Lesson 1: Introduction to Control Systems Technology

Transcription

1 8/7/05 Lesson : Introduction to ontrol Systes Technology ET 48a Autoatic ontrol Systes Technology lessonet48a.pptx Learning Objectives After this presentation you will be able to: Explain the function of an autoatic control syste. Identify a block diagra representation of a physical syste Explain the difference between an open loop and closed loop control syste Define a transfer function and copute the gain for sinusoidal input/output cases. educe block diagra systes using algebra. lessonet48a.pptx

2 8/7/05 The ontrol Proble Fundaental ontrol oncepts Maintain a variable of process at a desired value while rejecting the effects of outside disturbances by anipulating another syste variable. Exaples: eating and ooling hoes and offices Autoobile cruise control old the position of a echanical linkage Maintain level in a tank h Q out depends on h If Q out = Q in, h constant Q out > Q in, tank epties Q out < Q in, tank overflows lessonet48a.pptx Basic Subsystes of ontrol Feedback ontrol Subsystes Measureent ontrol decision Syste odification Measureentsight glass ontrol Decision uan adjusts Q out to aintain h = 4 eference (setpoint) h = control variable lessonet48a.pptx Process Maintain tank level Final ontrol Eleent alve

3 8/7/05 Autoatic ontrol Systes Use sensors and analog or digital electronics to onitor and adjust syste Level Measureent Sensor ontroller Final control eleent Eleents of Autoatic ontrol Process single or ultiple variables Measureent sensors Error Detection copare to h ontroller generate corrections Final ontrol Eleent odify process 5 lessonet48a.pptx Maintain level alve Position Block Diagras Autoatic control systes use atheatical descriptions of subsystes to reduce coplex coponents to inputs and outputs Input signal ontrol Syste oponent Output signal Energy Source (Optional) Signals flow between coponents in syste based on arrow direction 6 lessonet48a.pptx

4 8/7/05 Typical oponent Block Diagras T ( ) Teperature Sensor out () in () Aplifier out () Arature a () Dc Motor n (rp) alve Position (% Open) ontrol alve Liquid Flow ( /s) L (ft) Level Transitter urrent (A) Error E () ontroller orrection () 7 lessonet48a.pptx Transfer Functions Transfer function ratio of the output to the input of a control syste coponent. enerally a function of frequency and tie. A sin(wt+a) B sin(wt+b) Block ain onvert to phasors and divide B A Output Signal Input Signal Bb B b a Aa A Phase shift related to tie delay 8 lessonet48a.pptx 4

5 8/7/05 Transfer Functions Exaples Exaple : Find transfer function of teperature sensor in block diagra T ( ) Teperature Sensor out () Output Signal Input Signal T out / Exaple : a currenttovoltage converter takes an input of 7.50 A and produces an output of 8.57 Deterine the transfer function gain and sketch the block diagra. I in 8.57 o 7.50 A Output Signal Input Signal o Iin 8.57 /A 7.50 A I in (A) Ito onverter out () /A 9 lessonet48a.pptx OpenLoop ontrol Open loop control odifies output based on predeterined control values. There is no actual easureent of controlled quantity. ontroller Final control eleent Tank level ay vary with outside disturbances and syste changes ontroller alve setting ontrol alve Output flow Tank Tank Level 0 lessonet48a.pptx Disturbances 5

6 8/7/05 losed Loop ontrol losed loop control odifies output based on easured values of the control variable. Measured value copared to desired value and used to aintain desired value when disturbances occur. losed loop control uses feedback of output to input. + Desired alue ontroller alve setting ontrol alve Output flow Tank Tank Level Level Measureent Measured level lessonet48a.pptx losed Loop ontrol Exaple: Auto ruise ontrol Disturbances Set Speed + ontroller Fuel flow Fuel Injectors Mechanical Power Engine Auto Actual Speed Error Speed Sensor Disturbances: Up hill/ down hill ead wind/ tail wind lessonet48a.pptx 6

