INFICON SQM-242 Thin Film Deposition Controller Card Operating Manual - Manual (Page 85)

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SQM-242 Operating Manual
little ringing or overshoot. If there is more than about 10% overshoot, lower the
P Term. If the time to reach PWR
DR
is very slow, increase the P Term. A lower
I Term will increase response time, a higher value will eliminate ringing and
setpoint deviations. Unless you have a very slow source, It is unlikely you will
need any D Term. If you do have a slow source you will need to determine the
response time from when you adjust power to when a change in rate occurrs.
Continue to adjust P & I values, alternating between Manual Power 0% and
Auto mode until steady-state response is smooth and the step response is
reasonably controlled. You don’t need to totally eliminate ringing during this
step if the steady-state response is smooth; preconditioning will minimize step
changes. Typical I values for thermal systems are 4 to 10; Ebeam I values are
0.5 to 2. It’s impossible to predict P values, but it is best to select the lowest
value that provides adequate rate control.
Ebeam systems may require additional steps to limit the control loop’s
response during arcing. First, be sure Max. & Min. power are set to limit the
output to reasonable values for this material and rate. Slew Rate can further
limit too-aggressive power changes. Remember that slew rate is % of full scale
per second. At rates below 10 Å/s, a slew rate of 1-2% per second is common.
Finally, decreasing the filter Alpha will limit the PID response to occasional
large noise spikes, such as from arcing.