To improve the reliability of PLC control system design method - Database & Sql Blog Articles

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1, attach importance to installation

Improving the reliability of the plc control system is a long-term, long-lasting task. First of all, construction and installation are very important links, and must be strictly checked, which can reduce the failure rate of production. Secondly, it is imperative to ensure the quality of maintenance, especially the technical transformation line changes and system transformation. Otherwise, after several years of system transformation, a large number of lines are replaced, the line number is lost and the program is changed, and the record backup is not recorded. As a result, the maintenance workload is increased and the reliability is not guaranteed. This item is extremely easy to neglect and must be highly valued.

2, aging screening method

Usually we use the "aging screening" method, which is to end the "early", extend the "accidental period", and replace the "loss period" in time to improve the reliability of the PLC system. This method is mainly used for non-repairable components. The failure rate of the PLC control system is time dependent. We divide the failure rate y(t) of the equipment components into three periods for analysis, as shown in Figure 2. This curve is often referred to as the failure rate curve, also known as the bathtub curve.

(1) Early failure is high (O~t0 period). Mainly due to unreasonable reasons such as internal design errors, component quality, installation and process defects, but the failure rate decreases rapidly with time. The main task of this period was to find out the unreliable factors as early as possible to stabilize the system as soon as possible.

(2) Accidental period of failure (d0~t1 period) is relatively stable, and can also be called random failure period. Faults occur randomly during this period, and the system's failure rate is the lowest and stable, which can be regarded as a constant. This period is the best period of the system. During the operation, the maintenance period should be extended and extended, and regular maintenance and maintenance work should be done.

(3) The loss rate (after t1) increases the failure rate because some parts of the system have been aging and wear out, the mechanical and electrical wear and the aging of the insulation. Most of the components will fail during this period. If you know the time when the loss starts, replace the components beforehand to extend the effective life of the system. Delay the arrival of the wear and tear period.

3. Safety design method of PLC control system

Although the operation of PLC is safe and reliable, as a system, stability and reliability are still issues that cannot be ignored. System safety design should make full use of the characteristics of PLC to make the operation of PLC truly safe and reliable.

(1) Hardware protection. Mainly include: interlock protection, limit protection and emergency stop protection.

(2) Software protection. Mainly include: interlock protection, limit protection, time-limited protection and self-test protection. The PLC is controlled by a stored program, and is installed and protected by a stored program, or it can perform only correct operations and reject the wrong command. Software protection mainly uses self-test information to detect hidden dangers in time and clear faults. It can also solve the faults according to the characteristics of the project and self-programming diagnostic procedures to ensure reliable, stable and safe operation of the PLC.

4. Management of PLC control system reliability

1. Human management

With the development of science and technology, the scientific content of automation continues to increase. This will place higher demands on the quality of the staff. The staff should not only be familiar with the equipment, maintenance, planning and design, but also know the computer and have a certain level of technology. Therefore, we must start with the training of personnel, training methods and training content. Continuously improve the professional quality and ideological quality of the staff to be competent for their jobs.

2. Maintenance management

The main reason for the reliability of the PLC control system is to do the maintenance work in the later stage. The main parts of the maintenance equipment: power supply, external environment, installation status, power supply (Ps), central processing unit (CPU), signal template (SM) ) and peripheral components such as life component input and output intermediate relay.