User guide

30 Rev. 5
Operation
Single-key Commands : Persistent Switch Control
persistent switch is installed in the Load submenu and specifying the
switch heating current, heated time, and cooled time
1
.
The nominal switch heating current is listed on the magnet specification
sheet, and may be entered in the Model 430 Programmer by accessing the
Load submenu
2
. In addition to the heating current, the user must also
specify a heated time, cooled time, PSw P/S Ramp Rate and cooling gain.
The heated time allows the Model 430 Programmer to delay compensating
the internal control logic until the magnet is guaranteed to be in the
circuit. The heated time can be set from a minimum of 5 seconds to a
maximum of 120 seconds within the Load submenu
3
. The default heating
period of 20 seconds is adequate for the majority of persistent switches.
If the magnet appears unstable just after the switch heating period
expires, increase the switch heated time to allow for complete heating. The
cooled time allows the persistent switch sufficient time to be cooled to
superconducting state before the current is changed in the magnet. The
cooled time can be set from a minimum of 5 seconds to a maximum of 3600
seconds within the Load submenu
4
. The default cooling period of 20
seconds is adequate for the majority of wet persistent switches.
Conduction cooled switches typically require longer time to transition from
resistive to superconducting.
The default cooling gain of 0.0% may be adequate for the majority of wet
persistent switches. However, this setting may result in some magnet drift
during persistent switch cooling, especially with conduction cooled
switches. Increasing the cooling gain adds control loop gain during the
switch cooling cycle. Too little may result in magnet drift during switch
cooling. Too much may result in power supply instability during switch
cooling, which could potentially prevent the switch from cooling. Most
systems requiring some cooling gain to control magnet drift will likely
work with value set to 25%.
Note
During the period the switch is being heated or cooled, the Model
430 Programmer will not allow ramping functions to be executed
and will beep once if the user attempts to initiate a ramping
operation.
Refer to section 3.13 on page 77 for a complete description of magnet
persistent switch control. A flowchart of the persistent switch control
functions are located in the Appendix beginning on page 188.
1. Refer to section 3.10.2.6 on page 54, section 3.10.2.8 on page 55, section 3.10.2.9
on page 55, and section 3.10.2.10 on page 56.
2. Refer to section 3.10.2.8 on page 55.
3. Refer to section 3.10.2.9 on page 55.
4. Refer to section 3.10.2.10 on page 56.