Block Diagram of PLC

A typical block diagram of PLC is shown in the top picture.

There are 3 essential part available in plc. These are below.

• CPU (Central Processing Unite)
• Programming Device.
• Input/Output Module.   

Input output module:

There are two types input/output module available in PLC

• Digital Input Module
• Analog Input Module
• Digital Output Module
• Analog Output Module

Analog Input Module:

• Thermocuple
• RTD (Resistance temperature detector)
• 0 volt to 10 volt.
• 4 mili amp to 10 mili amp

Digital Input:

• AC and DC
• Proximity switch

Analog Output Module:

• 0 Volt to 10 Volt  
• 4 mili amp to 10 mili amp

Digital output Module:

There are three type of digital output available in PLC system.

• Relay Type. (AC & DC)
• Transistor Type (DC)
• Trick Type (AC)