are power hungry too, and this

high power consumption results leads in heat generation. When a relay fails, either due to

an opening of coil or due to a pitting of the hardwired, any change in control circuit needs

the relays to be rewired, which proves to be very costly.

In Hard-Wired Control Prior to PLCs, many of these control tasks were solved

with contactor or relay controls. This is often referred to as hardwired control. Circuit

diagrams had to be designed, electrical components specified and installed, and wiring

lists created. Electricians would then wire the components necessary to perform a specific

task. If an error was present the wires had to be reconnected correctly. A change in

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function or system expansion required extensive component changes and rewiring. Wiring

between devices and relay contacts is done in the PLC program hard wiring, though still

required to connect field devices, is less intensive. Modifying the application and

correcting errors are easier to handle. It is easier to create and change a program in a PLC

than it is to wire and rewire a circuit.

4.2.4: Component of PLC :-

The controller consists of a built-in power supply, central processing unit

(CPU),memory, inputs, which you wire to input devices (such as pushbuttons, proximity

sensors, limit switches), and outputs, which you wire to output devices (such as motor

starters, solid-state relays, and indicator lights). Fig (4.9) shows functional block diagram

of Allen-Bradley Micrologix-1400.

Fig.(4.9):Block Diagram Of Allen Bradley Micrologix-1400.

Programmable controllers have grown throughout industrial control applications because of the ease they bring to creating a controller: ease of programming, ease of wiring, ease of installation, and ease of changing. PLCs span a wide range of sizes, but all contain six basic components:

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processor or central processing unit (CPU); rack or mounting; input assembly; output assembly; power supply; programming unit, device, or PC/software

We will start with explaining the physical components you see when looking at a PLC system – and then explore what goes on inside each part, and how the components relate to each other.

Rack Assembly :-

Most medium to large PLC systems are assembled such that the individual components – CPU, Input/Output, Power Supply – are modules that are held together within a rack.

In smaller PLC systems – all of these components may be contained in a single housing or “brick” – these smaller systems are sometimes referred to as “bricks” or “shoebox” PLCs.

Power Supply :-

The power supply provides power for the PLC system. The power supply provides internal DC current to operate the processor logic circuitry and input/output assemblies. Common power levels used are 24V DC or 120 VAC.

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Processor (CPU) :-

The processor, central processing unit, or CPU is the “brain” of the PLC. The size and type of CPU will determine things like: the programming functions available, size of the application logic available, amount of memory available, and processing speed. Understanding the CPU can be a complex subject and we will tackle that in other articles.

 

Input/Output Assembly :-Inputs carry signals from the process into the controller, they can be input switches, pressure sensors, operator inputs, etc. These are like the senses and sensors of the PLC.

Outputs are the devices that the PLC uses to send changes out to the world. These are the actuator the PLC can change to adjust or control the process – motors, lights, relays, pumps, etc.

Many types of inputs and outputs can be connected to a PLC, and they can all be divided into two large groups – analog and digital. Digital inputs and outputs are those that operate due to a discrete or binary change – on/off, yes/no. Analog inputs and outputs change continuously over a variable range – pressure, temperature, potentiometer.

Programming Device :-

The PLC is programmed using a specialty programmer or software on a computer that can load and change the logic inside. Most modern PLCs are programmed using software on a PC or laptop computer. Older systems used a custom programming device.

4.2.5: Inputs :-

They examines state of physical components of user input devices like limit

switches, sensors, toggle switches, thermocouples, push buttons, etc.

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INPUT

DEVICE

ELECRICAL AND OPTICALISOLATION

FILTER ANALOG

TO

DIGITAL

CONV.

INPUT

DEVICE

ELECRICAL AND OPTICALISOLATION

FILTER

INPUT

DEVICE

ELECRICAL AND OPTICALISOLATION

FILTER

C

P

U

Input signals from input devices through input relays are fed to A/D converter

through isolation circuit and filters. Filters are used to reduce the ripple contents and noise

from the input signals and isolation circuits are used to protect A/D converter and

processor from any fault occurrence at input side. A/D converter converts this analog

input into equivalent digital form which is suitable form for the CPU operation .CPU

process on this converted signals as per programmed. Fig (4.10) shows functional block

diagram of INPUTS of PLC.

Fig. (4.10): Input Working Circuit

The term PLC inputs refers to the

devices and transducers which are entrusted with taking in information about the physical world to the PLC. Keep in mind that it also refers to the PLC hardware that connects to those devices, sensors and transducers. The PLC uses this input information to make decisions based upon its program whether to energize and de-energize the outputs controlled by the PLC. It very important to know about the different input types discussed below.

The two types of PLC inputs are commonly referred to DI and AI (Digital and Analog). Analog inputs are those like temperature and pressure which span over a range of values. Digital inputs are simply two states, like those of a switch position indicating as On or Off.

