American Magnetics 05200PS-430-601 Integrated Power Supply System - Manual (Page 160)

142 Rev. 5
Service
Troubleshooting Hints
power loop. Loose or oxidized interconnections often exhibit
excessive resistances.
5.2.7 Cannot discharge the magnet at the selected ramp rate
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
heated time has expired. Ramping is disabled during the switch
heating period.
2. Check the value of the Voltage Limit. Refer to section 3.7.2.
3. 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
either by a voltmeter on the front of the supply or by a DVM
measurement. If the supply output voltage is approximately zero,
the resistance of the power leads (not the Model 430 Programmer)
is dictating the maximum ramp down rate. An energy absorber is
necessary to increase the rampdown rate.
5.2.8 Cannot charge the magnet to desired field.
1. If the power supply ramps to full output current after the supply
output voltage exceeds approximately 0.7 V, verify the polarity of
the power supply protective diode. Ensure the protective diode
remains installed across the output terminals of the power
supply with the anode at the negative terminal and the cathode at
the positive terminal.
2. Ensure that the Model 430 Programmer supply setup submenu is
configured to match the connected power supply, e.g. check that the
Model 430 Programmer is configured for the proper voltage-to-
voltage programming range according to section 3.10.1.1.1.5.
5.2.9 Cannot place the magnet in persistent mode.
Ensure there is adequate LHe level in the cryostat to allow the
persistent switch to cool to the superconducting state.