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LMT70: LMT70

Big Bill
Expert 1980 points
Part Number: LMT70
Other Parts Discussed in Thread: LM70

Dear All:

       i use the LMT70 to measure the temperature ,  the precision is  0.1℃   at the  20 ℃--45℃,      when i store the LMT70 to the -15℃    then  take it out and place it at room temperature for one day to measure the temperature at the 20 ℃--45℃, i find the precision  is only  0.15℃ at  the 35-38℃ ,what cause the result？ can you help to  explain it？ Thanks~

 

  • 0
    TI__Expert 6475 points
    Hi Bill,

    The accuracy of an analog temperature sensor is affected by a number of factors including the ADC. The datasheet specifies a 0.13C max from 20C to 42C. This assumes no additional error from the data converter side.

    In your case, how accurate is your reference temperature probe? How are you measuring the LMT70 output?

    -Kelvin
  • 0 in reply to Kelvin Le THS
    Expert 1980 points
    Dear Kelvin:

    thanks for your reply. I use the MCU's ADC to measuring the LMT70 output, the reference temperature is an environmental test box that dedicated to measuring temperature.
    i means that the wrong data from when i store the LMT70 to the -15℃ then take it out and place it at room temperature for one day to measure the temperature at the 20 ℃--45℃. if i don't store the LMT70 to the -15℃, it's no problem.
  • 0 in reply to Big Bill
    TI__Expert 6475 points
    Bill,

    What is the accuracy spec of the test box for 20C to 45C?
    When you store the LM70 at -15C, does this include the MCU as well?

    The point I'm trying to make is that you are trying to resolve the accuracy within the system uncertainty/error band.

    -Kelvin
  • 0 in reply to Kelvin Le THS
    Expert 1980 points
    Dear Kelvin:

    the accuracy spec of the test box for 20C to 45C is 0.01℃.

    Yes , include the MCU， but why the accuracy is the same as other temperature range except at the 35-38℃. Thanks~
  • 0 in reply to Big Bill
    TI__Expert 6475 points
    Bill,

    What is the sample size of this test?
    Is this result repeatable?
    Also what is the soak time for these measurements?

    Temperature uniformity in the test box is an important control. The air flow from the fan can have a significant impact on the measurement.
    There might be a temperature gradient within the box if the convection isn't adequate.
    Typically, an oil bath is the preferred method for temperature test because the temperature uniformity can be controlled fairly well.

    Another test that you can do is to replace the LMT70 with a controlled voltage source. Perform your test as you done before and see if you get the same offset? This may narrow down your error source (maybe due to the ADC).

    -Kelvin