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TMP007 as body temperature sensor - super slow response

Xiaowei Feng
Prodigy 40 points
Other Parts Discussed in Thread: TMP007

Hi,


We are now developing a body temperature sensor using TMP007, which measures the temperature on the eardrum. TMP007 is quite new to us, yet we have the expectation that it should response quickly since it is based on IR measurement.


However, what we observed from our prototype is a super slow response. Every time when we plugged our sensor into the ear, the direct reading of Tobj started from about -10°C. Then, it took about five minutes to reach a stable reading about 40°C.

We haven't done a calibration that can possibly adjust the final reading to a normal body temperature. All the configurations are default, while a full FOV is used.

What we now do not understand is:

1. Why is the response so slow?

2. Why does the measurement always start from a negative temperature?

We must admit that our PCB layout didn't strictly follow the guideline. Can it be the problem? We just designed a single layer PCB with very small size where the chip was placed.  It is then connected to the main board using wires back on the PCB. The main board is placed far away from the sensor and does not have direct contact with it.


At last, we would like to post the measurement we got:

THX

  • 0
    TI__Mastermind 35835 points
    Can you show the output of Sensor Voltage Register during the test?

    I have to assume the output is negative because it has not been calibrated yet. Calibration establishes the relationship between infrared radiation and die temperature in the system.

    Ren
  • 0 in reply to Ren Schackmann
    Prodigy 40 points

    Sure:

    We know that a calibration is necessary for the  precise measurement. However, we are more concerned about the slow response we got. It takes almost five minutes to reach its final value. That wasn't normal, was it?

    Additionally, I would like also to share the PCB design with you. It is very small and single layer:

  • 0
    Prodigy 40 points

    Sorry, don't know why the second picture wasn't there.

    I will upload again:

  • 0 in reply to Xiaowei Feng
    TI__Mastermind 35835 points
    The sensor voltage is negative and approaching zero. This implies that the object starts out colder than die temperature and approaches die temperature over the course of the test. It seems it is not getting any external signal.
    Have you tested more than one TMP007?
    Is there an obstruction or window?

    Ren
  • 0 in reply to Ren Schackmann
    Prodigy 40 points

    Hi Ren,

    "The sensor voltage is negative and approaching zero. This implies that the object starts out colder than die temperature and approaches die temperature over the course"

    Yes, but actually it wasn't so in the test. In the test. The chip itself was placed in the ear canal facing the eardrum (theoretically). Hard to imagine that object temperature can be lower than the die temperature. We can only assume that there is something wrong with the TMP007.

    "Have you tested more than one TMP007?"


    Yes, we've tested two prototypes with the same design. The measurements were similar.

    "Is there an obstruction or window? "

    No, the chip was totally exposed in the air.

    Best Regards


  • 0 in reply to Xiaowei Feng
    TI__Mastermind 35835 points
    It seems that you are some how thermally shorting the hot junction and cold junction.
    Is the TMP007 touching the ear or the casing?
    Do you see any positive voltage response if you point the TMP007 at a different black body source? Pick a hot object like a heating element so you're certain there is a lot of signal. Maintain a safe distance from the object.
    Is there an assembly defect or obstruction between the TMP007 and circuit board? It seems unlikely since you have verified on two assemblies.

    Ren