Since their inception in the automotive industry during the 1960s, programmable logic controllers (PLCs) have
made significant advancements in both hardware and software. These advancements have had a great impact on
the process controls industry. Despite these enhancements, the international industrial community recognized
that a defined standard for the control languages required to program the different vendor offerings did not
exist. 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 a
programming standard with the intent to "conform the languages being utilized for PLC programming and the
graphical user interface". The IEC 61131-3 standard documents five different programming languages: relay
ladder 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 discussion
of the individual languages. Additionally, a case study is presented on how the IEC 61131-3 standard allowed
the San Antonio Water System to perform a detailed analysis to determine the standardized language that
should 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, how
staff has built increased knowledge into their system, and how the utility has minimized reliance on outside
vendors for programming support. Finally, the case study demonstrates how the re-usable code has allowed for
increased familiarity among all field technicians, thereby minimizing the support time required by programming
staff. Includes 2 references, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 790 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 12 |
| Published : | 06/01/2006 |
