Program Logic Controller
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Program Logic Controller. PLCs were invented in answer to the needs of the automobile industry, and were introduced in the late 1960’s. They were designed to take the place of older, more complicated relay based equipment systems. ゥ Emil Decker, 2009. Program Logic Controller.

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Program logic controller

Program Logic Controller

PLCs were invented in answer to the needs of the automobile industry, and were introduced in the late 1960’s. They were designed to take the place of older, more complicated relay based equipment systems.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

Relays were invented in 1835 by Joseph Henry. Relays use an electro- magnet to close or open a switch. This circuit is isolated from the power that runs through the main circuit involved.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

This allows a low voltage relay to “throw the switch” on a higher voltage line and keep the operator safe. Relays are used in many electrical systems, including automobiles.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

Relays are complicated, and systems using a lot of them tended to be very costly to operate and maintain. If production requirements changed, then the control system had to change also.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

The mechanical relays had a limited lifespan, and troubleshooting them were often problematic. Imagine a system using literally thousands of relays.

Typical Relay

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

By replacing bulky mechanical components with solid state circuits under the control of a microcontroller makes a lot of sense.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

The microprocessor is the brain of a PLC system. It consists of the microprocessor, memory, and circuits necessary to store and retrieve data from that memory. It also includes communications ports to other devices.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

Processors vary in their capabilities to control devices. Some control as few as 6 inputs and outputs (I/O) and others control as many as 40,000 or more.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

One processor can control more than one process or manufacturing line. Processors are often linked together in order to provided continuity throughout the process.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

Ram, or random access memory, is necessary for PLCs. Like computers, this is the area where all instructions are stored during operations. Everything happens in RAM.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

ROM, or read only memory, is important too. Instructions burned into ROM cannot be changed. This is where the basic program is stored. You load this and your routines into RAM to run them.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

EEPROM, or Electrically Erasable Programmable Read Only Memory, is like ROM, but with the correct equipment, can be reprogrammed, making it more versitile.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

Input modules are simply what they say they are. The input signals, whether via a push button, limit switch, electric eye, or an electrical input .

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

If there are input modules, then there must be output modules as well. LED readouts, solenoids, relays, DC or AC outputs to machinery, are a few options you have for output.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

PLCs, at their simplest, are ON / OFF switches, sequentially operated to send signals to an output device.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

Electromagnetic interference (EMI) and Radio Frequency Interference (RFI) can cause problems in most solid state control systems, and PLCs are not immune.

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

PLCs are used in a variety of applications from manufacturing assembly lines to equipment control in the harshest of environments.

Coal mining machine controlled by PLCs

ゥEmil Decker, 2009


Program logic controller

Program Logic Controller

  • Lamps

  • Relays

  • Motor controllers

  • Solenoid valves

  • Machine inputs

  • Other inputs

PLC

Power

supply

Programmable

Logic

controller

  • Switches

  • Sensors

  • Machine

  • outputs

  • Other

  • outputs

PLC

input

modules

PLC

processor

PLC

Output

modules

Standard

networks

PLC

Communications

modules

Proprietary

networks

Smart I/O

interfaces

PLC special

Purpose

modules

Remote

racks

ASCII I/O

interfaces

ゥEmil Decker, 2009


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