IC's to measure barometric pressure

Are there any?

Here's one that's exceptionally easy to use (built-in 14-bit ADC and serial synchronous or asynch comms):

It's available at Digikey (not cheap, though).

Best regards, Spehro Pefhany

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Interesting part. May be in the price range for an application of mine. Odd data sheet that doesn't seem to indicate the All Sensors' part #!?? Mentions "compatible with their GA142 series," but that's not _the_ part.

Thanks to Digi-Key's search...

DigiKey # BARO-A-4VPRIMEREF-ND All Sensors # BARO-A-4V-PRIME-REF, per Digi-Key.

$104, not in stock, or perhaps they just soldout...

Thanks, Steve

442-1097-ND BARO-DO $140.00 3 in stock 442-1098-ND BARO-DO-MIL $296.00 3 in stock

Best regards, Spehro Pefhany

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"Tim Wescott" wrote

They can be linearized in software. The problem is temperature compensation: they often make better thermometers than barometers.

TC'd units are available (and the only way to go for making a barometer), if the environment is household indoors I am sure one would work fine.

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Do a search on the MPX2100. This was the original Motorola sensor family (now made by Freescale), and are quite good _provided they are fed with a accurate reference, and high quality op-amps are used for the amplifier_. These units are largely temperature compensated (a big advantage). Honeywell do a more accurate sensor, but the price goes up proportionately. The full scale, still changes by +/-1% with temperature, and if you want to get the best accuracy, tweaking for this is worthwhile.

Best Wishes

Interesting reading the other responses. Another question is to what precision, I suppose. I've built my own with the ability to detect changes in altitude of

50cm out of an empty spray can, some glass tubing, two LEDs, some nichrome wire, a tiny circuit and power supply, and some DOT brake fluid. Cheap and sensitive, but it won't work upside down!

Jon

I'd love to see that one. Is there a description and diagram on-line somewhere?

- YD.

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Thinking aloud here (please don't flame me for this).

If one had mercury in a vessel, wouldn't the resistance change with pressure (since the molecules are being compressed together under higher pressure). If so, could you measure that difference to provide an accurate mmHG reading.

Just a thought.

Also, I'm sure you could use a laser reflected also to get very accurate measurements (especially if a mirror was floated on the surface of the mercury).

I don't know how the industial grade Barometric sensors work so please forgive me if I've stated the obvious.

"crzndog" wrote in news: snipped-for-privacy@comcast.com:

And an interesting idea. Except that fluids in general, and mercury (a liquid metal) are *mostly* incompressible. (OK, they can be compressed, as Howard Hughs found out, but only under *extreme* pressure - not barometric.)

Another neat idea. Depending upon the diameter of the container the mercury was in, and the purity, you might be able to bounce the laser off the top of the mercury directly.

What might work better would be to make either a simple sealed vertical tube manometer, or a U-tube manometer with one sealed end, and pass a nichrome wire through the end of the tube, down into the mercury. As the pressure changes, the mercury would rise and fall in the tube. This changes the length of nichrome wire above the mercury. Since the resistance of the wire would be proportional to the length above the mewcury, the resistance is proportional to the pressure. Do a google search on McLeod Gauge - used to measure vacuum.

Well, you are inventive. "Industrial" sensors can come in a variety of mechanical designs, depending upon the range of pressures needed to be measured, the type of signal needed, and the accuracy needed. I've seen designs that were steel bellows where the end of the bellows formed a capacitor. There is the bourdon-tube design - like a regular pressure gauge, except that instead of the needle rotating on a dial face, it is the wiper rotating around a potentiometer. Others used a sealed chamber with a diaphram across one end. A strain gage of some sort is attached to the diaphram. As pressure changes, the diaphram flexes, causing changes in the strain gage. Strain gage could be replaced with a piezo-resistive element. One of the most interesting gauges I've worked with was the Leybold-Heraeus spinning ball viscometer. It was used as a reference to calibrate all the other vacuum gauges. It suspended a small metal ball in a magnetic field. The ball was spun up to an exact RPM than allowed to coast down to a lower, set RPM. The rate at which the ball slowed down indicated the drag from gas friction, and is proportional to the absolute pressure.

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In message , Dan Major writes

And an interesting idea. Except that fluids in general, and mercury (a

ITYM 'liquids'.

Cheers

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Keith Wootten

On Wed, 01 Dec 2004 19:26:33 -0300, YD wrote:

precision,

wire,

sensitive,

I believe it was an amateur scientist column in scientific american, years ago. But the basic thrust is this: The glass tubing is bent into a U shape, with one side of the U curving back downwards and hooking into the top of the spray can. That entry into the can needs to be sealed well with something that doesn't outgas or leak. Some cans already have a rubber insert you can use for the purpose. There are some epoxies, as well. The other end of the U is left upwards pointing and open. The U will be filled with DOT fluid (it has some wonderful properties for this purpose, if you think about it.) You wrap the can with the nichrome wire. This will be used to heat the can and expand the air inside. The two LEDs are used, one for an emitter and the other for a detector. You can use a real detector, instead, though. This pair is then placed on the leg of the U furthest away from the can. The nichrome is controlled as an "on/off" type of control (simple) -- when the DOT brake fluid rises of its own accord above the point on the U tube where the emitter/detector pair are at, the trapped gas is expanding and you need to cut the heating current to the nichrome; when the DOT brake fluid drops below, then the heating current is turned on until the trapped gas heats enough to compensate. I forgot to add in the earlier post that a thermistor or other means of measuring the can's temperature is needed. Anyway, the can temperature is then interpreted. Even slight up/down motions can be 'observed' as a change in temperature with enough precision to see that 50cm adjustment. It drifts (or mine did) a fair amount and absolute calibration gets lost over periods of days. But for measurements over periods of hours to look for relative changes, it was great!

Jon

precision,

of

wire,

sensitive,

Thanks, I recall having seen a variant of this, using a glass bulb and resistors for heating. The temperature was kept well above ambient (some 50 or 60 C) and the heater current was read off. The control was analog keeping the meniscus at the midpoint between LED and sensor.

I recall thinking that ambient temperature variations and drafts must play hell on any kind of long term stability.

A pity about that Amateur Scientist column, it used to be quite good up till the mid-80's when it took a nosedive, as did the magazine itself.

- YD.

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If you're into 1-Wire...

Works well with