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ADS131E08: Resistive strain gauge measurement

Damien_Effi
Intellectual 495 points
Part Number: ADS131E08

Hello guys,

I am designing a project to measure 8 resistive strain gauge at the same time and values returned by SPI.

I plan to use the ADS131E08. Do you think this component can satisfy this need?

Thanks

Regards,

Damien

  • 0
    TI__Guru* 92655 points

    Damien,

    I think that the ADS131E08 is a possible candidate for your application. What sort of data rate are you looking for? Would this be for a set of full bridge or half bridge measurements?

    The device is good for this application because it does have 8 simultaneously sampling ADCs and it has some available gain to amplify the signal. The reference ranges all the way to AVDD, which allows for a ratiometric measurement with AVDD driving both the ADC and the bridge excitation.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Intellectual 495 points

    Hi Joseph,

    That is perfect!! It was also my feeling.

    thanks

    Damien

  • 0 in reply to Joseph Wu
    Intellectual 495 points

    Hi Joseph,

    Data rate is less than 1KHz.

    What do you mean by full bridge or half bridge measurement?

    We are using resistive strain gauge.

    Do you have full bridge or half bridge application  note which fit with resistive strain gauge to the ADS131E08?

    Regards

    Damien

  • 0 in reply to Damien_Effi
    TI__Guru* 92655 points

    Damien,


    I don't have any application notes specifically for the ADS131E08, but I did find this application note for bridge measurement systems, which would include strain gauges.


    Using this note as a guide, I think of a full-bridge as something like this:



    For this, you need to make a measurement from VO- to VO+.

    On the other hand, a half bridge would be something like the right side of this:

    In this second case, it's a bit different, the left side of the bridge is completely stationary. Because of this, you could share VO- for all measurements while each VO+ would be a measurement from each half-bridge. For example, if you measure 8 full-bridges, you need 8 fully differential ADCs each with two inputs. If you have 8 half bridges, you could use VO- for one common AINN measurement, and then 8 AINP inputs. If you have an ADC with a fully configurable multiplexer, then you could use 9 inputs with 2 outputs.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Intellectual 495 points

    Thank you Joseph for the explanation and datas.

    I will do the the half bridge with your remarks.

    How can I send you the schematic for review? As there is a NDA, I don't want the schematic can be seen by everyone in this forum.

    Thanks

    Damien

  • 0 in reply to Damien_Effi
    TI__Guru* 92655 points

    Damien,

    I'll contact you and we can continue this discussion offline.

    Joseph Wu

  • 0 in reply to Joseph Wu
    Intellectual 495 points

    Hi Joseph,

    I didn't find the way to send you an email through E2E.

    I attached the schematic. I included your remark:

    - all IN_N inputs are connected to the same ref level

    Thanks to have a look and let me know if you have any remarks.

    EFT-SCHC19210001_V1.0-Schematic(PROTO).PDF

  • 0 in reply to Damien_Effi
    TI__Guru* 92655 points

    Damien,



    I'm sorry I didn't respond earlier to your post, but I was out of the office for the latter half of last week and I'm just getting situated at work again.

    I've looked at the schematic you've provided and it seems like a standard setup, but I do have a few comments and questions.

    I would also add some bypass capacitors for the analog and digital supplies. There are some recommended values in the datasheet starting on page 62. CLK should be grounded to DGND if it is not being used. I would use some RC filtering on the front end of the ADC if you think there might be noise in your system.

    What are you using for the reference? Generally you would want the driving voltage of the bridge to be the reference to maintain the ratiometric measurement. Right now, there's only a connection to C19 and C20 to VREFP. If you're driving the strain gauges with the 3.3V supply, then you would probably want to connect VREFP to 3.3V as well.

    Also, I'm not sure if you have the strain gauges connected correctly in your schematic. I wouldn't have expected the 10k resistors at the bottom of each gauge. What strain gauge are you using? Is that the normal use case connection for that element?




    Joseph Wu