American Magnetics 420 Power Supply Programmer - Manual (Page 77)

Rev. 7 59
Operation
Persistent Switch Heater
3.4 Persistent Switch Heater Control
The Model 420 includes an integral persistent switch heater that provides
the capability of controlling the persistent mode of the magnet either
locally from the front panel of the instrument using the switch heater
control, or remotely through a communications interface.
If the switch heater control is illuminated, the Model
420 is supplying current to the appropriate pins
(9 & 10) of the Magnet Station Connectors in order to
drive the persistent switch into a normal state. The
switch heater control illuminates if activated via the
front panel, or if a remote command activates the
heater.
The Model 420 will beep once (indicating an error) if
the user attempts to activate the switch heater control without first
indicating a persistent switch is installed in the load setup submenu and
specifying the switch heating current and heating time (see page 46).
The nominal switch heating current is provided with the magnet
specification sheet and may be entered in the Model 420 by accessing the
load setup submenu (see paragraph 3.2.2.5). In addition to the heating
current, the operator must also specify a heating time. The heating time
allows the Model 420 to delay compensating the internal control logic until
the magnet is guaranteed to be in the circuit. The heating time can be set
from a minimum of 5 seconds to a maximum of 120 seconds within the load
setup submenu (see paragraph 3.2.2.6). The default heating period of 15
seconds is adequate for the majority of persistent switches. If the magnet
appears unstable just after the switch heating period expires, increase the
switch heating time to allow for complete heating.
Note
If the persistent switch function is enabled, press the 1 key in the
default display to show the switch heater voltage for 3 seconds. The
feature is provided to allow for a quick sanity check for the heater
operation. This voltage, divided by the switch heater current, should
be approximately equal to the switch heater resistance during proper
operation. If this is not the case, check all hardware connections.
Note
During the period the switch is being heated, the Model 420 will not
allow ramping functions to be executed and will beep once if the
operator attempts to initiate a ramping operation.
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