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A feedback control system is shown for maintaining a desired constant pressure in a dynamic sputtering chamber 1, where the pressure may vary due to changes in pumping speed, outgassing, etc.
English (United States)
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Automatic Pressure Control of Mixed Gases
A feedback control system is shown for maintaining a desired constant
pressure in a dynamic sputtering chamber 1, where the pressure may vary due to
changes in pumping speed, outgassing, etc.
Initially, the controller is zeroed by a calibration device 8 in the manual mode
with a calibration device 2 set to zero. Then the calibration device 2 is set to
read + 5 volts on the digital voltmeter (D.V.M.) 3. With the device 4 monitoring
pressure and the flow controller 5 for gas G2 in the off position, the flow controller
6 for gas G1 is set to the desired partial pressure P(1) (e.g., 10 microns). The
flow controller 5 for gas G2 is then set to the pressure P1 + P2 (10 + 40 microns).
The device 4 is then set to the total desired pressure (50 microns) and amplifier
A1 is switched to the AUTO position to regulate that pressure.
The device 4 readout is directly proportioned to the pressure deviation. The
pressures of gases G1 and G2 are directly proportional to the applied voltage.
Thus, the error signal can be fed via line 7 to the amplifier A1, where the desired
gain is selected to minimize offset and maximize stability. Amplifier A2
conditions the error signal and feeds it to the summing junction of amplifier A3.
Amplifier A3 then drives the reference line 9 for the controllers 5 and 6 to
simultaneously increase or decrease the flow while maintaining the set ratio and