PLC is a new type of highly reliable general industrial automation control device, it has a strong control capability, flexible configuration, simple programming, easy to expand and so on, is the main means of today's and future industrial control and important automation control equipment, in various industries have rapid development and application. PLC programming for beginners often appear in the study of some difficult to understand the difficulties, the following summarizes the PLC programming several common problems.
1, the same brand of plc programming line is not compatible, not universal.
2, PLC program is not assembly language or C language, but ladder diagrams, instruction tables, is to be compiled into a binary machine language.
3, PLC and personal computer connection, can be directly on the personal computer to set up the operation, the upper computer means: people can directly issue control commands of the computer, is a personal computer but must have PLC corresponding programming software, the system does not have too high requirements, in general, ordinary computers can be completed.
4, according to the actual needs of the project, function block planning, writing subroutines
In PLC, subroutines are relatively independent programs prepared for some specific control purposes. Execute the subroutine call instruction CALL, etc., if the conditions do not meet the subroutine call, the scanning of the program will only be carried out in the main program, and no longer go to scan this subroutine, which reduces the unnecessary scanning time.
5, with the word or double word data transfer to the DO point method to control the output
PLC applications usually have a large number of output control, with the word or double word data sent to the DO point method to control the output can improve the speed, as long as the actual application of the requirements of a reasonable allocation of the output address, change the control of the output control word, you can greatly reduce the number of steps in the execution of the PLC program to speed up the PLC program running speed.
6, pulse-triggered SET, RESET
PLC, the use of SET instruction can be executed only once, do not have to execute this instruction for each scan, very suitable for use with the pulse output (PLS/PLF) instruction. Some engineers ignore this problem, the use of conventional methods to drive the SET instruction, inadvertently increasing the PLC program scanning run time.