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A
andrea6388
Visitor II
August 3, 2015
Question

LPS25H differential mode

  • August 3, 2015
  • 4 replies
  • 888 views
Posted on August 03, 2015 at 12:37

Good morning,

I'm trying to set up a LPS25H sensor to read the same value as another one, which is the reference, in a controlled environment. 

My first guess has been to set up REF_P registers as the difference between readings from the 2 sensors which is initially stored by firmware.

I set up REF_P registers, I enable the DIFF_EN bit in CTRL_REG1 (while sensor is disabled) and finally I enable the sensor again.

The problem is that measures coming from sensors still differ for the same amount of pressure,  while if I subtract the previously evaluated difference by firmware readings are very near.

Could someone please describe the correct procedure to setup differential mode?

Thank you,

Andrea

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    4 replies

    N
    Nickname3482_O
    ST Employee
    August 5, 2015
    Posted on August 05, 2015 at 15:23

    Hello Andrea,

    after DIFF_EN you should enable AUTO_ZERO, then set your REF_P and

    run your measurement.

    AUTO_ZERO gets enabled setting writing 1 into bit 1 of CTRL_REG2 (at address 0x21).

    Best Regards,

    Adalberto

    A
    andrea6388Author
    Visitor II
    August 5, 2015
    Posted on August 05, 2015 at 16:49

    Thank you Adalberto,

    as soon as possible I'll check the procedure.

    Andrea

    P
    pfeiferm
    Visitor II
    December 20, 2015
    Posted on December 21, 2015 at 00:51

    Hello,

    I have a similar problem. I'm trying to use the LPS25HB pressure-sensor sensor in differential mode with my own settings in the REF_P registers. As Adalberto suggested, I tried to first enable DIFF_EN, than AUTOZERO and after that setting the REF_P registers. But it seems that my settings of REF_P are irgnored and only the auto-copy-values form the AUTOZERO-enable are stored, because the sensor-output is always around 0 afterwards (independent of which value I've written in REF_P).

    Am I doing something wrong? Or is there an other solution for that?

    Andrea, did you solve your problem?

    Thank you,

    Marc

    N
    Nickname3482_O
    ST Employee
    December 22, 2015
    Posted on December 22, 2015 at 19:31

    Hello Marc,

    proceeding step by step : first set DIFF_EN bit then enable your sensor with a given

    ODR, at this point you will see ordinary measurements. Next set AUTOZERO, if everything

    is correct this is the point where you will see an allmost 0 ouput as consequence of initial

    pressure value being automatically copied in REF_P registers. Only after you get here REF_P

    registers can be overwritten with a value of you own choice.

    Regards,

    Adalberto

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