final control element(chp3)

FINAL CONTROL ELEMENT

FINAL CONTROL ELEMENT

The final control element adjust the amount of energy/mass goes into or out from process as commanded by the controllerThe common energy source of final control elements are:ElectricPneumaticHydraulic

*MASON/FINAL CONTROL ELEMENT/2010

MASON/FINAL CONTROL ELEMENT/2010

ELECTRIC FINAL CONTROL ELEMENT

Electric current/voltageSolenoidStepping MotorDC MotorAC Motor



CHANGING CURRENT/VOLTAGE

Current or voltage can be easily changed to adjust the flow of energy goes into the process e.g. in heating process or in speed controlHeater elements are often used as device to keep the temperature above the ambient temperature. Energy supplied by the heater element is

W = i2rt (i=current, r=resistance, t=time)Motor is often used as device to control the speed



CHANGING CURRENT/VOLTAGE

Using PotentiometerAmplifierWard Leonard systemSwitch (on-off action)



Changing Current/VoltageUsing Rheostat

I = V/(R1+R2)Power at rheostatP1 =I2R1Power at heaterP2 =I2R2Disadvantage loss of power at rheostatRheostatHeaterR1R2VI*MASON/FINAL CONTROL ELEMENT/2010


Example of Heating elements



Changing Current/VoltageUsing Amplifier

VPotentiometerR1R2amplifierV+VHeaterDisadvantage loss of power at potentiometer (very small) and at Amplifier*MASON/FINAL CONTROL ELEMENT/2010


Changing Current/VoltageUsing Ward Leonard System

Introduced by Harry Ward Leonard in 1891Use a motor to rotate a generator at constant speedThe output of generator voltage is adjusted by changing the excitation voltageSmall change in excitation voltage cause large change in generator voltageAble to produce wide range of voltage (0 to 3000V)Ward Leonard system is popular system to control the speed of big DC motor until 1980sNow a days semi conductors switches replaces this system



Changing Current/VoltageUsing Ward Leonard System

MOTORGENERATOR

excitation voltage*MASON/FINAL CONTROL ELEMENT/2010


Changing Current/VoltageUsing Switch

The switch is closed and opened repeatedlyNo power loss at switch

VLOADSwitchtVLVLVSwitch closedSwitch opened*MASON/FINAL CONTROL ELEMENT/2010


DUTY CYCLE

T is period time typical in millisecond order (fix)Ton is switch on time (adjustable)Toff is switch off time

Duty Cycle is: (Ton/T) 100%tVLVTonToffTOf course we can not use mechanical switches to carry on this task, electronic switches to be used instead.E.g. Transistor, Thyristor, or IGBTThis methods is often called as Pulse Width Modulation (PWM)



SOLENOID

When the coil is energized the core will be pulled in

SOLENOIDcorecoilcoilcore*MASON/FINAL CONTROL ELEMENT/2010


SOLENOID

When the coil is energized the core will be pulled in

VSIMULATE*MASON/FINAL CONTROL ELEMENT/2010


SOLENOID

Tubular solenoidOpen frame solenoidRotary solenoid*MASON/FINAL CONTROL ELEMENT/2010


Solenoid



Solenoid Usage

pushing buttons, hitting keys on a piano, Open closed Valve, Heavy duty contactorjumping robotsetc



STEPPING MOTOR

The top electromagnet (1) is turned on, attracting the nearest teeth of a gear-shaped iron rotor. With the teeth aligned to electromagnet 1, they will be slightly offset from electromagnet The top electromagnet (1) is turned off, and the right electromagnet (2) is energized, pulling the nearest teeth slightly to the right. This results in a rotation of 3.6 in this example. *MASON/FINAL CONTROL ELEMENT/2010


STEPPING MOTOR

The bottom electromagnet (3) is energized; another 3.6 rotation occurs. The left electromagnet (4) is enabled, rotating again by 3.6. When the top electromagnet (1) is again enabled, the teeth in the sprocket will have rotated by one tooth position; since there are 25 teeth, it will take 100 steps to make a full rotation in this example. *MASON/FINAL CONTROL ELEMENT/2010


STEPPING MOTOR

Practical stepping motor can be controlled for full step and half step.Common typical step size is 1.8o for full step and 0.90 for half stepFull step is accomplished by energizing 2 adjacent electromagnet simultaneously. Half step is accomplished by energizing 1 electromagnet at a time.



