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ADS1220EVM: ADC Drift, not the same as offset

Peter Twiss74
Prodigy 40 points
Part Number: ADS1220EVM
Other Parts Discussed in Thread: ADCPRO, , ADS1220

Hello,

I have written a labview GUI to control the EVM because the ADCPro doesnt work at all. My results show there is a drift (downward) after starting to grab real-time data. I have attempted to calibrate out the offset using the MUX setting 14, but this reading actually comes out fine.

Here are my results:

- Actual voltage using Agilent DMM: 0.489V

- Gain: 1

- Samplerate: 20 Hz

- MUX: A0-A1, and for calibration I use Mux (AVdd - AVss)/2

- Referencs: 2.048V

- I take 25 measurements and the take the avg, and subtract it off.  The offset comes out to be 16 as an avg, seems logical.

Here is a screen shot of the drift. As soon as a press Run, I do get the exact value but then after a few samples, the reading start to drift, does anyone know what this drift is?

  • 0
    TI__Guru** 113765 points
    Hi Peter,

    I'm sorry that you had issues getting ADCPro to work with the ADS1220EVM. Perhaps there is some conflict within the LabVIEW runtime if you have another version of LabVIEW installed.

    One potential issue for the result you are seeing is if you are making a single-ended measurement with PGA enabled. It looks like most of your settings are the default register settings. The default setting for the PGA is enabled. With the PGA enable, setting one of the AIN pins to AGND will place the PGA input outside of the common-mode input range. See section 8.3.2.1 on page 22 of the ADS1220 datasheet. To disable the PGA, bit 0 of Register 0 must be set to '1'.

    Another potential issue is if you are using a voltage source that is floating with respect to the ADS1220.

    Best regards,
    Bob B
  • 0 in reply to Bob Benjamin
    Prodigy 40 points

    Hi Bob,

    Thanks for getting back to me....

    Shoot you know what you may be right with the floating source. The system is designed using a wheatstone bridge but  I was testing the input (Ain0 - Ain1) with a power supply on my desk (3.3V/Gnd), so maybe maybe this was it.

    The error did come back and forth popped in and out. I noticed when toughing around R28 and R29 on the back of the board had some affect on the offset coming in and going away. I looked up those resistors and they are just zero-ohm. So I may be having some sort of ESD problem. 

    I'll fix both issue and get back to you,

    -Peter