运用PID控制英文文献.docx

1、运用PID控制英文文献Application Note 83402Original InstructionsPID ControlWoodward wishes to thank and acknowledge E. I. Du Pont De Nemours & Company, Inc. for grantingpermission to use information presented in Du Ponts ELIAS Instrumentation Training Program booklet in thisWoodward publication. Du Ponts copy

2、right to the above mention document is as follows:Copyright (1970) E. I. Du Pont De Nemours & Company, Inc.Written by Larry McLeisterWoodward Governor Company reserves the right to update any portion of this publication at any time. Information providedby Woodward Governor Company is believed to be

3、correct and reliable. However, no responsibility is assumed by WoodwardGovernor Company unless otherwise expressly undertaken. Woodward 1992All Rights ReservedApplication Note 83402 PID ControlWoodward 1ContentsCHAPTER 1. INTRODUCTION. 2Process Control Loop . 2Automatic Control . 3Control Loop . 4Co

4、ntrol Modes . 4Control Modes (Car Analogy) . 5Proportional Control . 5Integral (Reset) . 5Derivative (Preact and Rate Time) . 5Control Responses . 6CHAPTER 2. SINGLE-MODE CONTROL . 7On-Off Control . 7Proportional Response . 9Proportional Gain (Effect of Settings) . 9Chapter 2 Summary . 10Chapter 2 R

5、eview Questions . 10CHAPTER 3. INTEGRAL AND DERIVATIVE CONTROL . 11Proportional + Integral (Open Loop) . 11Integral . 12Proportional + Integral (Closed Loop) . 13Integral (Effects of Settings) . 14Derivative Response . 15Derivative (Minutes) . 16Proportional + Derivative (Closed Loop) . 17Derivative

6、 (Effects of Settings) . 18Proportional + Integral + Derivative (Closed Loop) . 19Chapter 3 Summary . 19Chapter 3 Review . 20CHAPTER 4. TUNING GUIDELINES . 22Controller Tuning Method Sample. 24Controller Field Tuning General . 25Controller Field Tuning Procedure . 27PID Control Application Note 8340

7、22 WoodwardChapter 1.IntroductionProcess Control LoopWith this block diagram of a control loop, the following can be shown: The dashes surrounding the measurement transmitter, the control station, andthe controller indicate the local control station since all parts are within onecase. The dashes sur

8、rounding the control station and controller only indicate theremote control station.The controller in this case may be mounted one of three ways: on the control station behind the control panel on a rack with other controllers in the field on or near the control valve.It may also be an integral part

9、 of the control station as the one used in the trainingsetup.Both types of control stations will have some way of indicating (or recording) theprocess variable, some means for adjusting the desired set point, and a means forreading the controller output to the control valve. The local control statio

10、n may ormay not have a means for manually controlling the control valve. The remotewill always have this facility. The local control station requires frequent visitationto determine quality of control. The remote station is centrally located, thereforereducing travel time and allowing side-by-side c

11、ontrol quality scanning.Application Note 83402 PID ControlWoodward 3The function of each block of the diagram is as follows:1. Measurement transmittermeasures the process variable (temperature,pressure, level, flow, or analysis) and converts the measurement to unitsuseful to the controller (psig, kP

12、a, etc) or some electronic value such as 420mA.2. The control station provides facility for setting the desired control point,reading the value of the measurement, transferring the operation from manualto automatic or automatic to manual, and allows manual loading of the controlvalve.3. The controll

13、er takes the set point value of the control station, compares itsvalue to the measurement and reacts to the difference according to the valuesset on each response, proportional, reset and derivative.4. The output signal from the controller positions the control valve.5. The process changes resulting

14、 from the valve changes are felt by themeasurement and the procedure continues.Automatic ControlThis chart is a simplified form of the previous chart. There are three things that takeplace: measurement decision actionMeasurement, of course, is the process variable to be controlled.The decision is th

15、e controller.The action is the control valve, sometimes called the final element.Note that the arrows flow continuously as does the function of any closed loopcontrol system. All sections of the control system are continuously connected, eventhough action does not take place unless a change takes pl

16、ace that results in theprocess variable measured deviating from the set point (desired control point).PID Control Application Note 834024 WoodwardTo break the connection between any section of the loop would result in an openloop configuration. Of course, the process will then not respond to control

17、ler action.However, as later charts will show, open loop configuration is a unique way ofobserving controller actions or responses on an individual basis and without theinterfering process response.Control LoopMeasurement (Transmitter)1. Temperature2. Pressure3. Level4. Flow5. X-AnalysisDecision (Co

18、ntroller)1. Set point vs. measurement2. Controller responseAction (Final Element)1. Control valve2. Pump3. RheostatControl loop components consist of those shown on the above chart. As mentionedearlier, three things take place in a closed loop control systemMeasurement,Decision, Action, whenever the

19、 system is in automatic. The measurement sectionis connected directly to the process and transmits the variable to be controlled tothe control station, usually some distance away. The control station, whichtechnically includes the controller, allows comparison between the desired controlpoint (set p

20、oint) and the measured control point. The amount of the deviation, therate of the deviation and the duration of the deviation all predict controller responseaccording to the controllers gain, derivative and reset settings.The action is simply the result of the controller output. It may be something

21、otherthan a control valve.Control Modes On-Off Or (Deadband) Proportional or (Prop_Gn) Integral or (Int_Gn) Derivative or (S_D_R)As mentioned earlier, modes of control refer to the various types of controlavailable. Also it must be remembered that the type of control should match theprocess. For exa

22、mple, on-off control is quite adequate for home heating systems,but would be very unsatisfactory in most petroleum/chemical applications becauseof its cyclic characteristic.Proportional control eliminates the cyclic characteristics of the on-off mode.Integral and Derivative are refinements of and wo

23、rk in conjunction with proportionalcontrol. Special studies of each follow.Application Note 83402 PID ControlWoodward 5Control Modes (Car Analogy)ON-OFFOne speed windshield wiper in light rain.One way to describe terms normally unfamiliar is to draw an analogy to somethingwhich is familiar.The analogy here for On-Off control is turning the windshield wiper on then off.Its speed is not changed. It is simply turned on for one wipe, then turned off.A