CPM2A_PROGRAMMING MANUAL (W353-E1-2) (986750), страница 69
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(Content of *DM word isnot BCD, or the DM area boundary has been exceeded.)The content of S is not BCD.CY:CY is not changed by SCL3(––). (CY shows the sign of S before execution.)ON when the result, R, is 0000.EQ:395Section 7-18Data Control InstructionsExampleThe status of 00101 determines the sign of the BCD source word in the followingexample.
If 00101 is ON, then the source word is negative. When 00100 isturned ON, the BCD source data in LR 02 is converted to signed binary according to the parameters in DM 0000 to DM 0004. The result is then written toDM 0100. (In the second conversion, the signed binary equivalent of –1035 isless than the lower limit specified in DM 0004, so the lower limit is written toDM 0100.)25313(Always ON)AddressCLC(41)00000000010000200101000040000500101STC(40)00100@SCL3(––)InstructionOperandsLDCLC(41)LDSTC(40)LDSCL3(––)LR 02253130010100100LRDMDMDM 0000DM 01000200000100Signed hex.CY=1CY=0DM 0000DM 0001DM 0002DM 0003DM 0004630005BCD00050003000607FFF800LR 020100LR 021035DM 010000CDDM 0100F8007-18-4 PID CONTROL – PID(––)Ladder SymbolOperand Data AreasIW: Input data wordPID(––)IR, SR, AR, DM, HR, LRIWP1: First parameter wordP1OWIR, SR, DM, HR, LROW: Output data wordIR, SR, AR, DM, HR, LRLimitationsThis instruction is available in the CPM2A/CPM2C and SRM1(-V2) only.DM 6144 to DM 6655 cannot be used for P1 or OW.P1 to P1+32 must be in the same data area.! Caution396A total of 33 continuous words starting with P1 must be provided for PID(––) tooperate correctly.
Also, PID(––) may not operate dependably in any of the following situations: In interrupt programs, in subroutines, between IL(02) andILC(03), between JMP(04) and JME(05), and in step programming(STEP(08)/SNXT(09)). Do not program PID(––) in these situations.Section 7-18Data Control InstructionsDescriptionPID(––) performs PID control based on the parameters specified in P1 throughP1+6.When the execution condition OFF, PID(––) is not executed. When the execution condition is ON, PID(––) carries out PID control according to the designatedparameters.
It takes the specified input range of binary data from the contents ofIW and carries out the PID action according to the parameters that are set. Theresult is then stored as the manipulated variable in OW.The following table shows the function of the parameter words.WordBitsParameter nameP100 to 15Set value (SV).P1+100 to 15P1+200 to 15Proportional bandwidth.Integral time (Tik)/sampling period (τ)P1+300 to 15Derivative time(Tdk)/sampling period (τ)P1+400 to 15Sampling period (τ)P1+500 to 03Operation specifier04 to 15Input filter coefficient(α)Function/Setting rangeThis is the target value for PID control.
It can be set to any binary numberwith the number of bits set by the input range parameter.This parameter specifies the proportional band width/input range ratio from0.1% to 999.9%. It must be BCD from 0001 to 9999.Sets the strength of integral action. Increasing this value strengthens theintegral action. It must be BCD from 0001 to 8191, or 9999. A setting of9999 disables integral control.Set the integral time divided by the sampling time.Sets the strength of derivative action. Increasing this value strengthens thederivative action.
It must be BCD from 0001 to 8191, or 0000.(A setting of 0000 disables derivative control.)Set the derivative time divided by the sampling time.Sets the interval between samplings of the input data. It must be BCD from0001 to 1023. The period will be from 0.1 to 102.3 sSets reverse or normal operation. Set to 0 to specify reverse operation or1 to specify normal operation.Determines the strength of the input filter. The lower the coefficient, theweaker the filter.This setting must be BCD from 100 to 199, or 000. A setting of 000 setsthe default value (0.65) and a setting of 100 to 199 sets the coefficientfrom 0.00 to 0.99.P1+6P1+7 toP1+3200 to 03Output range08 to 15Input range00 to 15Work area! CautionDetermines the number of bits of output data. This setting must be between 0 and 8, which sets the output range between 8 and 16 bits.Determines the number of bits of input data.
