• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 38 subscribers
  • Views 211 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.

TIDA-010232: Analog Value error for isolation resistance measurement

Sibi Selvaraj
Prodigy 60 points
Part Number: TIDA-010232

Tool/software:

Hi 

I am using the TIDA-010232 board to calculate the isolation resistance between PE and a 345VDC bus. The measured isolation resistance are with high values of error% as described below.

Calculated Vp and Vn using the below formula equation 18 of the design guide document.

After finding the Vp and  Vn I used these values in equation 13 and 14 of the design guide document

The actual Risop and Rison used between DC+ and PE and DC- and PE are 20K respectively, however by using the above given equations I am getting an Risop of 48K. By analysing the equation 18 I presume that in order to get an Risop of 20K the VinADC value must be 2.08VDC however I am measuring a voltage of 2.343VDC at VinADC measured at singleEndedinADC in pin 6 of J5 in the TIDA board.

I request to understand why I am getting such deviations and how to resolve these deviations.

  • 0
    TI__Expert 4400 points

    Hi,

    Thanks for reaching out. 
    You are correct, if SP is closed a voltage of 2.08V is expected at the input of the ADC.
    When SN is closed a voltage of 1.21V is expected at the ADC. 


    To find the root cause of the problem, I think its the easiest way to check the voltages across the signal chain.
    I recommend to simulate the equivalent circuits shown in Figure 1-5 and Figure 1-6 and check where the voltages in the measurement differ from the voltages in the simulation.

    Voltages to check are:

    - VP and VinAMC when SP is closed,
    - VN and VinAMC when SN is closed.


     For a symmetrical scenario for RisoN and RisoP = 20k VN would be expected -150V and VP would be expected +150V,  while VinAMC would be expected 264mV and -264mV.

    Best regards,

    Andreas