# -50 to +50 Pascal differential pressure sensor with low-drift

Hi everybody,

I have an application (measureing the chimney draft)

where I have to measure really low pressure-differencies
-20 to + 20 Pa = 0.0002 bar = 0,2 mbar

right now 'm using this differential-pressure sensor

the library

has a function

``````  //Auto correct pressure drift
lwlp.autoCorDrift();
``````

But this autocorrection of drift seems not to work reliably

I discovered that this pressure-sensor has a drift over a longer time. (10 days)
After power off/on with no differential pressure applied I was able to re-calibrate it.

For automating this process I would need an extra valve that switches between measuring and calibrating

So if somebody knows of a sensor with a smaller differential-pressure range -50 Pa / + 50 Pa
that also has longterm-stability of the measured differential-pressure this would be a really good solution.
Second best solution is a small elektromagnetic gas-valve that switches between measuring pressure inside the chimney and outside the chimney for calibration.

As the pressure is so small I have doubts if a standard pressured air valve will work.
Maybe a small ball-valve moved by a RC-servo would be better suited.

best regards Stefan

Hello
Take two BME280.

Hm... --- ... the sensor-housing looks like this

I would have to place one sensor inside the chimney or build a sealed box with the sensor inside and have a connection between inside the box and the inside of the chimney through a silicon-hose.

The datasheet says:
RMS-noise 0,2 Pa (where the main range to measure is -15 Pa to +5 Pa (1% yes acceptable)
what I don't understand is
Offset temperature coefficient +- 1,5 Pa/K

Does this sensor have temperature-compensation or not?

If the sensor has temperature-compensation what does this spec mean?

best regards Stefan

Hello
you may read the spec provided by Bosch?

well the datasheet says
When changing by e.g. 10°C at constant pressure / altitude, the measured pressure / altitude will change by (10 * TOC)

10K * 1,5 Pa/K = 15 Pa

Strange to me that they don't apply temperature compensation to the pressure measuring

In the meantime I found this sensor

Datasheet: Product Summary
The SDP600 sensor family is Sensirion’s series of digital differential pressure sensors designed for high-volume applications. They measure the pressure of air and non- aggressive gases with superb accuracy and no offset drift.

Let's see if the can hold what the promise. I ordered tqwo of those sensors

best regards Stefan

Generally it’s not a great idea to push the abilities of such a sensor if you want any sort of accuracy. 1.5% accuracy is 7.5 Pa and your range of interest is 50Pa , so your basic measurement accuracy for 50Pa is 15%. Not great .

For low pressures , you need a better performing ( more expensive) transducer . For very low pressure consider measuring flow instead - look at Honeywell micro bridge

The datasheet of the sensirion-sensor SDP600-025 says

which is pretty good I think
zeropoint accuracy: 0.1 Pa / 25 Pa = 0,4%

span-repeatability 0,5%

best regards Stefan

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