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Question about LTC2986

Hello,

I received a question about LTC2986 from our customer. He is checking LTC2986 by following setting.

When the customer sets YOKOGAWA 2553A to 0.0 deg C. The measurement result of LTC2986 is -0.5 deg C.

Then he sets 2553A to 100.0 deg C. The measurement result of LTC2986 is 99.5 deg C. There is -0.5 deg C offset.

Do you have any ideas for a cause of the offset? Can we correct this offset by resistor setting of LTC2986?

Best regards,

Akira

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  • Hi Akira - what is the configuration of the LTC2986 - is this without cold junction correction? Likewise, is the 2553A set to use an external correction or no CJC?

    If they both have cold junction correction turned on this may just be the difference between the temperature at the 2553A jack vs. the board temp of the LTC2986. 

Reply
  • Hi Akira - what is the configuration of the LTC2986 - is this without cold junction correction? Likewise, is the 2553A set to use an external correction or no CJC?

    If they both have cold junction correction turned on this may just be the difference between the temperature at the 2553A jack vs. the board temp of the LTC2986. 

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  • Hi,

    Thank you for your reply. He didn't use CJC both LTC2986 and 2553A. Is this a cause of 0.5 deg C offset? Can we adjust like this offset by resistor setting of LTC2986?

    Thanks & regards,

    Akira

  • Unless they are using a resistive sensor for cold junction, no resistor offset here. 

    Could you send a photo of the test setup? Are they using the demo board DC2508 and DC2210 or a different setup? 

    They could be seeing a combination of offsets from thermocouple effects and the combined accuracy limits of the 2553A (0.11C specified accuracy 1yr from cal) and the reference of the LTC2986. What is the ambient temperature in the test lab?

    I would also disable open-circuit detection if enabled in the LTC2986 - the 2553A specifies an output resistance of 1ohm but it is not clear if it can sink the pulsed open-circuit detect current. 

    0.5C is only 20uV - thermocouple effects are possible, air drafts from HVAC can cause this if the terminals are separated.

    -Logan