At present, some well-known brand manufacturers at home and abroad almost judge the entire industrial automation control field, such as: Emerson and Siemens abroad; Domestic: Zhejiang University Central Control, He Lishi, etc., then the most conventional PID control in these control systems How it is implemented, and how they perform the PLD operation obtained by programming and configuration. This article summarizes and applies the conventional PID and starting modules to make a brief introduction:
1. PID calculation in DCS and PLC control system
1 Instructions
l The above formula T is the periodic output of the ladder diagram time relay, here referred to as the sampling and adjustment cycle.
l S1 is the set target value, also known as the given value
l S2 is the actual measured value.
l S3 is the starting parameter unit of PID control parameters, and the control parameters occupy 25 subsequent D data registers of S3. The specific instructions are as follows:
S3 + 0: TS sampling time is set to K1 (1T)
S3 + 1: ACT. The calculation direction is generally set to H0001;
When set to H0000, it is inverse PID operation.
S3 + 2: L filter coefficient 0-99% 0% no filter. Reference setting is K50
0000-99.00
S3 + 3: KP proportional gain 0-32767% The reference setting is K2000.
0000-327.67
S3 + 4: TI integration time 0-32767 (• 1T) reference setting is K500.
S3 + 5: KD differential gain 0-32767% is generally set to K0.
0000-327.67
S3 + 6: TD differential parameter 0-32767 (• 1T) is set to K0, no differential
S3 + 7: Deviation, expressed as a floating point number, which occupies two bytes: S7 + 7, S7 + 8.
E (K) = SV-PV (ACT.0 = 1)
E (K) = PV-SV (ACT.0 = 0)
S3 + 8:
S3 + 9: The first derivative of the deviation, expressed as a floating point number. S3 + 9, S3 + 10
E (K) '= E (K) -E (K-1)
S3 + 10:
S3 + 11: The second derivative of the deviation, expressed as a floating point number. S3 + 11, S3 + 12
E (K) '' = E (K) '-E (K-1)'
S3 + 12:
S3 + 13: The measured value after this filtering, expressed by floating point number. S3 + 13, S3 + 14.
PVF (K) = PV (K) + L • [PVF (K-1) -PV (K)]
S3 + 14:
S3 + 15: PID differential adjustment item, expressed by floating point number. S3 + 15, S3 + 16.
PID_D (K) = [TD • E (K) '' + KD • TD • PID_D (K-1)] / (TS + KD • TD)
S3 + 16:
S3 + 17: PID adjustment output this time, expressed as a floating point number. S3 + 17, S3 + 18
DMV (K) = DMV (K-1) fractional part + KP [E (K) '+ TS • E (K) / TI + PID_D (K)]
S3 + 18:
S3 + 19: Output value of PID control, value range: 0-32767.
MV (K) = MV (K-1) + INT (DMV)
S3 + 20: SH upper limit alarm is set to K20000
S3 + 21: SL lower limit alarm is set to K20
S3 + 22: OH upper limit amplitude is set to K10000
S3 + 23: OL lower limit amplitude value is set to K20
S3 + 24: ON when ALM.0 SH upper limit alarm
ALM.1 ON when SL lower limit alarm
ALM.2 ON when OH upper limit output
ALM.3 ON when OL lower limit output
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