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National Instruments PID Control Toolkit 371685C-01 manual

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Table of contents for the manual

  • Page 1

    LabWindows TM /CVI TM PID Control Toolkit User Manual LabWindows/CVI PID Control T oolkit User Manual May 2008 371685C-01[...]

  • Page 2

    Support Worldwide Technical Support and Product Info rmation ni.com National Instruments Corporate Headquarters 11500 North Mopac Expressway Aust in, Texas 78759-3504 USA Tel: 512 683 0100 Worldwide Offices Australia 1800 300 800, Austria 43 662 457990-0, Belgium 32 (0) 2 757 0020, Brazil 55 11 3262 3599, Canada 800 433 3488, China 86 21 5050 9800,[...]

  • Page 3

    Important Information Warranty The media on which you receive Natio nal In struments software are warranted not to fail to execute p rogramming instruction s, due to defects in materials and workmanship, for a period of 90 days from date of shipment, as eviden ced by receipt s or other documentation. N ational Instruments will , at its option, repa[...]

  • Page 4

    © National Instruments Corporation v LabWi ndows/CVI PID Contro l Toolkit User Manual Contents About This Manual Conventions ............ .............. .............. ........... .............. ............... .............. .............. ....... v ii Related Documentation ............ .............. ........... .............. .............. ...[...]

  • Page 5

    Contents LabWindows/CVI PID Control Toolkit User Manual vi ni.com Converting between Percentage of Full S cale and Engineering Units ........... 3-9 Using PID on Real-Time (RT) Targets ......................... .............. .............. ...... 3-10 Using PID with DAQ Devices . ......................... ............... ........... ..............[...]

  • Page 6

    © National Instruments Corporation vii LabWi ndows/CVI PID Contro l Toolkit User Manual About This Manual The LabWindows/CVI PID Contro l Toolkit User Manual descri bes the PID Control T oolkit for LabWindo ws ™ /CVI ™ . The manual describes the features, functions, and operation of the toolkit. T o use this manual, you need a basic understand[...]

  • Page 7

    © National Instruments Corporation 1-1 LabWin dows/CVI PID Control T oolkit User Manual 1 Over view of the PID Control T oolkit This chapter describes how to install the toolkit and describes Proportional-Integral-Deriv ati ve (PID) control applications. System Requirements Y our computer must meet the follo wing minimum sys tem requirement s to r[...]

  • Page 8

    Chapter 1 Overview of th e PID Control T oolkit LabWindows/CVI PID Control T oolkit User Manual 1-2 ni.com Activation Instructions The first time you launch LabWindo ws/CVI after installing the PID Co ntrol T oolkit, you are prompted to activ ate the toolkit. Complete th e following steps to act iv ate the PID Control T oolkit. 1. Click Activate Pr[...]

  • Page 9

    Chapter 1 Overview of th e PID Control T oolkit © National Instruments Corporation 1-3 LabWin dows/CVI PID Control T oolkit User Manual PID Control Currently , the PID algorithm is the most comm on control algorithm used in industry . Oft en, PID is used to control processes that incl ude heating and cooling systems, fluid lev el monitoring, flow [...]

  • Page 10

    © National Instruments Corporation 2-1 LabWin dows/CVI PID Control T oolkit User Manual 2 PID Algorithms This chapter explains the f ast PID, precise PID, and autotuning algorithms. The PID Algorithm The PID controller compares the setpoint (SP) to the process va riable (PV) to obtain the error ( e ), as follo ws: e = SP – PV Then the PID contro[...]

  • Page 11

    Chapter 2 PID Algorithms LabWindows/CVI PID Control T oolkit User Manual 2-2 ni.com Implementing the PID Algor ithm with the PID Functions This section describes how the PID Control T oolkit fu nctions implement the fast (positional) PID algorith m. The f ast PID algo rithm is th e default algorithm used in the PID Control T oolkit. Error Calculati[...]

  • Page 12

    Chapter 2 PID Algorithms © National Instruments Corporation 2-3 LabWin dows/CVI PID Control T oolkit User Manual Output Limiting The actual controller output is limited to the range speci fied for control output, as fo llows: and The follo wing formula sho ws the prac tical model of the PID controller . The PID functions use an inte gral sum corre[...]

  • Page 13

    Chapter 2 PID Algorithms LabWindows/CVI PID Control T oolkit User Manual 2-4 ni.com The Precise PID Algorithm This section describes how the PID Control T o olkit functions implem ent the precise PID algorithm. Error Calculation The current error used in calculating integral act ion for the precise PID algorithm is sho wn in the following formula: [...]

