I'm trying to measure DC 25A across a .005 ohm shunt resistor. From my research I've found the TI INA169 which is a current shunt monitor ic. However the datasheet says it has a total output error of ~1%. At 25A, this would be .25A. I'm trying to measure to 0.01A accuracy.
With 25A through the resistor, that is 125mV. If I had a differential ADC like the ADS1115 (16-bit, 1 for sign and 15 for value), then if I had it measuring the voltage differential between the shunt would that not be a more accurate solution?
With the INA169, what is the real accuracy I could expect if I measured the output with the ADS1115 in a single ended configuration? Would it realistically be more than 1%?
Best Answer
The advantage to the INA169 is that it can measure current on the high side of the voltage, 30 or 40 volts above your logic level supply. You could make a more accurate measurement with the ADC directly, but you must have a voltage that is both proportional to the current and in the 5-volt range of the ADC inputs, so you will need additional circuitry to perform this task. It is a challenge to build this type of circuit, since all of the components will have to be at the precision you are looking for. Remember that the shunt resistor you have chosen will dissipate 3.125 W so I agree with @dim that the sense resistor will probably not remain in this accuracy range as it heats up, and even board traces will have an effect on the measurement at this low resistance.