Regarding CN0350 60Hz common mode noise reduction

Hello, everyone in this forum.

Thank you very much for your usual support.

BTW, I would like to develop an sensor instrument with the piezoelectric accelerometer.

Therefore I've tested with CN0350 and almost the result is OK.

But I guess the background noise is relatively large, that is caused by 60Hz ground

induction common mode noise.

Attached picture is Showa Sokki's charge amplifier model 4050-50 and accelerometer

model 2300A (measured as 5.21pC/m/s2).

And actuator is a Haptic driver that vibrates the model 2300A .

model 4050-50 settings are, PU sense = 5.12pC/Unit, Unit/Volt = 1.

It means if input charge is ±5.21pC, the amplifire outputs ±1V.

This time, the oscilloscope displays approximately ±200mVpeak,

then the vibration peak charge probably be ±5.21x0.2 =±1.04pC.(0.2m/s2)

but unfortunately connecting to CN-0350, there appears much 60Hz ground AC noise.

Those common mode noise should be reduced to develop a charge amplifire in house.

The software measurement result without vibration (just noise) is shown below.

This shows amplitude of the noise is about -0.2pC and +0.5pC, relatively large compare to the signal.

I guess the circuit of CN-0350 input would be amended to differential input

to reduce ground induction common mode noise.

Could anyone kindly help me to solve this issue?

Your assistance is Highly appreciated!

Best Regards, Yoshiaki.M.



add some comments regarding background
[edited by: Yoshiaki.M at 11:51 PM (GMT -4) on 19 Jul 2021]
Parents
  • 0
    •  Analog Employees 
    on Jul 27, 2021 11:59 AM

    Hi Yoshiaki,

    Regarding how you setup the probe going to the J1 terminal of the CN0350, is the ground pin in J1 connected somehow to the shielded  wire from the sensor or is it not connected?

    Cheers,

    Erbe  

  • Hi Erbe-san

    Thank you for your respond.

    At that time, J1 was not connected as shown below picture.

    Shielded wire was just connected to J2 NEG pin.


    But I had tested to connect Shielded wire to J1 GND pin or etc.
    The noise situation was not changed.


    Then, I tried shield by copper tape ( connected to GND) with the in house test board,
    then the AC induction noise had reduced a bit.

    This time I had connected the PZT sensor cable shield to GND and the PZT signal was coupled with 1uF to avoid 1.25V bias voltage effect to signal to GND.

       

    Curious thing is, when I touch the copper tape the noise was reduced.

    (I guess when GND level was same as AC ground loop the induction reduced.)

    Of course, when the PCB board was disappear away from the desk, noise was reduced also.

    The AC noise situation changes a bit, but I can't find a definitive way until now.

    Therefore, your help is highly appreciated.


    Best regards,
    Yoshiaki M.

Reply
  • Hi Erbe-san

    Thank you for your respond.

    At that time, J1 was not connected as shown below picture.

    Shielded wire was just connected to J2 NEG pin.


    But I had tested to connect Shielded wire to J1 GND pin or etc.
    The noise situation was not changed.


    Then, I tried shield by copper tape ( connected to GND) with the in house test board,
    then the AC induction noise had reduced a bit.

    This time I had connected the PZT sensor cable shield to GND and the PZT signal was coupled with 1uF to avoid 1.25V bias voltage effect to signal to GND.

       

    Curious thing is, when I touch the copper tape the noise was reduced.

    (I guess when GND level was same as AC ground loop the induction reduced.)

    Of course, when the PCB board was disappear away from the desk, noise was reduced also.

    The AC noise situation changes a bit, but I can't find a definitive way until now.

    Therefore, your help is highly appreciated.


    Best regards,
    Yoshiaki M.

Children
  • 0
    •  Analog Employees 
    on Jul 28, 2021 3:18 AM in reply to Yoshiaki.M

    hi Yoshiaki M.,

    Good to hear that you find a way to minimize the ac induction noise.  I would like to suggest that if you can power the interposer board, where the CN0350 is connected, using a clean power supply such as a power bank in that way we can isolate the supply as a source of the induction noise coupling in your test setup.

    Cheers,

    Erbe

  • Hi Erbe-san

    Thank you for your rapid respond.

    At this time, I've tried following your advice.

    1、I provide the power from battery, this time AC noise amplitude is not different.

    2、I don't have GND line near the bench, so I made a counterpoise by laying an aluminum plate instead of GND line.

    This seems to work efficiently, and I touched the plate,  the noise is reduced even smaller.

    The conclusion is "Connecting to GND is important".

    But unfortunately, our new product is battery operate and can't connect to AC GND.

    Anyway, thank you very much for your support.

    Due to your help,  I am able to find the real cause of this problem.

    Then, I'd like to consider in detail more from now on.

    Best regards,

    Yoshiaki M.

  • 0
    •  Analog Employees 
    on Jul 28, 2021 8:09 AM in reply to Yoshiaki.M

    Hi Yoshiaki M.,

    Good to hear from your end that you manage to fix the issue by improving the grounding of your test setup. 

    if you encountered any more issues with your setup using this board, please feel free to post it in this EZ Forum.

    Cheers,

    Erbe