Mitsubishi Electric MELSEC iQ-R Series - Page 1161

10 PID CONTROL INSTRUCTIONS
10.2 PID Control Instructions (Inexact Differential)
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10
• Operational expressions
The meaning of the symbols in the operational expressions is as follows.
The PV
fn
is calculated by using the following operational expression. If the filter coefficient is not set to the input data, the PV
fn
will be same as the process value of the input data.
PV
fn
= PV
n
+ (PV
fn-1
- PV
n
)
PV
n
: Process value for the sampling period this time, : Filter coefficient, PV
fn-1
: Process value for the sampling period last
time (after filtering)
PV
fn
is stored in the I/O data area. ( Page 1155 I/O data)
Action Operational expression
Direct action
Reverse action
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
fn
Process value of the sampling period this time (after filtering)
PV
fn-1
Process value of the sampling period last time (after filtering)
PV
fn-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
T
S
Sampling period
K
P
Proportional constant
T
I
Integral constant
T
D
Derivative constant
K
D
Derivative gain
EV
n
= PV
fn
- SV
MV
n
= ΣΔMV
ΔMV = K
p
{(EV
n
- EV
n-1
) +
 EV
n
+ D
n
}
D
n
= (PV
fn
- 2PV
fn-1
+ PV
fn-2
) +
T
I
T
S
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
fn
MV
n
= ΣΔMV
ΔMV = K
p
{(EV
n
- EV
n-1
) +
 EV
n
+ D
n
}
D
n
= ( - PV
fn
+ 2PV
fn-1
- PV
fn-2
) +
T
I
T
S
T
S
+
K
D
T
D
T
D
T
S
+
K
D
T
D
K
D
T
D
 D
n-1