AMI 420, Installation, Operation And Maintenance Instructions, Page: 74 / 134

56
Rev. 7
Operation
Ramping Functions : Manual and Programmed Modes
3.3.4 Ramp to Zero Mode
If a quench condition does not exist, the
5(6(7=(52
key activates an
immediate ramp to zero current. When the zero mode is activated, the
5(6(7=(52
key is illuminated and the Model 420 automatically ramps
the current to 0 A at the set ramp rate while observing the voltage limit.
The zero mode may be interrupted at any time by pressing the
5(6(7
=(52
key to deactivate the function or pressing the , , or
5$033$86(
keys. If the
5(6(7=(52
key is deactivated, the Model 420
will automatically enter the PAUSED mode and maintain the operating
current present at the point it was paused.
3.3.5 Dial Adjustment of Current/Field in PAUSED Mode
If the programmed current/field menu is active and the instrument is in
PAUSED mode (indicated if the
5$033$86(
button is illuminated), the
dial can be used to directly manipulate the operating (shunt) current.
Note
The encoder dial is velocity-sensitive, meaning that the faster the
dial is turned, the more coarse the adjustment. Slow manipulation
of the dial will yield very fine resolution even beyond that displayed
by the instrument.
When the dial is manipulated the Model 420 will follow at a compliance of
less than or equal to the voltage limit. The ramp rate setting is not
observed in this operational mode, however, the voltage limit is strictly
observed and is never exceeded.
Adjustment of the current in this mode is also prevented from exceeding
the current limit specified in the Load setup menu (see paragraph 3.2.2.3).
The adjustment may, however, exceed the programmed current/field
setting. The resolution of the adjustment is 15 digits, which is greater than
the resolution of the display.
Caution
Entering a voltage limit via the
92/7$*(/,0,7
key is strongly
advised if you wish to adjust the current using this method.
Otherwise, large changes using the dial can result in voltages across
the terminals of the magnet capable of causing a quench in some
magnets.