Why measure 4-20mA loop current?

Question

Electronics

Some models of multimeters have this function. I want to know what it is for and where it can be used.

Answer 1

This is for debugging the standard protocol for the exchange of sensors that are part of SCADA systems.

Answer 2

There are a bunch of sensors with 4-20mA output. 4 mA corresponds to the minimum reading, 20 mA to the maximum.
Why such difficulties, why are sensors sources of current and not voltage? In order to transmit the signal from the sensor over long distances. If 5mA comes from the sensor as a current source, then it will pump these 5mA stably into the communication line, this will be little affected by pickups and interference.
And they start with 4mA, and not from 0, to understand if the sensor is inoperative or transmits "0" readings.