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Original question:

ADS1220EVM: How to reduce ADS1220 EVM noise

ADS1220EVM: ADS1220EVM

Jaehoon Lee
Prodigy 90 points
Part Number: ADS1220EVM
Other Parts Discussed in Thread: ADCPRO, ADS1220,

How can I reduce the noise?

I measure the Load cell signal by EVM Module. but there are about 118Hz signal noise with 2KSPS, Gain 128, Internal Reference Voltage....

Please let me know the source of the frequency 118Hz.

Take care.

  • 0
    TI__Guru** 113765 points

    Hi Jaehoon,

    Welcome to the E2E forum!  Most likely you are picking up power line-cycle noise that may be aliasing back into the pass band of the ADC.  The cabling on the load cell will act as an antenna and then this noise will be amplified by the PGA.  To minimize issues from cabling from the load cell, a shielded cable should be use that is properly terminated.

    The EVM has many possible configurations and the input resistors are populated with 0 Ohm resistors.  To allow for a ratiometric measurement the load cell connector at J1 is designed to use AIN0/REFP1 input as the excitation and (+) reference input while AIN3/REFN1 as the (-) reference input.  Installing jumpers at JP1 and JP2 then use AVDD/AGND as the reference input and bridge excitation source.  Setting the configuration to use the REF1 reference will also help reduce noise and drift error.  The bridge inputs would connect to AIN1 and AIN2.  I would suggest creating analog input filters by changing R5 and R6 to 1k resistors and adding a 100nF cap ant C4.  I would also suggest doing something similar at R7 and C7 to add some filtering at the reference input.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 90 points

    Hi Bob

    Thanks your guides.

    I installed jumpers at JP1 and JP2, so I used AVDD/AVSS as the reference input(External  using AIN0-AIN3). Also, I changed the value of capacitor, resistor as below.

    R5, R5, R7, R5 = 1kohm

    C1,C3,C5,C7 = 10nF

    C4, C32 = 100nF

    yet, there are about 118Hz signal noise.

    Do you have any solution?

    Take care

  • 0 in reply to Jaehoon Lee
    TI__Guru** 113765 points

    Hi Jaehoon,

    Unfortunately there is no easier answer to give you for the source of the 118Hz noise .  You will be required to do some investigation. and troubleshooting.  

    • Can you send me some screen shots from ADCPro showing the noise? 
    • By adding the input filters did the noise lower?
    • Have you tried other settings (like 20sps normal mode to see if this noise lowers)? 
    • Have you tried using the external reference for ratiometric measurement that I suggested in my previous post?  
    • Have you tried observing the analog inputs with an oscilloscope to see if the noise is coming on cabling?
    • Have you tried an external analog supply voltage to make sure that there is no power supply noise from the USB power from your computer?
    • If you short the inputs at the terminal block do you still see the 118Hz noise?
    • Can you send me pictures of how you have the load cell connected to the EVM?

    In the end you need to discover where the noise is coming from to know how to adequately deal with it.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 90 points

    Hi Bob

    Thanks for all.

    I checked as below.

    1) By adding the input filters, the amplitude of the noise is lower but there is still about 118 Hz noise.

    2) At lower data rate like 20sps, the noise is different from the previous.

    3) There is the same noise in the case of using the external reference for ratio-metric measurement.

    4) I plugged off the power code of notebook, then the noise of 118Hz disappeared.

       so, It is necessary to take measures against power noise on the EVM board.

    5) If I try an external analog supply voltage by J7 Connector, the EVM Board don't work and ADCPro cannot connect the EVM Board.

    6) I wonder if the simultaneous 50/60 Hz Rejection function works. There is no difference between turning on and off the simultaneous 50/60 Hz Rejection function.

    I attached the image of ADCPro.

    Thanks  for you comments.

    Take Care

    ADS1220EVM.zip

  • 0 in reply to Jaehoon Lee
    TI__Guru** 113765 points

    Hi Jaehoon,

    It does appear to be power line-cycle noise.  Note that the ADS1220 50/60Hz rejection only works in normal or duty-cycled mode at 20sps.

    For test 4, I'm not totally clear what you did.  Are you running your system on a notebook computer?  Did you unplug the charging power cord and then just run from the battery and then the noise went away?  Is this correct?  You might see a large improvement if you use a desktop computer instead of the notebook as the power supply on a desktop system is usually much cleaner than the notebook supply.

    For test 5, when applying external 5V power to the board at J7, you should also disconnect/remove the jumper JP7 so that the external supply does not interfere with the USB supplied voltage.  See the schematic in the ADS1220EVM user's guide.  Both 5V and 3.3V power indicators should light.up.

    The analog input filters (1k and 100nF) are not going to filter power line-cycle noise.  You would need to have much more aggressive filtering.  Your current filter cutoff is about 800Hz.  So now you are looking at tradeoffs.  The key element still remains as to how the noise is actually entering the system.  This determines what you need to do in the end.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 90 points

    Hi Bob

    For test 4, I used the notebook. I unplugged the charging power cord then just run from the  battery and then the noise went away.

    For test 5, I saw the schematic in the ADS1220EVM user's guide and and followed up  the guide. Also Both 5V and 3.3V power indicators light up.

    But, the notebook don't recognize the EVM Board. (USB Device, Virtual COM Port)

    I tried to recognize the USB device by pushing the reset button.

    I tried the several value of the analog input filters (fc = 39Hz ~795Hz) but there are still the power noise. 

    So, I tried the another board(OLIMEX Board, BB-ADS1220). I added  the passive analog filter and the regulated 5V. I gathered data by the arduino board. The result is not too bad and has no power noise.

    Anyway, thanks for your support.

    Take care.

         

  • 0 in reply to Jaehoon Lee
    TI__Guru** 113765 points

    Hi Jaehoon,

    The noise does appear to be power supply related with respect to the USB source and the ADS1220EVM.  Applying the external supply voltage at J7 should have worked to properly supply the EVM, and pressing the RESET button on the EVM should have re-enumerated the device.  So I'm not sure what might be happening.

    One other option to try is to connect the analog only voltage to the ADS1220 instead of supplying the entire board.  You can do this by removing the AVDD jumper at JP3 and connecting +5V to the left side of the JP3 jumper and - to ground test point TP1.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 90 points

    Hi Bob

    Thanks your guide.

    I followed up your guide and had a good result with small variation.

    But sometime, there is still about 118Hz noise.

    I think that the noise probably due to the direct connection of DGND and AGND.


    Thank you again for your kind help.

    Take care