Mitsubishi Electric MELSEC iQ-R Series - Page 1137

9 PID OPERATION INSTRUCTION
9.1 Overview
1135
9
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
The meaning of the symbols in the operational expressions is as follows.
PV
n
f (process value of the sampling period this time (after filtering)) is calculated by using the following operational
expression. If the input filter coefficient is not set, the value will be the same as the input process value (PV).
PV
nf
= PV
n
+ L(PV
nf-1
- PV
n
)
Where, PV
n
f: Process value for the sampling period this time, L: Filter coefficient, PV
nf-1
: Process value for the sampling
period last time (after filtering)
Action
(Bit 0 of (s3)+1)
Operational expression
Direct action
(Off)
Reverse action
(On)
Symbol Meaning
EV
n
Deviation in the sampling period this time
EV
n-1
Deviation in the sampling period last time
SV Set value
PV
nf
Process value of the sampling period this time (after filtering)
PV
nf-1
Process value of the sampling period last time (after filtering)
PV
nf-2
Process value of the sampling period two times before (after filtering)
MV Output variation amount
MV
n
Manipulated value this time
D
n
Derivative term this time
D
n-1
Derivative term of the sampling period last time
K
P
Proportional gain
T
S
Sampling period
T
I
Integral constant
T
D
Derivative constant
K
D
Derivative gain
EV
n
= PV
nf
- SV
MV
n
= ΣΔMV
ΔMV = K
p
{(EV
n
- EV
n-1
) +
EV
n
+ D
n
}
T
I
T
S
D
n
= (- 2PV
nf-1
+ PV
nf
+ PV
nf-2
) +
T
S
+ K
D
• T
D
T
D
T
S
+ K
D
• T
D
K
D
• T
D
• D
n-1
EV
n
= SV - PV
nf
MV
n
= ΣΔMV
ΔMV = K
p
{(EV
n
- EV
n-1
) +
EV
n
+ D
n
}
T
I
T
S
D
n
= (2PV
nf-1
- PV
nf
- PV
nf-2
) +
T
S
+ K
D
• T
D
T
D
T
S
+ K
D
• T
D
K
D
• T
D
• D
n-1