I have found Strip connectors where wires are crimped onto tube and pin pairs cause all kinds of problems that seem to be heat related. It is a major fault point in old video arcade games and pinball machines also in more modern centrifuges. Inspect all connections closely both visually and with thermal images with a hand gun. If you use a funnel to focus a heat gun onto small areas it can sometimes expose weak connections. Mouse urine may have caused corrosion. Most of this requires the equipment be powered up...happy hunting!
________________________________
From: Rainer Haessner <rainer.haessner_at_tum.de>
Sent: Saturday, October 28, 2017 4:46:09 AM
To: 'ammrl_at_ammrl.org'; Dr. Gerd Gemmecker; Stehle, Ralf; Asami, Sam
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 - 16:50:37 MST