What are performance indicators of PLC programming language - - programmable logic

Performance of the PLC is a lot of, today give you said is with several, constructing the relation between PLC control system is directly respectively are: the input/output points, application of storage capacity, scanning speed, programming languages, instruction function, together and see it!

1.

input/output points as mentioned earlier, is input and output points of PLC control system can access the maximum amount of input and output signals, said when the composition of PLC system may be the largest scale. Here have a question to note that in total points, the proportion of input and output points are always in a certain set of, often be input points is greater than the output points, and the input and output points can not substitute each other.

2, the application of storage capacity

application storage capacity is to store the user program memory capacity. Words (usually with K 千瓦) , K bytes ( kB) For the unit, 1 k = 1024. Also some PLC controller with the program that can store directly. In some literature said storing the addresses of program in the PLC unit to 'step', each step takes up two words, normally a basic instruction step. Function of complex instruction, especially the function instruction, often there are several steps, so use 'steps' to represent the process capacity, often in the most simple basic instruction, what is called K steps. Like or use bytes, minicomputer memory to a few K, 1 K mainframe decades even can reach 1 ~ 2 K m bytes.

3, scanning speed is generally to carry out the basic instructions article 1000 the time required to measure. Milliseconds per thousand step, also have to perform a step of instruction time, such as subtle/step. General logic instructions and operation instruction has bigger difference of the average execution time, and therefore most occasions, scanning speed is often need to show is that kind of program execution.

here are the scanning speed reference value: the current PLC adopts CPU frequency, scanning speed is slow to 2. 2 ms/k logic operation procedures; Faster can reach 0. 75 ms/k logic operation procedure or shorter.

4, programming language programming language refers to the user and the method of information exchange of PLC, the method is easy to use by more people. IEC announced in May 1994 the standard of the PLC programming language IEC1131 - 3. Its detailed description of the PLC can use five programming languages: instruction sheets ( IL） The ladder diagram ( LD) , the sequential function chart ( SFC） , the function diagram ( FBD） And structure of the text ( 圣) 。 The current instruction table, ladder diagram, sequence function diagram is the most used programming language. Especially the ladder diagram, all the PLC to support the programming method. But must also pay attention to different manufacturer of PLC programming language is different and incompatible with each other, even as ladder diagram language, language nor instruction sheet.

5, instruction function instruction function is the embodiment of the programming ability. To measure the strength of the instruction function has two aspects: one is the number of article instruction, the second is how much comprehensive instruction. A comprehensive instruction in general can finish a special operation. Equivalent to a built-in a subroutine, such as PID, CRC instruction, etc. The stronger the instruction function, use these instructions to complete the easier it is to a certain control purpose.

in addition, PLC, scalability, reliability, operability, and cost-effective performance index is also often used as indicators of the comparison of PLC.

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