Stepping motor



DC Motor

The brush*MASON/FINAL CONTROL ELEMENT/2010


DC Motor



Practical DC Motors

Every DC motor has six basic parts axle, rotor (a.k.a., armature), stator, commutator, field magnet(s), and brushes. For a small motor the magnets is made from permanent magnet*MASON/FINAL CONTROL ELEMENT/2010


2 pole motor

Animate*MASON/FINAL CONTROL ELEMENT/2010


2 pole motor

Animatecontinue*MASON/FINAL CONTROL ELEMENT/2010


3 pole DC motors

+The coil for each poles are connected serially. The commutator consist of 3 sector, consequently one coil will be fully energized and the others will be partially energized.132*MASON/FINAL CONTROL ELEMENT/2010


3 pole DC motors

animatenextThe commutator and the coil is arranged in such a way that the polarity of each pole is as shown*MASON/FINAL CONTROL ELEMENT/2010


DC motors

As the rotor is rotating, back emf (Ea) will be produced, the faster the rotor turn the higher Ea and the smaller Ia.The starting current of motors will be much higher then the rating current.

motorVEaIa*MASON/FINAL CONTROL ELEMENT/2010


DC motors

For big motors the magnet is made from coil and core. The current flowing in the coil is called If and the current flowing in the armature is called Ia.The armature winding and the field winding are connected to a common power supply The armature winding and the field winding are often connected in series, parallel, or compound. The torque characteristic will be different for each connection.The figure shows a parallel connection

Field windingArmature winding*MASON/FINAL CONTROL ELEMENT/2010


SERIES DC MOTOR

Field and armature winding are series connected, this type of motor is called series DC motor*MASON/FINAL CONTROL ELEMENT/2010


DC motors

Field and armature winding are parallel connected, this type of motor is called shunt DC motor*MASON/FINAL CONTROL ELEMENT/2010


DC MOTOR

Compound DC motor is DC motor having 2 field winding the first one is connected parallel to the armature winding and the other is connected series*MASON/FINAL CONTROL ELEMENT/2010


DC MOTOR

Torque: T = KIaK is a constant magnetic flux Ia is armature currentMagnetic flux is constant if it is from permanent magnetIt is depend on the If if it is produced by current



DC MOTOR TORQUE-SPEED CURVE

Torque: T = KIa*MASON/FINAL CONTROL ELEMENT/2010


SERIES DC MOTOR TORQUE-SPEED CURVE

Torque: T = KIaT= KIa2*MASON/FINAL CONTROL ELEMENT/2010


SHUNT DC MOTOR TORQUE-SPEED CURVE

Torque: T = KIa*MASON/FINAL CONTROL ELEMENT/2010


COMPOUND DC MOTOR TORQUE-SPEED CURVE



SYNCHRONOUS AC MOTOR

~The rotating field.When alternating current is applied to the field coil the magnetic field will also alternating. Therefore the permanent magnet will rotate

o311-311




~

o311-311

This motor has 2 polesIf the frequency of the current is f hertz (cycle/s) then the rpm n = f rps n = (120f)/p rpmWhere p is the number of the poles*MASON/FINAL CONTROL ELEMENT/2010



4 pole motor*MASON/FINAL CONTROL ELEMENT/2010


THREE PHASE SYNCHRONOUS AC MOTOR

4 pole 3 motor

TSRRST*MASON/FINAL CONTROL ELEMENT/2010


SYNCHRONOUS AC MOTOR USING EXTERNAL EXITER

The magnetic flux of permanent magnet is low for a bigger motor we have to use externally exited magnetic field*MASON/FINAL CONTROL ELEMENT/2010


