PLC’s high reliability, high anti-interference, strong self-correction and self-diagnosis ability promote the wide application of the market, the innovative development of PLC technology, and the variety of PLC products are also more and more, so the reasonable selection of PLC, for It is of great significance to improve the technical and economic indicators of the PLC control system. The selection of PLC is mainly considered comprehensively from the aspects of PLC model, capacity, I/O module, power supply module, special function module, communication networking capability and so on.
Selection of PLC model
After confirming the use of PLC in the system, it is necessary to carry out the selection of PLC. When selecting models, the following aspects should be considered comprehensively:
1.110 Point problem
The number of I/O points is one of the most important factors in determining PLC selection. Generally speaking:
When the I/O points of the control object are within 60 points and the ratio of the I/O points is 3/2, it is more economical to choose an integral (small) PLC;
When the I/O points of the control object are between 100 and 200 points, it is more reasonable to choose a small modular type;
When the I/O point of the control object is about 300 points, select the PLC;
When the I/O point of the control object is above the YO point, a large PLC must be selected.
Selection of switch I/O modules
After confirming the PLC model. It is necessary to select various modules. The selection of switch modules mainly involves the following issues:
1. External wiring problem
I/O modules are generally divided into independent, grouped and sink. Usually, the independent point average price is higher. If the isolation between the switching input signals in the actual system is not required, the latter two can be considered.
2. point problem
As mentioned earlier, the number of points is an important factor affecting the selection of PLC. Similarly, when selecting the I/O module, the appropriate I/O module must be selected according to the number of specific points. Usually I/O modules have 4, 8, 16, 24, 32, 64 points. Generally speaking, the higher the number of points, the lower the average price.
3. Digital input module
Common switch input module types include active input, passive input, photoelectric proximity sensor and other inputs. When selecting the digital input module, it must be comprehensively considered according to the requirements in the actual system operation. Of course, specific to the active input module, it is also divided into AC input, DC input and TTL level input.
AC voltage class 24 V, 120 V, 220 V.
DC voltage class 24 V, 48 V, 10 to 60 V.
AC/DC voltage class 24 V.
4. Switch output module
Common switch output module types include relay output, thyristor output and transistor output. In the selection process of the switch output module, the corresponding selection must be made according to the actual system operation requirements and the required output voltage level.
At present, conventional application isolators include MOR217, MOR356, MOR816, MOR354, MQY214, MQY212, MQY212G, MOR814A, MOR214.......