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## Absolute pressure vs gauge pressure on the LPS35HW & LPS33HW Moderators: adafruit_support_bill, adafruit

Absolute pressure vs gauge pressure on the LPS35HW & LPS33HW

Hi,

I'm using two Adafruit LPS35HW breakout boards to read pressure drop in a pipe. The board is also identical to the LPS33HW bar some minor differences.

According to the Adafruit datasheet the boards can measure from 260 to 1260hPa absolute and is able to withstand pressure up to 20 times their measurement range.

• 260 hPa = 26000 Pa = 0.26 bar = 3.77 psi
• 1260 hPa = 126000 Pa = 1.26 bar = 18.27 psi

Clearly absolute pressure = atmospheric pressure + gauge pressure.

My Question

When I use this sensor under atmospheric conditions I've "lost" 100000 Pa / 1 bar / 14.7 psi reading atmosphere pressure, giving me a usable range of only 260 hPa / 26000 Pa / 0.26 bar / 3.77 psi.

Is there a way to "zero" the sensor so that under standard atmospheric conditions the pressure reading is close to 0 Pa / 0 bar / 0 psi (effectively making it a gauge sensor).
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JuSiPan

Posts: 2
Joined: Tue Aug 11, 2020 11:39 am

Re: Absolute pressure vs gauge pressure on the LPS35HW & LPS

Hi JuSiPan,

Interesting question about getting around the pressure range which is quite limited when you are starting at sea level. Short of doing your experiments on the to of Mt Everest there are not a lot of options. I looked at the driver and the sensor is spitting out raw pressure values and temperature. The only configuration option is the rate at which it is posting data 1HZ, 7Hz, 12.5Hz, 25Hz.

We do not sell a differential pressure sensor, but that might be the kind of solution you are looking for.

mikeysklar

Posts: 1730
Joined: Mon Aug 01, 2016 8:10 pm

Re: Absolute pressure vs gauge pressure on the LPS35HW & LPS

Thanks for the response mikeysklar.

I'll have to think about ways to do measure my pressure drop. I could pull a vacuum and essentially reduce the atmospheric pressure but then that adds complexity...

JuSiPan

Posts: 2
Joined: Tue Aug 11, 2020 11:39 am