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Re: torr/fill guage calibration

Posted By: SVP Neon Equipment
Date: Friday, 28 June 2013, at 12:04 a.m.

In Response To: torr/fill guage calibration (oldskool)

> Hi there....I have an EGL Torr guage I
> bought in 1999. In recent months it seems to
> have lost the ability to be
> calibrated...when I turn the calibration
> screw many time over, either way, not much
> happens.

> Does this mean my guage is hooped? Does
> anyone work on these or do calibration? Ive
> read on here many times about Transco fill
> guages being really good, so if mine isnt
> repairable does anyone have or know where I
> can find a reasonably priced fill guage?
> [doest matter what kind...I dont want to go
> back to manometer]. I also dont want to
> spend alot of cash as Im only doing a few
> tubes here and there :( ... Thank you all in
> advance.

This is real simple: Do you want accuracy or convenience?

Your EGL "Torr gauge" was out of calibration a long time ago, whether or not you realize it - probably from day one. Turning the pointer zero set screw like you have been doing does nothing more than zero the needle on the scale. It *does not* calibrate the meter. Quite the opposite. It more than likely makes the actual calibration worse, not better.

Regardless of the source (manufacturer) they all work on the same Bordon tube principle, all of which have a poor accuracy rate: Typically +/- 2% FSD (Full Scale Deflection) at best. For a 0-40 Torr range that's +/- 0.8mm, or a potential shift of 1.6mm fill pressure from unit to unit. None of them were ever intended for repetitive cycling from ATM to high vacuum while pumping large quantities of water vapor (80%+ of neon tube processing gas load is water vapor).

Beyond the inferior accuracy, they ALL exhibit virtual leaks. These reasons, as well as the cost to have them factory re-calibrated, is why I stopped selling them in the early 90's. Others continued selling them for one main reason: They made a lot of money doing so; typically more than doubling (sometimes close to triple) the price of what they paid for them through quantity purchases.

For the cost of having your gauge truly factory re-calibrated, you could buy a (Heaven forbid - dreaded) 100% accurate manometer that never goes out of calibration (provided you keep it relatively clean).

Here is some more info for review:

http://www.svpneon.com/Gauges.html

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