HollySys PLC - What are the design requirements that need to be met for PLC programs?

Simplicity

Make the PLC program as simple as possible. Simplicity means using a standardized procedural framework as much as possible and using simple instructions as much as possible.

In order to make the program simple, in a large way, it is necessary to optimize the program structure, simplify the program with process control instructions, and replace the single-function instructions with powerful instructions in a small aspect, and pay attention to the arrangement order of instructions.

　　readability

The designed program is required to be readable. This is not only convenient for the programmer to deepen their understanding of the program and facilitate debugging, but also to make it easy for others to read your program and facilitate user maintenance. If necessary, the program can also be promoted.

To make a program readable, the program should be designed to be as clear as possible. Pay attention to the hierarchy and implement modularity to the point of designing with an object-oriented approach. Use more standard designs.

In case of special cases, language programming is used, and in most cases, please use ladder programming for easy reading.

The second is that the I/O allocation should be regular, easy to remember and understand. If necessary, do some annotation. The use of internal devices should also be regular, and do not use them casually.

Readability is something to keep in mind at the beginning of programming. It's not easy to do it completely. Because in the process of program debugging, the increase or decrease of instructions and the change of the use of internal devices may make the original clearer program become a little chaotic. Therefore, there is a certain leeway for debugging to increase or decrease during the design, and then tidy up after the debugging is completed, so that the designed program has higher quality.

The comments of the program should have at least the following aspects:

A. System note: the copyright company of the whole set of programs and the purpose of this set of programs

B. Block Notes: The main purpose and author of this block

C. Paragraph comment: The purpose of this piece of code

D. Variable annotation: Needless to say, the importance includes I/O annotation and intermediate variable annotation

As for the consideration of confidentiality, I think it should be considered in the encryption algorithm of the program or the encryption of the block, rather than the clever idea of reducing comments.

　　correctness

The program of the PLC must be correct, and it must be verified by the actual work to prove that it can work correctly. This is the most fundamental requirement for the PLC program, and if this is not done, nothing else is useful.

In order to make the program correct, it is necessary to use the instructions accurately and use the internal components correctly. Accurate instructions are linked to an accurate understanding of instructions, and it is important to understand the meaning and conditions of use of instructions. If necessary, you can make some small programs to test some unclear instructions.

For the same instruction, due to the different factory batches of PLC or the different series and models of PLC, some instruction details may be different, and the programming manual should be carefully consulted.

It is also important that the internal components are used correctly. Some PLCs have power-off protection, while others do not. It must be done that the power-down protection device must be used, and the power-down protection device cannot be used.

In short, it is necessary to use instructions accurately, use internal devices correctly, and make the program work correctly, which is the most fundamental requirement for PLC programs.

As a simple example, the rising and falling edges of Siemens need to use a variable with storage function as an intermediate variable, such as M point or DB point, and if you use the temp variable of FC, it will be problematic.

　　reliability

The program must not only be correct, but also reliable. Reliability reflects the stability of the PLC program, which is also the basic requirement for the PLC program.

Some PLC programs can work correctly under normal working conditions or legal operation, but after abnormal working conditions (such as temporary power failure, and power on soon) or illegal operation (such as some buttons are not pressed in order, or several buttons are pressed at the same time), the program can not work normally. This kind of program is not very reliable, or unstable, and it is a bad program.

A good PLC program can identify the occurrence of abnormal working conditions, and can connect it with normal conditions, which can make the program adapt to a variety of situations. A good PLC program rejects illegal operations and leaves no "traces". Only lawful operations are accepted.

Interlocking is a common means of rejecting illegal operation, relay circuits commonly use this method, and PLC can also inherit this method.

　　Easily modifiable

To make the program easy to modify, that is, to be easy to modify.

One of the characteristics of PLCs is that they are convenient and can be flexibly adapted to various situations. The way to do this is by modifying or redesigning the program.

When a redesign program is used to change the use requirements of a PLC process, not only the program is reprogrammed, but the I/O is also reassigned. In most cases, you don't need to reprogram the program, just make some changes. This requires the program to be easy to modify and easy to modify.

Easy to change is flexible, which requires only a few changes to achieve the purpose of changing parameters or easy to change actions.

　　Scalability

Many programs may have been programmed before entering the site, but when they arrive on site, additional programs may need to be added, and in order to avoid disrupting the structure of the entire system, a certain amount of space needs to be reserved in each functional area as a backup.

Leave enough margin on the hardware, and the software will consider manual, automatic, and semi-automatic when writing, and leave the position.

　　Complete alarm system

PLC system is often used in industrial environment, every accident will cause large or small losses, in order to achieve accident pretreatment or minimize the loss in the accident, we must pay attention to the alarm and protection of PLC, here it will be extracted as an important part of the system.

　　Program simulation

In order to ensure the commissioning progress of the site or to show the customer, it is often necessary to carry out a fully automatic simulation of their own procedures before entering the site. To do this, it is necessary to add a simulation part to the program, which is disconnected after normal field operation. In order for the program to be emulation, you need to do the following:

(1) Convert the actual I/O points of the PLC into intermediate variables or data block variables of the PLC;

(2) Write the simulation program of each equipment according to the process requirements.

HollySys PLC - What are the design requirements that need to be met for PLC programs?

HollySys PLC - What are the design requirements that need to be met for PLC programs?

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