Analog input is a continuous input from the field to the PLC. Unlike digital signals, input levels change continuously (there are no high and low levels). It can vary depending on the field conditions. The commonly used analogue signals are 4–20mA signal or 0–10Vdc Signal. 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.