INFICON MDC-360 Thin Film Deposition Controller - Manual (Page 93)

MDC-360 DEPOSITION CONTROLLER
6-5 Tuning the MDC-360 Control Loop
With the Proportional Gain at an acceptable value, the next step is to adjust the
Derivative Time if necessary. Disturb the system again by changing the target
rate. Watch the rate graph as the rate approaches the target. If the rate overshoots
the target then increase the Derivative Time and change the target rate again to
see the effect. Repeat these steps slowly increasing the Derivative Time until the
rate goes right to the target without overshoot.
In very slow systems such as large filament boats, the Proportional Gain
parameter may have to be set so low to maintain stability where the rate smoothly
levels off but remains below the target value. In this case you will need to adjust
the Integral Time parameter. This parameter works in reverse meaning the
smaller the value the larger the effect. So, slightly decrease this parameter then
watch the rate graph. The rate should ramp up to the target without overshoot. If
the ramp takes too long then slowly decrease the Integral Time again and repeat
these steps until you are satisfied with the control.