American Magnetics AMI Superconducting Magnets - Manual (Page 21)

20
Troubleshooting
Slow charging, discharging, or quenching
b. Make sure the programmer or power supply is not current limiting. Refer
to the power supply operating manual to remove front panel control.
Refer to the programmer operating manual for operation setup.
Voltage developed across magnet but magnet field less than predicted
1. If the magnet current ramps but the magnetic field increases slowly and the
helium boil-off rate is significant, the protective diodes may have turned on
and current is flowing thru them. This may occur when the diode is subjected
to a voltage which is larger than it’s turn on voltage (typically 4-6 volts). The
magnet current should be reduced to zero as rapidly as possible. Wait for the
current in the magnet to reach zero and the helium boil-off to return to normal.
Make sure the ramp rate previously attempted is low enough to keep the
inductive voltage of the magnet at or below the voltage listed on the Magnet
Specification Sheet.
2. If the magnet current ramps but the magnetic field increases slowly and the
helium boil-off rate does not increase significantly, one of the protective
diodes may be shorted and consequently shunting the magnet current. If these
conditions occur, call AMI and speak with a sales representative.
Magnet discharges when attempting to enter persistent mode
Make sure the persistent switch heater is completely de-energized and allowed
sufficient cooling time before de-energizing power supply system.
Magnet quenches lower than rated field
1. For typical standard magnets, ramping the magnet fast enough to produce a
magnet voltage of approximately five volts has the possibility of turning on
the protective diodes. Attempt to reach rated field at a lower charge rate.
2. Verify proper liquid helium level to make sure the magnet and switch are
completely covered.
3. Verify rated field and rated current on the Magnet Specification Sheet.
4. If oscillations occurring with the programmer/ power supply system are
occurring, refer to the programmer/ power supply documentation.
If the cause of the problem cannot be located, contact an AMI customer service
representative for assistance. DO NOT SEND A UNIT BACK TO AMI WITHOUT
PRIOR RETURN AUTHORIZATION.