Difference between discrete signals and analog signals:-

Digital Signal:-

Discrete (digital) signals behave as binary switches, yielding simply an ON or OFF signal (1 or 0, True or False, respectively).

Examples of digital signals:-Push buttons, limit switches, and photoelectric sensors are examples of devices providing a discrete signal.

Discrete signals are sent using either voltage or current, where a specific range is designated as ON and another as OFF.

For example, a PLC might use 24 V DC I/O, with values above 22 V DC representing ON, values below 2VDC representing OFF, and intermediate values undefined. Initially, PLCs had only digital I/O.

Analog Signal:-

Analog signals are like volume controls, with a range of values between zero and full-scale.

These are typically interpreted as integer values (counts) by the PLC, with various ranges of accuracy depending on the device and the number of bits available to store the data.

As PLCs typically use 16-bit signed binary processors, the integer values are limited between -32,768 and +32,767.

Examples of analog signal:-Pressure, temperature, flow, and weight are often represented by analog signals.

Analog signals can use voltage or current with a magnitude proportional to the value of the process signal. For example, an analog 0 to 10 V or 4-20 mA input would be converted into an integer value of 0 to 32767.

Current inputs are less sensitive to electrical noise (e.g. from welders or electric motor starts) than voltage inputs.