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Current measuring

Andrej Pajnic
Prodigy 20 points
Other Parts Discussed in Thread: INA219

Hello,

working on a project where up to 25A AC current is used and must be measured. We decided to go with Honywell S&C CSNX25 (http://sensing.honeywell.com/index.php?ci_id=3108&la_id=1&pr_id=4967) closed loop current sensor. Output current should be between 12mA and 12,5mA and I would like to measure this with standard ADC with 3,3V reference. Since this is 0V/5V powered device it has it's own reference voltage at 2,5V. From this current measurement resistor was found to be 200R.

Now, I need to detect this AC current and transfer it to 0V to 3,3V output.

Is anyone who had same situation? Anyone saw any application note or there is already TI's solution for my problem? :-)

Thank you for help,

Andrej

  • 0
    Guru 21975 points

    Andrej,

    I think the circuit below will do what you want. The ratio of R2/R1 sets the offset between 2.5V and 3.3V to center the output voltage of U1 to 1.65V. R1 is set to give a 0V to 3.3V output range for a +/-12.5mA sensor current.

    Regard, Bruce.

  • 0 in reply to Bruce Trump
    Prodigy 20 points

    Bruce,

    thank you very much for excellent hint. However in the mean time I “discovered” INA 219.

    Idea I have and will try to test it next week is to use mentioned 200R resistor as a shunt resistor. I will put INA into 16V bus voltage with  +-160mV range. Using 128 samples (68,10ms per one reading) for averaging result, I will have something like RMS current measurement over three cycles at AC voltage in 50Hz system. With proper setting of INA219 I can even have direct current and power measurement.

    But of course, this is how I see work with INA219 – without knowing of its existence till yesterday. :-)

     I would much appreciate any corrections to this idea. When it is not digital world, I am lost. And this one is very analog… :-)

     Best regards,

    Andrej