Sensor Electrical output question

Discussion in 'Electronic Design' started by James Lerch, Aug 17, 2007.

1. James LerchGuest

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 <= output<= 10 V d.c.
Impedance 0.1
Max Current Source 1 mA

Would it be "proper" and assume it is a differential output and build
with that assumption? (worse case I've added some extra hardware to a
single ended output

""" Why do they make things so complicated???? """

--
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. "

2. MooseFETGuest

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.

3. Fred BloggsGuest

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.

4. James LerchGuest

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.

--
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. "

5. Jim ThompsonGuest

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

...Jim Thompson

6. JosephKKGuest

James Lerch -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.