IDEC MicroSmart Pentra - Manual (Page 114)

C ONFIGURING PID M ODULE USING W IND LDR
F C5A MicroSmart PID Module User’s Manual FC9Y-B1283 6-49
(4) Control Register+183: Proportional Term
The output of the proportional action varies in proportion to the deviation between the set point (SP) and the
process variable (PV). When the heating/cooling control is enabled, this parameter becomes the heating
proportional band. The control action will be ON/OFF control when the proportional band/proportional gain is 0.
If the proportional band is broadened (proportional gain is made smaller), the control output starts turning on or
off at the significantly low temperatures from the set point (SP), overshoot or hunting is reduced; however, it
takes time for the process variable (PV) to reach the set point (SP), and offset between the process variable
(PV) and the set point (SP) is broadened.
If the proportional band is narrowed (proportional gain is made larger), the control output starts turning on or 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, the hunting phenomenon is frequent. If the proportional band is greatly
narrowed, the control action becomes similar to the ON/OFF control action.
An appropriate proportional band/proportional gain for the control target can be automatically calculated using
auto-tuning (AT) function. It is unnecessary to configure the proportional band/proportional gain in the
WindLDR when using the auto-tuning (AT) function.
(5) Control Register+184: Integral Time
In the proportional control action, the offset is generated even when the control is stabilized. The integral action
corrects the offset. The integral action is disabled when the integral time is 0.
The integral time is a coefficient to determine the output manipulated variable (MV) of the integral action.
If the integral time is shortened too much, the integral action becomes strong. The offset can be corrected in a
shorter time; however, the hunting phenomenon may be caused over a long cycle. On the contrary, if the
integral time is extended too much, the integral action becomes weak and it takes time to correct the offset.
An appropriate integral time for the control target can be automatically calculated using auto-tuning (AT)
function. It is unnecessary to configure the integral time in the WindLDR when using the auto-tuning (AT)
function.
(6) Control Register+185: Derivative Time
When the set point (SP) is changed or when the deviation between the set point (SP) and the process variable
(PV) is increased due to a disturbance, the derivative action increases the output manipulated variable (MV) to
rapidly correct the deviation between the process variable (PV) and the set point (SP). The derivative time is a
coefficient to determine the output manipulated variable (MV) of the derivative action. The derivative action is
disabled when the derivative time is 0.
If the derivative time is shortened, the derivative action becomes weak. The response to the rapid temperature
change becomes slower. Because the action to suppress the rapid temperature rise becomes weaker, the time
for the process variable (PV) to reach the set point (SP) is shortened; however, overshoot can occur.
If the derivative time is extended, the derivative action becomes strong. The response to the rapid temperature
change becomes faster. Because the action to suppress the rapid temperature rise becomes strong, the time
for the process variable (PV) to reach the set point (SP) is extended; however, overshoot can be decreased.
An appropriate derivative time for the control target can be automatically calculated using auto-tuning (AT)
function. It is unnecessary to configure the derivative time in the WindLDR when using the auto-tuning (AT)
function.
(7) Control Register+186: ARW (Anti-Reset Windup)
When the control is started, there is a large deviation between the set point (SP) and the process variable (PV).
The integral action continues its action in a given direction until the process variable (PV) reaches the set point
(SP). As a result, an overshoot is caused by the excessive integral action. ARW suppresses the overshoot by
limiting the integral action area.
When ARW is 0%, the integral action area becomes the minimum and the suppression of the overshoot is
maximized. When ARW is 50%, the integral action area becomes the intermediate and the suppression of the
overshoot is intermediate. When ARW is 100%, the integral action area becomes the maximum and the
suppression of the overshoot is minimized.
An appropriate ARW for the control target can be automatically calculated using auto-tuning (AT) function. It is
unnecessary to configure the ARW in the WindLDR when using the auto-tuning (AT) function.