Basic Operation Expressions In Pid Instruction (Reference) - Mitsubishi FX3U-4AD User Manual

FX /FX /FX PLC User's Manual - Analog Control Edition
3G 3U 3UC
PID Instruction (FNC 88)
1.2

Basic Operation Expressions in PID Instruction (Reference)

The PID instruction executes using the speed type or measured value differential type operation expression.
According to the contents of
either for forward operation or backward operation is executed.
Each value required in the operation is specified by a corresponding parameter
1. Basic operation expression for PID control
Operation
direction (ACT)
S S +1, b0
3 3
Forward operation
(OFF)
Backward
operation (ON)
1) Symbols
EVn : Deviation in sampling at this time
EVn : Deviation in previous cycle
-1
SV : Target value
PVnf : Measured value in sampling at this time (after filter) T
PVnf : Measured value in previous cycle (after filter)
-1
PVnf : Measured value in two cycles before (after filter)
-2
∆MV
: Output variation
MVn : Operation quantity at this time
2) 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
PVn
L
PVnf
-1
L-4
+1, bit 0 (operation setting (ACT)) specified by
S
3
∆MV = K {(EVn − EVn
P
EVn = PVn -SV
f
T
Dn =
T + K
S
MVn = Σ∆MV
∆MV = K {(EVn − EVn
P
EVn = SV − PVn
T
Dn =
T + K
S
MVn = Σ∆MV
: Measured value in sampling at this time
: Filter coefficient
: Measured value in previous cycle (after filter)
1.2 Basic Operation Expressions in PID Instruction (Reference)
PID operation expression
T
S
) + EVn + Dn}
-1
T
I
D
(−2PVn + PVn + PVn
f−1 f
T
D D
T
S
) + EVn + Dn}
−1
T
I
f
D
− PVn − PVn
(2PVn
f−1 f
T
D D
Dn
Dn
K
T
T
K
-PVn)
-1
in the PID control,
S
3
or later.
S
3
K T
D D
) + Dn-
f−2
T + K T
S D D
K T
D D
) + Dn-
f−2 1
T + K T
S D D
: Differential term at this time
: Differential term in previous cycle
-1
: Proportional gain
P
: Sampling cycle
S
: Integral constant
I
: Differential constant
D
: Differential gain
D
1 Outline
1