7 8/7/05 eneralized losed Loop ontrol Block Diagra of Servo ontrolexaple Positioning Systes + E= ontroller =/E Measureent = / lessonet48a.pptx eference = Error = E ontrolled ariable = Measured ariable = eneralized losed Loop ontrol Find overall transfer function using signal flow algebra For servo control Find (Input)(ain)=(Output) E E E E E 4 lessonet48a.pptx ( ) 7

8 8/7/05 Overall Transfer FunctionServo ontrol Find ( ) Multiply through by ( ) ( ) ( ) Add to both sides Factor out of right hand side Divide both sides by (+) Divide both sides by 5 lessonet48a.pptx eneralized losed Loop ontrol Block Diagra of Process ontrolexaple heical eactors SP + E= ontrol Modes c =/E Manipulated ariable =M/ M Process p =/M Measureent = / D=Disturbances 6 Setpoint = SP Error = E ontrolled ariable = lessonet48a.pptx Measured ariable = Manipulated ariable = M ontroller Output = 8

9 8/7/05 9 Overall Transfer Function Process ontrol lessonet48a.pptx 7 Find overall transfer function of process control using signal flow algebra Series blocks ultiple M M E p c M M E p c E Find overall transfer function /SP not directly easurable in process control lessonet48a.pptx 8 Overall Transfer Function Process ontrol As before SP E SP SP ) (SP ) (SP ) (SP E SP SP ) ( SP Substitute in for E Substitute in for eliinate it Multiple both sides by Multiple L.. side by Add to both sides Factor fro right side Divide both sides by (+) Divide both sides by SP

10 8/7/05 ontrol Syste Drawings Industrial syste standard ANSI/ISAS5.984 Unifor designation for Instruents, instruent systes and control. eneral Instruent Sybol First ID Letter A = Analysis L = Level T = Teperature Functional Identifier Loop Identifier Following ID Letter = ontroller I=Indicator =ecorder T= Transitter = alve Y = elay/onverter Instruent Line Sybols 5 psi pneuatic line 40 A electric current Filled Syste apillary lessonet48a.pptx 9 ontrol Syste Drawings eating Fluid Supply T 0 urrent to Pneuatic onverter I/P LY 0 L 0 LI LT 0 0 Water Supply Syrup Supply A 0 A 0 0 =level control 0 = teperature control 0 = concentration control 40 A current oncentration alve oncentration ecorder/ontrol TI TT 0 0 eating Fluid eturn AT 0 Syrup oncentration eated Product oncentration Transitter 0 lessonet48a.pptx Teperature Transitter Teperature Indicator/ontrol 0

11 Output Signal Output Input Signal Output Output 8/7/05 Linear and Nonlinear esponse Linear esponse Input 0 Linear transfer functions give proportional outputs. In this case the factor is Tie Input Output lessonet48a.pptx Nonlinear esponse Saturation NonLinearity Saturation NonLinearity Tie Input Signal 0 Input Saturation NonLinearity Saturation nonlinearity typical of practical systes that have physical liits. Aplifiers, control valves 0 lessonet48a.pptx Tie Output Signal

12 Output Output 8/7/05 Other NonLinearities ystersis NonLinearity 40 eneral NonLinearity Input Typical in agnetic circuit and in instruentation transducers 40 0 Input Nonlinearities cause distortion in sine waves response that is not proportional to inputs value for all signal values. lessonet48a.pptx Block Diagra Siplifications + Also reeber that blocks in series ultiply Block diagra at left siplifies to the above. an use this to reduce ultiple loops into one Block. Equivalent Block 4 lessonet48a.pptx

13 8/7/05 Block Diagra Siplification Exaple lessonet48a.pptx educe the inner loop obine outer feedback block obine reduced inner loop with reaining forward gain blocks Block Diagra Siplification Exaple () lessonet48a.pptx 6 + = opute the value of Substitute the values of and into forula and siplify

14 8/7/05 4 Block Diagra Siplification Exaple () lessonet48a.pptx 7 Answer Multiply top and botto of ratio by (+ ) and siplify educed block End Lesson : Introduction to ontrol Systes Technology ET 48a Autoatic ontrol Systes Technology lessonet48a.pptx 8