4~20mA Signal.

It's an intersting study exercise.

These things are also available commercially.

Hello Imran Hussain, The simple way to generate a signal would be to use a resistor for a single milliamp. If you want to do a range from 4-20mA then a resistor bridge with a variable resistor could be used. Best to use precision resistors and multi-turn resistor with values picked for your range or a little above and below what your needing to read.

This way is a just a quick test to do a range. If you need accuracy or for calibration then one of the processor meters like from Fluke would be a good start. They can generate the test voltage, the test current and they can read and or measure the same.

Oh one other thing most loops need a limiter resistor typically 250ohm in series is a good value and as a bonus you can read a voltage across the resistor 4-20mA = 1-5vDC.

Generally you would have a power supply "+" side goes to a sensor "+" in then "-" out to the meter/recored "+" in then "-" out to the power supply "-" to complete the circuit.

Charles