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'[EE]: Barometric pressure? (was: 8- vs 12-bit A/D '
2002\02\01@155239 by Michael Vinson

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Paul Hutchinson wrote, in part:
>Barometric pressure measurement for example is expected to be readable from
>27.5 to 31.5 inHg with a resolution of 0.01inHg or 0.001inHg. At 8 bits you
>only get ~0.016inHg resolution, 12 bits would give you 0.00098inHg
>resolution.

That reminds me of something I've been meaning to ask. What kind of
sensor would one use to measure barometric pressure electronically?
I've seen "pressure sensors" that only measure a few PSI, but never
something that is optimized for collecting weather data. Surely there
is such a thing?

And on a similar topic, I'm interested in the Philips H1 humidity
sensor, but I can't find a source (even a price) for it. Part of
the problem is the name "H1" is too short for some of the search
engines (e.g. findchips.com). Thanks in advance for any help!

Michael V

Thank you for reading my little posting.


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2002\02\01@162829 by Paul Hutchinson

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There aren't many sensors optimized for Barometry and, the few I've seen are
very expensive. Any pressure sensor rated for 0-15psia (a=absolute) will
work OK.

SenSym has a good selection http://www.pressure.invensys.com/. Fujikara and
Motorola also have good units.

Not sure about the H1 designation from Phillips. The only Phillips %RH
sensor I've seen is part# 2322-691-90001 also referred to as the Series 691
Relative Humidity Sensor. It works well but is for indoor use only. It's
primarily intended for use in humidifiers and clothes dryers for automatic
shutoff. Phillips had it in their 1990-91 resistor/capacitor data book in
the non-linear resistor section. We used it in a design and the purchasing
guys nearly went nuts trying to find it because the vast majority of
Phillips salespeople and engineers didn't even know it existed.

Paul

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2002\02\01@164258 by Martin Peach

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For humidity I figure a piece of cotton or wool between two electrodes might
work. The resistance changes with absorbed water. What do you think? Also
will be sensitive to airborne pollutants like SO2 and NOx.
All the serious humidity sensors I have seen are expensive and the detectors
need to be replaced frequently.
/\/\/\/*=Martin

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2002\02\01@213558 by Peter Anderson

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I have used a Motorola MPX4115 to measure atmospheric
pressure.

We fussed with a Philips capacitor in a 555
arrangement but didn't consider it any too rugged for
outdoor temperatures.

I have had good luck with the Honeywell HIH-3605 RH to
voltage converter.

There are BasicX BX24 routines for both the MPX4115
and HIH-3605 at http://www.phanderson.com/basicx/.

Peter H Anderson, http://www.phanderson.com

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2002\02\01@215744 by jim korman

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Peter Anderson wrote:

> I have used a Motorola MPX4115 to measure atmospheric
> pressure.
>
> We fussed with a Philips capacitor in a 555
> arrangement but didn't consider it any too rugged for
> outdoor temperatures.
>
> I have had good luck with the Honeywell HIH-3605 RH to
> voltage converter.
>
> There are BasicX BX24 routines for both the MPX4115
> and HIH-3605 at http://www.phanderson.com/basicx/.
>
> Peter H Anderson, http://www.phanderson.com
>
<snip>

I've noticed in your post, and others in a different
group, the idea of mounting pressure sensors outdoors.
Bad idea really. Much better to site the pressure
sensor inside. It won't make any difference for
the pressure reading as the pressure outside is the same
as inside AND the temperature inside is much more
stable!! You will have small pressure spikes from doors
opening and closing but that is easy to deal with.

Jim

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2002\02\01@234949 by Herbert Graf

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{Quote hidden}

       I'm using a Motorolla one mounted indoors and I still recommend you
temperature compensate it, I've seen fluctuations as large as 2kPa from just
a few degrees difference in temperature! :) TTYL

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2002\02\02@114442 by Kris Wilk

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> > That reminds me of something I've been meaning to ask. What kind of
> > sensor would one use to measure barometric pressure electronically?
> > I've seen "pressure sensors" that only measure a few PSI, but never
> > something that is optimized for collecting weather data. Surely there
> > is such a thing?

So far the only solutions you've been offered are basically raw
piezoresistive bridge sensors that might require considerable glue
circuitry (amplification, temp comp., etc).

An absolutely BEAUTIFUL sensor module is made by Intersema
(http://www.intersema.com). They have a 0-15 psi surface mount package that's
completely temperature compensated, has a digital interface (i.e. talk to
it directly from your uC), and is also a temperature sensor. Literally
plug-and-play. And it's *VERY* power efficient...designed for building into
wristwatches and other portable devices.

They also make an identical module with 0-14 bar range, which is what we
have been using in our marine data logging equipment to measure depth.

What's really amazing is that they're not expensive (probably $20 in
singles, and about 11 bucks in 1000s). If you've seen the new Swiss Army
knife with the built-in altimeter, that's one place this module has been
used...

I have no ties to Intersema other than being a very happy customer of theirs.

Kris Wilk
ReefNet Inc.
http://www.reefnet.on.ca

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2002\02\02@123252 by Cosmin Buhu

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>
> An absolutely BEAUTIFUL sensor module is made by Intersema
> (http://www.intersema.com). They have a 0-15 psi surface mount package that's
> completely temperature compensated, has a digital interface (i.e. talk to
> it directly from your uC), and is also a temperature sensor. Literally
> plug-and-play. And it's *VERY* power efficient...designed for building into
> wristwatches and other portable devices.
> What's really amazing is that they're not expensive (probably $20 in
> singles, and about 11 bucks in 1000s). If you've seen the new Swiss Army
> knife with the built-in altimeter, that's one place this module has been
> used...
>
> I have no ties to Intersema other than being a very happy customer of theirs.
>
> Kris Wilk
> ReefNet Inc.
> http://www.reefnet.on.ca

       It sounds great, where to buy (Europe ?)? One or two pieces ? Does
Intersema sell directly ?


Cosmin Buhu
Easy Control/Rack Designer
http://www.easyvitools.com/index.html
Easy Virtual Instrumentaion Tools

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2002\02\04@202439 by Kris Wilk

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At 12:33 PM 2/2/2002, you wrote:
{Quote hidden}

They do sell direct (I think), but the duties/shipping from Switzerland
might make it costly. I believe they have a distributor in the US, but I
don't know the name offhand. They can give you that info...

Kris

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