Granville-Phillips 275 analog output?

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Sven Andersson
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Granville-Phillips 275 analog output?

Post by Sven Andersson »

A quickie; there are a lot of Granville-Phillips 275 gauge heads for sale on the "Bay". Now, can you just feed them the right voltage for power and then read a voltage on two pins and translate that into the correct pressure? How accurate is that?

Sven
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Rich Feldman
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Re: Granville-Phillips 275 analog output?

Post by Rich Feldman »

There's no loss in accuracy if you apply power, measure the analog output voltage, and refer to a lookup table, calibration curve, or formula -- all of which are given in Convectron user's manuals.

To get readings more quickly, you can apply the voltage to a panel meter with DIY nonlinear scale, as I did. viewtopic.php?f=10&t=10092&p=67650#p67650

Or find a friend who will let you borrow & photocopy an analog meter card printed with the nonlinear model 275 scale.
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Rich Feldman
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Re: Granville-Phillips 275 analog output?

Post by Rich Feldman »

Hey Sven,
Your picture in OP shows a model 275 with Linear Analog Output feature.
If you get one of them, it's even easier. Here's a link to a brochure:
http://www.physike.com/oldweb/%D5%E6%BF ... odules.pdf
with a picture.
conv.PNG
The diptych brings up a little question about gas physics. In linear chart we see that up to 1 Torr, neon conducts heat more poorly than nitrogen. Same is true in the natural (nonlinear) chart. But above 1 Torr, as convective cooling takes over, Ne pulls ahead to win the little horse race of cooling power. In that high pressure region the order & spacing of the gases seems to follow their molecular weights (thus densities). Does anyone reading this want to give us an explanation?

note: the natural curve shows voltage on a Wheatstone bridge that includes vacuum sensor filament. Voltage is regulated to maintain the filament at constant resistance, thus constant temperature.
Last edited by Rich Feldman on Tue May 03, 2016 11:16 pm, edited 1 time in total.
All models are wrong; some models are useful. -- George Box
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Dennis P Brown
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Re: Granville-Phillips 275 analog output?

Post by Dennis P Brown »

I believe it is degree's of freedom, not molecular weight, for most gases (not noble, of course) but the two are related in general. Now, as density increase, electrons tend to transfer heat more easily between atoms, so then higher proton number will mean more electrons. That in turn would allow more heat transfer between atoms as they collide.
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