American Magnetics 420 Power Supply Programmer - Manual (Page 79)

Rev. 7 61
Operation
Quench Detection
SWITCH mode and disallow any ramping during the switch
heating period.
5. Once the switch heating period expires, the Model 420 will enter
the PAUSED mode and will maintain the operating current or
field.
Note
If the actual current in the magnet and the operating current of the
Model 420 exhibit a mismatch at the time the switch heater is
activated, the Model 420 will track the actual current of the magnet
during the switch heating period. At the expiration of the switch
heating period, the Model 420 will attempt to maintain the last
measured current value.
3.4.3 Optional Switching of External Power Supply
The Model 420 offers the option of using an external power supply for the
persistent switch heating current if the requirements for the switch heater
exceed the capabilities of the integrated switch heating output of the
Model 420. The external power supply, if properly connected, will be
switched via an internal relay that opens and closes with the switch heater
control functions of the Model 420.
To use an external power supply for the switch heater current, connect an
external power supply to J4 pins 4 and 5 (any polarity). Then connect pins
18 and 19 of J7A or J7B to the switch heater terminals of the
superconducting magnet. Ensure that the external power requirements
are within the limits shown in the specifications table on page 7.
3.5 Quench Detection
The Model 420 continuously monitors the superconducting magnet load
and can automatically detect a quench condition. If a quench is detected,
the quench detection LED will become illuminated and the display will
appear as shown below. When a quench is detected, the Model 420
automatically sets the power supply output voltage to zero, provides a
quench output signal to the rear panel connector J4 (see page 109 of the
Appendix for the connector pinout), and will not respond to further input
until the
5(6(7=(52 button is pressed to clear the quench detect
condition, or until the quench condition is cleared by a remote command.
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