Is it possible to enclose the LPS22CH sensor in a separate housing and to generate a negative pressure via a hose connection so that the sensor serves as a negative pressure sensor?

[AMaro.2]

Hello, everyone.

At the weekend I got a STEVAL-MKI109V3 board on loan with which I can use the same STEVAL-MKI219V1 sensor.

Starting the UNICO GUI software is successful and the sensor is also correctly recognized.

The plot shows the temperature and pressure.

The temperature changes as soon as I put my finger on the sensor.

Now to the negative pressure: I started the same experiment as I did before as shown in the two pictures.

This time to confirm that the system is tight, I hung another vacuum measuring device in the line.

The negative pressure on the second measuring device is displayed correctly.

Unfortunately not from the lps22ch?

The negative pressure value only changes when the temperature changes.

Does one of you have contact to the chip manufacturer?

I would like to find out where the problem with the sensor is.

Because according to the data sheet, this is how the application should work.

It works with the BMP280 sensor from Bosch, which has similar properties.

[AMaro.2]

To confirm that my application is tight, I installed the board with the sensor in a separate housing.

Unfortunately, the value does not change in the Unico GUI.

The GREISINGER measuring device shows a negative pressure of approx. 78 mbar in the housing.

Thus the value in the Unico GUI should show approx. 931 hPa.

[Eleon BORLINI]

Hi @AMaro.2​ ,

thank you for the details and the pictures of your application.

Actually, as reported by @Peter BENSCH​ , the minimum pressure that the LPS22CH can measure is 260 hPa, or equivalently 260mbar. Does the 78 mbar refer to absolute pressure or to "ambient pressure - 78mbar"?

Did you try with pressures of, for example 500mbar? And did you have the possibility to test more than 1 device?

I also suggest you to try submitting the parts to baking process.

-Eleon

[AMaro.2]

oh yes I forgot to mention that the 78mbar are relative.

I have two of the sensors.

Which also amazes me that the two sensors will display different ones when idling.

one sensor shows 1021 hPa absolute when idling and the second sensor 996 hPa.

I don't understand why the values show such a large difference.

But nonetheless, when I create a negative pressure, both show no change.

[AMaro.2]

Hi @Eleon BORLINI​ 

My conversion is correct. Even if I didn't have the conversion right, the value would at least have to move in some direction, but it doesn't. The value that my software outputs is identical to that of the Unico GUI in connection with STEVAL-MKI109V3 and STEVAL-MKI219V1.

I mean, I not only use the software I developed with the lps22ch_reg library, but I also use the ST Microelectronics developed environment and it doesn't work there either.

I was made aware that maybe the ventilation openings are blocked, to be honest, when I looked under a microscope, I did not see any openings in the chip. Are there any at all.

Meanwhile I tend to switch back to the BOSCH BMP280.

[AMaro.2]

please have a look at that tooplease have a look at that too

https://community.st.com/s/case/5003W00000Bt1aPQAR/lps22ch-does-not-work

[Eleon BORLINI]

Hi @AMaro.2​ ,

I was made aware of the OLS case by internal colleagues, and they'll in case suggest other.

Are you able to see differences in pressure when you, for example, blow on the device?

Or are the device stuck?

-Eleon

[AMaro.2]

when i don't blow but when i breathe, i.e. warm air, the value changes.

As I have already described before that the pressure only changes when I put my finger on it and the sensor assimilates my body temperature.

the device does not hang because the temperature changes yes.

[Eleon BORLINI]

Hi @AMaro.2​ ,

so it looks as the pressure is varying only with temperature, for example when the chip is heated.

This would indeed resemble a "contamination" issue like clogged holes, as suggested by OLS team.

Please refer only to them for the support, and please come back here once the ticket is closed.

-Eleon