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OPA387: Want to use K-type thermocouple with OP amp.

Chase Jeong
Genius 4660 points
Part Number: OPA387
Other Parts Discussed in Thread: TLV333

Hello TI experts,

My customer want to use OP amp with K-type thermocouple, to measure the temperature of the device.

actually they used thermocouple to digital converters before, but now they have to change due to delivery issue.

anyway, I found OPA387. it has 0.003uV for offset drift. do you think it is suitable for thermocouple amplifier?

or it would be helpful that you recommend another op amp.

Best regards,

Chase

  • 0
    TI__Guru 60570 points

    Hello Chase,

    With its extremely low input offset voltage (max +/-2uV) and offset drift (max +/-0.012uV/C), OPA387 is uniquely well-suited for the implementation of the non-contact sensors in temperature measurements like thermocouple and thermopile applications. Following please, find the link to the article I wrote addressing the use of OPA387 in thermopile applications: 

    https://e2e.ti.com/blogs_/b/analogwire/posts/how-to-achieve-microvoltage-level-precision-in-thermopile-applications

  • 0 in reply to Marek Lis
    Genius 4660 points

    Dear Marek,

    Thank you for your reply.

    How about TLV333? it has 0.015mV offset voltage and 0.02uV/C offset drift. It is little worse than OPA387, but I want to know it is good to use or not. (because it would be easy to get TLV333.)

    and do you have any maximum value of offset voltage and offset drift for thermocouple application?

    (for example, I cannot use the part which offset drift is over 0.5mV for thermocouple application.)

    and one more question, is there any other value that I have to check carefully except those 2 values above, considering thermocouple application?

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Guru 60570 points

    The broadband noise of TLV333 is much higher than OPA387 (55nV/rt-Hz vs 8.5nV/rt-Hz, respectively) but depending on the required precision your customer may be able to use it in thermocouple application.  The required maximum offset voltage and offset drift depends whether your customer performs initial calibration of their system and what is the required precision of temperature reading?  In short, they need to do worst-case analysis based on the details of their circuit configuration.

    The typical TLV333 offset drift value of 0.02uV/C represents one standard deviation; thus, only 1 out of 1.7 million units may have a drift higher than 0.1uV/C (5-sigma) - if this is acceptable, the highest offset voltage at 125C (100 deg C temp change) would be: +/-15uV +/- (100C*0.1uV/C) = +/-25uV.