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INA220: Current measuring problem while using the INA220

Part Number: INA220

Hi, 

We need some support and advice about the best way to configure the INA220 and to measure the current/voltage on R141.

Our configuration is :

bus_adc='9bit', bus_voltage_range=0, mode='shunt_voltage_triggered', pga_gain='40', reset=0, shunt_adc='12bit')

the output is:

Current: 0.01800A Voltage: 0.84V Shunt Voltage: 0.00007V

Which is extremely low according to our expectations.

Thx

Neta

  • Hey Neta,

    Thanks for posting to the forum.

    To best assist you, would you please try sending your schematic again. The best way to upload an image is to use the paper clip icon and browse your files to attach the image. The schematic should show the shunt resistor and the expected bus voltage and load currents you are trying to measure.

    Also, could you send the value you chose to program the calibration register to as well.

    Sincerely,

    Peter

  • Hi Peter,

    Thanks for the answer.

    Actually I uploaded the image using the attachment clip but I'll go for it again, please let me know if now it's fine.

    Regarding the configuration - we will be happy to some support on this topic as well.

    We need to measure the voltage/current on the resistor on R141, with the following requirements:

    1. continues mode
    2. the maximum voltage may only be 5V.
    3. Accuracy of the measurement is not the most important thing, we mostly need a good inspection and observation.
    4. Sampling rate is around once in one second (1Hz).

    Please let me know if anything more is needed,

    Thx

    Neta

     

  • INA220A_calc.xlsxHey Neta,

    We still need more information as to what current you are trying to measure, but the error is high. Also, we need to know how the expected current value was approximated and whether you could use an ammeter to verify if the actual current is as expected.

    Some more information on whether or not you have developed other prototypes which also show the same error or if this is from testing just one system would be great.

    With the device configured in the schematic as shown, the total input offset voltage (Vos) will be around 1mV (see attached calculator). At 500mA load, the shunt voltage is 5mV, so trying to measure this with 1m of offset will generate significant error. To significantly reduces Vos, I would connect the VBUS pin directly to the 24V rail on the other side of the 10-Ohm. Connecting VBUS and IN- together is generating a larger difference between the IN+ and IN- bias currents which flow across the 10-Ω resistors and generate error. You can also reduce offset by using a lower gain (PGA=/1) and using the B version of 
    INA220.

    I would also increase the conversion time and averages of the internal ADC to make sure you are getting the most accurate measurement.

    One way to check the load current is to measure the shunt voltage with a voltmeter. This would help ensure the current is what is should be and that the shunt layout is proper.

    Hope this helps.

    Best,

    Peter

  • Hi Peter,

    Thanks for the reply, it was very helpfull.

    We will follow.

    Thx

    Neta