Analog Inputs include temperature sensors/transmitters, current sensors, voltage sensors and others that can convert a physical quantity to a electrical signal. These electrical signals used for PLC input are typically 4-20ma or 1-5vdc.

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Digital Inputs include push-buttons, limit switches, relay contacts, proximity switches, photo sensors (On/Off), pressure switches and more. Digital inputs devices are available in both DC as well as AC and some are voltage independent such as a switch contact.

A less common PLC input is the High Speed Counter (HSC). It is very similar to the digital input type, but the hardware is capable of detecting rapid ON/OFF inputs. It is common that 10KHz or 10,000 on/off transitions per second are within the abilities of these input types. A photo optic eye counting parts on an high speed assembly line would be example of when a HSC module would be needed.

A HSC PLC input module may also have quadrature capable inputs. This would be used with an rotary encoder to sense speed and direction of a motor for instance.

Depending on the particular PLC, the different inputs discussed above will require a separate hardware module for each type. However mixed I/O (input/output) modules or cards are available and some smaller integrated PLC models have some I/O included.

PLC Digital Inputs have a LED indicator on the module itself for setup and troubleshooting. Simply, if the LED is ON the input is ON.

If the LED is ON and it should not be, then you need to look at your wiring, the input sensor position or adjustment, or the possibility that the input device may be defective.The same applies if the LED is OFF and you expect to to be ON, with the addition of checking input protecting fuses.

PLC Analog Inputs generally don't have a display on the module (I know that Automation Direct's newest top of the line PLC does!) to aid in troubleshooting. In this case you are going to need your multimeter or other suitable measurement tool.

The PLC input module itself would generally would be considered the last step in troubleshooting the problem.

Now that you understand the differences and uses of Digital and Analog inputs, be aware that the PLC input hardware is part of a system made of several different components that comprise a PLC. These components consist of the CPU or the central processing unit, the input and output modules, memory and power supply.

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C

P

U

4.2.6: Outputs :- They give signals to the output devices like solenoids, lights, power drives, etc.

Processed digital signal from CPU is then fed to D/A converter.

D/A converter convert this digital signal into equivalent analog output which is

first store in to the memory and then fed to the output device through isolation circuit

which protects mal-operation of output device due to improper programming and faults

occurred at D/A converter side .Fig (4.11) shows functional block circuit of OUTPUTS of

PLC.

Fig. (4.11): Output Working Circuit

PLC Outputs are the control circuits of the PLC and also refers to the devices controlled by the PLC. Be aware when talking about PLCs the devices like motors and lights are also referred to as PLC Outputs. Devices called actuators convert the electrical signal of the PLC to a physical movement for instance a valve solenoid stoke or a motor contactor. With regards to the variable output, the I/P (current to pneumatic) actuator, is an example.

There are two types, the ON/OFF output and the variable output. Digital output (DO) are for the ON/OFF in your control scheme. Some examples are motors that need just be ON or OFF, Lighting, solenoid valves, door locks. Analog output (AO) are for variable level or range of output between OFF or stopped and ON or full speed as for an electric motor

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DATA

STORAGE

ELECRICAL AND OPTICALISOLATION

OUTPUT

DEVICE

DATA

STORAGE

ELECRICAL AND OPTICALISOLATION

OUTPUT

DEVICE

DATA

STORAGE

ELECRICAL AND OPTICALISOLATION

OUTPUT

DEVICE

DIGITAL

TO

ANALOG

CONV.

for instance. Examples of analog outputs are a VFD (Variable Frequency Drive), a valve position actuator, and a industrial variable power supply.

Now lets touch on the types of control circuits within the PLC Output Module. PLCs have four typical output types. Three are DO and the other is AO.

For the Digital Outputs they are transistor, relay, and the triac. Relay dry contacts are the quick choice since they are voltage independent and they are a easy interface to a customer's system. Relays generally have a higher current rating than transistors, but have a mechanical life span that has to be considered.

Transistor types are for DC applications. They are smaller and thus offer higher I/O count per unit of circuit board real estate. You may also choose them for faster switching speeds and longevity over relays.

Triacs are the solid state choice for AC and may require additional circuity called snubbers. Also keep in mind to check the leakage current spec of the transistor or triac to make sure it will not have the the possibility of turning on your output when it is OFF!

The PLC Analog Output is usually configurable for loop or internally powered and externally powered, a voltage (typically 0 to 10VDC) or current (typically 4-20ma). In this case the PLC uses a DAC (Digital to Analog Convertor) to drive the output. Other available Analog outputs supply these typical ranges: -5 to 5 vdc, -10 to 10 vdc, or 0-5 vdc.

You must be aware of the inductive loads that are switched by the PLC outputs. These include, motor starters, solenoids, and relays. If these devices are too large for direct connection a interposing relay will be be required. These inductive loads will produce a sizable reverse voltage, known as Back EMF. This Back EMF and corresponding current can damage the PLC outputs and therefore has to be redirected.

