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Energy Metering - ADC Configuration Issue

abhay shinde
Intellectual 400 points
Other Parts Discussed in Thread: MSP430I2041

Hi,

I'm using MSP430i20401 Embedded Metering EVM. Also I'm having my own board which is based on MSP430i2041. I'm working with energy metering code. I can see EVM is giving correct reading for Vrms, Irms etc. With my board, I’m getting Vrms correct (I had to apply some scaling factor other than that used for EVM board), but I’m not getting Irms anywhere near to the ideal value. The values of Irms are all over the place. I tried with different scaling factors to correct Irms, but it did not help. So I did inspection of the board and I found one difference in configuration of EVM board and our board.

As per EVM, the ADC channel signal routing is as below -

IIN_P -> A1.0+

IIN_M -> A1.0-

As per my board, the ADC channel signal routing is as below -

IIN_M -> A1.0+

IIN_P -> A1.0-

 

I think that as ADC is working in differential mode, it (the reversing of signals as per above configuration) would affect the current sense readings. Is that correct?  Can I change the adc configuration settings as per my board in energy metering code?

 

Thanks,

Abhay

 

  • 0
    TI__Guru 56685 points
    Hello Abhay,

    Usually if you reverse the connection, it would cause current to be 180 degrees out of phase. This would cause the current values to be the same but the active power to be negative. You could fix this in software by multiplying current samples by -1.

    However, based on the observation that the current is jumping around, I am not sure if the problem is the reversed connection. You might want to check that similar software is running between the two boards and that both boards use the same sensors. I'll also be checking with the i2040 EVM owner to see if there are any particular quirks with this EVM that show something similar to what you are seeing. Unfortunately, the owner is on vacation until mid August.

    Regards,
    JH
  • 0
    TI__Intellectual 960 points

    Abhay,

    If the only difference is the polarity of the ADC you should still get the Irms correct. The power related parameter will be negative instead. With the information given I am not able to figure out why this happens, please check also your board to see if the shunt is mounted properly or you have a malfunction i2040 mounted. Also please try to re-flash the code to see if the problem persist. Please let me know more information so that I can get closer to what went wrong. Thank you.

    mars

  • 0 in reply to Mars Leung
    Intellectual 400 points

    Hi Mars,

    Thanks for the reply.

    My hardware lead had closer inspection of board and there was some problem with board layout. We tried to replicate the same circuit on general purpose board and got the stable values for current (off course I had to adjust scaling factors) and other parameters as well.

    Regards,

    Abhay  

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