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ADS1292: Spikes on Raw Data ECG

Eckart Hanl
Prodigy 70 points
Part Number: ADS1292

Hi,

I'm using a ADS1292 and have problems with spikes in my ECG. I take only the raw samples over the SPI interface for two channels and sometimes I find spikes in the ECG. There are no filters activated. Only the raw data from ADS1292.

This is the picture:

This is the raw data and there is a jump from 0xFCC4DB to 0xFD2DC6 and later after several samples the jump is back from 0xFD18EB to 0xFCCF85.

16565481 FCC4E9
16565427 FCC4B3
16565467 FCC4DB
16574756 FCE924
16592326 FD2DC6
16594300 FD357C
16594171 FD34FB
16594137 FD34D9
16594070 FD3496
16594003 FD3453
16594126 FD34CE
16594138 FD34DA
16594171 FD34FB
16594170 FD34FA
16594210 FD3522
16594165 FD34F5
16594105 FD34B9
16594067 FD3493
16594120 FD34C8
16594052 FD3484
16594013 FD345D
16594015 FD345F
16593985 FD3441
16594009 FD3459
16594045 FD347D
16594103 FD34B7
16594078 FD349E
16594076 FD349C
16594027 FD346B
16593962 FD342A
16594045 FD347D
16594123 FD34CB
16594126 FD34CE
16594140 FD34DC
16594193 FD3511
16594130 FD34D2
16594097 FD34B1
16594108 FD34BC
16594010 FD345A
16594087 FD34A7
16594130 FD34D2
16594033 FD3471
16593994 FD344A
16593977 FD3439
16594024 FD3468
16593962 FD342A
16593868 FD33CC
16593839 FD33AF
16593753 FD3359
16593696 FD3320
16593739 FD334B
16593683 FD3313
16593777 FD3371
16593810 FD3392
16593827 FD33A3
16593867 FD33CB
16593908 FD33F4
16593985 FD3441
16593955 FD3423
16593990 FD3446
16593964 FD342C
16586987 FD18EB
16568197 FCCF85
16565034 FCC32A
16565124 FCC384

Have you an idea where the spikes came from? They are sometimes in the ECG raw data.

Can this be a timing problem of the SPI interface?

Regards

Eckart

  • 0
    Prodigy 70 points

    Find here our schematic:

    We have one electrode using for channel 1 and channel 2.

  • 0 in reply to Eckart Hanl
    TI__Mastermind 19815 points

    Hi,

    apology for the delay.

    What might be your signal source?
    Please check if you could read the Device/Revision ID correctly or not?
    Then Check if you could read the internal test signal correctly or not?

    Thanks

  • +1 in reply to ChienChun Yang
    Prodigy 70 points

    Hi,

    signal source are dry electrodes of stainless steel.

    The Device/Revision ID can read correctly and the square wave test signal looks like this:

    Regards

    Eckart

  • 0 in reply to Eckart Hanl
    TI__Mastermind 19815 points

    Hi,

    "signal source are dry electrodes of stainless steel." could be the problem and issue as they are much higher impedance and may not have good contact.
    ADS1292 was not designed for dry electrode.
    Did you use&connect RLD electrode?
    Could you try connect to a ECG simulator to test,

    and then

    after above, try with a wet/gel electrode?

    Thanks

  • 0 in reply to ChienChun Yang
    Prodigy 70 points

    Hi,

    sorry for late reply but in the last weeks we test many things. We don't use RLD electrode and when using a simulator we see also spikes in the ECG.

    We tried with wet electrodes and see also spikes.

    Now we changed to DC lead off with internal 6 nA and there are no spikes to see.

    So is AC lead off so sensitive that this can produce such spikes in ECG?

    So we also think that read from SPI and our data handling in the firmware is ok.

    Regards

    Eckart

  • 0 in reply to Eckart Hanl
    TI__Mastermind 19815 points

    Hi,

    I would not say nor use this statement "AC lead off so sensitive that this can produce such spikes in ECG".

    As described in the datasheet, AC lead off detection generates/switches the current source in high frequency, so as described, 

    "The ac excitation signals are introduced at a frequency that is above the band of interest, generating an out-of-band differential signal that can be filtered out separately and processed."

    Thanks