Twospoons
International Hazard
Posts: 1282
Registered: 26-7-2004
Location: Middle Earth
Member Is Offline
Mood: A trace of hope...
|
|
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]
Helicopter: "helico" -> spiral, "pter" -> with wings
|
|
|
Sulaiman
International Hazard
Posts: 3558
Registered: 8-2-2015
Location: 3rd rock from the sun
Member Is Online
|
|
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
CAUTION : Hobby Chemist, not Professional or even Amateur
|
|
|
Twospoons
International Hazard
Posts: 1282
Registered: 26-7-2004
Location: Middle Earth
Member Is Offline
Mood: A trace of hope...
|
|
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.
Helicopter: "helico" -> spiral, "pter" -> with wings
|
|
|
12thealchemist
Hazard to Others
Posts: 181
Registered: 1-1-2014
Location: The Isle of Albion
Member Is Offline
Mood: Rare and Earthy
|
|
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).
|
|
|
Sulaiman
International Hazard
Posts: 3558
Registered: 8-2-2015
Location: 3rd rock from the sun
Member Is Online
|
|
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 1114 times
[Edited on 21-11-2019 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
|
|
|
Steam
Hazard to Others
Posts: 238
Registered: 25-3-2014
Location: Minnesota
Member Is Offline
Mood: Triple Point
|
|
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...
DISCLAIMER: The information in this post is provided for general informational purposes only and may not reflect the current law in your jurisdiction.
No information contained in this post should be construed as legal advice from the individual author, nor is it intended to be a substitute for legal
counsel on any subject matter. No reader of this post should act or refrain from acting on the basis of any information included in, or accessible
through, this post without seeking the appropriate legal or other professional advice on the particular facts and circumstances at issue from a lawyer
licensed in the recipient’s state, country or other appropriate licensing jurisdiction.
|
|
|
Sulaiman
International Hazard
Posts: 3558
Registered: 8-2-2015
Location: 3rd rock from the sun
Member Is Online
|
|
That vacuum gauge costs more than my vacuum pump, oil, and accesories combined 
CAUTION : Hobby Chemist, not Professional or even Amateur
|
|
|
Twospoons
International Hazard
Posts: 1282
Registered: 26-7-2004
Location: Middle Earth
Member Is Offline
Mood: A trace of hope...
|
|
Congratulations on completely missing the point of this thread.
Helicopter: "helico" -> spiral, "pter" -> with wings
|
|
|
Texium
|
Thread Moved
29-11-2023 at 12:00 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
