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Nick Brewer: Difference between revisions
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'''<big>6/27/14</big>'''
This week we got liquid helium and cooled the cryostat down. Everything seemed to be working. We currently have no way of monitoring how much liquid helium we use though so it might be nice to come up with a way to do that.
After playing with the PID settings on the temperature controller I was able to keep the temperature mostly at 5.00 K +/- 0.01 K, which is what Janis said we should expect for a stability (P=220, I=50, D=0). Once in a while it jumps out of this range though. We can probably get it better than what it is now though. Hooking the temperature controller up to a computer so we can see a graph of temperature vs time might help us more fine tune the PID settings. The flow rate of the LHe probably is a big factor in how stabilized the temperature is. So far the only way we have to control the flow rate is the flow regulator valve on the transfer line. Once the cryostat is cooled down to ~4.5 K I close the valve until the temperature starts to rise, then slowly open it until it begins to drop again. If it can't make it back to ~4.5 K I open it a smidgen more, etc, until it just reaches 4.5 K. It's not as easy as that though, there seems to be quite a bit of lag in the control, especially when it is at it's minimum temperature.
'''<big>5/30/14</big>'''
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