LPS25H pressure range?

cphelan · ‎2016-02-19

Posted on February 19, 2016 at 17:26

Greetings. I would like to use the LPS25H/B as a pressure measuring device up to ~15 psi ''differential''. I know that the datasheet lists the functional range from 260 to 1260hPa absolute, how does this translate to ''differential'' measurements? I realize that the differential measurements reported are simulated and that physical access to a reference pressure cannot be used. Regardless, looking at the 24 bit, twos complement, 4096LSB per hPa pressure output, you ''should'' have no electrical issues reporting up to ~2048hPa or about 30 PSI absolute - more than enough range for my purposes. During my tests, I can achieve up to a 8.3psi differential output, but above 8.3psi applied, the reported output no longer changes. What is the limiting factor, what am I missing? Note that at ~15psi, I do not need particularly great accuracy.

If the LPS25H/B isn't up to the task, can you recommend a sensor that is?

cphelan · ‎2016-02-23

Posted on February 23, 2016 at 14:09

Greetings. I confirmed two things yesterday.

First, if in differential mode and I change the reference pressure via software (no external pressure applied), I can get a reported pressure up to ~29psi as mentioned below. This of course bypasses the MEMS element output, so hardware/software-wise, there is nothing preventing the sensor from reporting up to ~29psi.

Second, if in absolute mode, I cannot achieve a sensor output greater than ~23psi once the applied pressure exceeds this. Of course this corresponds to the differential measurements I collected below (14.7 psi atmospheric plus 8.3psi differential applied).

So, it appears that there is some mechanical (or otherwise) limiting factor in the MEMS element itself. Does anyone know what this is? Does it exist in the LPS25HB version of the device (currently I am using the LPS25H)? Is there something wrong with the sensor I am using? Can someone confirm my results - I'm guessing someone else at some point has tried to max out this sensor.

Any help will be greatly appreciated.

Thanks,

Chris

Nickname3482_O · ‎2016-02-26

Posted on February 26, 2016 at 09:59

Hello,

LPS25H will still respond outside of the specs pressure range showing correlation

between register data and applied pressure, but we only guarantee reliable data within

200 and 1260 mbar as specified in the datasheet, which is more than enough for most

consumer applications.

Other than that unfortunately there is no public test report for out of specification behavior of our sensors;

outside the operating range of the sensors you might find significant deviations from the expected behavior running across a set of sensors under test.

Regards,

Adalberto

cphelan · ‎2016-02-28

Posted on February 28, 2016 at 14:51

Adalberto-

Thanks, I already assumed that performance wouldn't be guaranteed outside the recommended range, this isn't an issue for our application considering the accuracy we need.

To close the loop on this, and for future reference for those that trip over this same question, I have confirmation from ST that at ~23.2 psi absolute, the sensing element ''hits'' its mechanical stop.

-Chris