Ⅱ、
PID Function
1
、
Brief introduction of PID function
Among XC series PLC special modules, digital input module (A/D module) and temperature control
modules both have PID control function. It is widely used and flexible. When using, only four parameters
(Kp
、
Ki
、
Kd and Diff) should be set.
2
、
Parameter’s usage
Usage of four parameters: Proportion parameter
（
Kp
）、
Integral parameter
（
Ki
）、
Differential
parameter
（
Kd
）、
Control proportion band
（
Diff
）
Kp—
parameter
P
is proportion parameter, mainly reflect system’s wrap. When wrap occurs, carry on control to
decrease this wrap.
Ki—
parameter
I
is integral parameter, mainly used to eliminate whisht
difference, improving system’s no
difference degree.
Kd--
parameter
D
is differential parameter
,
mainly used to control signal’s changing trend, decrease system’s
shake.
Diff—
Control bound means in the assigned bound, carry on PID control, out the bound, do not carry on PID
control.
3、 Control characteristic
The bound of PID adjustment is, when the testing value is low than QD-Diff, controller output with the
full scale; when the testing value is larger than QD+Diff, the controller stop output; in the bound of
（
QD-
Diff
，
QD+Diff
）
, carry on PID adjustment.
The control curve of PID is the following:
Each parameter’s reference value: Kp=20~100
；
Ki=5~20
；
Kd=200~700
；
DIFF=100~200.
