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TMP006 first sample after power up

Thomas Iglseder
Prodigy 40 points
Other Parts Discussed in Thread: TMP006

Hi,

 

I have a question about the TMP006 infrared thermopile sensor. We use this sensor in a mobile application and a low energy consumption is therefore very important for us. A short time period for the measurement is crucial.

the process:

The sensor is supplied with power and gets configured with 0x7000. After the data ready bit is set, the temperature values are read out once and finally the power supply is switched off. This process is repeated every 60 seconds.

the problem:

We have found out that the values ​​of the IIR measurement at the first sampling is incorrect. Until the second sample process the values are correct. Is this circumstance known? In the datasheet I can’t find anything about this. Is there any workaround?

Would be happy about some information’s about this situation.

 

Thank you!

Thomas

 

  • 0
    Prodigy 40 points

    Hi,

     

    Recent measurements have shown that the Vobj voltage only after several samples approximates the correct final value. It seems that the sensor needs a certain amount of time to reach correct measurements.

     

    Next step is to use the power down mode... i will keep you up to date!

     

     

    With best regards

    Thomas

  • 0 in reply to Thomas Iglseder
    TI__Expert 7945 points

    Hello Thomas,

    How are you communicating with TMP006, are you using TMP006EVM GUI for this application? Are you observing this issue on a consistent basis?

    Let me know,

    Regards,

    Abhi

  • 0 in reply to Abhishek Muppiri
    Prodigy 40 points

    Hello Abhishek,

     

    We communicate with the TMP006 over the i2c-interface with a PIC microcontroller. The board is designed according to the specifications in the datasheet.


    Here's what I have now figured out:
    It makes no difference whether the sensor is disconnected from the supply voltage or it is woken from sleep mode. The first three samples are always wrong. The fourth sample of the IIR value is almost correct.

     

     

    With best regards

    Thomas

  • 0
    Intellectual 670 points

    Hi Thomas,

    I have noticed the same effect with my project. I assumed your reading the sensor using a 'one-shot' read with no averages.

    Have you tried to delay the first read for 2 - 3 seconds to see if it's a sensor problem or if it's in the PCB?

    Dan Ross

  • 0 in reply to Thomas Iglseder
    TI__Expert 7945 points

    Hello Thomas,

    I just learnt from the TMP006 designer that this is an expected behavior of the part. The first 3 reading are going to be inaccurate. This is the time it takes for the internal thermopile sensor to settle and reach a thermally stable state.

    If you need a power saving mode in your system its best to wait for about 3 seconds after power up and then read the sensor voltage. How are you able to go to sleep mode? We do not have support such functionality fr TMP006.

    Regards,

    Abhi

  • 0 in reply to Abhishek Muppiri
    Prodigy 40 points

    Hello,

    Thank you for your contributions which confirm our problem! The current solution is as follows: power up, waiting for four samples (microcontroller in sleep mode), read out the values ​​and power off. The energy consumtion is unfortunately not satisfying, so we are looking for alternatives ...

     

    With best regards,

    Thomas