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TMP006: local heating causes cooler readings error

Will McLeod
Prodigy 20 points
Other Parts Discussed in Thread: TMP006

Hello,

I am using a TMP006 to read the temperature of a room from inside a heated airstream and am getting strange results. The airstream is 32 C. 1-3 meters from the airstream the wall we are reading is measured directly at 25 C. The TMP reads 16 C. When the heated airstream is turned off, the readings climb and eventually read correctly at 25 C.

I have poked around the forums and seen that transient local temperature error is expected and can be corrected. I have also read through this document: 2728.TMP006_Accuracy_Ian_Williams_10312011.pdf

However, my error is inverse from the one reported and is steady state in that a higher local temperature shows a lower measured temperature than actual and continues to do so indefinitely after being heated. Is this potentially indicative of a bad module, or is this expected behavior?

  • 0
    TI__Expert 7945 points

    Hello Will,

    Thanks for posting your TMP006 questions on E2E forums. I understand that TMP006 is trying to measure the airstream internally but what is it pointer toward? the outside room or towards the air duct?

    Error caused in this case could be due to 2 reasons - depending on the way your setup is with respect to TMP006 placement.

    1. TMP006 sensor has a diaphragm that is exposed and unprotected. So, if you are pointing the sensor towards  the air duct or in the direction facing air stream the sensor will be prone to stress and you will observe noisy/inconsistent readings. 

    2. If you are pointing the sensor towards room/wall - even though you intention is to measure the rooms temperature this effect is disturbed/offset by the airflow through the duct. This effect is causing the local sensor to heatup/cooldown basedon the airstream temperature 

    Solution: You can try to reduce this effect by using a foam material around the sensor (except for the sensors active region). Also, make sure it's not thick enough to cover up and block the sensors field of view. 

    You may also try calibrating the part for various TMP006 ambient temperatures (air stream temperatures) and check to obtain a better accuracy. 

    A picture of your setup might help me better analyse your situation.

    Best Regards, 

    Abhi Muppiri

    Applications Engineer

    AIP- Sensing Products

    Texas Instruments 

  • 0 in reply to Abhishek Muppiri
    Prodigy 20 points

    Hi Abhi,

    Thanks for getting back to me. The sensor is pointing towards a wall. It is inside of a foamcore box with the eye facing out.

    The below image shows the box in the center of an airstream. Air at 100 F is blowing out. 

    We will try implementing your suggestions but I had a couple of followup questions.

    1. Given our setup, do you still suggest simply trying to insulate the module more? Should we put an IR transparent hemisphere over the lens?
    2. From your experience, should the tmp006 be able to give us accurate measurements given enough experimentation or should we switch to a different module/methodology?
  • 0 in reply to Will McLeod
    TI__Expert 7945 points

    Hello Will,

    To answer your questions...

    1. Yes please use foam/ insulation materials behind the TMP006 PCB in order to reduce the effect of air through duct acting as a noise source. This will allow the TMP006 mocal temperature to be stable.

    2. It all depends upon the kind of accuracies that you intend to achieve. You will not obtain more than 2degC accuracy for such large target distance applications. Can you collect the data after insulating the device and see if your issue is resolved?

    Regards,

    Abhi