Instruction/ maintenance manual of the product CNT-APG002-EN Trane
Go to page of 70
® CNT -APG0 02-EN Applications Guide PID Contr ol in T r acer Contr ollers.
Applications Guide PID Contr ol in T r acer Contr ollers CNT -APG0 02-EN Oct ober 200 1 ®.
PID Control in T racer Controll ers This manual and the information in it are the property of Am erican Standard Inc. and shall not be used or reproduc ed in whole o r in part, except as inte nded, without the written perm ission of American Standard Inc.
CNT -APG002-EN iii ® Cont ents C h a p t e r 1 Ov er view of PID cont r ol . . . . . . . . . . . . . . . . . . . . . . 1 What PID loops do . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 How PID loops work . . .
® Conte nts iv CNT -A PG002-EN C ha p t e r 4 A pplicat ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Disc harge-air temperature control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Building pres sure control .
CNT -APG002-EN 1 ® Chapt er 1 Ov erview of PID contr ol This guide will hel p you set up , tune , and troubleshoo t proportional, inte- gral, derivative (PID) control loops used in Tracer controllers . Thes e con- trollers in c lude the Tracer MP580 /581, AH540/541 , and MP501 controllers .
® Chapter 1 O v erview of PI D control 2 CNT -A PG002-EN Ho w PID loops w or k A PID l oop p erfo rms pr opor tio nal, inte gra l, an d deri vati ve cal cul ati ons to calculat e syst em output. Figure 2 i llustrat es how a typi cal PID l oop works .
PID calculations CNT -APG002-EN 3 ® PID calculatio ns A PID loop pe rforms three calculati ons: the proportion al ca lculatio n, the integral ca lculation, and the derivative calcu lation. Thes e calculations are indep endent of ea ch other but are combi ned to determine the response of the controller to the error .
® Chapter 1 O v erview of PI D control 4 CNT -A PG002-EN Figure 4: The ef fects of propor tional bias on system output Integr al calculation The int egral calculatio n responds t o the leng th of time the measured vari- able is not at setpo int.
PID calculations CNT -APG002-EN 5 ® Figure 5: Integral output adde d to propor tional output The value of the inte gral calculation can build up o ver time (becau se it is the sum of all past errors) , and this built -up value must b e overcome before the system can change direction.
® Chapter 1 O v erview of PI D control 6 CNT -A PG002-EN Because of these d isadvantages , derivati ve control is rarely used in HV AC applicatio ns (with the ex ception of ste am valve controlle rs and static pressure control).
V elocity model CNT -APG002-EN 7 ® V elocity model Trane controllers use a type of PID cont rol known as the velocity model. The velocity model minimizes the problem of integral windup , which occurs.
® Chapter 1 O v erview of PI D control 8 CNT -A PG002-EN.
CNT -APG002-EN 9 ® Chapt er 2 PID set tings This chapter describes some of the key variables used to set up and tune PID loop s . The variabl es discuss ed here are: • Throttling range • Gain •.
® Chapter 2 PID se t tings 10 CNT -A PG002-EN The throttling range determines the responsive ness of a contro l system to disturbances . The smaller the throttling range , the more respons ive the control.
Calculating the gains CNT -APG002-EN 11 ® Calculating th e g a ins T able 1 shows recommen ded initial values for the p roportional and inte- gral gai ns for several ap plications. Most applica tions do not re quire a derivative contribution, so the derivative gain is not shown.
® Chapter 2 PID se t tings 12 CNT -A PG002-EN Sampling f r equenc y The samp ling frequency is the rate at w hich the input s ignal is sample d and the PID calculations are performed. Using the right sampli ng fre- quency is v ital to achieving a res ponsive and stab le system.
S ampling frequency CNT -APG002-EN 13 ® Proble ms also a rise fr om samplin g too q uick ly . So me systems ha ve nat u- rally slow response times , such as when measuring room temperature . Slow res ponse time s can also be caused b y equipmen t lags .
® Chapter 2 PID se t tings 14 CNT -A PG002-EN Calculat ing the sampling fr eque nc y PID loops are carried out by programs , such as process cont rol language (PCL) progra ms and Tracer g raphical prog ramming (TGP) programs .
Calculating the sampling frequency CNT -APG002-EN 15 ® 6. Calcul ate two-thirds ( 66%) o f the change in meas ured variable d eter- mined in s tep 4. Add t his va lu e to the init ial temper at ure to deter - mine at what po int two-third s of the total change occurs.
® Chapter 2 PID se t tings 16 CNT -A PG002-EN Example In this scenario, we want to find the sa mpling frequency for a PID loo p control ling a heating application. 1. Full y cl ose the out put. 2. The s tabilized tempe rature is 60 ° F (1 6 ° C). 3.
