On Mon, 17 Jul 2006 18:32:44 GMT, Lloyd E. Sponenburgh wrote:

"Ignoramus18860" wrote in message
...
On Mon, 17 Jul 2006 17:48:44 GMT, Lloyd E. Sponenburgh
wrote:
BTW... could YOU scratch-build your own thermistor-based vacuum gauge for
refrigeration work and calibrate it? I did, and I know several HSMs here
on
the metalworking group who have the skills. Bet not ONE of you could.
Could you build a diffusion pump? Bet you don't even know what one is.

Lloyd, I am interested in making a "deep vacuum" gauge, for up to
fractions of a micron. My vacuum pump can supposedly go down to one
micron, IIRC. (nothing fancy, it is a small Sargent-Welch DuoSeal
pump, but it would be interesting to measure vacuum accurately)

Large fractions of a micron aren't really "deep vacuum" like you'd obtain
with an oil diffusion pump backed with a cold baffle and a really fresh vane
pump. But that's still pretty high. You're talking better the range of
what a good, new Robinaire refrigeration pump can do (down to ... oh... 20
microns, or so).

That's right.

For your range, thermistor gauges are well-suited. Here's a good writeup of
one that will measure down to 0.5u:

http://www.ece.ualberta.ca/~schmaus/vacf/thermis.html

However, he doesn't go into calibration very much. Borrow a couple of
commercial gauges, and average their readings to do that. With a small
manifold and carefully assembled, leak-free fittings, you should be able to
pull down and scour your new gauge within an hour or so of pumping.

Sounds great. I printed that page and will read it. Would be great to
have a gauge for measuring micron range vacuum. (I have a dial gauge
now, would be a big improvement).

i