Chromatography Forum

I'd venture a guess that if the behavior didn't stop the instant the humidifier was turned off, then your situation is definitely related to the RH. Might it be possible to actually increase the RH in the area to ~50%? My thinking is that perhaps the instruments won't be as sensitive to small variations in RH at a higher RH level.

To DR: I am unaware of any provision on the 2996 to run an N2 line to the cell, though the 2998 does have a barb & plumbing for an N2 line.

I'm not aware of any good way to sparge the optic pathway of the 2996 with nitrogen, either, although if I can think of anything and I can find the time I would be very interested in trying it.

That's a really good suggestion about trying to set the humidifier to a higher RH, I'll have to check with maintenance and find out what those units can do. I think it's actually possible that the 2996 may be less sensitive to fluctuations in RH at higher RH, and I'd love to confirm or disprove that.

Anything I do, though, has to contend with the backlog of samples that urgently want to get on those two instruments . But as much as possible I would like to fully characterize the behaviour of the detectors with respect to humidity. That's useful information.

Stephen

Nice you have found the source of the problem.

I could think of combining the two observations:
Maybe the RH has an impact on the level of the baseline by increasing/lowering the output signal in some way and as for second it makes it more sensitive to some other electric fields present in the air (e.g. the cyclic freuquency of 5-6 mHz)?

How are the detectors connected to you workstations?
Are the cable well shielded? Are you using (high quality) LAN-cables or the older IEEE cables? In case of the IEEE, are the "end connector" (unused side of the plugs) open or protected? In case of the LAN, are the "Shield-ports" correctly grounded on both side?

What I try to say is, is it really the detectors electronic which is sensitive or is the problem induced somewhere else on the connecting part? (I never obeserved something similar with our 2996 @ 17-20%rH)

Still thinking of additional grounding of the detectors by attaching some additional cooper wire on the surface.
Beside this: Is the grounding of the electrical installation really working or is there something wrong with it... (would be a dangeours situation)?

You said that the systems are placed near the inner wall of the two rooms.
What about some static fields between the two rooms, which are strongest in this part of the room, as there is the lowest possibility for some charge transfer (low humidity, low air flow)? If so, you maybe invented something like a "room-battery"...

Could you connect the two rooms by means of a window or something else to reduce the potential difference across the wall?

At least, I also would go with a higher humidity if possible

The 2996 and 2487 detectors are connected via IEEE cables with the ends protected. Basically we have kept the configuration that Waters originally installed for these instruments, pretty much without modification.

I don't have the latitude to have any modifications made to the walls, unfortunately. For the most part, I'm stuck with the configuration of the room.

I might be able to get the humidifier to create a much larger output and see what happens, or temporarily seal the inner portion of the instrument room and increase the humidity by some other means, and I plan to try that when and if I get some idle time, or if there are future concerns raised about the apparent sensitivity to humidity. I am quite interested to watch it at a higher level of humidity, particularly with the humidifier on and generating fluctuations in the humidity, to see how it behaves at different levels.

I think that the problem has to be a direct result of the humidity rather than a feedback from the power supply related to the humidifier, just based on the way the system acted when the humidifier turned off. However, I do agree that the problem could still be electrical in nature, perhaps related in some way to the physical connections, but associated somehow with the humidity.

I may not be able to address this issue again over the near term due to the backlog of work that has been created in the interim, but I'm definitely keeping all options in mind to further characterize the issue and I'll report back if I find anything interesting.

You could just grab a drugstore humidifier, park it in the corner of the lab, plug it in, monitor RH, and see what happens. As long as it doesn't end up raining in your lab, you might be OK. It would be cheap if nothing else....