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Programmable Controls

Description

Programmable controls or programmable logic controllers (PLC) are microprocessor based industrial computer systems for providing automation to electromechanical processes. Multiple inputs, outputs and other circuitry system are used to simulate the relays and switches for controlling the equipment in a process. They are programmable by using computer interfacing software through proprietary languages and with other network options. These programs which are used to control a machine’s operation are temporarily stored in a non-volatile memory. Programmable controls are designed to suite multiple input and output setups, resistance to impact and vibration and to withstand a wide range of working temperatures.

Software used for PLC

Programmable logic controllers use different software for operation. Some of them are given below:

  • C and Basic
  • IEC 61131-3
  • Structured text (ST)
  • Sequential function chart (SFC)
  • Ladder diagram (LD)
  • Instruction list (IL)
  • Function block diagram (FBD)
  • Relay ladder logic (RLL)

Specifications

The specifications to be considered for I/O channels of PLCs are:

  • Total number of points - Sum of inputs and outputs
  • Expansion of I/O channels - For increasing the total control capacity, the units may be connected together
  • Total number of I/O channels – Final number of I/O channels after expansion
  • Scanning  time - Time taken  by the PLC to check  its inputs and outputs
  • Memory Data -  Total capacity for storing data
  • Program memory - Capacity for control software

Advantages

The advantages of programmable controllers are:

  • Long term reliability in difficult environments
  • Can be easily modified for precise applications

Applications

The applications of programmable controllers are:

  • Used for controlling machines on assembly lines, controlling  amusement rides or light fixtures
  • PLCs are used in wide range of industries like semiconductor, automobile, process

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