Watlow Series PD - Manual (Page 136)

To view or change the Proportional Band value, go to
Device Configuration > Control Loops > Loop 1 or
2 > Loop Settings > PID Parameters > PID Set #1
Prop Band Heat (Indirect) or PID Set #1 Prop
Band Cool (Direct). Enter a value for Proportional
Band and click the Submit button to send the new val-
ue.
Proportional plus Integral (PI) Control
The droop caused by proportional control can be cor-
rected by adding integral (reset) control. When the sys-
tem settles down, the integral value is tuned to bring
the temperature or process value closer to the set point.
Integral determines the speed of the correction, but this
may increase the overshoot at startup or when the set
point is changed. Too much integral action will make
the system unstable. Integral is cleared when the
process value is outside of the proportional band.
Integral is measured in minutes per repeat. A low
integral value causes a fast integrating action and a
high integral value causes a slow integrating action. In-
tegral is the inverse of reset.
To view or change the Integral value, go to Device
Configuration > Control Loops > Loop 1 or 2 >
Loop Settings > PID Parameters > PID Set #1
Integral Heat (Indirect) or PID Set #1 Integral
Cool (Direct). Enter a value for Integral and click the
Submit button to send the new value.
Proportional plus Integral plus Derivative
(PID) Control
Use derivative (rate) control to minimize the over-
shoot in a PI-controlled system. Derivative (rate) ad-
justs the output based on the rate of change in the tem-
perature or process value. Too much derivative (rate)
will make the system sluggish.
Rate action is active only when the process value is
within twice the proportional value from the set point.
To view or change the Derivative value, go to De-
vice Configuration > Control Loops > Loop 1 or 2
> Loop Settings > PID Parameters > PID Set #1
Derivative Heat (Indirect) or PID Set #1 Deriva-
tive Cool (Direct). Enter a value for Derivative and
click the Submit button to send the new value.
Time
Temperature
Set Point
Reduced Overshoot
Proportional Band
Proportional Band x 2
Heating Slows
Time
Te
mperature
Set Point
Proportional Band Droop
Overshoot
W a t l o w S e r i e s P D ■ 1 3 4 ■ C h a p t e r 1 0 F e a t u r e s