Re: [AMMRL] Cryomech Helium Recovery System - Critical Vulnerability

Hi, colleagues,

We had the same problem with an upper laser one year ago. The upper laser was not able to observe the reflected laser beam and continuously forced the helium compressor to pump helium from the bag. In contrast to the case of Hanno (lower laser problem) we observed a very short on/off cycle of the helium compressor (with a very short period of one minute) because the lower laser successfully switched the compressor off and passed the control to the upper laser. In our case the compressor did not pump helium from the magnets and the issue was found by me the next morning after one night of such cycling.

In our case, the problem was not because of the laser/retroreflector misalignment, they were accurately installed and the upper laser did observe the signal from the retroreflector. For diagnostics, we disconnected the laser system from the compressor, namely removed one of the wires that go from the laser's self-locking relay circuit to the compressor external start switch. Then we tested the laser system. We have two Banner QS30LLPQ polarized lasers/sensors that have eight indicators on the back side to show the reflected beam intensity. Our problem was because of the low intensity of the reflected beam: it was three points out of eight, while two points mean the absence of the reflected signal. Sometimes the upper laser occasionally measured two points and switched on the compressor.

We temporarily disabled the upper laser and ordered larger reflectors with narrower reflected beam size from the Banner catalog (BRT-92X92CB). Our laser path distance is 8 meters to one side and 8 meters back, that path is too large for the default retroreflectors supplied "in box". When the new reflectors arrived, the problem with the upper laser was not resolved, although the signal intensity of the lower laser increased from 4 points upto 8, we have got the maximum intensity of the reflected signal on the lower laser. After that we ordered the new laser of the same model and now the system works fine at least for three months.

To finalize, my strong recommendation to everyone: please check the signal intensity of your laser system (disconnect from the compressor before testing!). If it is near the lower limit, you are in danger of potential malfunction, you should consider laser/retroreflector replacement. Please note that the retroreflector changes the laser polarization and you can't use a simple mirror for testing.

Additionally, the Bauer Verticus helium compressor may be configured to stop permanently with a red alarm on the control panel if negative input helium pressure occurs (i've set the alarm value of -0.03 bar). The alarm should be cleared manually by the operator to start the compressor again. I do not recommend larger thres hold values for Bauer Verticus compressors because the internal sensor is not stable enough. Moreover, the values of the input helium pressure should be controlled from time to time (at least one per week) and the pressure value should be adjusted by changing the sensor upper/lower values in the compressor config panel, again because the pressure sensor is not stable. Any external sensor with external switch should be preferred to the Bauer Verticus internal sensor/alarm functionality.

Maxim

 

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Sincerely,

Maxim A. Dubinnyi

 

 

 

 

15.08.2023, 18:37, "jl167_at_gatech.edu" <jl167_at_gatech.edu>:

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