• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 46 subscribers
  • Views 405 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS131M08: Please can you give me advice about my procject (shielding, EMC, EMI ...)

Alexandre Bourrieau
Prodigy 30 points
Part Number: ADS131M08


Hello everyone,

I have a project consisting of making an ADC main board with a raspeberry PI4B which will allow me to measure differential voltages from a analog accelerometer sensor on remote micro-boards.

The fact I cannot use digital accelerometer is that I cannot synchronize them and so my vibration data will be delayed each with other... It is why I must use multiple analog souce which will then be all acquire in a synchronozed way.

I will use these vibration data to get frequency response for extracting modal frquency with specialized softwaez (using OMA - Operation Modal Analysys). If my data are not synchronized the extraction will be biased...

My ADC have differential inputs so my idea is this but I dont know if it is correct ? It multiply the number of GND and so perhaps it is a bad idea ? (I have 32 sensors)

Also, is it a problem that differential signals are not referenced by the GND in the main board ?

Perhpas I need to connect GND to both ends in this case ??

Else I can do that wich is less expensive by taking power from main board. In this case there is only one GND so perhaps it is better ?

What do you think is better ?

  • 0
    TI__Mastermind 18900 points

    Hey Alexandre,

    In short, I'm a little confused by this statement:

    Alexandre Bourrieau said:

    Also, is it a problem that differential signals are not referenced by the GND in the main board ?

    Perhpas I need to connect GND to both ends in this case ??

    Shielded twisted pair have the braided or solid sleeve that acts as the shield for the differential and twisted pair within the cable. This sleeve is electrically connected to every connector I've ever seen for STP cables. Do you mean that you intend to electrically float this sleeve connection and not establish a connection between the ADC or main board GND nor the vibration sensor board AVSS?

    From what I could tell, all systems will at least capacitively couple the shield connection and reference the twisted pair, or inputs to the ADC. From the ADCs perspective, the signals need to satisfy the PGA's common mode range. 

    From a rule of thumb and EMI/EMC standpoint, I don't think I can tell you what the best way to do it is, let me ask the team for some guidance here the team recommends tying both board's GND or return to the same voltage or reference. From what I can tell, shielding cables and connecting the shielding directly to GND (or through capacitors) seems to be fine for low frequency signals with lots of filtering in the signal path for high frequency signals. For high frequency signals like ethernet, its much more common to use unshielded cables and add a common mode choke in the signal path to suppress any noise picked up by the cable.

    You might want to check out this app note where we look into EMC compliance testing. The ADC is single ended but it might give you some other tips about layout and other helpful information.

    Here's some other things to consider for IEC type testing for ESD, surge protection and more:

    Alexandre Bourrieau said:

    The fact I cannot use digital accelerometer is that I cannot synchronize them and so my vibration data will be delayed each with other... It is why I must use multiple analog souce which will then be all acquire in a synchronozed way.

    I will use these vibration data to get frequency response for extracting modal frquency with specialized softwaez (using OMA - Operation Modal Analysys). If my data are not synchronized the extraction will be biased...

    Let me know if you have any questions about the SYNC/RESET pin on the device. If you derive all of the main clocks for the ADCs from the same source and use the SYNC/RESET pin, you should have an easier time to phase correct the data you get from each ADC. 

    Best,

    -Cole

    Edit: asked team for guidance. Added that above