Lake Shore 625, User Manual

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Lake Shore Model 625 Superconducting MPS User’s Manual
4-6 Operation
The output current setting is not allowed to change while the persistent switch heater is warming or cooling. The amount
of time it takes for the PSH to warm or cool is system dependant and can be setup under the PSH Setup key. Refer to
Paragraph 4.14 to setup the persistent switch heater.
Change not allowed while
in External Current Program Mode.
The output current setting is not allowed to change if the instrument is setup so that the output current is programmed
solely by an external voltage. Refer to Paragraph 4.18 to setup the external program mode.
Change not allowed while
ramp rate > current step limit.
The output current setting is not allowed to change if the current ramp rate is greater than the current step limit and
quench detection is on. The current step limit is a parameter of quench detection. If the current were allowed to change at
a rate greater than the current step limit, then a quench would be falsely detected. Refer to Paragraph 4.16 to setup
quench detection.
Change not allowed while
max ramp rate > current step limit.
As stated above, the current ramp rate cannot exceed the current step limit used for quench detection. To insure that the
ramp rate will never accidentally exceed the current step limit either by entering a ramp rate from the front panel or by
having the ramp segments function set a new ramp rate, the maximum ramp rate must be less than the current step limit.
Refer to Paragraph 4.11 to setup maximum settings.
4.6 CURRENT RAMP RATE
The output current of the Model 625 will always ramp from one current setting to another. There is no way to turn off the
current ramping function, but if a very fast ramp rate is desired, a ramp rate as large as 99.999 A/s can be entered to
simulate a step change. On most superconducting magnets, the maximum rate at which it can be charged is usually
stated. Exceeding the maximum charging rate can cause the magnet to quench. When the current ramp rate is entered or
changed by crossing into a different ramp segment, it will be limited in magnitude by the maximum ramp rate. Refer to
Paragraph 4.12 to setup the ramp segments and to Paragraph 4.11 to setup the maximum settings.
To change the current ramp rate press the Ramp Rate key. The ramp rate value on the normal display will be
highlighted to prompt for the new ramp rate value.
Rate: 1.0000 A/s
Use the data entry keys to enter the ramp rate value between 0.0001 and 99.999 A/s. Press Enter to accept the new
value. Press Escape to restart the setting sequence and enter a different value. Press Escape again to leave the setting
sequence.
If the persistent mode ramp rate is enabled and the magnet is in persistent mode, then the current ramp rate will not be
allowed to change using the
Ramp Rate key. To change the current ramp rate, either disable the persistent mode ramp
rate feature or enter a new persistent mode ramp rate using the PSH Setup key. Refer to Paragraph 4.14.4 to setup the
persistent mode ramp rate. The error box shown below will pop up explaining why the new setting is going to be
ignored.
Change not allowed while
using persistent mode ramp rate.