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ISO224: Power Quality Analyzer

sebastian wynen
Prodigy 10 points
Part Number: ISO224
Other Parts Discussed in Thread: AMC3302, AMC1300

Tool/software:

Hello, good morning.

I am trying to design a power quality analyzer that senses line voltage and current, and detects transients, harmonics, peaks, frequency, apparent and reactive power, among others.
I wanted to know if this device would be suitable for this application.

The idea is to sense 300VAC from the line, reduce this voltage to a value below 12V (which is what the ISO224 input supports) using resistors, and then add a follower on the output to get an ADC input from 0 to 3.3V.
I understand that the ISO224 gain is 0.333, so with a 12V input, I would get almost 4V on the other side, correct?

My question is that in all the diagrams I've seen, there’s a low-pass filter on the input. Could I remove this filter in my design? Because I actually want to capture line imperfections on my ADC. Also, at what speed should I sample with my ADC?

Any information or diagrams would be very helpful.

Thank you very much for your help.

  • 0
    TI__Expert 4220 points

    Hi Sebastian,

    sebastian wynen said:
    I am trying to design a power quality analyzer that senses line voltage and current, and detects transients, harmonics, peaks, frequency, apparent and reactive power, among others.
    I wanted to know if this device would be suitable for this application.

    What is the max frequency you are trying to measure?  Bandwidth of this device is about 185kHz and 275kHz for the A and B versions respectively.

    sebastian wynen said:
    I understand that the ISO224 gain is 0.333, so with a 12V input, I would get almost 4V on the other side, correct?

    Correct.

    sebastian wynen said:
    My question is that in all the diagrams I've seen, there’s a low-pass filter on the input. Could I remove this filter in my design? Because I actually want to capture line imperfections on my ADC. Also, at what speed should I sample with my ADC?

    You will still want a filter on the input and output of the device to remove high-frequency noise and prevent any aliasing effects.

    Thanks.

  • 0 in reply to Saleh Ahmad
    Prodigy 10 points

    Dear

    Thank you very much for your response.

    To continue the conversation, I’d like to share my idea with you. I plan to filter the signal digitally as soon as it enters my microcontroller, as the goal is to measure a 220V RMS line voltage. Using a resistive divider, I’ll step it down to 12V to input it into the ISO224. On the right side of the ISO224, I will convert the differential output to a unipolar output, add an offset, and input it to the microcontroller, which accepts a range of 0 to 3.3V.

    Please correct me if this setup seems appropriate!

    Additionally, I’d like to ask if there is any document available that shows how to measure line current with a shunt resistor and use this same device. Are shunt resistors available in SMD? How could I calculate the appropriate values?

    Thank you very much in advance.

    Best regards,

  • 0 in reply to sebastian wynen
    TI__Expert 4220 points

    Hi Sebastian,

    sebastian wynen said:

    To continue the conversation, I’d like to share my idea with you. I plan to filter the signal digitally as soon as it enters my microcontroller, as the goal is to measure a 220V RMS line voltage. Using a resistive divider, I’ll step it down to 12V to input it into the ISO224. On the right side of the ISO224, I will convert the differential output to a unipolar output, add an offset, and input it to the microcontroller, which accepts a range of 0 to 3.3V.

    Please correct me if this setup seems appropriate!

    This would be fine.  You'll still want to filter the analog signal before your microcontroller to prevent aliasing from high frequency noise.

    sebastian wynen said:
    Additionally, I’d like to ask if there is any document available that shows how to measure line current with a shunt resistor and use this same device. Are shunt resistors available in SMD? How could I calculate the appropriate values?

    Shunt resistors are available in SMD.  You'll want to choose the shunt based on the max current, power dissipation, and accuracy you require.  You can take a look at this app note for reference.

    Thanks.

  • 0 in reply to Saleh Ahmad
    Prodigy 10 points

    After doing a couple of calculations, if I want to measure a maximum current of 35 A with a typical Shunt resistance of 0.001Ω, the input voltage to the ISO224 would be 35mV. Isn’t this too low? Since after passing through the ISO224, which has a gain of 1/3, it would be reduced to 11mV. According to your knowledge, could I amplify this voltage with a simple amplifier, or what would be the best way to handle this?"

    Thank you very much

  • 0 in reply to sebastian wynen
    TI__Expert 4220 points

    Hi Sebastian,

    You can add an amplification stage to the input/output.  It may be better to move to one of our current sensing devices, which have a smaller input range.

    The AMC1300 targets current sensing applications, and the AMC3302 also does current sensing and has an integrated DC-DC.

    Thanks.