I have a device that outputs a 4-20mA signal from a NIDAQ via two ports, NIDAQ-0 and NIDAQ-1. NIDAQ-0 is the positive and NIDAQ-1 is the negative. I connect the current loop receiver to an Arduino Uno directly using 5V, GND, A4(SDA) and A5 (SCL). As I understand, 4mA is supposed to give 6430 on the Arduino, and 0mA should give 0. I get a reading of about 78 when nothing is connected.
For the following, I set the NIDAQ to output 4mA.
When I connect a multimeter across the NIDAQ ports, with the COM port at NIDAQ-1, I am able to read the 4-20mA current.
However, when I try to connect the IN port on the current loop receiver to NIDAQ-0 (+ve) and GND to NIDAQ-1 (-ve), with the multimeter in series, I get no current on the multimeter, and the Arduino reads a 78.
If I switch the connection, so the IN port on the current loop receiver is to NIDAQ-1 (-ve) and GND to NIDAQ-1 (+ve), with the multimeter in series, I get 1mA on the multimeter and about 1600 on the Arduino.
Am I using the wrong module or making the wrong connection?