🚀 go-pugleaf

"David Lesher" <wb8foz@panix.com> wrote in message
news:b2r75d$951$1@reader1.panix.com...
> "Antony N. Lord" <antony_lordX@hotmail.com> writes:
>
>
> >>   Actually, the LM35 and variants are more accurate than most
commercial
> >> thermometers; one has to shell out a fairly good chunk of change to get
> >> a calibrated thermometer as good as or better than these ICs.
> >>   No calculations, lines of best fit, or any other trash like that.
>
> >I suppose that is true - but surely there has to be calculations /
> >adjustments made due to voltage loss etc. in the cable run between the
> >sensor and the interface.
>
> I'm missing the original post, but I installed about a dozen LM35's
> several years ago. The data sheet had a spiffy current loop scheme
> that solved that issue. The price was some fixed error that you
> could easily offset in software if need be. (We ignored it as we were
> concerned about delta, not absolute, data.)

The AD590 (from Analog Devices and Intersil) operate by regulating the
current passing through them, rather than outputting a voltage.  This means
you could have a wire run of thousands of feet and not have to worry about
the voltage drops along the way.  In the simplest case, the current can be
converted to a voltage with a precision 10K resistor.

The Intersil data sheet has a neat circuit for multiplexing 64 sensors to
one A/D.

- Michael
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