For protection, devices like MOVs (metal Oxide Varistors) and diodes are installed as close to the inductive device as possible to suppress or divert these voltages. Without surge suppression relay contacts can pit from arching, generate electrical noise and may weld closed! Manufacturers often provide guidelines for choosing and even supplying suppression devices, but others may already have the suppression built-in and will not need a separate component.

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As I mentioned above, inductive devices produce voltage spikes and snubbers are used for thyristor (Triac ) PLC outputs. Snubbers for this use are RC circuits that reduce the voltage rate of change as not to falsely trigger the triac .However, most industrial applications have low enough voltage and current ratings they can be connected directly to the PLC outputs and some have built-in protection anyway. Most industrial solenoids are energized by 24Vdc and consume only about two to three hundred mA.

Finally, we must talk about sinking and source outputs. A source output will connect the voltage to the load, its return or ground is always connected. A sinking output will connect the load to its return or ground, it is always connected to its voltage source. Okay, do you see a potential problem?! What happens in this case if the circuit is made complete by a short to ground?! That is right! Unintentional turning on of the output! For this reason and the fact that I just consider connecting a circuit to power to energize more logical, I prefer sourcing outputs.

Remember that outputs come in two main flavors, DO and AO. You have to consider what you are going to control and to choose the right combination of PLC output module and supporting components such as interposing relays. Oh, one more tip, create a spreadsheet of all your inputs and outputs and all their requirements before you buy anything!

4.2.7 Processor :-

It performs the necessary task to fulfill the PLC function such as scanning of I/O

bus traffic control, program execution, communication between external devices and

peripheral components, etc. It also performs data handling execution and self-diagnostics.

4.2.8 Programming Devices (PC) :-

We can connect the Micrologix 1400 programmable controller to personal

computer (Programming Device) using a serial cable(RS-232) from personal computer’s

serial port to the microcontroller for download the executable program from PC to PLC. 53

Here the PC is the programming device which programs executive logic diagram using

software like RSLogix™ 500. Fig (4.12) shows interconnectivity between PC and PLC

using RS-232 connector. Optical Isolator is used as safety device due to which duplex data

transmission between PC and PLC can be achieve safe mode.

Fig. (4.12): Interconnectivity Between PC And PLC

4.2.9: Supply Unit:

It is DC supply unit which is of order of +5V, +12V, + 24V, etc., provide for

working of CPU, input modules and output modules of PLC. Also 230V AC supply is

available there.

4.2.10: Memory :-

Fig.(4.13): Memory Used In PLC

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It is the library where the executable programs are stored. The executable program

functions as the operating system of PLC. Memory unit is the part of programmable

controller where process data from input modules are stored as well as control data from

output modules are stored.

The memories used on CPU PCB are semiconductor memories. One or more than

one memories are used in single PCB. The Micrologix 1400 programmable controller uses

two memories for storing processor files: RAM and EEPROM. The RAM provides easy

access storage (i.e., its data is lost on a power down), while the EEPROM provides long-

term storage (i.e., its data is not lost on a power down). Fig (4.13) shows how the memory

is allocated in the micro controller’s processor (PLC). The memory device that is used

depends on the operation being performed.

4.2.11: Use of Memory :-

The following description tells how memory is stored and accessed during the

following operations:

1) Download

2) Normal Operation

3) Power Down

4) Power Up

1) Download :-

When the processor file is downloaded to the micro controller, it is first

stored in the volatile RAM. It is then transferred to the non-volatile EEPROM,

where it is stored as both backup data and retentive data. Fig (4.14) shows

memories used during DOWNLOAD process.

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Fig. (4.14): Memories Used During Download Process

2) Normal Operation :-

During normal operation, both the micro controller and your programming

device can access the processor files stored in the RAM. Any changes to retentive data

that occur due to program execution or programming commands affect only the retentive

data in the RAM. The program files are never modified during normal operation.

However, both the CPU and your programming device can read the program files stored

in RAM as shown in Fig (4.15).

Fig.(4.15): Memories Used During Normal Operation

2) Power Down :-

When a power down occurs, only the retentive data is transferred from the RAM to

the EEPROM. (The program files do not need to be saved to the EEPROM since they

cannot be modified during normal operation.) If for some reason power is lost before all

of the retentive data is saved to the EEPROM, the retentive data is lost. This may occur

due to an

56

unexpected reset or a hardware problem. Fig (4.16) shows memories used during POWER

DOWN.

Fig. (4.16): Memories Used During Power Down

2) Power Up :-

Fig.(4.17): Program Files And Retentive Data Transmission

During power up, the micro controller transfers the program files from the

EEPROM to the RAM. The retentive data is also transferred to the RAM, provided it was

not lost on power down, and normal operation begins as shown in fig (4.17).

