Full Description

Since their inception in the automotive industry during the 1960s, programmable logic controllers (PLCs) havemade significant advancements in both hardware and software. These advancements have had a great impact onthe process controls industry. Despite these enhancements, the international industrial community recognizedthat a defined standard for the control languages required to program the different vendor offerings did notexist. Thus, the programming of different PLCs was as varied as the models offered by each vendor.In 1992, the International Electro-technical Commission (IEC) addressed the issue by developing aprogramming standard with the intent to "conform the languages being utilized for PLC programming and thegraphical user interface". The IEC 61131-3 standard documents five different programming languages: relayladder logic (RLL); sequential function charts (SFC); function block diagram (FBD); structured text (ST); and,instruction list (IL). Instruction list is also referred to as statement list (SL).Each language has advantages and disadvantages depending on their use. This paper provides a discussionof the individual languages. Additionally, a case study is presented on how the IEC 61131-3 standard allowedthe San Antonio Water System to perform a detailed analysis to determine the standardized language thatshould be used for future phases of the control system associated with the existing water production facility.The case study demonstrates how development time has decreased, how staff efficiency has increased, howstaff has built increased knowledge into their system, and how the utility has minimized reliance on outsidevendors for programming support. Finally, the case study demonstrates how the re-usable code has allowed forincreased familiarity among all field technicians, thereby minimizing the support time required by programmingstaff. Includes 2 references, figures.

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Edition: Vol. - No. Published: 06/01/2006 Number of Pages: 12File Size: 1 file , 790 KB