Act ion CNT -APG002-EN 17 ® Ac t i on The acti on of a P ID loop det ermines how it reacts t o a cha nge in the mea - sured variable (such as a room temperature). A cont roller using direct actio n increases the out put when the me asured v ariable incre ases .
® Chapter 2 PID se t tings 18 CNT -A PG002-EN Deter mining the act ion T abl e 3 shows the action s ettings for s everal applicat ions . Thes e settings are a good starting place for most applicat ions. T o find the action for other appl ications, determine whe ther the actuato r and measured v ariable move in the same d irection.
Er ror d eadband CNT -APG002-EN 19 ® Er r or dead band Error deadband is typically used to minimize actuator acti v ity . It can also be used to allow for some slack in sys tem sensor s and actua tor mechanics. Error deadba nd preven ts the PID out put from c hanging whe n the abso- lute value of the error is less than the error deadband.
® Chapter 2 PID se t tings 20 CNT -A PG002-EN Adjusting er ror deadband f or modulating outpu ts In most a pplications, start with an erro r deadband o f five or ten times t he sensor res olution . F or example , thermis tors hav e a resolut ion of app roxi- mately 0.
Other PID set tings CNT -APG002-EN 21 ® With the precedin g guidelin es in min d, use the follow ing proc edure to determine error d eadband. T o adjust the er ror deadband f or stag ed outputs: 1. Run the syst em manually . If possible, do so under wo rst case conditions for the site .
® Chapter 2 PID se t tings 22 CNT -A PG002-EN.
CNT -APG002-EN 23 ® Chapt er 3 Pr ogr amming PID loops This chapter presents programs wr itten in process control language (PCL) and t he Trace r grap hical prog ramming (TGP ) editor . This cha pter does not dis cuss how to use the PCL or TGP e ditors .
® Chapt er 3 Progr amming PID loops 24 CNT -A PG002-EN Fol lo w these steps t o pr ogram PID loops in PCL: 1. Mak e su re th at the setpo int is wi thin r eas onab le li mits . Use the MIN an d MAX operators to set a ceilin g and floo r for the set- point, as shown in l ines 1 and 2 o f T abl e 7 on page 25 .
Pr ogramming in PCL CNT -APG002-EN 25 ® T abl e 8 sh ows a PCL prog ram with separate d enable/dis able and fail-sa fe logic . The l ogic is separate d becau se in this case t he enabl e/disab le and fail-saf e conditions h a ve dif f eren t results.
® Chapt er 3 Progr amming PID loops 26 CNT -A PG002-EN Pr ogr ammin g in TGP Figu re 17 shows the PID blo ck use d to program PID loops in T GP edit or . The PID block is more flex ible t han the DD C function in PCL. The e nabl e/ disable and failure inputs can accept any binary value, regardless of source.
Pr ogramming in TGP CNT -APG002-EN 27 ® Fol lo w these steps t o pr ogram PID loops in TGP: 1. Use th e Limit blo c k to m ake sure tha t the setp oint is within reason- able l imits . 2. Run the PID calc ulation. 3. Define fai lure and other op eration- dependent cond itions .
® Chapt er 3 Progr amming PID loops 28 CNT -A PG002-EN.
CNT -APG002-EN 29 ® Chapt er 4 Applications This chapter describes several HV AC applications that use PID control. It includes specific setting s and recommendations for each application.
® Chap t e r 4 App lic ati ons 30 CNT -A PG002-EN Figure 20 shows a TGP pro gram to control a hot-water valve. Output Sta- tus 1 (an a nalog outp ut) pro vides t he po sition of t he c hilled -w ater valve . If the chil led-water valv e position is greater than zero, the hot-water val ve will not open.
Disc harge - air tem perature co ntrol CNT -APG002-EN 31 ® After the i niti al in stal lat ion a nd test ing , the tech nici an n otice d that the discharge-air temperature w as oscillating in a 10 ° F (5.
® Chap t e r 4 App lic ati ons 32 CNT -A PG002-EN Building pr essur e contr ol Space pre ssure is typically co ntrolled by openin g and closing relie f damp- ers . A P ID loop con trols these da mpers ba sed on a s pace press ure setpoi nt and the mea sured space pressu re.
Building pressu re control CNT -APG002-EN 33 ® T abl e 12 lists t he settings for the PID loo p controlling building press ure . The sampli ng freq uency is slow b ecause b uilding pres sure cha nges slo wly . F or programs written in PCL, the er r or deadban d is 1.
