Operation
The Minimum Output can now be set in a similar way by lowering the setpoint value to
well below the actual value displayed. The PID controller will now try to give minimum
output. Set the Minimum Output level of the PID controller to be such that the filament
current reached is ~1.5 A less than that required for evaporation. This will stop excess-
ive filament current swing and filament stress when the PID controller is adjusting the
filament control (especially during an auto-tune operation).
Put the controller back to “MANUAL” mode and re-establish the required evaporation
conditions and stability as before.
4.4.3 Setting up Auto Control
First set the PID controller to Man control if not already set. The green MAN light will
be glowing if in manual control mode. The arrow keys can now be used to directly con-
trol the PID controller output. Raise the output and watch the filament current on the
main power supply rise accordingly.
Set the HV to 1 kV and increase the filament current until emission current begins to be
seen (this can be seen on the HV supply and on the main power supply).
Carefully and slowly allow the material to come to thermal equilibrium. Adjust the fila-
ment current using the PID output as necessary to maintain stable emission. Once satis-
fied that operation is stable and the required evaporation rate has been reached press
“Scroll” once to get “SP xx” where “xx” is the value of the setpoint. Adjust this to be
the same as the measured value of flux which has been reached.
Press “Scroll” once more to get to the “m-A mAn” screen and use the arrow keys to se-
lect AUTO.
The PID controller will now be in AUTO control and will automatically adjust the fila-
ment current to maintain the flux current at the required value.
If stable control is not achieved it may be necessary to run the auto-tune function to es-
tablish new PID parameters. If control is still not sufficiently stable, the maximum out-
put of the PID controller should be gradually reduced (say 5 % at a time). At each de-
crease the control stability should be seen to improve. If the PID controller cannot bring
the flux up to the required set-point it will be necessary to increase the maximum out-
put setting of the PID controller.
16
Summary of Contents for EBE-1
Page 1: ...EBE 1 Electron Beam Evaporator 1 11...
Page 8: ...Inspection 4 EBE 1...
Page 22: ...Operation 18 EBE 1...
Page 28: ...Drawings 24 EBE 1 Figure 4 Evaporator details...
Page 30: ...List of Figures II EBE 1...
Page 32: ...List of Tables IV EBE 1...