Author Topic: humidity control  (Read 67 times)

Mike Jercinovic

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humidity control
« on: November 19, 2020, 10:05:51 AM »
Our university is actually considering replacing our old AC split systems with something much better, and finally with humidity control.  What target relative humidity value seems best?  Cameca suggests <75%, but if it is too low, then ESD is a big problem (we deal with this every winter), but if it's too high, it effects ion pump performance (we deal with this every summer as water vapor can enter via sample exchange), and if you have any sort of shutdown, condensation on chilled water lines can be problematic.  There must be a good middle ground.

Probeman

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Re: humidity control
« Reply #1 on: November 20, 2020, 10:12:30 AM »
Our university is actually considering replacing our old AC split systems with something much better, and finally with humidity control.  What target relative humidity value seems best?  Cameca suggests <75%, but if it is too low, then ESD is a big problem (we deal with this every winter), but if it's too high, it effects ion pump performance (we deal with this every summer as water vapor can enter via sample exchange), and if you have any sort of shutdown, condensation on chilled water lines can be problematic.  There must be a good middle ground.

Hi Mike,
Not sure if this applies to floors other than polished concrete, but when we built the new labs they added a (permanent) sealing coat to the floors, that utilized a compound that was designed to minimize static buildup.  Even though it's wet all winter here in Oregon, it does get very dry inside. And in the old lab we always had to remember to touch something grounded before touching the instruments or computers. 

I remember one time in the old lab where we had *carpets*, I walked across the room, touched one of the stage rollers, there was a spark, and the entire instrument shutdown!
john

Maybe there's something like this for other floors as well?
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Mike Jercinovic

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Re: humidity control
« Reply #2 on: November 20, 2020, 10:39:05 AM »
Yes, we have had our share of static charge problems in winter, so we have tried to adopt a policy of 'self grounding'.  We had one user who had a particular ability to generate a lot of voltage, don't know if it was footware or genetics, but the same thing eventually happened - spark hit the rollers and we were down (SX50).  When it came back up we found a 68000 board had failed, so the ESD killed some DRAM... ouch.  I have tried through the years to get some ESD dissipative flooring solution like they use in semiconductor Fab rooms, but for reasons we don't need to get into, those efforts failed.  Both Cameca and JEOL seem to have maximum humidity level requirements, but not minimum.  Unofficially, I hear now that 40 to 60% relative humidity is a good target range.  I would still be interested in input regarding everyone's lab environment, and experiences.

Anette von der Handt

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Re: humidity control
« Reply #3 on: November 20, 2020, 06:51:02 PM »
I was told (and had specified for my lab) that keeping humidity between 30% and 60% as the target. Of course the architects of our building nodded and then did nothing (because it is expensive or they just didn't care),. So now my lab has no humidity control and I often have a humidity of 10% in the dry Midwest winter and feel I need to drink gallons of water besides getting shocked often. On the upside, the machine reaches a good vacuum in no time after sample change :)

I had bought the largest stand-alone humidifier I could find but it would only raise the humidity by 5% (large lab though) and made a giant ruckus and needed to be refilled constantly so I eventually gave up on it. To get proper humidity control, I was told I need to tap into the steam system which was too expensive. A different lab in the building did that though and now they have controlled humidity but the controllers in their hallway generate so much heat that the heat load is causing other problems for them.

I have dissipative flooring though, so it could be worse. I also got these 5$ anti-static key chain eliminators that you can find on Amazon/ebay.

Would be interested to learn if there are other solutions. Obviously it depends strongly on the humidity range in the region how difficult it is to maintain within a range.
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Mike Jercinovic

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Re: humidity control
« Reply #4 on: November 21, 2020, 07:55:44 AM »
Thanks for the info Anette.  We tried a stand alone humidifier too, not even close to keeping up in our case, and filling constantly like you say.