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NAT/SEMI-LM-34CZNOPB

Cheem Ang
Prodigy 40 points
Other Parts Discussed in Thread: LM34, TMP116EVM

I am trying to find a quick way of testing/verifying this component meet specification. Would appreciate any information. Thank you.

  • 0
    TI__Expert 6475 points

    Hi Cheem,

    Typically, you would want to validate the accuracy in an oil bath or at the very least with a temperature oven.
    You will need a high accuracy reference probe as this will determine the best accuracy you can measure.

    -Kelvin

  • 0 in reply to Kelvin Le THS
    Prodigy 40 points
    I need more detail information on how to perform this testing etc. Thank you.
  • 0 in reply to Cheem Ang
    TI__Expert 6475 points

    Cheem,

    You will need a temperature controlled oil bath with an RTD reference probe.
    Place about 10 LM34 devices on a pcb board and test them in the oil bath.
    Sweep the temperature over the range of interest. Make sure to have enough soaking time at the set points (10 min is a good start).
    You will also need to have a precision data acquisition system to measure the analog output of the LM34.
    This way you can validate the accuracy of the LM34 without including external error sources.

    -Kelvin

  • 0 in reply to Kelvin Le THS
    Prodigy 40 points

    Thank you so much for your help Kelvin. Greatly appreciate your help and providing the details in testing this component. Thanks again.

  • 0 in reply to Kelvin Le THS
    Prodigy 40 points
    I just need a quick way to verify whether the unit is operating within specification. Kelvin's respond is helpful but it is not a quick way of testing. In addition, what type of oil can we use? What temperature are we testing this to? What are the ranges? etc. etc.
  • 0 in reply to Cheem Ang
    TI__Expert 6475 points
    Cheem,

    Unfortunately, there isn't a shortcut to validate the accuracy of a temperature sensor without reducing the quality of the test. You can reduce the number of set points to shorten the test time but you still need the oil bath and reference probe for the best result. You need to get a thermally conductive but electrically non-conductive oil for the bath.

    An alternative way to validate the accuracy is by using a temperature oven (less uniform). If you go this route, you will need to make sure that the temperature is uniform within the oven and allow enough soak time. The heat capacitance of air is lesser than oil so you will get more temperature fluctuation within the oven. You can increase the heat capacitance of the oven by adding rocks in the oven. A convection oven is preferred. Place the reference probe as close as possible to the LM34 to get a fair measurement.

    Like I pointed out earlier, you want to sweep the temperature over the temperature range of your interest. For example, if your system operating temperature range is from 0-60C then you would want to validate in the range.

    -Kelvin
  • 0 in reply to Kelvin Le THS
    TI__Expert 6475 points

    Cheem,

    Here is another way to easily/cheaply validate the LM34 accuracy:

    Use hot plate with magnetic stirrer
    Use mineral/vegetable oil + beaker for your oil bath
    Use TMP116EVM as an alternative reference to RTD. This is a very accurate digital temperature sensor (0.2C accurate) and you can get this EVM for $25 on ti.com. The accuracy is more than enough to validate LM34 accuracy

    Keep in mind that if you don't have insulation between the beaker and air there will be a temperature gradient at the edge.  So at the end of day, it might be worth it to buy an oil bath.
     
    Let me know what you think.

    -Kelvin