I have also had some struggles with the Banner Engineering laser sensors
(QS30LLPQ). My initial installation used the old ATC IR sensors (that are
no longer available) and they worked great with retroreflective tape.
After switching to the Banner sensors, the behavior was very inconsistent.
After months of frustration, it turned out that these sensors worked
beautifully with actual retroreflectors but they simply do not perform
consistently with the retroreflective tape (I tried several different
brands, too). Because of this, I also had a few incidents with the top
sensor not triggering the compressor while filling a magnet several floors
away and the bottom sensor not triggering the compressor leading to a
completely empty bag and pumping on the LHe in my transfer dewars (luckily,
I have back-P regulators on my magnets, so they weren't affected).
I feel like I should also mention that user error can cause this same
problem. Before a LHe transfer, I always empty the collection bag so that
I have a record of how much He is in my system before and after the fill
for calculating the apparent flash %, etc. My bag is up on a shelf, so
it's not easy to see if the lasers are currently on the reflectors or not.
One time in the early days of using the system, I hit the bypass switch on
the compressor to start emptying the bag, not realizing that the lower
sensor was already detecting the signal from the reflector. It's the
*change* in signal that triggers the compressor to turn off, so if the
lower sensor is already engaged when you hit the bypass switch, it just
keeps on going even when the bag is completely empty and it's pumping on
the LHe in my transfer dewars. So
-Scott
On Wed, Aug 16, 2023 at 7:04 AM Maxim Dubinnyi <dumkas_at_yandex.ru> w=
rote:
> *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 threshold 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*
>
> --
> Sincerely,
> Maxim A. Dubinnyi
>
> ----------------------------------------------------------------
> IBCh RAS https://urldefense.com/v3/__http://www.ibch.ru/en__;!!PvDODwlR4m=
BZyAb0!XdlTHh0PalEfdEC8nw7Q6IQuY403ZsgwveNnV_DaJKOel15NvjWNy1v4Gllu73YIAi-n=
HuUoZejTPD1vz3s$ , Laboratory of biomolecular NMR-spectroscopy,
> phone: 7(905) 511-57-71,
> e-mail: maxim_at_nmr.ru, dumkas_at_yandex.ru
>
>
>
> 15.08.2023, 18:37, "jl167_at_gatech.edu" <jl167_at_gatech.edu>:
>
> Dear All,
> We recently observed a very dangerous vulnerability with our Cryomech (now
> Bluefors) Helium recovery system, which I feel is important to share here.
> This is the recovery system with a bag and the 350 PSI compressor.
> The fill level of the bag is controlled via two laser-switches. If the bag
> is near fully inflated the upper switch will start the compressor, which
> pumps the bag down to a lower level. Once the bag is almost empty the
> second (lower) laser-switch triggers a stop of the compressor.
> A failure in the lower laser switch (in our case the switch just had gone
> out of alignment) will not stop the compressor, the bag will completely
> deflate and the compressor will create a vacuum in the recovery line
> leading to the magnets. Obviously, this can cause a drastic increase in
> Helium-boiloff in a worse case scenario it can quench all magnets connected
> to the recovery system (let's just say we were lucky, all of our magnets
> are ok).
>
> In order to protect oneself from this vulnerability one should make sure
> that
> (1)
> backpressure regulators are installed and properly set at all magnets
>
> (2)
> the Cryomech compressor has a switch, which controls a shutoff pressure.
> For our system this switch was set to a negative pressure. This switch can
> be adjusted to 0 PSI. With the 0 PSI, the compressor will shut down prior
> to pulling a vacuum. We tested this by hooking a He-tank to our recovery
> line (magnets were disconnected).
> In order to reach the switch, the side panels of the compressor have to be
> removed and the switch has to be unbolted from the bottom-plate of the
> compressor, which is a bit of a hassle.
>
> Thank you to Davis and Abner from Cryomech for helping us to address this
> problem; they have no objections that I share this issue here.
> I suggested that they publish a service-bulletin describing the fix. In
> the meantime, I am happy to create a more detailed set of instructions to
> check and potentially change the setting of this switch.
>
> Kind Regards,
>
> Hanno
>
>
>
>
--
Dr. Scott Burt
Professor
NMR Facility Manager
Department of Chemistry and Biochemistry
Brigham Young University
C414 BNSN / C008A BNSN
Provo, Utah 84602-5700
Phone: (801) 422-2404
Fax: (801) 422-0153
chembio.byu.edu/nmr-facility/
email: scott_burt_at_byu.edu
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Received on Wed Aug 16 2023 - 06:32:55 MST