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LM34: AH

Cassie Robinson
Prodigy 10 points
Part Number: LM34

Hello, I am looking for information on the actual sensing region of this probe: LM34AH silicon based temperature sensor. Is the temperature averaged over the entire 5mm diameter top surface? Or is there a smaller sensing region within the surface? I am trying to measure the temperature within a 2mm channel by holding the sensor to the surface of the glass slide. I am concerned that overhang of the sensor on either side of the channel will cause an inaccurate representation of the temperature within that 2mm range. 

  • 0
    TI__Expert 4705 points

    Hi Cassie,

    The temperature sensor is a small die inside of the NDV package, and where the die will get its thermal information will depend on how its connected. These are the thermal specs for LM34

    A higher value here means increased thermal resistance, which means it is more challenging for heat to transfer to the die. Notice how the Junction-to-case thermal resistance is much less than the Junction-to-ambient values. What this practically means is that since you are putting the lid of the LM34 directly onto the glass slide (i.e., the heat source), the thermal resistance that applies will be the Junction-to-case value. The rest of the lid which is not in contact with the glass, will be contacting air which has a much higher thermal resistance. Hence, the temperature the LM34 reads will be from the glass making contact, not the air surronding the rest of the package.

    Now realistically, there will be some influence from the ambient air contacting the overhang parts of the package, and with that, the thermal response may be slow if a sudden change occurs. However, I would feel confident that by making direct contact with the glass slide, you are sensing that temperature and not an average of the whole package.

    Thanks

    -Alex Thompson