Reliability problem
According to the relevant data, the general small and medium-sized foreign PLC, such as Hitachi, IPM, the average time for 嫜 is as high as 100,000 h. Even the average trouble-free time of large PLCS is between 40,000 and 50,000 hours. Therefore, manufacturers believe that reliability is no longer a problem. As far as reliability is concerned, the relay contactor is beyond the pale. Therefore, reliability is no longer a technical indicator for Hitachi, IPM and other product data.
2. Economic comprehensive analysis of PLC
The economic analysis of PLC should be considered from the following aspects:
(1) From the comprehensive consideration of various factors affecting the cost from the current production equipment control device, there are three types :① relay control. ② Semiconductor device control. ③PLC control.
Price is only one factor in choosing a PLC brand, and reliability is another factor that needs to be considered when choosing.
(2) Considering the length of the design and production cycle, whether it is the transformation of old equipment or the design of new production machinery and equipment, there is no doubt that the shorter the production and design cycle, the better, and even hope that the design, installation, commissioning and production, especially the new generation of products, production process transformation, without changing the existing production equipment and its external wiring, you can immediately organize production. This not only saves labor, but also brings new products to market as quickly as possible. This will undoubtedly increase the vitality of the enterprise and improve the economic efficiency. If these requirements can be realized, relays or semiconductors can not meet, and PLC can be fully realized. This is because if the PLC does not need to change the external equipment wiring, as long as the software is used as an article. That is to say, as long as the ladder diagram is changed, the new program can be re-entered or the original program can be modified according to the new process requirements. This is both economical and simple, can achieve the purpose of twice the result with half the effort
As we all know, 75% of China's production machinery and equipment are controlled by relays, in addition to poor reliability, the design procedure is also very complicated. From the establishment of the scheme to the design of technical conditions and the design of construction, the workload of the drawing is the largest, which is bound to cause a long design cycle. The use of PLC control can greatly shorten the design cycle, and even some documents do not have to be drawn. The design can be input using the programmer's on-screen display, or the program can be modified so that the ladder diagram can accurately reflect the production requirements. Programming can also be based on the new product production of the new process requirements, re-write the program and store it in the EEPROM module, need to process which product of the program, the operation can be called at any time, which is convenient, simple and confidential. The development of this software is of practical significance to optimize the production process, improve the quantity and quality of products, and increase labor productivity. This alone is also welcomed by producers and designers.
