In the world of industrial automation, the efficiency of the PLC (Programmable Logic Controller) program often determines the performance of the entire system. In this highly competitive field, whoever can make the PLC program run faster will have the upper hand in production efficiency. Today, let's talk about how to improve the efficiency of the PLC program through several clever programming methods, so that your PLC can move forward at a high speed like a turbocharger.
1. Function block planning and subroutine writing: making programs smarter
A subroutine in a PLC is an independent program block written for a specific control purpose. The subroutine is executed by calling the CALL instruction. If the conditions are not met when calling the subroutine, the program will only be scanned in the main program, eliminating unnecessary subroutine scanning time. This not only reduces the scanning time, but also makes the program structure clearer. It can be said that the clever use of subroutines can make your PLC program more intelligent.
2. Use word or double word data to transfer control output
In PLC applications, a large amount of output control is unavoidable. Using word or double word data transfer to control DO points can significantly increase speed. As long as the output address is properly assigned and the output control word is transformed to control the output control, the number of steps in the execution of the PLC program can be greatly reduced, thus speeding up the program operation. In short, this approach is all about improving efficiency through batch processing, making programs more concise and efficient.
3. Pulse trigger SET and RESET instructions
The SET instruction only needs to be executed once in the PLC, not every time it is scanned. This method is particularly suitable for use with pulse output (PLS/PLF) instructions. Some engineers may ignore this problem and use conventional methods to drive the SET instruction, which inadvertently increases the program scan time. By accurately controlling the execution of the SET instruction, the number of unnecessary scans can be effectively reduced and the program running efficiency can be improved.
4. Avoid type conversion: reduce program redundancy
Taking a general PLC model as an example, the memory format is usually opposite to that of a common PC, that is, the high word is in front and the low word is in the back. We can put the word variable in the last two bytes and clear the first two bytes when the program is initialized. In this way, when defining a symbol, define the word variable in VW2 and keep the value of VW0 as zero to avoid type conversion. For example:
Simply zero out VW0 during program initialization. In this way, the variable wVarName can be accessed either as a literal or as a double literal, avoiding type conversion altogether. This approach not only reduces the number of program statements, improves the simplicity and readability of the program, but also significantly improves the operational efficiency. Although it takes up two more bytes of memory, this memory consumption is almost negligible considering the very large RAM space of the S7-200.
5. Use Hungarian-like notation
In order to avoid confusion when using variables, it is recommended to use the Hungarian-like notation, that is, add a prefix to the variable name to indicate the variable type, and use meaningful English words to form the variable name. For example:
b----Byte variable (byte)
w----Font variable (word)
d----Double word variable (double)
r----Real variable (real)
f----bit variable (flag)
btn—self-resetting push button input (button)
sw----switch or self-locking button input (switch)
sig—sensor, encoder, etc. level signal input (signal)
rly—output relay position (relay)
If there is a word type variable named VarName, to use the previous conversion technique, we can define it like this:
wVarName----VW2
dVarName----VD0
This naming method not only improves the readability of the program, but also avoids type conversion, further improving the running efficiency of the program.
6. Streamline program structure
When writing PLC programs, streamlining the program structure is also the key to improving efficiency. For example, in terms of output control, using one MOV instruction to complete the control of eight digital outputs is obviously more efficient than using eight MOV instructions to complete the control of eight digital outputs respectively. By optimizing the number of execution steps of the program and reducing unnecessary instructions, the scanning time and operating efficiency of the PLC can be significantly improved.
Optimizing the operating efficiency of the PLC program is like installing a powerful engine on an old car, which not only greatly increases the speed but also makes the entire system run more smoothly.
By properly planning function blocks and subroutines, using word or double-word data transfer, pulse-triggered SET and RESET instructions, avoiding type conversions, and adopting Hungarian-like notation, programmers can make PLC programs run faster, more stable, and more efficiently.
After all, in this world of industrial automation, efficiency is life, and what we need to do is to make every line of code perform to its full potential and help the entire system run efficiently.