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Fig.(4.18): Program Files And Back-Up Data Transmission

If retentive data was lost on power down, the backup data from the EEPROM is

transferred to the RAM and used as the retentive data as shown in fig (4.18). In addition,

status file bit S2:5/8 (retentive data lost) is set and a recoverable major error occurs when

going to run.

4.2.12: Data Transmission Between PC And PLC :-

Fig (4.19) shows schematic of RS-232 Cable which is used for interconnection

between 9-pin D-shell of PC to 8-pin Mini Din of PLC.

Fig.(4.19): Schematic Of Rs-232 Cable

Pin Description :-

Fig (4.20) shows pin configuration of Programming Device (PC) and Controller

used for serial data communication in between them.

[1] Data Terminal Ready (DTR) :-58

When a PC COM port is turned ON, after going through a self test, it sends out

signal DTR to indicate that it is ready to communication. If there is a fault with the COM

port, this signal will not be activated. This is OUTPUT pin of PC COM port and an input

to its own modem.

Fig.(4.20): Data Communication Between PC And PLC

[2] Data Set Ready (DSR) :-- When modem of PC is turned ON and has gone though the self test, it asserts DSR

to indicate that it is ready to communicate. When this signal is inactive, indicating to the

PC that it cannot accept or send data.

[3] Request To Send (RTS) :-

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When the PC has a byte to send, it asserts RTS to signal the modem of PLC that it

has a byte to transmit.

[4] Clear To Send :-

In response to RTS, when modem of PLC has room for storing the data it is to

receive, it sends out signal CTS to the PC to indicate that it can receive the data now.

Therefore it is OUTPUT from PLC and INPUT to the PC.

[5] Data Carrier Detect (DCD) :-

The modem asserts signal DCD to inform PC that valid carrier has been detected

and that contact between this modem of PC and modem of PLC is established. Thus DCD

is an INPUT to the PC and an OUTPUT from PLC.

[6] Ring Indicator (RI) :-

This is input to the PC indicates that the Telephone is ringing. It goes ON and

OFF in synchronization with the ringing sound. This is least often used, due to the fact

that modems take care of answering the phone. However if in a given system the PC is in

charge of answering the phone, this signal can be used.

4.2.13: Advantages of PLC :-

1) Smaller physical size than hard- Wire solutions.

2) Easier and faster to make changes.

3) PLCs have integrated diagnostics and override functions.

4) Diagnostics are centrally available.

5) Applications can be immediately documented; Applications can be duplicated

faster and less expensively.

6) Easily programmed or reprogrammed with a minimum of downtime.

7) Easily maintained.

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8) Rugged enough to operate in an industrial environment.

9) Able to consume less power and require less cabinet and floor space than the relay

control system and Competitive in cost.

4.2.14: Specification of Allen Bradley micrologix-1400 :-

Preconfigured 4K programming and data memory to ease configuration (bit,

integer, timers, counters, etc).

Fast processing allows for typical throughput time of 1.5 ms for a 500-instruction

program.

Built-in EEPROM memory retains all of your ladder logic and data if the

controller loses power, eliminating the need for battery back-up or separate memory

module. Multiple input commons allow you to use the controller for either sinking or

sourcing input devices and multiple output commons provide isolation in multi-voltage

output applications.

RS-232 communication channel allows for simple connectivity to a personal

computer for program upload, download and monitoring using multiple protocols,

including DF1 Full Duplex.RTU slave protocol support using DF1 Half-Duplex Slave

allows up to 254 notes to communicate with a single master using radio modems, leased-

line modems or satellite uplinks. Peer-to-peer messaging capability allows you to network

up to 32 controllers on a DH-485 (using a 1761-NET-AIC module).

Advanced communications networks, including Device Net and Ethernet/IP

through the 1761-NET-DNI and 1761-NET-ENI communication modules.

Controllers that have 24V dc inputs include a built-in high-speed counter (6.6 kHz).

Adjustable DC input filters allow you to customize the input response time and noise

rejection to meet your application needs.

Regulatory agency certifications for world-wide market (CE, C-Tick, UL, c-UL, including

Class 1 Division 2 Hazardous Location).

This little powerhouse is both inexpensive and compact, with footprints as small as

120mm x 80 mm x 40 mm (4.72" x 3.15" x 1.57"). The analog I/O circuitry is embedded

61

into the base controller, not accomplished through add-on modules, providing compact

and cost-effective analog performance.

4.3 Advantages and disadvantages of System :-

4.3.1 Advantages :-

1. Fast and Reliable in operation.

2. Less power consumption and highly efficient.

3. Less space is sufficient for control room due to minimization of relay panels

(which are essential in conventional elevator system).

4. User friendly.

5. Less maintenance and competitive in cost.

6. Programming of PLC is simple; no need of skilled programmer is required.

7. Due to these advantages it is became more popular in industrial, commercial

and residential field.

4.3.2 Disadvantages :-

1. Program failure due to program corruption may cause system collapse.

2. Construction of LADDER LOGIC becomes tedious as numbers of floors are

increased.

