• Types of PLC Software: Controlling an Amusement Rideamusement ride 1 image by Pat Lalli from Fotolia.com
  
  PLC, or programmable logic controller, is a digital device (typically a computer) that is used to automate electromechanical processes such as lighting fixtures and amusement rides, and to control assembly line machinery. PLC software is a set of programmable rules that allow the hardware equipment to function. The software is typically stored in a nonvolatile memory device (flash memory, ROM, hard disks and magnetic tape). PLC software is the heart of the PLC system, and it is made up of instructions, functions and elements that monitor or control the PLC.
  
  

RLL Format Software

• The RLL-format (or relay ladder logic format) PLC software is one of the most frequently used set of programmable instructions that control a PLC system. RLL includes various types of data handling functions, comparison blocks, counters, timers, registers, coils and contacts. These functional elements of the software are saved on the rungs of the RLL and executed by the PLC processor. The RLL software controls all hardware components of the PLC device. PLC processor executes software rung by rung by scanning (top to down) through the RLL. It sequentially executes each individual RLL rung and activates all hardware devices linked with the executed RLL programs. Programs and instructions stored on RLL rungs can be added and removed from operation without needing to dismantle their associated hardware device. PLC brands that support RLL include ABB, Siemens, Mitsubishi, Allen Bradley and Direcsoft.
  
  

State Logic-Based Software

• The stage logic programming system is used to control PLCs. A state logic software uses a state transition diagram (which diagrammatically shows a system as being comprised of a number of steps, or states) as a model, and employs the fundamentals of the finite state machine (FSM or a model that represents the transitions between states in the form of a diagram. It is similar to a flow chart. An FSM can be thought of as an abstract concept or model of the functioning of a machine). State logic is comprised of tasks, which are made up of states that are made up of statements (commands to control each individual component). ECLiPS is an English-language-based state logic software developed by Adatek. Inc.
  
  

Structured Text-Based Software

• Structured text is a programming language that is used to control PLCs. ST is comprised of variables (that hold data), operators (assignment and arithmetic operations), expressions (combination of variables and operators--the software code itself) and the control flow (that defines the sequence of executable statements). An example of an ST-based software is the Mod51, developed by Mandeno Granville Electronics for the programming for PLCs.