  • Page 14

    Chapter 2 PID Algorithms © National Instruments Corporation 2-5 LabWin dows/CVI PID Control T oolkit User Manual T rapezoidal Integration T rapezoidal integration is used to a void shar p changes in integral action when there is a sudden change in the PV or SP . The following formula represents the trapezoidal integration action for the precise PI[...]

  • Page 15

    Chapter 2 PID Algorithms LabWindows/CVI PID Control T oolkit User Manual 2-6 ni.com Figure 2-2 illustrates the auto tuning procedure excited by the setpoint relay experiment, which connects a relay and an e xtra feedback si gnal with the SP . Noti ce that the PID Library autotuning functions directly implement this process. The existing controller [...]

  • Page 16

    Chapter 2 PID Algorithms © National Instruments Corporation 2-7 LabWin dows/CVI PID Control T oolkit User Manual Table 2-2. T uning Formula under P-Only Control (Normal) Contr oller K c T i T d P 0.2 K u — — PI 0.18 K u 0.8 T u — PID 0.25 K u 0.5 T u 0. 12 T u Table 2-3. T uning Formula under P- Only Control (Slow) Contr oller K c T i T d P [...]

  • Page 17

    Chapter 2 PID Algorithms LabWindows/CVI PID Control T oolkit User Manual 2-8 ni.com Note During tuning, the process remains under closed-loop PID control . It is not necessary to switch off the e xisting controll er and perform the experiment under open-loop conditions. In the setpoint relay experiment, the SP sign al mirrors the SP for the PID con[...]

  • Page 18

    © National Instruments Corporation 3-1 LabWin dows/CVI PID Control T oolkit User Manual 3 Using the PID Control T oolkit This chapter contains the basic information you need to design a control strategy using the PID Control T oolkit functions. Designing a Control Strategy When you design a control strategy , sketch a flo wchart that incl udes the[...]

  • Page 19

    Chapter 3 Using the PID Control T oolkit LabWindows/CVI PID Control T oolkit User Manual 3-2 ni.com T uning Controllers Manually The following controller tuning procedures are based on the work of Zi egler and Nichols, the dev elopers of the Quarter -Decay Ratio tuning techniques deri ved fr om a combination of theory and empirical observations (Co[...]

  • Page 20

    Chapter 3 Using the PID Control T oolkit © National Instruments Corporation 3-3 LabWin dows/CVI PID Control T oolkit User Manual Open-Loop (Step T est) T uning Procedure The open-loop (step test) tuning procedure as sumes that you can model an y process as a first-order lag and a pure deadtime. This method requires more analysis t han the closed-l[...]

  • Page 21

    Chapter 3 Using the PID Control T oolkit LabWindows/CVI PID Control T oolkit User Manual 3-4 ni.com Using the PID Librar y The following sections describe how to use th e PID Library to implement a control strateg y . PID Controller The PID controller requires several inputs, includ ing SP , PID gains, timer interval (in case the internal timer is [...]

  • Page 22

    Chapter 3 Using the PID Control T oolkit © National Instruments Corporation 3-5 LabWin dows/CVI PID Control T oolkit User Manual The fast PID algorithm is faster and simpler than the precise PID algorithm. Use the fast algorithm in fast control lo ops. The precise PID algo rithm uses the T wo Degree of Freedom algorithm to control the PV , which g[...]

  • Page 23

    Chapter 3 Using the PID Control T oolkit LabWindows/CVI PID Control T oolkit User Manual 3-6 ni.com Using PID with Autotuning Y ou can use autotuning to improv e controller pe rformance. There are tw o ways in which you can autotune a controller . • Wizard-Based Autotuning —Y ou can use the PID Autotuning W izard to tune the parameters. • Cla[...]

  • Page 24

    Chapter 3 Using the PID Control T oolkit © National Instruments Corporation 3-7 LabWin dows/CVI PID Control T oolkit User Manual If you are using LabW indows/CVI 8.0 and later , click Add Addi tional Mod ule in the Drivers & Components tab of the Edit Installer dialog box. In the Select Merge Module dialog box, browse to and select CVIPIDRunti[...]

  • Page 25

    Chapter 3 Using the PID Control T oolkit LabWindows/CVI PID Control T oolkit User Manual 3-8 ni.com Using PID with Lead-Lag The lead-lag compensator uses a positional algorithm that approximates a true exponential lead-lag. Feed forwar d control schemes often use this kind of algorithm as a dynamic compensator . Using lead-lag, you can simulate ine[...]

  • Page 26

    Chapter 3 Using the PID Control T oolkit © National Instruments Corporation 3-9 LabWin dows/CVI PID Control T oolkit User Manual Y ou can use the setpoint profiler as follo ws: 1. Call PidSetpointProfileCreate to create a setpoint prof il e. Use a pair of time and setpoint value arrays to specify the setpoint profile with the time v alues in ascen[...]