3. Though the programming is simple basic knowledge of programming with ladder

logic is necessary.

4. As the number of INPUTS and OUTPUTS are increased with the number of

floors, PLC of different configuration (higher version) must have to replace the

original PLC.

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4.3.3 Application of System :-

The PLC controlled elevator system become popular in the commercial,

residential and industrial sectors in cities and metro’s.

They are used in residential buildings consisting large number of floors.

They are extensively used in hospitals, schools and colleges.

They are used in commercial sectors like shopping malls, multiplexes, towers,

commercial buildings, etc.

They are used in industrial sectors like IT zones, processing industries, etc.

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WORKING OF MODEL

64

5. WORKING OF MODEL

In all there are 3 floors. There are three limit switches provided, one on each floor

to sense the UPWARD and DOWNWARD motion. These limit switches are of roller

type.

An operating bracket for the limit switch is being provided on the elevator cage.

The position of operating bracket is so adjusted that when this bracket operates the limit

switch, the supply to the motor is cut off and then the lift will stop at the exact defined

level and there will not be any over rider. There is an arrangement of oblong holes

provided on the limit switch bracket so that they can be moved vertically up and down as

per desired position. Oblong holes are also provided on limit switch operating bracket

placed on elevator cage, so that they can be adjusted horizontally.

The elevator cage must travel a distance of 20 cm i.e. from one floor to another

in about 4-5 seconds; which is visible. Hence the motor pulley is designed of diameter

6.5cm, so that its periphery is 3.5cm and thus there is large area available for the contact

of rope i.e. the arc of contact of the rope with pulley is large. Also there is large arc of

contact of the rope with motor pulley. These pulleys are V-grooved and thus avoid

slipping of the rope from the pulley. These pulleys provide the tension to the rope on the

motor pulley and thus it enables the motor to move the lift UP and DOWN easily.

Four cross legs are also provided at the base of the main frame for balancing the

height of the frame. The operation of the lift will be tedious if doors are made on the

elevator cage. Hence instead of doors, toggle switches are provided on every floor. The

ON and OFF operation of the toggle switch indicates the closing and opening of the cage

door. Push buttons are also provided on each floor which is used for calling the lift from

any floor.

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TEST & EXPRIMENTAL

RESULT

66

6. TEST & EXPRIMENTAL RESULT6.1 Programming of PLC :-

6.1.1 Introduction :-

Programmingof PLC is one of the important part of the project. The hardware

operation of elevator system is directed by PLC PROGRAMMING, based on LADDER

DIAGRAMS.

The logic you enter into the micro controller makes up a ladder program. A ladder

program consists of a set of instructions used to control a machine or a process. Ladder

logic is a graphical programming language based on electrical relay diagrams. Instead of

having electrical rung continuity, ladder logic is looking forlogical rung continuity. A

ladder diagram identifies each of the elements in an electromechanical circuit and

represents them graphically. This allows you to see how your control circuit operates

before you actually start the physical operation ofyour system. Fig (6.1) shows ladder

diagram representation.

Fig. (6.1)Graphical Representation Ladder Logic

In a ladder diagram each of the input devices represented in series or parallel combinations across the rung of the ladder. The last element on the rung is the output that receives the action as a result of the conditional state of the inputs on therung. Each output instruction is executed by the controller when the rung is scanned and the conditions on the rung are true. When the rung is not scanned or the logic conditions on the rung do not create a true logic path, the output is not executed. The programming device allows you to enter a ladder logic program into the micro Controller. A Programmable Logic Controller,

67

or PLC, is more or less a small computer with a built-in operating system (OS). This OS is highly specialized to handle incoming events in real time, i.e. at the time of their occurrence.

The PLC has input lines where sensors are connected to notify upon events (e.g. temperature above/below a certain level, liquid level reached, etc.), and output lines to signal any reaction to the incoming events (e.g. start an engine, open/close a valve, etc.).

The system is user programmable. It uses a language called "Relay Ladder" or RLL (Relay Ladder Logic). The name of this language implies that the control logic of the earlier days, which was built from relays, is being simulated.

Programmable Logic Controller :-A Programmable Logic Controller, or PLC, is more or less a small computer with a built-in operating system (OS). This OS is highly specialized to handle incoming events in real time, i.e. at the time of their occurrence.The PLC has input lines where sensors are connected to notify upon events (e.g. temperature above/below a certain level, liquid level reached, etc.), and output lines to signal any reaction to the incoming events (e.g. start an engine, open/close a valve, etc.).

