Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001

17.1 BASIC PLCs

 

· A Programmable Controller (PC) is an input/output processing computer.

 

· Advantages of PLCs,

  1. - cost effective for complex systems
  2. - flexible
  3. - computational abilities
  4. - trouble shooting aids
  5. - reliable

 

· Ladder logic was originally introduced to mimic relay logic.

 

· A thorough review of the research literature is available in Sobh et. al. [1994].

 

· The PLC can be programmed like other computers using specialized "languages".

 

  1. - Ladder Logic - A programming technique using a ladder like structure. This was originally adopted because of its similarity to relay logic diagrams to ease its acceptance in manufacturing facilities. The ladder approach is somewhat limited by the lack of loops, etc. (Uses JIC standards)
  2.  
  1.  

 

  1. - Mnemonic - instructions and opcodes, similar to assembly language. More involved to program, but also more flexible than ladder logic.

 

 

  1. - Sequential Function Charts (SFC) - an alternative to a flowchart method for concurrent operations. Currently this is not widely used, but it (or a similar version) should become more prevalent in the upcoming years.

 

 

· Structured text allows programs that are similar to high level languages such as BASIC.

 

 

 

17.1.1 PLC Connections

17.1.2 Ladder Logic

17.1.3 Ladder Logic Outputs

17.1.4 Ladder Logic Inputs