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Re: Gauges

Posted By: SVP Neon Equipment
Date: Sunday, 31 March 2013, at 9:27 p.m.

In Response To: Re: Gauges (Romarrk)

You specifically said “DV6”, which was the predecessor to the DV-6M. Split all the hairs you want: I doesn’t wash with me.

Hastings VT-6 (with the VT-6A being the new generation) gauges, used with the corresponding DV-6M tube are ambient temperature and barometric pressure compensated. Your suggested arrangement is not. A change in either parameter will alter any calibration you *think* you have done.

For example: You are preparing to set up your “vacuum gauge” to take a reading. When you do this, the ambient temperature is 70°F, and the BP is 30.0” Hg. (We won’t even get in to discussing dew point and water grains per lb. of air in the atmosphere). All of a sudden the weather changes. It doesn’t really matter *how* it changes, just the fact that it changed. You can throw your set up and so-called “calibration” out the window (or door if you don’t have any windows in your kitchen)!

I absolutely *DO NOT* mind correcting you on this one: It’s “American’s”, not americans. Get it right or get lost!

A circuit that automatically corrects ambient atmospheric conditions is not “dumb”. The stuff you are suggesting, which requires “calibrating” every time you use it, went out of style 60-70 years ago in the U.S. The newer technology (if you consider a half century old technology new) saves time and eliminates errors. In this country time is money. In Russia (notice I didn’t say that is where you are from) time is all they have.

I didn’t say the average neon shop was a “calibrated environment” run by “trained technicians”. You are taking what I said out of context. Re-read what I said.

You wrote: “…please tell me how one can ever read reliably that "critical" 2mm Hg pressure from 40 Torr gauge in common use?” No one can! Read my website discourse on the “Technical” page titled “A Word About Gauges & Meters” under “Gas Fill Pressure Gauge”. I strongly recommend NOT using a 0-40 Torr gauge for the reasons mentioned.

You wrote: “Once calibrated against ultimate vacuum, it will make great cheap tool to check if manifold and pumps are ok. Even when pumping down, micron gauge immediately shows the tube is leaky, without resorting to spark tester.” This is hilarious! See my previous comments about ambient atmospheric conditions concerning your “calibration”. As for “shows the tube is leaky”, not necessarily. If the pumping system has a decent size roughing pump in conjunction with a properly working secondary pump (diffusion preferred), they can pump against a small leak very well – enough to “mask” the leak from indicating on the vacuum gauge.

Btw, in experienced hands a spark tester can determine if a neon unit has a leak in a matter of a couple seconds. (Finding the leak may be a different matter). That is not the sole intention of a high vacuum gauge. In fact, that would be down on my list of priorities for use of one.

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