® Chap t e r 4 App lic ati ons 34 CNT -A PG002-EN Cascade contr o l—first stag e A PID loop can be used to automatically d etermine a discharge-air tem- perature setpoint. Other programs or control syste ms can then make use of this calculated setpoint.
Cas cade c ontr ol —first st age CNT -APG002-EN 35 ® Figure 25: TGP program for disc ha rge -air temperat ure setpoint in cascade contr ol If you use t he settings shown in T abl e 14, you sho uld not hav e to tune t he loo p. These value s ca n be u sed in a lmo st an y casc ade con tro l app lic ation without cha nge .
® Chap t e r 4 App lic ati ons 36 CNT -A PG002-EN Figure 26: Space temperatur e and calculated disc harge-air setpo int The disc harge- air tempera ture setp oint cal culated b y the PI D loop ma y not control the di scharge -air temperature de pending on ot her conditions that have priority , such as high and low se tpoint limits.
Staging cooling-tow er fans CNT -APG002-EN 37 ® Staging co oling-t ow er f ans Staging appl ications org anize indivi dual pieces of equi pment into a group to accomplish a singl e task. F or example, seve ral fans might be use d to maintain t he supply water tempe rature in a cool ing tower .
® Chap t e r 4 App lic ati ons 38 CNT -A PG002-EN The PCL program in T able 15 s tages two cooling-tower fans . Figure 28 shows t he same prog ram in TGP . Th e beha vior of the sta ges prog rammed in this pro gram is illustrate d in Figure 30 on p age 41.
Staging cooling-tow er fans CNT -APG002-EN 39 ® The TG P program fol lows th is sequ ence of ope rati on: 1. Ch illed-water pump sta tus is ch ecked. If there is f low , the cooling towers are allowed to op erate .
® Chap t e r 4 App lic ati ons 40 CNT -A PG002-EN The challe nge in stagin g applications is to find the correct propor tional bias . This value de termin es the ou tput whe n the error is zero .
Staging cooling-tow er fans CNT -APG002-EN 41 ® F or staging applica tions , the re sult of the P ID calculation co ntrols binary output s rather than an analog outp ut. F or this kind of staging app lica- tion, it is typical t o use the de adband to ma ke sure th at the binar y output state is maintained for some s pecific range.
® Chap t e r 4 App lic ati ons 42 CNT -A PG002-EN Deter mining the sta ging points This section de scribes how to fi nd the points at wh ich sta ges are turned on and off. Start with thes e guideline s: • T o avoid hav ing a s tage t urn off at the lo west extreme , alw ay s ha ve at least o ne stage on at 10% of th e output range.
Staging cooling-tow er fans CNT -APG002-EN 43 ® Example 1: T wo-stag e f an system The stag ing points are calculated as follows: 1. Calc ulat e the ove rlap range . 2. Calc ulat e the first stag e control po ints . 3. Calcul ate the second stage control points.
® Chap t e r 4 App lic ati ons 44 CNT -A PG002-EN Example 2: Th r ee-stag e f an system The stag ing points are calculated as follows: 1. Calc ulat e the ove rlap range . 2. Calc ulat e the first stag e control po ints . 3. Calcul ate the second stage control points.
CNT -APG002-EN 45 ® Chapt er 5 T r oubleshooting This chapter offers a general troubleshooting proced ure and tips for spe- cific problems . T r o ubleshooting pr ocedur e When fo llowing this tr oubles hooting pro cedure , ch ange only o ne th ing at a time , the n wa it to see t he effect the cha nge has on the sys tem.
® Chapt er 5 T r oubleshooting 46 CNT -A PG002-EN Tips f or specifi c pr oblems T able 17 provid es tips fo r troubl eshooti ng specifi c problems . Changing the sampling frequency The major ca use of actua tor cyc lin g is time la gs in th e system.
Examples CNT -APG002-EN 47 ® Exampl es This s ection p resents t rouble shooting scenarios from a h ot-water valv e applic ation. Th e three ex ample s have t he same sympt om but diff erent soluti ons t o the problem . Example 1 A hot-w ate r valve cyc les clo sed every few mi nutes .
® Chapt er 5 T r oubleshooting 48 CNT -A PG002-EN The applicati on is running in a cold cli mate during winte r , so the chille d- w ate r valv e shou ld not op en at a ll (becau se c hi lled wa ter is no t be ing used).
Examples CNT -APG002-EN 49 ® Figure 34: Hot-w ater valve position, sampling fr equency too sho rt Time (min utes) Discharge-ai r temper at ure s etpoint ( ° F) Disc h arge-air temperat ure ( ° F) H.
® Chapt er 5 T r oubleshooting 50 CNT -A PG002-EN Example 3 The tech nician ex periences t he same probl em as in the fi rst two exa m- ples: a hot-w ate r valve cyc les c lose d every few minutes , and the dis- charge-air tempe rature swings acros s a range of 10 ° F (5 .
