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ADS1258: Strain gauge reading configuration

Brad Redpath
Prodigy 10 points

Part Number: ADS1258

Hi,

 

I'm working on a design to use an ADS1258 for measuring the output from strain gauges. I'd be interested to get some input on the difference between doing fully differential and pseudo differential measurements.

Attached is an image which hopefully explains what I mean a bit better. In essance instead of having a full wheatstone completion for each quarter bridge and doing differential measurements would it be equivilant to set AINCOM to the midpoint voltage and measure each quarter bridge in a single ended configuration? I'm hesitant to do this as I haven't seen designs like this but can't see why it would function any differently, and the benifit of double the inputs and fewer components is attractive.

For some other details, I plan to RC filter each input and have a differential op-amp with some gain between MUXOUT and ADCIN. The sample rates will be sufficiently low (polled) that the settling time for the amplifier will be fine.

Thanks for any thoughts you might have, I feel like there should be some performance penalty to the simpler approach but can't quite work out what it is.

 

Regards,

Brad

  • 0
    TI__Guru 58971 points

    Hi Brad Redpath,

    This will start getting into the mechanics of measuring strain which is not really our purview, but a full bridge can measure different forces compared to a quarter bridge. And the transfer functions and strain gauge locations are different depending on different applications. You can google this to learn more. So depending on your needs a full bridge might be necessary, but that is up to you to decide

    If temperature variation is concern in your system I can see this being a challenge if the local resistor divider is exposed to a different temperature compared to the remote sensors.

    -Bryan

  • 0
    Prodigy 10 points

    Hi Bryan,

    Thanks for your fast reply.
    Sorry, there was probably too much background there. In essence I guess my question was is there any internal difference in the ADS1258 between measuring a differential signal between say AIN0 and AIN1 vs AIN0 and AINCOM?

    Regards,

    Brad

  • +1 in reply to Brad Redpath
    TI__Guru 58971 points

    Hi Brad Redpath,

    Thanks for clarifying your question

    No, there isn't any meaningful difference. Note that you can only measure signals with respect to AINCOM in auto sequence mode.

    -Bryan