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I intended to use the INA219 chip to read the 4-20 mA current loop of the industrial sensor for the automation project. the sensor voltage is 12 V, my first schematic was as follows:

enter image description here

The ground of the MCU and the sensor are the same. However when I connect the sensor, the INA chip always sends the same value and does not change with different sensor conditions, at first I've tried to change the regulation and calibration of the INA chip with regard to datasheet and library code, but also no big change.

It seems the voltage of the shunt resistor reaches the maximum value of the voltage reference for analog measurement.

Some searching on the internet shows that some application uses the following schematic for sensor connection, but I still don't figure out how the voltage across the shunt resister remains unchanged with different voltage input. Also, I ran the test to manually create the fixed current with the power supply.

My experiment consists of fixing known resister (180) which series with shunt resistor and power supply set to a specific value (.86 V to 3.3 V) to create the specific current in the path, but same result, no change with different voltage input which theoretically has different current on the shunt resistor.

note

Any tips to solve this mysterious behavior really appreciated.

JYelton
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Hamid s k
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    You want to measure 4-20mA on a sensor that has a full scale value of over 3A. Changing the sense resistor to 10Ohms might make it more sensitive - 32mA full scale. You might want to verify that the chip is actually being read correctly first up. – Kartman Apr 04 '22 at 15:05
  • Can you make a schematic of the shunt resistor circuit you tried? And you supplied it with a power supply, not the sensor? – Ralph Apr 04 '22 at 15:20
  • @Ralph R4 is the shunt resistor, what do you mean supplied it with a power supply, not the sensor?! this is a current loop which use in industrial automation? – Hamid s k Apr 04 '22 at 19:21
  • "My experiment consists of fixing known resister (180) which series with shunt resistor and power supply set to a specific value (.86 V to 3.3 V) to create the specific current in the path, but same result" <- this is what I meant – Ralph Apr 05 '22 at 14:36

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