CNT -APG002-EN 51 ® Chapt er 6 F r equently ask ed questions Wh y i s the output of m y PID loop alw a ys z er o? • Maximum PID output ma y be set to zero . • PID acti on setting ma y nee d to be cha nged. • Setpoi nt may be zero o r negative, dri ving the output to ze ro .
® Chapt er 6 Fr equently ask ed questions 52 CNT -A PG002-EN I tr ied the 4:1 ratio f or pr opor tional and integr al g ai ns, but this did not o ptimiz e m y syst em. Can I t ry anothe r r atio? W e recom men d maint ain ing a 4:1 r atio bet ween th e pr oport ion al an d integral gains .
F requently asked questions CNT -APG002-EN 53 ® What ’ s the best sampli ng fr equenc y ? The best sa mpling freque ncy depends on th e applicat ion. See “ Calculat- ing the sampling fr equency ” on page 14 for recommended sampling fre- quencie s.
® Chapt er 6 Fr equently ask ed questions 54 CNT -A PG002-EN.
CNT -APG002-EN 55 ® Appendix A The math behind PID loops This appendix presents the mathematical formulas used for PID con trol in Tracer MP580/581 controllers, the programmable control module (PCM), and the universal programmable control module (UPCM).
® Appendix A The math behind PID loops 56 CNT -A PG002-EN.
CNT -APG002-EN 57 ® Glossary action A PID se tting that de termines ho w the PID loo p reacts to a c hange in the measured varia ble (such as a room te mperature). A controll er using direct action i ncreas es the o utput when t he measured variab le incre ases .
® Glossa ry 58 CNT -A PG002-EN er r or deadband A PID setting that defines how much the error mus t change before the PID loop rea cts . Used to compens ate for bearings, linkages, and other mechanical items.
Glossa ry CNT -APG002-EN 59 ® pr ogr am fr equenc y The rate at which a prog ram executes or cycle s. pr opor tional contr ol Control action based on the error . T he most important determinant in how quic kly th e system re sponds t o the erro r . Some applicat ions us e pro- portional- only control.
® Glossa ry 60 CNT -A PG002-EN syst em time constant The time it takes t o reac h 63.2 1% of the di fference betwe en the sta rt point an d the end p oint when con trolling an out put over a k nown range. Used to calcu late the sampling freq uency . Using 2 / 3 (66%) r ather than 63.
CNT -APG002-EN 61 ® Index Numer ics 4 to 1 ra tio for g ain s, 11, 52 A acti on, 17 -18 determining, 18 direct, 17 , 52 examples , 18 recomm ended valu es, 18 reverse, 17 , 52 actu ator and er ror de.
Index 62 CNT -A PG002-EN ® E enable c onditions, 2 4, 25, 27 error and the ve locity model, 7 and thro tt ling range, 9-1 0 definition, 2 er ror dead band, 19 -21 and sensor res olution, 20 and stagi.
Ind ex CNT -APG002-EN 63 ® S sampling freque ncy , 1 2-16, 53 aliasing, 12 calcula ting, 14-15 causing outp ut to oscilla te, 13, 46, 48 example, 16 in di f feren t cont roller s, 14 recom mended v a.
.
® Sinc e The T r ane Comp an y ha s a policy of cont inuous pr oduct a nd produc t data im provemen t, it reserves t he right to c h ange design and sp ecifications wit hout notice.
An important point after buying a device Trane CNT-APG002-EN (or even before the purchase) is to read its user manual. We should do this for several simple reasons:
If you have not bought Trane CNT-APG002-EN yet, this is a good time to familiarize yourself with the basic data on the product. First of all view first pages of the manual, you can find above. You should find there the most important technical data Trane CNT-APG002-EN - thus you can check whether the hardware meets your expectations. When delving into next pages of the user manual, Trane CNT-APG002-EN you will learn all the available features of the product, as well as information on its operation. The information that you get Trane CNT-APG002-EN will certainly help you make a decision on the purchase.
If you already are a holder of Trane CNT-APG002-EN, but have not read the manual yet, you should do it for the reasons described above. You will learn then if you properly used the available features, and whether you have not made any mistakes, which can shorten the lifetime Trane CNT-APG002-EN.
However, one of the most important roles played by the user manual is to help in solving problems with Trane CNT-APG002-EN. Almost always you will find there Troubleshooting, which are the most frequently occurring failures and malfunctions of the device Trane CNT-APG002-EN along with tips on how to solve them. Even if you fail to solve the problem, the manual will show you a further procedure – contact to the customer service center or the nearest service center
