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Chapter 2 Operation
2-16
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. It is unlikely you will need any D Term.
Continue to Start the process and adjust PID until steady-state response is smooth and
the step response is reasonably controlled. You don’t need to totally eliminate ringing
during the step if the steady-state response is smooth, preconditioning will minimize
step changes.
Set Preconditioning: The power level you recorded as PWR
0R
is the power where
deposition just begins. That’s a good value for Ramp 1 power. PWR
DR
, or slightly less,
is a good value for Ramp 2 Power. This will eliminate a large step change when
entering the deposition phase.
Once PID terms are established for a material, they will typically be similar for other
materials. Only the P Term and preconditioning power levels may need adjustment.