Pressure Sensor 4-20ma

Hello Arduino Community,

I'm totally new to arduino and electronics so please bear with me as I embark on this steep learning curve :slight_smile:

I recently purchased some Arduino kits and sensors whilst on holidays in Shenzhen (China) and have been playing and learning but have now hit a bit of a hurdle with one of the sensors I purchased;

The sensor is a pressure sensor for reading liquid height and the specs are as follows;

Input: 12VDC (using external power supply to power sensor)
Output: 4-20ma
Range: 0-15kpa

1.Output (Green)
2.Power+ (Red)
3.GND (Black)

Protection Class: IP 68
Material: 304L Stainless Steel
Pressure Port: NPT 1/4

The sensor has no brand on it and that's all the technical information it came with besides the calculation on how to convert it to total volume in litres.

The issue is I need to convert the 1 wire output to be 1-5V so the Arduino can actually read the values using the analogread function (just using the example on Arduino site to try get some readings). I googled this and it said to place a 250ohm resistor on the output side to bring it up to 1-5V. Now with me having no real understanding of electronics I soldered a 250ohm resistor onto the sensor output wire and put the resistor leg into pin A3. The problem now is I just get the continual reading of 1023 as if its a constant 5V. I have read the resistor needs to be grounded but I tried several combinations on the breadboard on how I thought it needed to be wired but nothing worked. Is someone please able to explain how I need to wire the 250ohm into the single output wire to increase the output to 1-5V? Preferably explained like your dealing with an idiot because you are :stuck_out_tongue:


Try putting the 250 ohm resistor from output to ground and connect the junction of the output and resistor to analog input. The 4-20ma works by sending a current proportional to the pressure. That current flowing through the resistor to ground will cause a voltage across the resistor proportional the the current (Ohm's law).