the art of control systems 110915

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THE ART OF CONTROL

SYSTEMS

Prof. Moustafa M. Elsayed

(Consultant)[email protected]

By

Controlled

Variable

Process Disturbance

(sensing

element)

Controller:

set point

& error

Control Action:

actuator, control

agent

The Control Process

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Process

Final Control

Element

Disturbance Sensing

Element

Controller

Controlled Variable

(Controlled Medium)Manipulated Variable

(Control Agent)

Closed

Loop

Error Signal

Measurement

Information

Set Point

Disturbance ( Independent Variable)

Types of Control Action

Simple Two- Position Control

Timed Two- Position Control

The action occurs in a time interval

proportional to the deviation from set

point.

Two- Position

Control

- On / Off

- Open/Close

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(Floating Control)

�This is one type of proportional or modulating control

� Final control element moves (at a predetermined rate) in the corrective direction until the controller itself is satisfied or until a movement in the opposite direction is required by the controller

�The controlled variable is “Floating” writhing the differential range.

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�This is also called modulating control

or analogue control.

�Types:

� Proportional only control

� Proportional plus integral control

� Proportional, integral and

derivative control (PID)

Types of Control Action (Proportional Control)

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Proportional, Integral

and Derivative Control (PID)

Actuators�Actuator is a controlled motor, relay, or

solenoid. The actuator converts the

electric, electronic, or pneumatic

energy into rotary, linear or a switching

action as designed.

�Valves & Dampers.

�Normally open & normally closed.

�Types of valves

On/ off

2- way or 3- way

3- way mixing or 3- way diverting

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Valves

Controllers� Function: Compares sensor signal with

a designed set point and regulates an

output signal to a controlled device

�The controller and the sensor can be

combined in a single instrument (e.g.

room thermostat)

�Types: pneumatic, electric/ electronic,

digital

�Pneumatic controller uses pneumatic

elements with variable output air

pressure.

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Controllers�Electric/ electronic controller uses electric/ electronic elements with variable electric volt output.

�Digital controller uses a microprocessor to implement control algorithms on one or multiple control loops. The control algorithm is stored as a program.

Sensors

A sensor is a device that responds

to a change in the controlled

variable

(such as temperature).

The response could be a change in

some physical or electrical property

of the sensing element.

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Applications

�Pressure

�Flow

�Occupancy

�Volt

�Current

�Power

� Energy (Btu meter)

� Relative humidity

� CO2 level

� Dust contamination

� Temperature

� ...etc

DDC System Architecture

�The system architecture refers

to the location of intelligent

panels (microcomputer),

physical location of I/O points,

and how all of these devices

communicate with one another.

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� All DDC systems require an operator interface, called the operator machine interface (OMI), and formerly called the man-machine interface (MMI).

�Most DDC systems also include the abilityto communicate with remote OMI viatelephone lines.

� The disadvantage of the architecture shownin the following figure is that all of theintelligence is in a single location. Ifcommunication is lost, the points on thatpanel can no longer be monitored orcontrolled.


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�To mitigate this problem, DDC have

migrated towards a distributed

intelligence design using several

intelligent control panels instead of one

as shown in this figure.

�Typical the intelligent panel has stand-

alone capability so that if network

communications are lost, each panel

can continue to operate on its own.

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Control Network

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Control Network

Levels of Building Control Systems

1. Management Level: operator information, analysis of results, coordination, etc.

2. Automation Level: processing tasks view to detection, monitoring, closed-loop and open-loop control, etc.

3.Field Level: used for signaling, measuring (also counting), actuating and switching functions.

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Communication

� Proprietary Protocol

� BACnet Protocol

� LONWORKS Protocol

BACNET

�BACnet stands for Building

Automation Control networks.

� Its purpose is to standardize

communication between building

automation devices from different

manufacturers, allowing data to be

shared & equipment to work

together easily.

�BACnet is simply a set of rules for

communicating between building-

automation devices.

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BACNET

�The microprocessors of these

devices are programmed so they

will understand the same language

and conform to BACnet

requirements.

�BACnet may also be used to

interface the HVAC control system

to other building systems, such as

fire systems, access control

systems, security systems, etc.

� A system can also use an architecture that is BACnet-based at higher levels and non-BACnet-based at lower levels. This lets a system interface to other BACnet equipment at the higher levels, but requires a gateway device to translate data between the non-BACnet protocol and BACnet.

� Generally, the gateway complicates the system design and increases costs because of the extra hardware, set-up, and programming time involved with a gateway device.

BACNET

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LONWORKS

�LonWorks is a technology, not a final

product; its principal suppliers sell to

the OEM industry, not the end user.

For example, LonWorks technology is

not, in and of itself, a "home

automation" solution, any more (or

less!) than is the microprocessor.

� In a LonWorks network, no central

control or master-slave architecture

is needed. Intelligent control devices,

called nodes, communicate with each

other using a common protocol.

LONWORKS

�The overall network performs a

complex control application, such

as running a manufacturing line

or automating a building.

�Neuron chip is the “smart part”

of a node; it includes a three 8-bit

inline processor. Two optimized

for executing the Protocol,

leaving the third for the nodes

application.

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�The Lontalk protocol is the basic

communication protocol, which

is used by all participating

network devices.

�A “mark” was devised that

signified that any product bearing

this mark would be interoperate

with any other Lonworks based

product bearing the same mark.

This mark became known as the

LonMark®.

LONWORKS

Internet Building Control

�Physical connection to the

internet: (Internet Service

Provide, ISP)

�Communication protocol

transporting data & messages

between nodes: TCP/IP standard

governs transfer of data over the

internet

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�Gateway to convert information

from one communication

protocol to another and this allow

all devices to speak to one

another: The gateway may serve

an entire BMS, a set of sensor

control points, or an individual

server control point

Internet Building Control

Building Management

System, BMS

(Building Automation

System, BAS)

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BMS Typical Example

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Level 1

DDC- 101

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AHU-101

Internet BMS

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Displaying Building

Information on Internet

� To provide control information via web browsers, the information must be posted on web pages.

� This can be done:

� A supervisory computer for an entire building control system.

� Or an individual devices if they were connected directly to a TCP/IP network

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Improvement in Internet Remote Access

�Dial up access connection of one

building at a time: telephone line,

mobiles

�Dial out for reporting alarm to fixed

locations: pages, phone, email …etc.

�Wireless technology: wireless

sensors (This reduces installation

cost and allows the use of more

sensors, and that increase

availability of information).

Improvement in Internet

Remote Access

�Cell phones with web capabilities

�New servers and web-enabled

telephone: low-cost maintenance

sensors for sight (video), sound,

smell, and touch

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Internet BMS

�DDE = dynamic data exchange

�This enables two applications

running simultaneously to share

data and commands.

�OLE = Object linking and embedding

�This enables object developed in

one software application to be

displayed in another

Possible Connection to

Internet

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Internet BMS

At another facility

On the road

At home

be notified of alarms

“Your” facility with a KMC automation system featuring

WebLite

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Thank You

the art of control systems 110915

Engineering