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ADS1232REF drifting problem for single-ended load cell

Bo Qiang
Prodigy 110 points

Other Parts Discussed in Thread: ADS1232REF, ADS1232

Hi,

I have a ADS1232REF board and try to connect to a single-ended force sensor with internal amplifier. The output shows a drifting problem. The readout from the RS232 port drift down over time and it is so large that I cannot perform a calibration.

I also tried to connect a battery to the board and it also shows a drifting down problem.

For the connection: I connected In1- to GND as the data sheet suggested.

I did a shorted-input noise test. It did very well.

Then I tried to connect a load cell with internal bridge to the board, there is no drifting problem.

I am confused what is causing the drifting for single-ended connection.

Thanks!

  • 0
    TI__Guru** 113765 points

    Hi Bo,

    You must make sure that you are in the correct common mode range for single ended inputs, which means you must be in a gain of 1 or 2.  If you have the ADS1232 set to a gain of 64 or 128, your input must be 1.5V above ground and 1.5V less than AVDD.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 110 points

    Thanks for your reply. I am using gain 2x and the reading still drifts. I am using the internal +5VA as reference and the output measures around 1.2 volts with a multimeter. 

  • 0 in reply to Bo Qiang
    TI__Guru** 113765 points

    Hi Bo,

    Can you tell me more about the sensor you are using?  How have you connected power and ground to the sensor?  Are the grounds connected between the sensor and the ADS1232REF ground?  What value of reference voltage are you using and where is it derived (in other words are you using the ADS1232REF +5VA as the reference or some other external reference)?  What is the range of codes you are seeing (actual codes and not volts)?  What data rate are you using?  Are you using Scale or Analysis mode (SW8)?  Have you verified that jumpers J7 and J8 have been removed?  Are you using the front panel or the GUI for control?

    Thanks,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 110 points

    Hi Bob:

    Here are the answers:

    1. sensor: Honeywell FS01

    2. Power connection: from the terminal block +5VA to sensor +Supply, terminal block GND to sensor Ground.

    3. Reference: ADS1232REF +5VA

    4. Range of output code: around B73XXXXh - B74XXXXh (it is actually hard to say because the output drifts constantly)

    5. data speed: I am using 80 samples/second.

    6. Mode: analysis (I actually found it doesn't matter)

    7. J7 and J8 are removed. Because it is a single-ended sensor, the IN1- of the terminal block is shorted with GND of the terminal block.

    8. I am reading data from COM port.


    Thanks!

  • 0 in reply to Bo Qiang
    Prodigy 110 points

    I did a long-term test over about one hour. The measurement kept drift during the course. I almost think single-ended measurements is not properly supported on this board. Any suggestions?

  • 0 in reply to Bo Qiang
    TI__Guru** 113765 points

    Hi Bo,

    You can measure single ended inputs, however you need to be very careful with respect to connections.  If you are seeing codes from 0x800000 (negative full-scale) to 0xFFFFFF, then the ADC input is seeing negative input voltages.  You should see values from 0x000000 to 7FFFFF (positive full-scale).

    Best regards,

    Bob B