Types of PLC (Based on Output configuration)

1. Relay type
2. Transistor type
3. Triac type

Relay Type

With relay type, the signal from the PLC output is used to operate a relay and so is able to switch currents of the order of few amperes in an external circuit. The relay isolates the PLC from the external circuit and can be used for both d.c and a.c switching Relays are relatively slow to operate.

Transistor Type

The transistor type of output (fig) uses a transistor to switch current through the external circuit. This provides a faster switching action. Opto isolators are used with transistor switches to provide isolation between the external circuit and the PLC. The transistor output is only for D.C. switching.

Triac Type

Triac outputs can be used to control external loads which are connected to the a.c power supply. Opto isolators are again used to provide isolation.

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Ladder logic

Ladder logic is a programming language that represents a program by a graphical diagram based on the circuit diagrams of relay-based logic hardware. It is primarily used to develop software for programmable logic controllers used in industrial control applications. The name is based on the observation that programs in this languages resemble ladders, with two vertical rails and a series of horizontal rungs between them.

Each rung of ladder language typically has one coil at the far right. Some manufacturers may allow more than one output coil on a rung.

• ----( )----- A regular coil, energizer whenever its rung is closed.
• ----(/)----- A "not" coil, energized whenever its rung is open.
• ----[ ]----- A regular contact, closed whenever its corresponding coil or an input which controls it is energized.
• ----[/]----- A "not" contact, closed whenever its corresponding coil or an input which controls it is not energized.

The "coil" (output of a rung) may represent a physical output which operates some device connected to the programmable controller, or may represent an internal storage bit for use elsewhere in the program.

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Types of PLC ( Based on I/O capacity)

Based on no of Input and output we classify in to three

1. Fixed (Micro or small) - 16 I/O

           It is one solid piece that have input and output port.

      2.  Modular (Medium) - 1064 I/O

          

           This type of PLC we can connect many fixed type of PLC through extension port up to 1064 connection only.   

      3.  Rack (Large) - 16,000 I/O

           It has separate input, output and CPU kit connect with crass rail connection.

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Programmable Logic Controller Languages 

Following five languages are used in PLC.

1. Ladder logic 
2. Instruction list
3. Functional block diagram
4. Sequential function chart
5. Structural text 

In these five languages, ladder diagram is commonly used all kind of PLC manufacture.

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Programmable Logic Controller ( PLC )

A programmable logic controller is an industrial computer control system that continuously monitors the state of input device and makes decisions based upon a custom program to control the state of output device.

Almost any production line, machine function or process can be greatly enhanced using this type of control system. However, the biggest benefit in using a PLC is the ability to change and replicate the operation or process while collecting and communicating vital information.

Another advantage of a PLC system is that it is modular. That is you can mix and match the types of input and output and output devices to best suit your application.

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The grace of the LORD JESUS be with God's people.