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How can I design a wheatstone bridge signal processing of gas sensor?

Dankim
Prodigy 40 points

Hello there,

I am going to develop a thermal conductivity gas sensor application like below image.

I don’t yet know a actual bridge output value, but I expect that bridge output value is approximately 0~200mv and it is dependent on tolerance and Temperature Coefficient of sensor heater.

Also, analog output of gas sensor application is 0.5~4.5V corresponding to gas concentration and output resolution is under 0.1V.

I have questions about sensor signal processing.

First, How do I design AFE Circuits using TI’ ICs or others after wheatstone bridge output?

Second, how many bit ADC resolution does mcu need?

I would like to need your many help and ideas.

  • 0
    TI__Guru* 91206 points

    Dear Seunguk - 

    Thanks for the post and welcome to E2E! Which gas sensor are you using? (Please provide part number, datasheet link, and any other information about the application requirements that you have)

    You may be able to use AFE or you may need something else - so let's start with the sensor. 

  • 0 in reply to Josh Wyatt
    Prodigy 40 points

    Thank you for your reply.
    I am going to use thermal conductivity gas sensor for automotive application. I don't have other information about parts yet. 
    The gas sensor has two heat elements with 100 ohm resistance. The sensing element's resistance change when gas concentration change. 

  • 0 in reply to Dankim
    TI__Guru* 91206 points

    Seunguk - 

    I would imagine then here you would need to arrange your circuit something like this, where they elements in yellow circles would represent your sensor, in the bridge and then going to the device used in this reference design. I am moving this post to the appropriate product line for further support. 

    https://www.ti.com/lit/ug/tidubh0b/tidubh0b.pdf 

  • 0 in reply to Josh Wyatt
    Prodigy 40 points

    Josh, Thank you for your answer. 
    In addition to your answer, I would like to know how to design AFE circuit  without ASIC(PGA400). 

    The reason is that I must use MCU to calibrate and compensate our gas sensor to meet our customer's requirement.

  • 0 in reply to Dankim
    TI__Guru**** 180831 points

    Hi Seunguk,

    Take a look at this App Note on Wheatstone Bridge signal conditioning: www.ti.com/lit/an/sloa034/sloa034.pdf  From there you can go to your micro-controller and there is no need for the ASIC,.