This setting must be between00 and 08, which sets the input range between 8 and 16 bits.Do not use.(Used by the system.)Changes made to the parameters will not be effective until the execution condition for PID(––) goes from OFF to ON.Note Do not use PID(––) in the following situations; it may not be executed properly.In interrupt programsIn subroutine programsIn interlocked program sections (between IL and ILC)In jump program sections (between JMP and JME)In step ladder program section (created with STEP)When the execution condition is ON, PID(––) performs the PID calculation onthe input data when the sampling period has elapsed.
The sampling period is thetime that must pass before input data is read for processing.397Section 7-18Data Control InstructionsThe following diagram shows the relationship between the sampling period andPID processing. PID processing is performed only when the sampling period(100 ms in this case) has elapsed.1 cycle70 ms60 ms70 ms70 msPID processingNo processing(70+30=100 ms,(70 ms)no carryover)PIDprocessingPID processingNo processingwith initial values(130 ms, 30 ms carryover)(60 ms)(0 ms)PID CONTROL ActionExecution Condition OFFAll data that has been set is retained. When the execution condition is OFF, themanipulated variable can be written to the output word (OW) to achieve manualcontrol.Rising Edge of the Execution ConditionThe work area is initialized based on the PID parameters that have been set andthe PID control action is begin.
Sudden and radical changes in the manipulatedvariable output are not made when starting action to avoid adverse affect on thecontrolled system (bumpless operation).When PID parameters are changed, they first become valid when the executioncondition changes from OFF to ON.Execution Condition ONThe PID action is executed at the intervals based on the sampling period, according to the PID parameters that have been set.Sampling Period and PID Execution TimingThe sampling period is the time interval to retrieve the measurement data forcarrying out a PID action. PID(––), however, is executed according to CPUcycle, so there may be cases where the sampling period is exceeded.
In suchcases, the time interval until the next sampling is reduced.PID Control MethodPID control actions are executed by means of PID control with feed-forward control (two degrees of freedom).When overshooting is prevented with simple PID control, stabilization of disturbances is slowed (1).
If stabilization of disturbances is speeded up, on the otherhand, overshooting occurs and response toward the target value is slowed (2).With feed-forward PID control, there is no overshooting, and response towardthe target value and stabilization of disturbances can both be speeded up (3).Simple PID ControlFeed-forward PID control(1)As the target response is slowed,the disturbance response worsens.(2)Overshoot398As the disturbance response is speededup, the target response worsens.Target responseDisturbance responseSection 7-18Data Control InstructionsControl ActionsProportional Action (P)Proportional action is an operation in which a proportional band is establishedwith respect to the set value (SV), and within that band the manipulated variable(MV) is made proportional to the deviation.
An example for reverse operation isshown in the following illustrationIf the proportional action is used and the present value (PV) becomes smallerthan the proportional band, the manipulated variable (MV) is 100% (i.e., themaximum value). Within the proportional band, the MV is made proportional tothe deviation (the difference between from SV and PV) and gradually decreaseduntil the SV and PV match (i.e., until the deviation is 0), at which time the MV willbe 0% (i.e., the minimum value). The MV will also be 0% when the PV is largerthan the SV.The proportional band is expressed as a percentage of the total input range.
Thesmaller the proportional band, the larger the proportional constant and the stronger the corrective action will be. With proportional action an offset (residual deviation) generally occurs, but the offset can be reduced by making the proportionalband smaller. If it is made too small, however, hunting will occur.Proportional Action (Reverse Action)Adjusting the Proportional BandProportionalbandProportional band too narrow (hunting occurring)100%OffsetManipulatedvariableSV0%SVProportional band just rightProportional band too wide (large offset)Integral Action (I)Combining integral action with proportional action reduces the offset accordingto the time that has passed.
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