That should be 35F ??
Neal J Stolowich, PhD
NMR Facilities Manager
Senior Instructor
Chemistry Department
University of Louisville
(502) 852-7894
From: Stolowich,Neal J.<mailto:njstol01_at_exchange.louisville.edu>
Sent: Sunday, October 29, 2017 9:44 AM
To: Rainer Haessner<mailto:rainer.haessner_at_tum.de>; 'ammrl_at_ammrl.org'<mailto:ammrl_at_ammrl.org>; Dr. Gerd Gemmecker<mailto:gerd.gemmecker_at_tum.de>; Stehle, Ralf<mailto:ralf.stehle_at_tum.de>; Asami, Sam<mailto:sam.asami_at_tum.de>
Subject: RE: AMMRL: Unexpected shutdown of CNS61-D compressor
Well this is interesting- my coldprobe failed sometime early yesterday – which happened to be the coldest morning of the season so far this year (~35C). I think we also have a CNS61 compressor with the aircooled unit, and in past years had failed on cold mornings. The previous times was attributed to the outdoor unit being dirty, but I think its been kept cleaner more recently. So, I hope this is not a sign of more problems to come.
Neal
Neal J Stolowich, PhD
NMR Facilities Manager
Senior Instructor
Chemistry Department
University of Louisville
(502) 852-7894
From: Rainer Haessner<mailto:rainer.haessner_at_tum.de>
Sent: Saturday, October 28, 2017 12:14 PM
To: 'ammrl_at_ammrl.org'<mailto:ammrl_at_ammrl.org>; Dr. Gerd Gemmecker<mailto:gerd.gemmecker_at_tum.de>; Stehle, Ralf<mailto:ralf.stehle_at_tum.de>; Asami, Sam<mailto:sam.asami_at_tum.de>
Subject: AMMRL: Unexpected shutdown of CNS61-D compressor
Dear cryoprobe specialists,
we have a very funny malfunction of an about 45 000h old air cooled helium compressor CNS61-D.
We already ordered a new one, nevertheless I am very, very curious, what's going on.
The obervation: as soon as the outside temperature falls below a limit somewhat around 5 and 6 degree centigrade,
the compressor switches off without any warning.
Of course we made some checks. The very first one was cleaning the heat exchanger. There is a sensor outside of
the heat exchanger, which switches the cooling fan inside the housing to lower speed at ... 5 degree centigrade.
If the heat exchanger is not clean, this might result in overpressurized helium gas, which definitely is a shutdown
condition.
Very easy ... but wrong. The heat exchanger is perfect clean, using ice and hot water we triggered the temperature switch to change
the fan speed multiple times without any effect. Even more, to be really sure, we deactivated the temperature sensor
to ensure, the cooling fan is running with full speed all time.
No effect, as soon as the outside temperature falls below 5 ...6 degree centigrade ... see above.
There is a second temperature sensor inside the cabinet. At temperatures below 4 degree centigrade this switches on
6 wires to heat the oil inside the compressor. These wire are driven by 230V (at least in Europe). Now I have to
append, that we had a mouse living inside the cabinet. This mouse caused some minor destruction work at these wires.
At some places the insulation shows teeth marks from the mouse. It is very difficult to see, whether there was a significant
damage or not. But anyway, tentatively we deactivated this sensor as well.
No effect, deeper outside temperature, sudden breakdown of the compressor.
There is a low pressure sensor for the return gas. Deactivated ... no effect.
I am out of ideas, replacement compressor will arrive soon, nevertheless that's a real challenge. There *has to be* a
deterministic reason.
Looking for any idea ...
Greetings
Rainer
Received on Sun Oct 29 2017 - 04:32:49 MST