Vaccum Sensor

[BTCAD]

Hello,
 
I would like to know what kind of vacuum sensor I need for my project.
 
 
I'm looking for something like -30psi to +30psi or at least -25psi to 0psi. I realy don't know which sensor will be the good one. 4-20ma or 0-10v or maybe 0.5 - 4.5v.
 
 
Someone would help me?

 

[CAI_Support]

Honeywell makes some good quality pressure sensor, I only know from 0-30 PSI, like this one:
http://www.ebay.com/itm/330900664151
They may also make from -30 to +30 PSI sensor.  You may need to add additional circuit to make the sensor output range match analog input.

 

[CAI_Support]

Since some of the Honeywell pressure sensors are amplified, some of them are not amplified, you probably could use non-amplified for negative pressure measurement, just add your own circuit to invert negative output and amplify signal into the range.  A lot of pressure sensor is based on piezometer, which produce positive or negative output depends on which direction it is being pressured.  However, the mechanical design may only work in one direction, just be careful there.

 

[Automate]

I'm looking for something like -30psi to +30psi

There is no way to get to -30psi gauge pressure. Atmospheric pressure is a little less than 15 psi absolute so you can't go less than -15 psi gauge pressure (difference from atmospheric with a perfect vaccum).

 

[BraveSirRobbin]

Possibly look at the Vacuum and Compound Ranges from Omega.

 

[rossw]

There is no way to get to -30psi gauge pressure. Atmospheric pressure is a little less than 15 psi absolute so you can't go less than -15 psi gauge pressure (difference from atmospheric with a perfect vaccum).

 
.... unless you are above atmospheric pressure!  Eg, a gauge IN a decompression chamber could read an "apparent vacuum" to outside of well over 15 PSI

 

[apostolakisl]

.... unless you are above atmospheric pressure!  Eg, a gauge IN a decompression chamber could read an "apparent vacuum" to outside of well over 15 PSI

 
Any kind of differential gauge can go plus minus anything.  In other words, if you are comparing the pressure in two chambers, then the sky is the limit.
 
I have used Freescale pressure transducers with my CAI.  The problem I have had is lots of noise in the CAI analog readings.  The transducers themselves are inexpensive and work quite well and come in lots of configurations.  0-5v models theoretically work well with the CAI, but I have had noise of .03v no matter what I do.  If this much noise isn't a problem, then you should be fine.

 

[CAI_Support]

To reduce the analog noise to minimum, you will need to change the input resistors to best match the ADC input impedance, which is about 2K.  Please see the analog input circuit showing here in the middle of this page:
http://www.cainetworks.com/products/webcontrol/webcontrol-faq.html
The R25/26, R27/28, R29/30 are dividing input voltage into about 1/3 of the input voltage, so that 10V will read full scale. Since most people don't plan to use amplifier in their analog inputs, we selected high value for those resisters.
To minimize the analog noise, the input resisters R26, R28 and R30 should be changed to 2K, then R25, R27, R29 change to 4K to get 5V full scale or 1K to get 10V full scale. When making this change, it will require to have analog amplifier in most application, because it will sink a lot more current from analog signal source.

 

[Automate]

.... unless you are above atmospheric pressure!  Eg, a gauge IN a decompression chamber could read an "apparent vacuum" to outside of well over 15 PSI

Except that vacuum by definition means less than atmospheric pressure http://en.wikipedia.org/wiki/Vaccum so the more appropriate term would be "differential pressure"

But getting back to the OPs original question they say "or at least -25psi to 0psi" in this case a 0-25 psi differential pressure sensor sensor with the port connections swapped would work.

 

[apostolakisl]

Except that vacuum by definition means less than atmospheric pressure http://en.wikipedia.org/wiki/Vaccum so the more appropriate term would be "differential pressure"

But getting back to the OPs original question they say "or at least -25psi to 0psi" in this case a 0-25 psi differential pressure sensor sensor with the port connections swapped would work.

 
 
Like this one
 
http://www.digikey.com/product-detail/en/MPX2202DP/MPX2202DP-ND/951802
 
The only ones I have seen that read plus/minus go -1 to 1psi.  So to get -30 to 30 psi you would need to use 2 of these with the ports connected opposite.  That also assumes you can back pressure the transducer up to 30 psi without damaging it, which I think is OK, but I suggest you check the specs first.