AD594 recalibration for Type K Thermocouple

I have purchased an AD594 IC and I would like to recalibrate it for connecting a K Type Thermocouple without having to buy an AD595. Can someone help me with this? Is it possible?. Please help

Hoare, Morgan

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    •  Analog Employees 
    on Feb 15, 2016 11:33 PM

    Hello Morgan,

    It can be done, but the process is a bit involved and it requires determining the right resistor values experimentally for each AD594 because there is a lot of variation in the internal resistance values from part-to-part. If possible, I suggest you switch to the AD8495, which is the next generation type K thermocouple amplifier after the AD595, and AD8495 is available to sample.

    If this is not an option and you must recalibrate your AD594, then you will have reduce the CJC voltage from 51.7μV/°C to about 40.44μV/°C (or the average type K slope over your CJC temperature range) with pulldown resistors from +T to COM and from -T to COM, like in figure 6 in the datasheet. This will naturally increase the gain because it reduces the resistance at -T, but you can adjust the gain if you find it is necessary by adding series or parallel resistance to the ~47kΩ between FB and -T. The procedure to determine the right resistor values is described in the datasheet "Recalibration Principles and Limitations" section.

    I hope this helps.

    Best regards,

    Scott

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  • 0
    •  Analog Employees 
    on Feb 15, 2016 11:33 PM

    Hello Morgan,

    It can be done, but the process is a bit involved and it requires determining the right resistor values experimentally for each AD594 because there is a lot of variation in the internal resistance values from part-to-part. If possible, I suggest you switch to the AD8495, which is the next generation type K thermocouple amplifier after the AD595, and AD8495 is available to sample.

    If this is not an option and you must recalibrate your AD594, then you will have reduce the CJC voltage from 51.7μV/°C to about 40.44μV/°C (or the average type K slope over your CJC temperature range) with pulldown resistors from +T to COM and from -T to COM, like in figure 6 in the datasheet. This will naturally increase the gain because it reduces the resistance at -T, but you can adjust the gain if you find it is necessary by adding series or parallel resistance to the ~47kΩ between FB and -T. The procedure to determine the right resistor values is described in the datasheet "Recalibration Principles and Limitations" section.

    I hope this helps.

    Best regards,

    Scott

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