The system is user programmable. It uses a language called "Relay Ladder" or RLL (Relay Ladder Logic). The name of this language implies that the control logic of the earlier days, which was built from relays, is being simulated.There are some other languages also used 1. Sequential Function chart 2. Functional block diagram 3. structured Text 4. Instruction List

The PLC's purpose life :-

The PLC is primarily used to control machinery. A program is written for the PLC which turns on and off outputs based on input conditions and the internal program. In this aspect, a PLC is similar to a computer. However, a PLC is designed to be programmed once, and run repeatedly as needed. In fact, a crafty programmer could use a PLC to control not only simple devices such as a garage door opener, but their whole house, including switching lights on and off at certain times, monitoring a custom built security system, etc.

Most commonly, a PLC is found inside of a machine in an industrial environment. A PLC can run an automatic machine for years with little human intervention. They are designed to withstand most harsh environments.

History of PLCs68

When the first electronic machine controls were designed, they used relays to control the machine logic (i.e. press "Start" to start the machine and press "Stop" to stop the machine). A basic machine might need a wall covered in relays to control all of its functions. There are a few limitations to this type of control.

Relays fail. The delay when the relay turns on/off. There is an entire wall of relays to design/wire/troubleshoot.

A PLC overcomes these limitations, it is a machine controlled operation.

Recent developments :-

PLCs are becoming more and more intelligent. In recent years PLCs have been integrated into electrical communications(Computer network|networks)i.e., all the PLCs in an industrial environment have been plugged into a network which is usually hierarchically organized. The PLCs are then supervised by a control centre. There exist many proprietary types of networks. One type which is widely known is SCADA (Supervisory Control and Data Acquisition).

Basic Concepts :- How the PLC operates :-

The PLC is a purpose-built machine control computer designed to read digital and analog inputs from various sensors, execute a user defined logic program, and write the resulting digital and analog output values to various output elements like hydraulic and pneumatic actuators, indication lamps, solenoid coils, etc.

Scan cycle :-

Exact details vary between manufacturers, but most PLCs follow a 'scan-cycle'format.

Overhead :-Overhead includes testing I/O module integrity, verifying the user program logic

hasn't changed, that the computer itself hasn't locked up (via a watchdog timer), and any necessary communications. Communications may include traffic over the PLC programmer port, remote I/O racks, and other external devices such as HMIs (Human Machine Interfaces).

69

Input scan :-A 'snapshot' of the digital and analog values present at the input cards is saved to an input memory table.

Logic execution :-The user program is scanned element by element, then rung by rung until the end

of the program, and resulting values written to an output memory table.

Output scan :- Values from the resulting output memory table are written to the output

modules.Once the output scan is complete the process repeats itself until the PLC is powered down.The time it takes to complete a scan cycle is, appropriately enough, the "scan cycle time", and ranges from hundreds of milliseconds (on older PLCs, and/or PLCs with very complex programs) to only a few milliseconds on newer PLCs, and/or PLCs executing short, simple code.

Basic instructions :-

Be aware that specific nomenclature and operational details vary widely between PLC manufacturers, and often implementation details evolve from generation to generation.Often the hardest part, especially for an inexperienced PLC programmer, is practicing the mental ju-jitsu necessary to keep the nomenclature straight from manufacturer to manufacturer.

Positive Logic (most PLCs follow this convention) :-True = logic 1 = input energized.False = logic 0 = input NOT energized.

Negative Logic :-True = logic 0 = input NOT energizedFalse = logic 1 = input energized.

Normally Open :-(XIC) - eXamine If Closed.

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This instruction is true (logic 1) when the hardware input (or internal relay equivalent) is energized.

Normally Closed :-(XIO) - eXamine If Open.This instruction is true (logic 1) when the hardware input (or internal relay

equivalent) is NOT energized.

Output Enable :-(OTE) - OuTput Enable.This instruction mimics the action of a conventional relay coil.

On Timer :-(TON) - Timer ON.Generally, ON timers begin timing when the input (enable) line goes true, and

reset if the enable line goes false before setpoint has been reached. If enabled until setpoint is reached then the timer output goes true, and stays true until the input (enable) line goes false.

Off Timer :-(TOF) - Timer OFF.Generally, OFF timers begin timing on a true-to-false transition, and continue

timing as long as the preceding logic remains false. When the accumulated time equals setpoint the TOF output goes on, and stays on until the rung goes true.

Retentive Timer :-(RTO) - Retentive Timer On.This type of timer does NOT reset the accumulated time when the input condition

goes false.Rather, it keeps the last accumulated time in memory, and (if/when the input goes true again) continues timing from that point. In the Allen-Bradley construction, this instruction goes true once setpoint (preset) time has been reached, and stays true until a RES (RESet) instruction is made true to clear it.

Latching Relays :-(OTL) - OuTput Latch.(OTU) - OuTput Unlatch.Generally, the unlatch operator takes precedence. That

is, if the unlatch instruction is true then the relay output is false even though the latch

71

instruction may also be true. In Allen-Bradley ladder logic, latch and unlatch relays are separate operators.However, other ladder dialects opt for a single operator modeled after RS (Reset-Set) flip-flop IC chip logic.

