We had a Lake shore 625 for controlling the superconducting magnet up to 5T. Cooling by LHe was good and stable down to below 4.5K before we start to charge the it. It works fine up to 4T and when we ramp up from 4T to 5T, it works well initially until almost reaches 5T (to be exact 4.98T) FAULT alarms came ON "Magnet quench detected", however do do not see any rise in temp from the external temp monitor and we don't understand why it quench. It works fine in our previous run. What or where is the controlling factor that Lake shore 625 detect quenching? Thanks
Post by Lake Shore Ogi on Nov 2, 2018 13:27:24 GMT -5
Thank you for posting on our forum!
For the most precise details on the quench detection method, please refer to the explanation in the manual section 4.16. Essentially, the 625 just monitors the rate of change of the current. If the current changes too fast, then it assumes a quench has occurred. If your magnet dropped to 0 A right after the detection, then a quench did actually occur. My guess is that you could be ramping too fast as you're approaching the maximum current of your magnet. Try slowing it down a little bit and see if it occurs again.
Thanks for the reply. The ramping current was fixed constantly throughout without any changes and the current to reach 5T is actually about 1 amps lower than the spec maximum current. The only difference is we charge the magnet using Field mode instead of Current mode, does it make a different?