When the fridge is in Hold Cold Mode, it means we have a liquid in the fridge nose and holding target material. In that case, we must keep the target material to preserve the paramagnetic centers. In the Hold Cold Mode, you will see the fridge parameters as follows:
We fill the fridge to Heat-Ex Top for the Cold Hold Mode and close the Run and Bypass valves. To reduce LHe consumption in the fridge nose, set the GV bypass opening at 8.1% at the lowest opening to keep the fridge pressure flat. pressure on PID at 100 torr and Set the Separator flow at 11slm20slm.
Keep monitoring the target parameters, say Insert#7, Insert #8, Annealing A, and Annealing B. Where Insert #7 and Insert# 8 are the Cernox (CX-1030) sensors on the Top and Bottom cup of the target insert. Where Annealing A and Annealing B are the metal temperature in the fridge, monitor these four target parameters. Where Insert#7 and Insert# 8 are in resistance (Ohm) and Annealing A and Annealing B are in temperature (K). Please see a screenshot below for these target parameters:
Below is the conversion table for the Cernox (CX-1030) from temperature resistance.
If you see the target parameters, Insert #7 and Insert #8 start lowering down to around 132 Ohms, which is around 50K, then open the Run valve at 0.55 or 0.65 turns to get the liquid in the fridge nose. Keep monitoring the resistance of sensors; it should start increasing after opening the Run valve. Wait for 30 minutes. If the temperature exceeds ~80K (lower than 101 Ohm), open the run valve at two turns, set the separator flow at 30slm, and call the target expertsay Nose LHe Level (%), when it comes to 50% then start filling the filling and replenish the level at Heat-Ex bottom.
Please follow this page to put the fridge in the Cold Hold Mode: Cryo-control parameters / conditions when the fridge is in Hold Cold Mode - Wiki Post Portal - Confluence (virginia.edu)