  • Page 27

    Chapter 3 Using the PID Control T oolkit LabWindows/CVI PID Control T oolkit User Manual 3-10 ni.com value of 1 produces an output of 10 fo r a difference between the SP and PV of 10, regardless of the output range and setpoint range. Using PID on Real-Ti me (RT) T argets Some PID applications are dete rministic and, therefore, cannot be run on des[...]

  • Page 28

    Chapter 3 Using the PID Control T oolkit © National Instruments Corporation 3-11 LabWi ndows/CVI PID Control T oolkit User Manu al The control loops can be timed in the following ways: • Software-Timed —In software-timed control loop s, the timing is controlled by the software loop rate. Y ou can implement a software loop with a timer c onstru[...]

  • Page 29

    © National Instruments Corporation A- 1 LabWin dows/CVI PID Control T oolkit User Manual A References The Instrument Society of America (ISA), the organization that sets standards for process control instrume ntation in the United States, offers a catal og of books, journals, and training materials to teach you the b asics of process control progr[...]

  • Page 30

    © National Instruments Corporation B- 1 LabWin dows/CVI PID Control T oolkit User Manual B T echnical Support and Professional Ser vices Visit the following sections of the award-winning National Instruments Web site at ni.com for technical support and professional services: • Support —T echnical support resources at ni.com/support include the[...]

  • Page 31

    Appendix B T echnical Support and Professional Services LabWindows/CVI PID Control T oolkit User Manual B-2 ni.com If you searched ni.com and could not find the answers you need, contact your local off ice or NI corporate h eadquarters. Phone numbers for our worldwide of f ices are listed at the front of this manual. Y ou also can visit the W orldw[...]

  • Page 32

    © National Instruments Corporation G-1 LabWin dows/CVI PID Control T oolkit User Manual Glossar y A algorithm A prescribed set of well-defined rules or processes for the solut ion of a problem in a finite number of steps. autotuning Automatically testin g a process under contr ol to determine the controller gains that will pro vide th e best contr[...]

  • Page 33

    Glossary LabWindows/CVI PID Control T oolkit User Manual G-2 ni.com D damping The progressiv e reduction or suppression of oscillation in a device or system. dead time (T d ) The interval of time, expressed in minutes, between initiation of an input change or stim ulus and the start of the resulting observable response. deri vati ve (control) actio[...]

  • Page 34

    Glossary © National Instruments Corporation G-3 LabWin dows/CVI PID Control T oolkit User Manual I Instrument Societ y of America (ISA) The organization that sets standards for process con trol instrumentation i n the United States. integral (control) action Control action in wh ich the output is proportional to the time int egral of the input. Th[...]

  • Page 35

    Glossary LabWindows/CVI PID Control T oolkit User Manual G-4 ni.com O output limi ting Pre ve nting a controller’ s output from trav eling beyond a desired maximum range. ov ershoot The maximum excursion beyond the fi nal steady-state value of output as the result of an in put change. P P Proportional. PD Proportional, deriv ati ve. PI Proportion[...]

  • Page 36

    Glossary © National Instruments Corporation G-5 LabWin dows/CVI PID Control T oolkit User Manual R ramp The total (transient plus steady-state) time respon se resulting from a sudden increase in the rate of change from zero to some f inite v alue of input stimulus. reentrant ex ecution Mode in which calls to mul tiple instances of a fu nction can [...]

  • Page 37

    © National Instruments Corporation I-1 LabWi n dows/CVI PID Control T oolkit User Manual Index A applications, 1-3 autotuning, 3-6 classic, 3-6 procedure, 3-6 wizard based, 3-6 distributing applications, 3-6 autotuning algorithm tuning formulas, 2-6 PI control (f ast), 2-7 PI control (normal), 2-7 PI control (slow), 2-8 P-only control (normal), 2-[...]

  • Page 38

    Index LabWindows/CVI PID Control T oolkit User Manual I-2 ni.com I installation instructions, 1-1 instrument driv ers (NI resources), B-1 integral action, 2-1 integral time, 2-1 K Kno wledgeBase, B-1 L lag compensation, 3-8 lead compensation, 3-8 lead-lag compensator, 3-8 N National Instruments support and services, B-1 Nichols, N. B., A-1 nonlinea[...]

  • Page 39

    Index © National Instruments Corporation I-3 LabWi n dows/CVI PID Control T oolkit User Manual S setpoint, 1-3 relay experiment, 2-6 software (NI resources), B-1 step test tuning procedure, 3-3 support, technical, B-1 system requirements, 1-1 T technical support, B-1 timing information, acquiring , 3-1 timing, setting, 3-1 training and certificati[...]