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TIDM-THREEPHASEMETER-F6779 Calibration issue

Other Parts Discussed in Thread: TIDM-THREEPHASEMETER-F6779, EVM430-F6779

Hi,

I am using TIDM-THREEPHASEMETER-F6779 3 phase energy measurement reference design and added extra circuits. I need to measure 3phase voltage,current and power

For one of my application, i am using 3 numbers 12V step down transformer to measure the 3phase voltages. I am using these transformer mainly to isolate the high voltage from my board. For current measurement, i am using 3 current transformers. With this set up, when i do calibration using GUI application, i get wrong value of output voltage. Voltage reads correctly 13.5V when not calibrated. I just want that instead of 13V, it should show 230V. Since the number of turns is fixed in transformer, so i think it should give be possible to do such calibration. My application doesn't require exact measurement and +/-5V difference is acceptable.

I want to know if it is possible to do such calibration. When i try to do such calibration, and read the calibration factor, it shows negative value and after that when i try to change the calibration value it doesn't change at all.

  • Hello Kumar,

    Thanks for your detailed post. It sounds like you're trying to adjust the phase calibration more than one whole sample, and it's overflowing. The TIDM-THREEPHASEMETER-F6779 design uses the legacy Energy Library code which allows you to adjust the phase by fractional sample delays up to one whole sample delay. However, if more delay is needed, you'll need to add whole plus fractional sample delays in the code to achieve your required delay.

    Have you heard about our newer Energy Measurement Design Center (EMDC) GUI and Software Library? There are many advantages to using this software over the legacy Energy Library including easier configuration, migration between devices, calibration, automated code generation, etc. We've also implemented both whole and fractional sample delays for the phase calibration. You can learn more about EMDC from the following resources:

    Regards,

    James

  • Hi James,

    Thanks for your response. I am not sure if i could have explained better. The TIDM-THREEPHASEMETER-F6779 is designed for 230V AC Input. In my design, i am using 3units 12V transformer to step down 230V AC input to 12V for 3 phases. My measurements are going to be based on 12V AC input.

    With this setup, i want to do calibration. Since i am stepping down the AC input by 230/12=19.67 factor using transformer, so i want that i set calibration value multiplied by 19.67 in GUI so that the system reads 230V in GUI.

    When i try to do manual calibration, using the formula given in datasheet,

    My readings are as follows

    Value Observed=12V

    Value Desired=230V

    So using above formula, correction% i calculate as (((12V/230V)-1)*100)= -94.78%. When i set this correction percentage in GUI for manual calibration, GUI shows very high value(around 600V). When i try to reduce it to 230V using above formula, it doesn't get changed thereafter. When i see calibration value, it shows negative value.

    I want to know if its possible to do such calibration. As i said some difference(+/-5V) is acceptable for my application

  • After the 12V voltage transformers, have you sized the burden resistors correctly? You'll want to make sure you're not exceeding the ADC's Full-scale Range (FSR). Also, if the signal is low, you'll need to increase the GAIN. Perhaps the scaling factor doesn't have enough bits in the code to compensate for such a correction (e.g. if it's a 16-bit number versus a 32-bit number). However, if you can get the 12V voltage transformer to output a voltage close to what the EVM430-F6779's voltage divider would output at 230V, then you should be able to compensate here. If it's much lower, then you should probably increase the ADC's GAIN.

    Regards,

    James
  • Hi James,
    Thanks for pointing out. I did rework and changed the burden resistor as you suggested. Now i am able to get the correct voltage reading.