Jump to Subroutine :-(JSR) - Jump to SubRoutineFor jumping from one rung to another the JSR (Jump to Subroutine) command is used.

6.1.2: Operating cycle :-

With the logic program entered into the controller, placing the controller in the

Run mode initiates an operating cycle as shown in fig (6.2). The controller’s operating

cycle consists of a series of operations performed sequentially and repeatedly, unless

altered by your program logic.

Fig.(6.2)Operating Cycle

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[1] Input Scan : -

The time required for the controller to scan and read all input data; typically

accomplished within mseconds.

[2] Program Scan : –

The time required for the processor to execute the instructions in the program. The

program scan time varies depending on the instructions used and each instruction’s status

during the scan time.

[3] Output scan : –

The time required for the controller to scan and write all output data; typically

accomplished within mseconds.

[4] Service Communications : –

The part of the operating cycle in which communication takes place with other

devices, such as an HHP or personal computer.

[5] Housekeeping and Overhead : –

Time spent on memory management and updating timers and internal registers.

You enter a logic program into the controller using a programming device. The logic

program is based on your electrical relay print diagrams. It contains instructions that direct

control of your application.

6.1.3 Processor File :-

The processor provides control through the use of a program you create, called a

processor file. This file contains other files that break your program down into more

manageable parts. Most of the operations you perform with the programming device

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involve the processor file with its two components created with it namely program files

and data files as shown in fig (6.3).

FIG.(6.3) Processor Files

The programming device stores processor files on hard disk (or floppy disk).Monitoring

and editing of processor files is done in the workspace of the computer. After you select a

file from disk and edit it, you then save the file hard to disk, replacing the originaldisk

version with the edited version. The hard disk is the recommended location for a processor

file as shown in fig (6.4).

Fig.(6.4)Saving Of Processor Files

Processor files are created in the offline mode using the programming device. These files

are then restored (downloaded), to the processor for online operation.

74

[1] Program Files :-

Program files contain controller information, the main ladder program;

interruptsubroutines, and any subroutine programs.

These files are:

System Program (file 0) – This file contains various system relatedinformation and user-

programmed information such as processor type, I/Oconfiguration, processor file name,

and password.

Reserved (file 1) – This file is reserved.

Main Ladder Program (file 2) – This file contains user-programmedinstructions defining

how the controller is to operate.

User Error Fault Routine (file 3) – This file is executed when a recoverablefault occurs.

High-Speed Counter Interrupt (file 4) – This file is executed when an HSCinterrupt

occurs. It can also be used for a subroutine ladder program.

Selectable Timed Interrupt (file 5) – This file is executed when an STI occurs.It can also

be used for a subroutine ladder program.

Subroutine Ladder Program (files 6 – 15) – These are used according tosubroutine

instructions residing in the main ladder program file or othersubroutine files.

[2] Data Files :-

Data files contain the status information associated with external I/O and all

otherinstructions you use in your main and subroutine ladder program files. In

addition,these files store information concerning processor operation. You can also use

thefiles to store “recipes” and look-up tables if needed.These files are organized by the

type of data they contain.

The data file types are:

Output (file 0) – This file stores the state of the output terminals for thecontroller.

Input (file 1) – This file stores the status of the input terminals for thecontroller.

Status (file 2) – This file stores controller operation information. This file isuseful for

troubleshooting controller and program operation.

75

Bit (file 3) – This file is used for internal relay logic storage.

Timer (file 4) – This file stores the timer accumulator and preset values andstatus

bits.rogramming

Counter (file 5) – This file stores the counter accumulator and preset valuesand the status

bits.

Control (file 6) – This file stores the length, pointer position, and status bits forspecific

instructions such as shift registers and sequencers.

Integer (file 7) – This file is used to store numeric values or bit information.

6.2 Software used for programming :-

Here we usedRSLogix™ 500 to construct elevator program on PC. The

RSLogix™ family of IEC-1131-compliant ladder logic programming packages helps to

maximize performance, save project development time, and improve productivity. This

family of products has been developed to operate on Microsoft®, Windows® operating

systems. Supporting the Allen-Bradley SLC™ 500 and MicroLogix™ families of

processors, RSLogix™ 500 was the first PLC® programming software to offer unbeatable

productivity with an industry-leading user interface. RSLogix™ 5 supports the Allen-

Bradley PLC-5® family of programmable controllers. TheseRSLogix products share:

Flexible, easy-to-use editors, Common look-and-feel, Diagnostics and troubleshooting

tools, powerful, time-saving features and functionality.

RSLogix programming packages are compatible with programs created with Rockwell

Software’s DOS-based programming packages for the PLC-5 or SLC 500 and MicroLogix

families of processors, making program maintenance across hardware platforms

convenient and easy. Fig(23)shows how RSLogix500 looks like on PC monitor screen.

