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Author: Subject: Vacuum gauge calibration without a calibrated vacuum gauge?
Twospoons
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[*] posted on 18-11-2019 at 20:46
Vacuum gauge calibration without a calibrated vacuum gauge?


I'd love to have a Pirani gauge to go with my vacuum pump, but I can't really justify the cost. Making the hardware is trivial for me, but then how do I calibrate it when I don't have a gauge to calibrate against?

Could I use boiling points of known liquids? I.E. pull vacuum until liquid boils, then measure temperature and use known data to get the pressure. Does that seem reasonable for a modest calibration method? I'd be happy with 5% accuracy at this stage.

[Edited on 19-11-2019 by Twospoons]




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Sulaiman
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[*] posted on 19-11-2019 at 00:43


This is exactly what I plan on doing
... measuring the b.p. of (in my case) mercury to determine the degree of vacuum.
https://www.sciencemadness.org/whisper/viewthread.php?tid=15...


A useful tool : https://www.sigmaaldrich.com/chemistry/solvents/learning-cen...

You could buy (or possibly fabricate) a McLeod gauge
https://en.wikipedia.org/wiki/McLeod_gauge




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Twospoons
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[*] posted on 19-11-2019 at 13:43


I'd prefer not using mercury, if possible. I have naughty cats that like to climb about in my garage, so the risk of glass breakage is reasonably high. And my garage is not a place I'd want to try to clean up a spill like that.

Thanks for the link to the BP tool - that looks really useful.




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[*] posted on 20-11-2019 at 10:37


You could use ethylene glycol (bp 196°C) and oligomers thereof as high-boiling point liquids that would give you a decent range for calibration. They're also reasonably cheap. Also glycerol (bp 290°C).



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Sulaiman
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[*] posted on 20-11-2019 at 20:08


Both of the above mentioned 'substitutes' are hygroscopic,
it may be best to check b.p. / boil off water at atmospheric pressure before using.
(with compensation of b.p. for local atmospheric pressure, if you want to be precise)

P.S. I just realised that the calculator that I pointed to is wrong,
e.g. set B to 100oC (at 760 mmHg) and lock it,
scale A reads 100oC at 700 mmhg ... wtf ?

On the same site, this calculator seems more accurate, but with restricted ranges.
https://www.sigmaaldrich.com/technical-documents/articles/ch...

Here is the 'best' data that I could find for mercury vapour pressure for the range that I am interested in
460C = 0.5 Pa
57oC = 1.0 Pa
60oC = 1.3 Pa
data is from here
Attachment: GOVPUB_C13_Mercury_Vapour_Pressure.pdf (1.7MB)
This file has been downloaded 334 times

[Edited on 21-11-2019 by Sulaiman]




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[*] posted on 21-11-2019 at 16:46


You could always calibrate your vacuum gauge.... *dramatic pause*... with another vacuum gauge. I have a VG64 which seems to be reasonably accurate.

https://controlscentral.com/eCatalog/tabid/63/ProductID/4147...




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Sulaiman
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[*] posted on 21-11-2019 at 17:58


That vacuum gauge costs more than my vacuum pump, oil, and accesories combined :P



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[*] posted on 21-11-2019 at 18:34


Quote: Originally posted by Steam  
You could always calibrate your vacuum gauge.... *dramatic pause*... with another vacuum gauge. I have a VG64 which seems to be reasonably accurate.

https://controlscentral.com/eCatalog/tabid/63/ProductID/4147...


Congratulations on completely missing the point of this thread.




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