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Problem in calculating Object temperature Tobj in TMP006 using the fixed point code for 8bit controller.

Dinesh Patil
Intellectual 285 points
Other Parts Discussed in Thread: TMP006

Hello,

          I am having trouble getting the correct value of object temperature tobj using the fixed point code . The value of Tdie is absolutely correct so the sensor TMP006 is working absolutely fine. However the output of the Fixed point calculation code is incorrect . It gives the value of Tobj such that it provides a value (on the LCD) in the range of 32 to 36 degree Celsius no matter what i place in front of it.

  • 0
    TI__Mastermind 27715 points

    Hello Dinesh,

    Are you using the latest version of the fixed-point code? I've re-attached it to this thread just in case.

    Best regards,

    Ian Williams
    Linear Applications Engineer
    Precision Analog 

    TMP006_Fixed_Point_Source_Code.zip
  • 0 in reply to Ian Williams
    Intellectual 285 points

    Hello Ian , I am using the fixed point code you had attached to an earlier post of mine about 3 weeks ago. I changed the sensitivity by varying the value of  'So' but still have an error of +or- 3 to 4 degrees.

    However I will go through the code you have attached now. Hopefully this will settle the issue.

    Thank You ! 

  • 0
    Prodigy 85 points

    Hello,

              I am also using the same fixed point code for tobj calculation.I am facing different problem. The tobj decreases when hot ojbect is placed infront of sensor & tobj increases when cooler object is placed in front of sensor.

              I have manipulated this by using tobj = tdie-(tobj-tdie). However i am not getting the accurate result. Also settling time(response time ) of tdie is much larger. 

             a better solution would be appreciated.

             Thank You.

  • 0 in reply to Dinesh Patil
    Prodigy 85 points

     I am not sure but you may also try using transient correction & filtered output.

     Also you can try  increasing S0 slowly in TMP006FixedPoint.c

  • 0 in reply to Akshay Bathe1
    TI__Mastermind 27715 points

    Hello Askhay,

    It sounds like you are observing the effect of local temperature transients. Is the hot/cold object close to the TMP006 when you place it in front of the sensor? If the TOBJ decreases/increases quickly and then moves in the correct direction, you are seeing the transient effect. 

    Best regards,

    Ian Williams

  • 0 in reply to Ian Williams
    Prodigy 65 points

    The response time issue has been solved.

    Yes the temperature sensor is kept closer to the object.

    When I tried measuring the temperature of my laptop from 3-4 cm it gave temperature @ 40-43 degree which was correct. But for plastic bowl containing water at @75 degree 

    it showed temperature as -23 degree.I tried using transient correction as well.In  second case may be tdie will be changing since temperature around the bowl is higher.

    Is type of plastic material i am using will matter much??

  • 0 in reply to Akshay Bathe
    TI__Mastermind 27715 points

    Hi Akshay,

    Most plastics are good radiators of IR, so if your target object is something inside a plastic bowl then you will only be able to measure the plastic. There are some exceptions to this, such as polyethylene and polypropylene.

    Best regards,

    Ian Williams

  • 0 in reply to Ian Williams
    Prodigy 65 points

    Hi lan,

              I tried to place the object little away from the sensor but the target object temperature doesn't increase or decrease in correct direction.It works exactly opposite than expected.So  i changed the sign of calibration factor & varied the Tref. Now the results are good & accurate up to 2 degrees.But this is a temporary solution.I will search for the exact cause later in month of June since my university exams are close. If i found exact problem will let you know.

    Thank You.