Basic Operation Expressions In Pid Instruction; Basic Operation Expression For Pid Control - Mitsubishi Electric FX5 User Manual

10.2

Basic Operation Expressions in PID Instruction

The PID instruction executes using the speed type or measured value differential type operation expression. According to the
contents of (s3)+1, bit 0 (operation setting (ACT)) specified by (s3) in the PID control, either forward operation or backward
operation is executed. Each value required in the operation is specified by a corresponding parameter (s3) or later.

Basic operation expression for PID control

Operation Operation expression
setting (ACT)
(s3+1: b0)
Forward operation
ΔMV=KP{(EVn-EVn-1)+
(OFF)
EVn=PVnf-SV
Dn=
TS+KD•TD
MVn=ΣΔMV
Backward operation
ΔMV=KP{(EVn-EVn-1)+
(ON)
EVn=SV-PVnf
TD
Dn=
TS+KD•TD
MVn=ΣΔMV
Expression for calculating the measured value (after the filter) in sampling at this time
(PVnf)
The value "PVnf" is obtained from the following expression based on the read measured value.
Measured value after filter: PVnf = PVn+L (PVnf-1-PVn)
PVn: Measured value in sampling at this time
L: Filter coefficient
PVnf-1: Measured value in previous cycle (after filter)
TS
EVn+Dn}
TI
TD
(-2PVnf-1+PVnf+PVnf-2)+
TS
EVn+Dn}
TI
(2PVnf-1-PVnf-PVnf-2)+
The meaning of the signs
EVn: Deviation in sampling at this time
EVn-1: Deviation in previous cycle
SV: Target value
PVnf: Measured value in sampling at this time
(after filter)
KD•TD
PVnf-1: Measured value in previous cycle
•Dn-1
TS+KD•TD
(after filter)
PVnf-2: Measured value in two cycles before
(after filter)
ΔMV: Output variation
MVn: Operation quantity at this time
Dn: Differential term at this time
Dn-1: Differential term in previous cycle
TS: Sampling cycle
KD•TD
KP: Proportional gain
•Dn-1
TI: Integral constant
TS+KD•TD
TD: Differential constant
KD: Differential gain
10.2 Basic Operation Expressions in PID Instruction
10 PID CONTROL FUNCTION
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