Maintenance
2. Remove the rupture disc assembly, including the copper gasket which forms the seal
between the two knife edges of the flange.
3. With a new rupture disc assembly, reinstall the parts in reverse order.
Standard Silicon Diode
An encapsulated silicon diode is furnished to measure the temperature of the cold head's
second-stage heat station. The diode signal may be used in a control system to automatically
shut down the cryopump system for regeneration. It may also be connected to a voltmeter or
digital temperature readout. For further information on automatic regeneration, consult
SCAI.
Functional Check
Tools required: Current source, 10 microamps ± 1%
Digital voltmeter, 3 1/2 digits.
To check if the diode is functioning properly:
1. Connect the positive side of a 10-microamp DC current source to pin A of the diode
connector. Connect the negative side to pin D. See Figure 18.
2. Measure the output voltage across the same two pins. The output voltage should
range from 0.54 to 0.59 volts DC at room temperature, 20 to 24°C (68 to 76°F).
If the voltage is outside this range, replace the diode.
Figure 18 Check the Standard Silicon Diode
Optional Dual Silicon Diode used with a Marathon
®
Cryopump Controller (MCC)
An encapsulated, dual, silicon diode is furnished to measure the temperatures of the first and
second stage heat stations when the cryopump is connected to a Marathon
®
Cryopump
Controller. The diode signal is required for the control system to automatically initiate
regeneration.
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