IDEC MicroSmart Pentra - Manual (Page 102)

C ONFIGURING PID M ODULE USING W IND LDR
F C5A MicroSmart PID Module User’s Manual FC9Y-B1283 6-37
(8) Control Register+28: 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.
(9) Control Register+29: 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.
(10) Control Register+89: AT Bias
Auto-tuning (AT) starting point can be specified with the AT bias.
When Process variable (PV)
≤ Set point (SP) – AT bias:
AT starting point = Set point (SP) – AT bias
When Process variable (PV)
≥ Set point (SP) + AT bias:
AT starting point = Set point (SP) + AT bias
When Set point (SP)
– AT bias < Process variable (PV) < Set point (SP) + AT bias:
AT starting point = Set point (SP)
For details about the AT bias, see page 4-6.
(11) Control Register+31: Reset
The reset corrects the offset between the set point (SP) and the process variable (PV) generated in P or PD
control action. Reset can be configured only in P (integral time and derivative time are 0) or PD (integral time is
0) control action.
P or PD control action is used for the control target in which overshoot caused by the integral action is hard to
be suppressed.
When the reverse control action is selected, the manipulated variable is calculated with the ratio of the reset to
the proportional band, and the calculated manipulated variable is added to the output manipulated variable
(MV). When the direct control action is selected, the manipulated variable is calculated with the ratio of the
reset to the proportional band, and the calculated manipulated variable is subtracted from the output
manipulated variable (MV).