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The problem of the data collected by the ADS1281

user4363186
Prodigy 80 points
Other Parts Discussed in Thread: ADS1281

 

Dear Sir or Madam, 

We are developing a set of data acquisition system with ADS1281. Software and hardware are ready in the test phase now, but some problems are found during the test, so we need some technical support about the situation.

1、We input a fixed signal at the input terminal, run the software and print the output data. Some irregular sudden jumps are found in the output data.

The output data is as follows

( nine channels AD test data, channel 2~9 are shorted, and channel 1 is fixed voltage input; unit: MV)

Channel1=127.386521

Channel1=127.249569

Channel1=127.310352

Channel1=127.383909

Channel1=127.345219

Channel1=127.498473

Channel1=127.304534

Channel1=124.137772

Channel1=127.364546

Channel1=127.473443

Channel1=127.416875

Channel1=127.366232

Channel1=127.390288

Channel1=127.041611

Channel1=127.098906

Channel1=127.173799

Channel1=127.160172

Channel1=127.288516

Channel1=127.359855

Channel1=124.134092

Channel1=127.476981

Channel1=127.510580

Channel1=127.222052

Channel1=127.148076

Channel1=127.109911

Channel1=127.076918

Channel1=127.320980

Channel1=127.323648

Channel1=127.335932

Channel1=127.337407

Channel1=127.514082

Channel1=127.499506

Channel1=127.233353

Channel1=127.072852

Channel1=127.067674

Channel1=123.945175

Channel1=127.091292

Channel1=127.107072

Channel1=127.306097

Channel1=127.267259

Channel1=127.167264

Channel1=127.316280

Channel1=152.818520

Channel1=127.350961

Channel1=127.266604

Channel1=127.258757

Channel1=124.101284

Channel1=127.240173

Channel1=127.267108

Channel1=127.234491

2、The SCLK and DRDY pins of the ADS1281 are connected to the oscilloscope, which has curves as below, showing a number of sudden jump pulses signal superimposed on the DRDY. Is the previous sudden jump in the data caused by this sudden jump pulses? 

      

 3、When we test the ADS1281EVM by the same method ,the output is the same. So we want to know if the demo board can be stabilized to 1 micro-volt by itself, if not, how can we improve the stability of it to 0.1 micro-volt or 1 micro-volt?

 

Best regards,

  • 0
    TI__Mastermind 44680 points

    Hi ,

    I'm afraid the image didn't make it into your post, would you able able to re-post it? Make sure to to use the "insert image" dialog, as cutting and pasting into the text box doesn't always work with images. Thanks!

    Regarding the data, I see the "jumps" you're referring to. This may very likely be related to the SPI communication issue you're seeing. Perhaps the MCU is periodically mis-reading a data bit, or if the ADC registers an extra clock pulse than the communication is no longer in sync.

    Might you be observing cross-talk between SPI signals, or some other signal in your system? If you can, try to capture additional signals on the oscilloscope and see if there is any correlation to the "jumps" observed on the /DRDY or SCLK signals.

    Regarding your last question:

    user4363186 said:
     3、When we test the ADS1281EVM by the same method ,the output is the same. So we want to know if the demo board can be stabilized to 1 micro-volt by itself, if not, how can we improve the stability of it to 0.1 micro-volt or 1 micro-volt?

    Do you mean that the EVM data is consistent, or that the data or SPI signals are still "jumping"? If you are observing this on the EVM as well than it may be that there is an environmental cause of this interference. You can try to shield your circuitry in conductive enclosure and ground the enclosure to prevent this interference.

    If your input signal and reference signals are clean, you should be able to achieve micro-volt stability. For gains of 4 V/V and above it is possible to achieve input referred noise performance of 0.1 uVrms or less! It would be a good idea to initially test the ADC's noise performance with the inputs shorted, because this removes most of the input and reference noise effects. From there you can apply an input signal and get an idea of how much noise is coming form the input and reference. (The reference noise will not have much effect when the input signal is small; however, as you apply signals closer to full-scale you'll see more reference noise.)

     

    Best Regards,
    Chris