6.2.1 Features of RSLogix™ 500 :-

The RSLogix™ family of IEC-1131-compliant ladder logic programming packages helps you maximize performance, save project development time, and improve productivity. This family of products has been developed to operate on Microsoft

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Windows® operating systems. Supporting the Allen-Bradley SLC™ 500 and MicroLogix™ families of processors, RSLogix™ 500 was the first PLC® programming software to offer unbeatable productivity with an industry-leading user interface. 

RSLogix 500 programming package is compatible with programs created with Rockwell Software DOS-based programming packages for the SLC 500 and MicroLogix families of processors, making program maintenance across hardware platforms convenient and easy. Supporting the Allen-Bradley SLC™ 500 and MicroLogix™ families of controllers, RSLogix 500 programming software helps you maximize performance, save project development time, and improve productivity with an industry-leading user interface.Developed to operate on Microsoft Windows® 2000 or later operating systems, RSLogix offers reliable communications, powerful functionality, and superior diagnostics. RSLogix 500 offers:

• Flexible, easy-to-use editors

• Diagnostic and troubleshooting tools

• Powerful, timesaving features and functionality

• Convenient and easy maintenance across hardware platforms

[1] Powerful, Flexible Programming :-Combine the ease of ladder logic with the power of Allen-Bradley software, and

you get a micro that makes it simple to program even the most difficult applications.

[2] Flexible communications :-

Both [Windows® & NT] and A.I. Series™ (DOS) for the MicroLogix 1400

programming packages support Allen-Bradley DF1 full-duplex communications. Direct

PC connectivity to your controller through the RS-232 port eliminates the need for

additional hardware interface, and allows remote programming by phone modem.

[3] Streamlined editing features :-

It's easy to create, edit, monitor, and troubleshoot ladder logic programs with such

functions as:

Command line entry of instructions and parameters — saves keystrokes and time

Search and replace — for fast modifications

Cut, copy, paste, drag & drop — lets you edit and re-use ladder logic

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[4] On-line context sensitive help :-

Guides you through common tasks and provides detailed instruction descriptions.

[5] Extensive documentation :-

Provide application comment for rungs, addresses, and instructions that can be

viewed on-line.

[6] Wide variety of reports :-

Include program listing (ladder logic), data table contents, cross-reference, and

documentation database listing.

[7] Available in five languages :-

The global design of this product supports English, French, German, Italian, and

Spanish language versions of application menus, prompts, messages, and all user

documentation.

[8] Family program :-

Our programming tools for the SLC 500, RS Logix 500, and A.I. Series can be

used to program all MicroLogix 1400 controllers. Programs for SLC 500s easily convert

for use on MicroLogix programmable controllers.

[9] Hand-Held Problem Solver :-

MicroLogix 1400 puts remarkable problem-solving capabilities at your fingertips

with an advanced, easy-to-use Hand-Held Programmer (HHP). This streamlined unit fits

right into your pocket and provides full programming support for the MicroLogix

controller while delivering among the most powerful troubleshooting capabilities in the

industry.

Search key simplifies address location.

Trace key reduces troubleshooting time by quickly locating the source of a faulty output.

Navigation keys let you move between rungs and from instruction to instruction, saving

time.Six user-selectable languages: English, French, German, Italian, Spanish, and

Japanese.

Textual fault messages convey information instantly, no need to look up codes.

EEPROM memory module lets you move programs to multiple controllers.

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6.3 Ladder diagram for elevator:

Main Program:

Floor Sensing Subroutine:

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Floor Calling Subroutine:

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6.4 Inputs & Outputs of PLC

Table 4.1: Inputs & Outputs of PLC

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INPUTS

I:0/10 Master Switch.

I:0/1 Limit Switch For 1ST Floor.

I:0/2 Limit Switch For 2ND Floor.

I:0/3 Limit Switch For 3RD Floor.

I:0/4 Push Button For 1ST Floor

I:0/5 Push Button For 2ND Floor.

I:0/6 Push Button For 3RD Floor.

OUTPUTS

Q1 UP motion of driving motor.

Q2 DOWN motion of driving motor.

CONCLUSION &

FUTURE SCOPE

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7. CONCLUSION & FUTURE SCOPE

7.1 Conclusion:

In this small attempt we have tried to control the elevator which is situated in a

three storied building with the help of a Programmable logic controller. We have tried to

reproduce the exact facsimile of the elevator PLCs are used in many real world

applications Almost any application that needs some type of electrical control has a need

for a PLC. The bigger process, the more is a need for a PLC. We can simply program the

PLC to count its inputs and give the required outputs. We have developed a system, which

is based on the electronic control of the PLC. With the help of PLC it is very easy to scan

inputs of the elevator to achieve faster operation.

7.2 Future Scope:

The elevator is not provided with generator back up. The door closure display is

not integrated; instead we have simulated the condition by having the toggle switch on

each floor. Digital displays may be included. Weight sensor can be added to indicate

overload condition. First come first serve method can be employed by making

changes in ladder programming.

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