# Measuring 4-20mA with differential ADC

I have a question. Is it a good way to measuring 4-20mA with differential ADC?

Assume that we have a ADC with 2 single ended inputs or 1 differential input. Input A+ is the first input and input A- is the last input. If we connect a 4-20mA sensor to A+ and a resistor between A+ and GND so we get a pressure drop just to convert mA to Voltage.

Then on A- we do voltage dividing so we get the same input voltage as the sensor gives us at 4mA. Assume that we get 0.2V at 4mA from the sensor. When A+ and A- have 0.2V, then our ADC value is 0. When we have 20mA from the sensor, then our ADC shows maximum value.

Is this a good strategy? Or should I use single ended ADC instead and accept that my ADC value will be a little bit higher because 4mA causes voltage input? So instead of the start ADC value will be 0, then we have e.g about 500 ADC value at start.

• It all depends on the receiver, what power supplies it has and whether they are earthed and if isolation is required to prevent ground loops. It also depends on the specification of the 4/20 mA transmitter and (sometimes) it's power connections. – Andy aka Jun 19 at 9:06
• @Andyaka The sensor have 24V power supply. The GND have 0Voltage. So the best strategy is to have single ended ADC and measure 4-20mA with that? Not differential ADC? – Daniel Mårtensson Jun 19 at 9:24
• All of my previous comment should be considered. – Andy aka Jun 19 at 9:26
• @Andyaka Sorry, can you elaborate that? – Daniel Mårtensson Jun 19 at 9:31
• Take it one by one, I believe I was clear. – Andy aka Jun 19 at 9:32