Sensor Electrical output question

Aug 17, 2007 5 Replies

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James Lerch 18 years ago

So I'm building an interface to an Edwards Active vacuum Gauge tube (aka a fancy sensor).

I'm reading the manual (go figure :).. and stumble upon this lovely little bit:

"Do not connect the electrical supply common (pin 2) to the signal common (pin 5). If you do, the AIM Gauge pressure output signal will be inaccurate."

Oh.. well, ok.. The question is, are they trying to tell me the output of the sensor (which is 2 - 10vdc depending on pressure) is actually a differential output?

IF it helps, here's the specs on the output signal (again from the manual)

Range 2

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MooseFET 18 years ago

They have a drop in the ground wire due to the current in it. It is a fairl;y common problem with fancy sensors that have long wires.

Going differential is the way to solve the problem. It only adds a little cost. You could also float the power and ground the signal return but that adds more cost.

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Fred Bloggs 18 years ago

It looks more like they provided a 4-wire active Kelvin connection and they don't want him to screw it up by sharing signal common with power ground. Sometimes the questions are just so odd it's difficult to fathom the lack of sense.

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James Lerch 18 years ago

Hmm.. so, do you think it would be ok to tie the commons together back at the display unit / power supply? IF it was really a differential output, they would probably mention that, right?

I guess a little op-amp wouldn't be the end of the world :)

My plan was to use the $20 AVR-Butterfly as the display unit, I'll need to go re-read the atmega169 docs and see if it has an analog differential input..... Hmm maybe.

Thanks for your time (again!)..

Take Care, James Lerch http://lerch.no-ip.com/atm (My telescope construction,testing, and coating site) http://lerch.no-ip.com/ChangFa_Gen (My 15KW generator project) "Anything that can happen, will happen" -Stephen Pollock from: "Particle Physics for Non-Physicists: A Tour of the Microcosmos" " Press on: nothing in the world can take the place of perseverance. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated derelicts. Persistence and determination alone are omnipotent. "

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Jim Thompson 18 years ago

Oh, Fred, You're just so brilliant! Swoon ;-)

...Jim Thompson

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JosephKK 18 years ago

James Lerch snipped-for-privacy@tampabay.no-spam-seeds.rr.com posted to sci.electronics.design:

No, don't do that.

The signal common is a derived reference, trying to connect it to other references or grounds defeats its purpose.

I like the perseverance sig.

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