Proportional Action (P Action) - Mitsubishi Electric MELSEC iQ-F FX5 User Manual

Proportional action (P action)

A proportional action is used to obtain the manipulated value (MV) proportional to the deviation (difference between the set
value (SV) and the temperature process value (PV)).
Proportional gain
In a proportional action, the relation between changes in the deviation (E) and the manipulated value (MV) can be expressed
using the following formula:
MV=K ⋅E
P
K is a proportional constant and is called proportional gain. The manipulated value (MV) varies within the range of -5.0% to
P
105.0%.
The following shows the difference of the actions depending on the proportional gain K
Condition
When the proportional gain K
When the proportional gain K
The following figure shows a proportional action of step responses of when the deviation (E) is a fixed value.
Deviation (E)
Manipulated
value (MV)
Offset
The certain amount of an error between the temperature process value (PV) and the set value (SV) is called an offset
(remaining deviation). In a proportional action, an offset (remaining deviation) is generated.
Set
value
(SV)
APPX
168
Appendix 5 PID
is small
P
is large
P
E
Time
K
P 
Time
Offset
Temperature process value (PV)
Time
Proportional action
A control action slows down.
The control action accelerates, but the temperature process value (PV) tends
to fluctuate around the set value.
E
Set
value
(SV)
.
P
Offset
Temperature process value (PV)
Time