Lakeshore Learning Materials 622 User Manual

Page 30

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Lake Shore Model 620/622/623/647 Magnet Power Supply User’s Manual

Operation

3-4

MGT END: 0 to ±50.000 A (620), 0 to ±125.000 A (622), 0 to ±155.000 A (623), 0 to ±72.000 A (647)
Magnet End Current. The desired magnet current. To set a new current, move to the MGT END line and enter

a new current, then move to the RUN line and toggle to activate Automatic Mode. The MPS automatically

ramps to the new current, returns the magnet to persistence, then ramps MPS current back down to zero.

MGT RATE: 0 to ±99.999 A/sec
Magnet Ramp Rate. Rate in amperes per second that the MPS charges the magnet. Exceeding the maximum

rated voltage or current ramp rate may damage the magnet. The user may configure the MPS to limit the

charging voltage.

The magnet manufacturer supplies the inductance of the magnet, maximum ramp voltage, and maximum
current ramp rate. The relationship for these parameters is given by the equation:

L

di
dt

V

<

max

where:

L = magnet inductance in henrys,

di/dt = maximum magnet current ramp rate in amps/second,

V

max

= rated maximum magnet ramp voltage in volts.

To set the Magnet Ramp Rate for automatic PSH control, move to the MGT RATE line and enter a ramp rate

less than the magnet's maximum ramp rate. Upon entering a new current set point, the magnet current ramps

at the entered magnet ramp rate.

PERS RATE: 0 to ±99.999 A/sec
Persistence Switch Ramp Rate. Rate in amperes per second of the MPS when in Persistence Mode. The

current is flowing in the Persistent Switch and the rate is chosen as such. To set the Persistence Switch Ramp

Rate, move to the PERS RATE line and enter a persistence switch ramp rate less than the maximum allowed.

This value is usually considerably higher than the magnet ramp rate as there is little inductance in the

persistence switch.

LAST END:
The ending charge current from the last time the MPS charged the magnet. The MPS sets this field after it

charges the magnet to the Magnet End value. Once it reaches Magnet End, the MPS sets the value of Last

End equal to the value of Magnet End. The user cannot change the Last End value. The MPS stores it in non-

volatile memory and remembers it even when the MPS is Off.

PERSISTENCE: <ON> or <OFF> (Read only)
Persistence Mode Status. If Persistence Mode is On, the PSH heater is Off. If it is Off, the PSH heater is On.

The persistent switch takes the superconducting magnet into and out of persistence mode.

To exit persistent mode, the MPS current ramps up to match the persistent current, and the persistent switch

heater coil heats the switch until it becomes normal (non-superconducting). A delay allows magnet current to

settle. Then the magnet current ramps to a new value.

To enter persistent mode, the MPS removes current from the persistent switch heater. After a delay to allow

the switch to superconduct, the MPS current ramps down to 0 at a rate low enough to ensure the switch

remains superconducting. The magnet current then circulates in the superconducting loop formed by the

magnet and the persistent switch.

Note: To set PSH current see Chapter 6 Options And Accessories.

RUN ¥

¥

¥

¥

:

Press either of the Data Entry up or down key to initiate Automatic Mode.

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This manual is related to the following products:

623, 620