what is the signal flow for recording a signal?

Answer 1

The usual standard is 4-20 mA DC. Below 4 means that the signal wire is broken. 4 means the minimum value of the signal (like 0 feet for bottom of a water tank). 20 means the maximum value of the signal (like 100 feet for the top of a tank.) Over 20 means a short circuit.

Occasionally 1-20 is used and rarely 1-50 is used. But 4-20 has been a standard for decades.