IDEC FC5A-F2M2 User Manual page 27

PID M M F
ODULE AIN UNCTIONS
• If the proportional band is narrowed (Proportional gain is made larger)
Because the control output starts turning on/off at around the set point (SP), the time until the process
variable (PV) reaches the set point (SP) is shortened, and the offset is small; however, hunting is
frequent. If the proportional band is greatly narrowed, the control action becomes similar to the ON/OFF
control action.
•
If the proportional band is broadened (Proportional gain is made smaller)
Because the control output starts turning on/off at the significantly low temperature from the set point
(SP), overshoot or hunting is reduced; however, it takes time for the process variable (PV) to reach to
the set point (SP), and the offset between the process variable (PV) and the set point (SP) becomes
broadened.
The offset caused by the P control action can be corrected by configuring the reset value. If the reset
value is configured, the proportional band range can be shifted as shown in the figure below. The reset
value can be automatically calculated by the auto-reset function.
Output Manipulated
Variable
PI Control Action (Proportional + Integral Action)
I (Integral) action automatically corrects the offset caused by P control action, and temperature control is
performed at the set point (SP). However, it takes time for the process variable (PV) to be stable if the
process variable (PV) is changed rapidly due to disturbance. PI control action is suitable for the
processes in which the temperature slowly changes.
If the derivative time of the PID module parameter is set to 0, the control action becomes the PI control
action.
Set Point (SP)
• If the integral time is shortened too much, the integral action becomes strong. The offset can be
corrected in a shorter time; however, hunting with a long cycle may be caused.
• If the integral time is extended too much, the integral action becomes weak and it takes time to correct
the offset.
4-4
Phone: 800.894.0412 - Fax: 888.723.4773 - Web: www.clrwtr.com - Email: info@clrwtr.com
Proportional Band
100
50
Proportional band area that
can be configured with reset
function.
Offset can be corrected within
±proportional band from the
set point (SP).
Temperature
Proportional Band
FC5A MicroSmart PID Module User's Manual FC9Y-B1283
Output Manipulated Variable
A: 100%
B: 50%
C: 0%
Set Point (SP)
Disturbance
Time