Electronic pressure sensors. gauges

Maybe you could pulse-heat a thermistor or thinfilm RTD or high-TC wire and observe the cool-down curve. Something low emissivity to reduce radiation cooling?

How about a shielded 3-terminal capacitor?

How much does a commercial vacuum gage cost?

We use this one in our SEM cathodoluminescence system to detect when the chamber starts to vent, so that we can turn off the MPPC bias and return to room temperature before water starts to condense on the cold plate. Its range is 10 to 1200 millibars, about $2 in hundreds.

Cheers

Phil

I copied this thermistor/ bridge 'recipe' from a vacuum guy. it was meh. I tried wrapping a bit of Al foil around it, made no difference AFAICT

Air capacitor? Don't know.

Oh boy...IDK. I'm going to say $500 gauge and meter. but probably cheaper somewhere... a cheap mechanical dial.. maybe $20-50?

OK looks like a mechanical gauge costs ~$10 in one from granger.

George H.

Nice, thanks. I'll give it a whirl. George h.

That's the principle of the thermocouple vacuum gage, and the thermocouple is a better choice than a thermistor, because it's tolerant of higher temperatures, and gives (intrinsically) a differential measurement. It takes an AC regulated current for the classical ones, and readout is just a voltmeter. They aren't expensive to make, but the commercial ones standardized back in the vacuum-tube era on odd connectors and awkward 'standard' specifications.

The capacitance manometer is a nice scheme. With modern electronics setting up an AC-excited Blumlein Bridge - sort of a Wheatstone Bridge, but with a centre-tapped transformer as two of the arms, and the capacitance to the (grounded) stretched metal diaphragm as the other two - is cheap and simple .

Berylium copper shim would have been my choice of diaphragm material back i n about 1965.

The ones I've seen have been expensive. For it's electron microscope chambe rs Cambridge Instrument went with Pirani gauges fro coarse vacuum and ion g auges for high vacuum, but that choice was made way back when capacitance m anometer electronics was a lot more expensive.

A turbo-molecular pum as a vacuum gauge?

You can get surface mount thermistors these days

Baratron was the best known supplier back then.

From my Ph.D. thesis

J.J Opsteleten and N. Warmholtz Applied Science Research Hague B4 page 329 (1955)

J.J Opsteleten, N. Warmholtz and J.J. Zaalberg von Zelst ibid B6 pages 129 (1956)

D.R. Lovejoy Rev. Sci. Instrum 32 page 41 (1961)

The first two were from the Philips research lab and meticulous. The third one was American, and less so.

At the time I was thinking about an electrostatic force balance version of the capacitance manometer. It wouldn't have been any good for pressure diff erences over a few torr, but it was an entertaining idea.

There was a vogue for using diaphragms etched into a silicon wafer with built-in strain gauges. Motorola and Honeywell both used to sell them fairly cheaply.

Since you claim to be OK with thread drift, I'll throw in "Crookes Radiometer". They are sensitive to low-range gas pressure, but I have no idea whether there is calibration data somewhere.

Also when I was playing with pumping on liquid helium I needed a silicone oil manometer measuring pressure relative to vacuum in the closed-off arm. But the oil would "stick" to the closed-off end and not measure. I solved by using liquid nitrogen (which we would always have handy if using helium) soaked into cotton waste to temporarily pack around the closed end. That would freeze the oil which cracked and released the stick. My own invention; worked every time!

Mike.

The usual t/c vacuum sensor is a 4-wire device, with separate heater and sensor elements, and works steady-state. Now that we have microprocessors, we could have a simpler 2-wire element that's both the heater and the sensor, probably with pulsed heating.

A thermocouple made of thin wire could be the heater and the sensor.

ng up an AC-excited Blumlein Bridge - sort of a Wheatstone Bridge, but with a centre-tapped transformer as two of the arms, and the capacitance to th e (grounded) stretched metal diaphragm as the other two - is cheap and simp le.

in about 1965.

bers Cambridge Instrument went with Pirani gauges fro coarse vacuum and ion gauges for high vacuum, but that choice was made way back when capacitance manometer electronics was a lot more expensive.

Yeah! According to 'Building Scientific Apparatus' they spin a magnetically suspended steel ball up to 415 Hz, and then measure how long it takes to slow dow to 405 Hz... (several minutes at the low pressure range.) A spendy bit of kit!

(Hey Bill thanks for the nice response.)

George H.

d one was American, and less so.

f the capacitance manometer. It wouldn't have been any good for pressure di fferences over a few torr, but it was an entertaining idea.