ASYNCHRONOUS AC MOTOR

IinducedWhen instead of exited, the rotor coil is shorted an induced current will be generated and the rotor will be magnetized and start to turn.The faster the speed the smaller the induced current and finally the current will cease at synchronous speed and so does the rotationThis motor will turn at speed less the its synchronous rotation that is why it called asynchronous motorThis motor is also called induction motor



Calculating Motor Speed

A squirrel cage induction motor is a constant speed device. It cannot operate for any length of time at speeds below those shown on the nameplate without danger of burning out.To Calculate the speed of a induction motor, apply this formula:

Srpm = 120 x F P Srpm = synchronous revolutions per minute.120 = constantF = supply frequency (in cycles/sec)P = number of motor winding polesExample: What is the synchronous of a motor having 4 poles connected to a 60 hz power supply?

Srpm = 120 x F PSrpm = 120 x 60 4Srpm = 7200 4Srpm = 1800 rpm*MASON/FINAL CONTROL ELEMENT/2010


Calculating Braking Torque

Full-load motor torque is calculated to determine the required braking torque of a motor.To Determine braking torque of a motor, apply this formula:

T = 5252 x HP rpm T = full-load motor torque (in lb-ft)5252 = constant (33,000 divided by 3.14 x 2 = 5252)HP = motor horsepowerrpm = speed of motor shaftExample: What is the braking torque of a 60 HP, 240V motor rotating at 1725 rpm?

T = 5252 x HP rpmT = 5252 x 60 1725T = 315,120 1725T = 182.7 lb-ft*MASON/FINAL CONTROL ELEMENT/2010


Calculating Work

Work is applying a force over a distance. Force is any cause that changes the position, motion, direction, or shape of an object. Work is done when a force overcomes a resistance. Resistance is any force that tends to hinder the movement of an object.If an applied force does not cause motion the no work is produced.To calculate the amount of work produced, apply this formula:W = F x DW = work (in lb-ft)F = force (in lb)D = distance (in ft)Example: How much work is required to carry a 25 lb bag of groceries vertically from street level to the 4th floor of a building 30' above street level?W = F x DW = 25 x 30W = 750 -lb



Pneumatic Actuator*MASON/FINAL CONTROL ELEMENT/2010


Pneumatic ActuatorReverse-Acting Actuator*MASON/FINAL CONTROL ELEMENT/2010


I/P Converter

A "current to pressure" converter (I/P) converts an analog signal (4-20 mA) to a proportional linear pneumatic output (3-15 psig). Its purpose is to translate the analog output from a control system into a precise, repeatable pressure value to control pneumatic actuators/operators, pneumatic valves, dampers, vanes, etc.

I/PAir supply 30 psiCurrent 4 to 20 mA Pneumatic 3 to 15 psiSupplied to actuator*MASON/FINAL CONTROL ELEMENT/2010


Sample of I/P Converter



Generation and distribution of pneumatic pressure

Compressor is needed for pneumatic system

compressor100 psiPSPC30 psiRegulator valveTo I/PTank *MASON/FINAL CONTROL ELEMENT/2010


Hydraulic Actuator



AdvantageDisadvantage *MASON/FINAL CONTROL ELEMENT/2010

ELECTRICPNEUMATICHYDRAULICAccurate positionSuit to advance control No tubingInexpensiveFastNo pollution No return lineNo stall damageLarge capacityLocking capabilitySelf lubricatingEasy to controlSmooth operation

Low speedExpensiveUnsafeNeed brakeoverheatingLow accuracyNoise pollutionDifficult speed controlNeed infrastructure ExpensiveLeakage problemsDifficult speed controlNeed return lineNeed infrastructure


final control element(chp3)

Documents

harry ward leonard

vward leonard system

heating process

i2r2disadvantage loss

wide range of voltage

speed controlheater

opened repeatedlyno

time adjustabletoff