--- In Jeff Cunningham <> wrote:
>
> Yan Seiner wrote:
> > The document that Jeff quoted shows two ways to wire a three-wire
> > setup, both on page 7. I can't quite figure out what the difference
> > is, which one I should use, and why there are 2 resistors in parallel,
> > one 499 1% and the other 22K 5%.... Are they just trying to adjust
> > the range of the sensor with the 22K resistor?
> >
> > What I have is 12 bit A/D that is currently set up for 0-10V; I can
> > reduce that down to 0-3.3 if need be. I need to measure normal room
> > temps; between 60 deg. F and 110 deg. F to an accuracy of about a
degree.
> >
> > The sensors will be powered from the TS7300 5v supply. It will be
> > remotely mounted (up to 10') in a low-noise environment. I have
> > shielded twisted pair available which I'd like to use.
> >
> > Could someone give me clue?
> >
> > Thanks,
> >
> > --Yan
> >
> If you are powering your sensor from the same supply as the sampling
> system, you will want to use the left circuit. The one on the left is
> missing the comment that the 20k resister should be a pot. The whole
> point of that resister pair is to allow you to calibrate the device.
The
> 499 ohm resister gets it in the ball park and the 20k (pot) is used to
> fine tune. If absolute accuracy is not that important, you can omit the
> 20k resistor. They are pretty close as is.
I think what has me confused about that one is the + / - on either
side of the top 499 resistor. The way I read it, I should bring +5v
at the top, read the sensor where the schematic shows -, and
shield/ground at the bottom. Right?
Thanks for all your help.
--Yan
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