• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 30 subscribers
  • Views 272 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.

FDC1004: FDC1004 Cross Channel Issued

Paul Wielgosz
Prodigy 10 points
Part Number: FDC1004

Hello

I am trying to detect liquid level in RV tanks.  I am using approximately 2 meters of shielded cable.   CIN2 will work fine alone when measuring to ground - When  I connect CIN1 with its shield the value of CIN2 will change unexpectedly.  This does not happen if I use CIN1 and CIN3.   This is using single channel read.

I have thought about using a differential channel reading on the cable.  I have two conductor with a shield.  I would like to use a reading on one conductor with a connection to the tank and use a differential reading using the other conductor bug after reviewing the specs this would require two separate shields.  When I do a differential reading - is it reading the two inputs in succession or simultaneously?

Thanks & Regards

Paul

  • 0
    TI__Expert 7599 points

    Hi Paul,

    In the differential mode configuration one thing to consider would be that each of the 2 inputs capacitance needs to be less than 115 pF. The absolute difference between the 2 inputs should be kept below 15 pF to avoid introducing errors in the measurement. Section 8.4.2 of the datasheet explain more details. 

    The Excitation signal generation is common to the SHLDx pins and the measurement of CHA and CHB is simultaneous. Is there a particular reason for the simultaneous need here ? The capacitance measurements will not change significantly if you are concerned about measurements perhaps averaging is an option.