Six applications of PLC
At first, PLC was mainly used for logic control of switching value. With the progress of PLC technology, its application field is expanding. Today, PLC is not only used for on-off control, but also for analog and digital control. It can collect and store data, and also monitor the control system; It can also be networked and communicated to achieve control and management across a wide range of regions. PLC has increasingly become an important role in the family of industrial control devices. 1. For on-off control The ability of PLC to control switching value is very strong. The number of input and output points controlled can be as few as ten or dozens of points, and as many as hundreds, thousands, or even tens of thousands. Because it can be connected to the Internet, the number of points is almost unlimited. No matter how many points can be controlled, the logic problems controlled can be varied: combined, sequential, real-time, delayed, non-counting, counting, fixed sequence, random work, and so on. The hardware structure of PLC is variable, and the software program is programmable. It is very flexible when used for control. If necessary, multiple sets or groups of programs can be written and called as needed. It is very suitable for the needs of multiple working conditions and multiple state changes in industrial sites. There are many examples of using PLC to control the switching value. Metallurgy, machinery, light industry, chemical industry, textile, etc., almost all industrial industries need it. At present, the first goal of PLC is that it can be easily and reliably used for the control of switching value, which is incomparable with other controllers. 2. For analog quantity control Analog quantities, such as current, voltage, temperature, pressure, etc., vary continuously. Industrial production, especially continuous production process, often needs to control these physical quantities. As an industrial control electronic device, if PLC can not control these quantities, it is a big deficiency. Therefore, PLC manufacturers have carried out a lot of development in this area. At present, not only large and medium-sized computers can carry out analog control, but also small computers can carry out such control. PLC shall be equipped with A/D and D/A units for conversion between analog quantity and digital quantity for analog quantity control. It is also an I/O unit, but a special I/O unit. A/D unit converts analog quantity of external circuit into digital quantity, and then sends it to PLC; The D/A unit converts the digital quantity of PLC into analog quantity and then sends it to the external circuit. As a special I/O unit, it still has the characteristics of anti-interference of I/O circuit, isolation of internal and external circuits, exchange of information with input/output relay (or internal relay, which is also an area of PLC working memory, readable and written), etc. A in A/D here is mostly current, or voltage, and also temperature. ...