Analog input is a continuous input from the field to the PLC. Unlike digital
signals, is not a constant voltage signal. It can vary depending on the field
conditions. The commonly used analogue signals are 4–20mA signal and 0–10Vdc
Signal. Depending on the field conditions the input signal can vary between
4–20mA or 0–10Vdc. For Example, if you are monitoring a pressure of water
flowing through a pipe using a pressure transmitter of range 0–10 Bar, the
transmitter will give a signal between 0 and 10V proportional to the pressure in the pipe.