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Lake Shore Model 625 Superconducting MPS User’s Manual
4-12
Operation
The persistent switch heater current can only be changed when the heater is off. If the current is changed while the heater
is on or warming, the following error box will appear and the new setting will be ignored.
Change not allowed while
PSH is on.
4.14.3
Persistent Switch Heater Delay
When a persistent switch heater is turned on or off, it is in an indeterminate state for a period of time while the switch is
warming or cooling. The persistent switch heater delay should be set to a value that insures that the persistent switch has
fully transitioned from one state to the other. This value is typically not given by the magnet manufacturer but can be
estimated by observation. For most systems, a delay time of 10 to 20 seconds is usually sufficient. During this delay
time, the Model 625 locks out any changes to the output (magnet) current to insure proper operation. The persistent
switch heater delay time can be changed at any time but the new value will not be used until the persistent switch heater
is turned on or off again.
To enter a value for the persistent switch heater delay time, continue from the persistent switch heater current screen or
press
PSH Setup
then
Enter
until the following persistent switch setup screen appears as a prompt for the persistent
switch heater delay time.
Persistent Switch Heater Output
Enter a Value For
PS Heater Delay: 10 s
Use the data entry keys to enter the persistent switch heater delay time between 5 and 100 seconds. 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.
4.14.4
Persistent Mode Ramp Rate
A magnet is said to be in persistent mode when the persistent switch heater is off and the magnet is shorted by the
persistent switch in its superconducting state. While the magnet is in persistent mode, the output current can be ramped
at a faster rate since it is not ramping against the inductance of the magnet. The Model 625 includes the persistent mode
ramp rate feature that will automatically switch to the faster ramp rate when the magnet is in persistent mode. If the
feature is enabled, the persistent mode ramp rate will be used when the magnet is in persistent mode. When the supply is
using this ramp rate, the rate cannot be changed from the front panel using the
Ramp Rate
key since this is setup under
the
PSH Setup
key. If the persistent mode ramp rate is disabled, then the ramp rate will remain the same if the magnet is
in persistent mode or not but it can be changed at any time from the front panel using the
Ramp Rate
key.
To enable the persistent mode ramp rate, continue from the persistent switch delay screen or press
PSH Setup
then
Enter
until the following persistent switch setup screen appears as a prompt for the persistent mode ramp rate.
Persistent Switch Heater Output
Select With °®
Persistent Mode Ramp Rate: Enabled
Use the
s
or
t
key to select the persistent mode ramp rate, either Enabled or Disabled. Press
Enter
to accept the new
selection and continue to other persistent switch heater features. Press
Escape
to cancel the new selection and return to
the normal display.
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