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Subject: Re: Idea - Cheap Pressure Gauge
Date: Aug 06, 5:56 pm
Poster: Jim Lux

On Aug 06, 5:56 pm, Jim Lux wrote:

>You might also think about a simple tungsten filament (such as from a flashlight bulb). A small constant current slightly heats the filament. The readout circuit is a simple voltmeter reading across the filament. As the pressure decreases, the filament gets hotter, its resistance rises, and the voltage across it increases. I built one that works down below 10 microns. The original used a multimeter on the resistance scale to read pressure!

Also known as a Pirani gage... A ThermoCouple gage (or TC gage) is similar in function.. The Amateur Scientist had a column about building such a thing last year or the year before.

And, for that matter, the next step is an ion gage, which is essentially a vacuum tube diode or triode across which you measure the current through. Various forms with cathodes cold and hot exist.. Nothing fancy here, readout wise, either. You could build the sensor yourself, but then you'd have to calibrate it, which is no easy feat. Spend the few tens of bucks (or a hundred) to get a real ion gage tube. ($60-100 from Leske, Duniway is probably cheaper, but I can't find my catalog here)