ONLINE extra More follows below on each of the languageswww.cechina.cn, with diagrams.
　　Long dismissed as just a European phenomenon, the IEC61131-3 programmable-controller-language standard is gaining traction in the United States. Many controls engineers are familiar with one or a few of these languageswww.cechina.cn, but not all. That makes it difficult for them to make the best choice for a given application based on programming-language characteristics.
　　Thanks to the International Electrotechnical Commission (IEC), five standard languages have emerged for programming both process and discrete controllers:
　　Ladder Diagram (LD)
　　Function Block Diagram (FBD)
　　Sequential Function Chart (SFC)
　　Instruction List (IL)
　　Structured Text (ST)
　　When should one be used over another? What are the benefits and disadvantages of each? For an in-depth look at each programming language with code examples控制工程网版权所有, see the online version of this article on the Control Engineering Website at www.controleng.com via the January 2009 archive.
　　Choosing an Appropriate Language
　　With the different programming languages availableCONTROL ENGINEERING China版权所有, it’s important to consider a few factors before deciding which to use for your application. Of course控制工程网版权所有, if you’re already familiar with a certain language, then the tendency may be to stick with what you know. HoweverCONTROL ENGINEERING China版权所有, consider the high-level benefits of each language, as detailed below, before making a decision:
　　Ease of maintenance by the final user: SFC;
　　Universal acceptance of language: LD;
　　Acceptance in Europe: IL or ST;
　　Speed of execution by the PLC: IL or ST;
　　Applications mainly using digital I/O and basic processing: LD or FBD;
　　Ease of changing code later: LD;
　　Ease of use by newer engineers: ST;
　　Ease of implementing complex mathematical operations: ST; and
　　Applications with repeating processes or processes requiring interlocks and concurrent operations: SFC.
　　Your PLC or PAC platform may also affect the choice of programming languageswww.cechina.cn, as not all automation vendor