American Magnetics 4Q1010PS-430 Integrated Power Supply System - Manual (Page 159)

Rev. 5 141
Service
Troubleshooting Hints
2. If a PSwitch Error was indicated when the PERSIST. SWITCH
CONTROL key was used to turn on the persistent switch heater
current, then there is a problem with the wiring to the persistent
switch heater. Check the continuity between the persistent switch
heater power supply output pins at the rear panel MAGNET
STATION CONNECTORS and the connectors on the magnet
support stand top plate. Refer to Table A-1 on page 145.
5.2.14 There is excessive LHe boil-off during operation.
Excessive LHe consumption is usually attributable to one or both of the
following: thermal energy being conducted into the cryostat or electrical
energy being converted into thermal energy within the cryostat. Analyzing
the circumstances under which the high boil-off occurs will help determine
what is causing the problem.
1. For magnets equipped with switches for persistent operation, verify
that the persistent switch heater power supply is operating at the
proper current for the installed switch. Excessive currents cause
excessive boiloffs. The typical switch requires approximately 45 mA
to function correctly. Refer to the documentation provided with the
magnet for proper operating current. See Figure 3-13 on page 73.
2. Verify that the protective diodes on the magnet are not turning on.
Damaged diodes may short causing current to flow through them
whenever magnet current flows and cause excessive heating. This
can be identified by observing a change in the apparent field-to-
current ratio since some of the current is bypassing the coil. If the
boil off rate returns to normal with the magnet de-energized, this
may indicate a defective diode.
3. Ensure that there are no inadvertent thermal paths between the
cryogenic environment and the 300K environment. Ensure all
transfer lines are removed from the cryostat; check the position of
break-away vapor-cooled current leads.
4. Ensure the LHe level sensor is not continuously energized if
continuous level indication is not necessary.
5. Ensure the vacuum in vacuum-jacketed dewars is of sufficiently
low pressure.
5.2.15 Cannot display the magnetic field strength, only current
Enter a coil constant in accordance with section 3.10.2.2 on
page 50.