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I have an application that is being controlled by an Arduino. At one point in the process, it needs to determine the level of vacuum in a chamber and adjust it to within a range of values.

I can control the vacuum pumps easily enough, but it is hard to find a vacuum sensor for the Arduino. I need a sensor that can be reasonably accurate down to roughly 28 inches mercury and would connect by a tube. I can't put the sensor directly into the chamber.

Does anyone know of an Arduino sensor that would work? If not, could someone suggest a sensor component that may work with an Arduino. I would prefer to not have to engineer a solution from the sensor component up but I can if I need to.

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  • Is that 94.8 kPa? So it is just a slightly below the normal baromic pressure?
    – Jot
    Commented Sep 11, 2018 at 16:27
  • A bmp280 can measure 300...1100 hPa.
    – Jot
    Commented Sep 11, 2018 at 17:12
  • @Jot Inches of mercury are a negative scale. The greater the number the closer to a perfect vacuum. 28 inches Hg is just short of the level of vacuum created by a good commercial vacuum pump you would use for fiberglass infusion.
    – drobertson
    Commented Sep 11, 2018 at 20:49
  • Then how many absolute hPa is it?
    – Jot
    Commented Sep 11, 2018 at 20:51
  • I would need to check this, but roughly 29.8 inHg is close to max mechanically achievable vacuum. Basicly the pressure difference between normal atmouspheric perssure and an empty volume of space.
    – drobertson
    Commented Sep 11, 2018 at 20:52

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Industrial pressure/vacuum sensors are sturdy and rigid. They have extra protection, for example to use it submersible. The manufacturer often make them for certain voltages (for example 24v) and with different outputs (0..5v output, or 5-20ma output, and so on).
There are cheap versions of those sensors. They are between 5 and 20 dollars on Ebay and Aliexpress.
The manufacturers do not tell which sensor they use inside, and it can be hard to find a sensor that is exactly the one that you need.

The bare sensor is often a piezoresistive sensor in a wheatstone bride configuration. The output voltage span of those sensors is very low and not suitable to connect directly to an arduino board.
The advantage can be that they do not have a operating voltage. Only a maximum voltage.

The ideal pressure/vacuum sensor has a temperature compensation and a gain and a output span that is near 5v. You find most of them at nxp.com.
Luckely they have also a vacuum sensor with a large range, for example the MPXV6115V.

Those sensors are ratiometric. Power them with the arduino 5v and use the arduino 5v as analog reference (that is the Arduino default setting). When the 5v changes, the resulting measured pressure does not change and is still accurate.

Never solder something to the unused pins. Those pins can be connected to something inside.

There are a few ways to calculate the pressure. One way is to use the formula from the datasheet, the other way is to map the output voltage span to the pressure span and correct for the offset of the output voltage.

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  • Thanks for the information. I have 4 of these sensors on order and will be testing them out. They look spot on for my application. I wish they were a shield, but I can't get everything.
    – drobertson
    Commented Sep 15, 2018 at 15:03

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