Chapter 2. SPECIFICATIONS
2 - 4
2.4 PID Control Action
2.4.1 Processing type
1) Velocity type
Velocity type is a processing that in PID processing, the present Manipulated Value(MV) is obtained by
adding the calculated variation of MV (
∆
MV) to the previous MV
2) Measured Value Derivative Type (Pre-derivative)
Measured value derivative processing, in PID processing, uses the process value(PV) for the derivative term.
Generally, PID processing, when a deviation occurs, operates toward the direction in which the deviation will
be reduced.
The deviation occurs due to alteration of set value(SV) or outside disturbances. Therefore, if the deviation is
used in the derivative processing, the output of the derivative term changes rapidly when the deviation occur
due to alteration of set value (SV). So, to prevent raid changes like that, this processing uses the process
value(PV) for the derivative term.
MV
n
====
MV
n-1
+
∆∆∆∆
MV
n
MV
n
: Present Manipulated Value
MV
n-1
: Previous Manipulated Value
∆∆∆∆
MV
n
: Variation of the Previous Manipulated Value
MV
n
====
MV
n-1
+ K
p
✕
✕
✕
✕
(E
n
−−−−
E
n-1
) + K
p
✕
✕
✕
✕
S/K
I
✕
✕
✕
✕
E
n
+ K
p
✕
✕
✕
✕
K
d
/S
✕
✕
✕
✕
(2PV
n
−−−−
PV
n-1
−−−−
PV
n-2
)
MV
n
: Present Manipulated Value
MV
n-1
: Previous Manipulated Value
∆∆∆∆
MV
n
: Variation of the Previous Manipulated Value
E
n
: Present Deviation
E
n-1
: Previous Deviation
K
p
: Proportional Constant
K
i
: Integral Constant
K
d
: Derivative Constant
S
: Control Cycle (100ms)
PV
n
: Present Process Quantity (Present Value)
PV
n-1
: One-step previous Process Quantity (Present Value)
PV
n-2
: Two-step previous Process Quantity (Present Value)
