American Magnetics 420 Power Supply Programmer - Manual (Page 117)

Rev. 7 99
Service
Troubleshooting Hints
the switch heater current should be approximately equal to the
persistent switch heater resistance.
4. Check the value of the voltage limit. Refer to paragraph 3.3.1.1 on
page 53.
Note
If an energy absorber is present in the system, the Model 420 must
command enough power supply voltage to overcome any forward
voltage drop due to the energy absorber. Increase the voltage limits
to account for the energy absorber voltage drop.
5. Check for excessive wiring resistances in the magnet-power supply
loop which may prevent proper charge/discharge voltages at the
magnet. Use the local voltmeter on the power supply to see if the
proper voltages exist across the various components in the magnet
power loop. Loose or iced interconnections often exhibit excessive
resistances.
5.2.6 The Model 420 will not discharge the magnet at the
selected
5$03 5$7( .
Note
Rapid discharging of the magnet requires either an energy
absorbing component or a four-quadrant power supply. If a
unipolar supply is used without an energy absorbing component,
only the resistance of the power leads is available as a mechanism
for discharging the magnet.
1. Ensure that the persistent switch heater is on and the switch
heating time has expired. Ramping is disabled during the switch
heating period.
2. With the persistent switch heater on, press the 1 key in the default
display to show the switch heater voltage. A value of 0 V indicates a
shorted switch heater connection. A value exceeding 17 V indicates
an open switch heater connection. The displayed voltage divided by
the switch heater current should be approximately equal to the
persistent switch heater resistance.
3. Check the value of the voltage limit. Refer to paragraph 3.3.1.1 on
page 53.
4. For unipolar power supply systems, an energy absorber is usually
required to ramp a magnet down in a reasonable amount of time.
When ramping the system down at the fastest rate achievable,
observe the voltage appearing at the power supply output terminals