Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 1137

Basic operational expressions of PID operation instruction [Reference]
The instruction performs PID operation in the velocity type or the process value derivative type.
An operational expression of direct action or reverse action is executed depending on the value of bit 0 in the device specified
by (s3)+1 (Action setting (ACT)).
The operation is performed using the control data stored in the device areas, (s3) and later.
• Operational expressions
Action Operational expression
(Bit 0 of (s3)+1)
Direct action
(Off)
ΔMV = K
EV = PV
n
D =
n
T
MV = ΣΔMV
n
Reverse action
(On)
ΔMV = K
EV = SV - PV
n
D =
n
T
MV = ΣΔMV
n
The meaning of the symbols in the operational expressions is as follows.
Symbol
EV
n
EV
n-1
SV
PV
nf
PV
nf-1
PV
nf-2
MV
MV
n
D
n
D
n-1
K
P
T
S
T
I
T
D
K
D
PV f (process value of the sampling period this time (after filtering)) is calculated by using the following operational
n
expression. If the input filter coefficient is not set, the value will be the same as the input process value (PV).
PV = PV + L(PV - PV )
nf n nf-1 n
Where, PV f: Process value for the sampling period this time, L: Filter coefficient, PV
n
period last time (after filtering)
T
S
{(EV - EV ) +
EV + D }
p n n-1
n n
T
I
- SV
nf
T
D
(- 2PV + PV + PV
nf-1 nf nf-2
+ K • T
S D D
T
S
{(EV - EV ) +
EV + D }
p n n-1
n n
T
I
nf
T
D
(2PV - PV - PV ) +
nf-1 nf nf-2
+ K • T
S D D
Meaning
Deviation in the sampling period this time
Deviation in the sampling period last time
Set value
Process value of the sampling period this time (after filtering)
Process value of the sampling period last time (after filtering)
Process value of the sampling period two times before (after filtering)
Output variation amount
Manipulated value this time
Derivative term this time
Derivative term of the sampling period last time
Proportional gain
Sampling period
Integral constant
Derivative constant
Derivative gain
K • T
D D
) + • D
n-1
T + K • T
S D D
K • T
D D
• D
n-1
T + K • T
S D D
nf-1
: Process value for the sampling
9 PID OPERATION INSTRUCTION
9.1 Overview
9
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