5. ( Model 412 )
Magnet Persistent Mode Operation
:
a. Record the current displayed on the Magnet Current meter.
b. Lock the current against the current limit by leaving the current control switch in the
UP position when the desired current limit has been established. Wait for the
inductive voltage across the magnet to reach zero. If the voltage is measured any place
except at the magnet terminals, it is more difficult to tell when the inductive voltage is
zero because the voltage drop in the lead system is added to the inductive voltage.
c. Turn the key operated switch to the OFF position. When the persistence switch heater
is turned off you should allow the switch to cool off for approximately 30 seconds.
This is a safe number. Actually, most AMI persistent switches cool adequately in a
few seconds.
d. A more reliable technique for ramping the current to zero is to program the current to
zero with the ramp down switch. The ramp rate range switch can be increased to
hasten the discharge. The voltage across the magnet should remain zero. A negative
voltage during magnet discharge means the current is decaying and the magnet is not
in the persistent mode. In this case, ramp the current back to the desired value and try
again.
e. To return to the programmed control mode of operation ensure the current limit is set
to the value recorded when you switched into the persistent mode.
NOTE:
The best method is to not have moved the current limit
setting after switching to the persistent mode.
f. Turn the power supply back on and put the Up/Down/Pause switch in the Up position.
The current indication should begin ramping up while the voltage across the magnet
remains zero.
NOTE:
If You switch the ramp selector to "10" to decrease the
time to ramp the current to the desired value. Be sure to return the
range switch to the appropriate setting before switching out of the
persistent mode.
g. When the current reaches the desired value turn the persistent switch heater ON.
There will be a 10 to 15 second time delay as the switch heats up. You may see a
small voltage across the magnet as the current of the magnet and power supply match
up but this should quickly decay to zero.
VI. CALIBRATION
NOTE:
This instrument was calibrated at the factory and should
require no further adjustment for many years. The following
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