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Inputs open in ADS1232

Jose Antonio Martinez
Prodigy 110 points

Other Parts Discussed in Thread: ADS1232, ADS1220, ADS1248

Hi all,

I have a question, I am having a problem when inputs are open in ADS1232. I am using a bridge sensor to measure a weight.

If I leave the inputs open I read in output almos 0 but other times I read a high value around 4800000, I think is normal this value is changing due to is floating.

Can I know when the bridge are connected or not reading the output value?

When the output is almost 0 its fine but when the value is high how can I now it, around which value?

I am using this configuration:

- Gain: 128

- AVDD: 5 V

- Vref: 5 V

- Data rate: 10SPS

- The voltage in bridge sensors is 5 V.

Thanks


Jose

  • 0
    TI__Guru** 113765 points

    Hi Jose,

    You are correct in that the floating inputs can float to any level.  Some of our ADCs, such as the ADS1220, ADS1248, etc., have internal current DACs that are used as burnout current sources for sensor detection.  These devices are register based and more complicated to use.  The ADS1232 is pin controlled and not register based, so the functions of the ADS1232 are limited.

    To accomplish sensor detection for an open requires a little more effort.  One option is to add a pull-up resitor on the AINP input and a pull-down on the AINN input and if the sensor is open you will measure full-scale.  The down side of this method is that the linearity of the bridge sensor will be affected even if the resistors are in the Meg ohm range.  This may or may not be significant in your system.  If it is significant, then you can add a MOSFET as a switch in the pull-up and pull-down path so that the pull-up/pull-down is not in circuit when the bridge measurement is taken.  When checking for the sensor open, you activate the switch.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 110 points

    Hi Bob,


    Thank you for your answer, I have been testing the system using the pull-up and pull-down resistors and it works fine, so now I can know when the load cells are connected or not.


    Best regards,


    Jose