7 Application Instructions API 50-99 S t PV is the differential value of t PV ; S t E 1 is the integral value of t E . When ( ) t E is less than 0 as the control direction is selected as forward or inverse, ( ) t E will be regarded as “0". The equation above illustrates that this instruction is different from a general PID instruction by the variable use of the differential value. To avoid the flaw that the transient differential value is too big when a general PID instruction is executed for the first time, our PID instruction monitors the differentiation status of the PV. When the variation of PV is too big, this instruction will reduce the output of MV. 4. Symbol explanation:
MV : Output value P K : Proprotional gain t E : Error value PV : Present measured value SV : Target value D K : Differential gain S t PV : Differential value of PV(t) I K : Integral gain S t E 1 : Integral value of E(t) 5. Temperature Control Equation: When S 3 +4 is K3 and K4, the equation used in diagram 2 (see below) will be changed as: S t PV K S t E K t E K MV D I P * 1 1 1 In which the error value is fixed as E(t) = SV – PV This equation is exclusively designed for temperature control.
Therefore, when the sampling time (T S ) is set as 4 seconds (K400), the range of output value (MV) will be K0 ~ K4,000 and the cycle time of GPWM instruction used together has to be set as 4 seconds (K4000) as well. If you have no idea how to adjust the parameters, you can select K3 (auto-tuning) and after all the parameters are adjusted (the control direction will be automatically set as K4), you can modify your parameters to better ones according to the result of the control. DVP-PLC APPLICATION MANUAL 7-137