RFI FILTER AD8221 Y AMPLIFICATION STAGE ... TO THERMOCOUPLE

Dear Community

I plan use the ad8221 for amplify the signal of thermocouple to 0 - 5V. 0 - 50ºc (considering the addition of the cold joint (+ 25ºC)

It is divided into two stages, the first stage is ad8221arm Gain = 100, and the second stage is G = 50. I am hesitating to use the op amp OPA27GP for the second stage because of the low noise, however its warm-up time since it was energizes for offset reduction is 4min, which is a lot. Can someone please recommend some opamp with low noise, high cmrr and the right component for this type of measurement. I have been reading the ad8221 datasheet and notice that an EMI filter with established resistors and capacitors is recommended, someone can help because the approximate 1.6KHz frequency is being used for this filter.

Thank you

  • 0
    •  Analog Employees 
    on Oct 14, 2020 3:36 PM 1 month ago

    Hi abedgarr,

    Regarding the RFI design for the AD8221, I would suggest reading this application note which would further discuss the design techniques for the EMI filter. (https://www.analog.com/media/en/technical-documentation/application-notes/AN-671.pdf)

    On the other hand, since you've mentioned that your application would be to interface and amplify a thermocouple, I would highly suggest you look into our zero-drift amplifier portfolio. In particular, the LTC2058 has a sample circuit when using a thermocouple on page 24 of the datasheet. The zero-drift architecture of the LTC2058 is the one responsible for suppressing the 1/f noise. Which results in an excellent DC performance across the board: it has a max input offset voltage of 5uV, it only has a 200nVp-p input noise voltage from DC to 10Hz.

    Let me know if this helps.

    Thanks,
    Donnie

  • Hi Donnie,

    I apreciatte your help. Unfortunately this question was asked weeks ago, for which I already made the purchase of other electronic components. I decided to buy the OP27GH, I think it is now from the LT brand. and OPA177, any of these could replace the LTC2058?
    I will mention that I will replace the ad8221 with the ad8495.

    Thanks!