What is the role of PLC control system in electrical automation
The ability of PLC to control the switch quantity is very strong. The number of input and output points that can be controlled can be as few as a dozen or tens of points, and as many as hundreds, thousands, or even tens of thousands of points. Because it can be connected to the Internet, the number of points is almost unlimited. No matter how many points you can control, Control logic problems can be varied: combined, sequential, immediate, delayed, non-counting, demand-counting, fixed sequence, random operation, etc., can be carried out.
The hardware structure of the PLC is variable, and the software program is editable, which is very flexible when used for manipulation. If necessary, you can write multiple or multiple sets of programs and call them according to your needs. It is very accustomed to the needs of multi-working conditions and multi-state changes in industrial sites.
There are many examples of switching control with PLC, metallurgy, machinery, light industry, chemical industry, textile, etc., almost all industrial occupations need to use it. Now, the first goal of PLC is that other manipulators cannot compare with it, that is, it can be conveniently and reliably used for the control of on-off values.
For analog control
Analog quantity, such as current, voltage, temperature, pressure, etc., its size is changed one after another. Industrial production, especially the continuous production process, often requires manipulation of these physical quantities.
As a kind of industrial control electronic equipment, if the PLC control system cannot control these quantities, it is a big shortcoming. For this reason, various PLC manufacturers have carried out a lot of development in this area. Now, not only large and medium-sized machines can carry out analog control, but also small machines can carry out such control. PLC carries on the analog quantity control, must be equipped with the A/D, D/A unit that the analog quantity and the digital quantity mutually transform each other. It is also an I/O unit, but a special I/O unit.
The A/D unit converts the analog quantity of the external circuit into a digital quantity, and then sends it to the PLC; the D/A unit converts the digital quantity of the PLC into an analog quantity, and then sends it to the external circuit. As a special I/O unit, it still has I/O circuit anti-interference, internal and external circuit blocking, exchange information with input and output relays (or internal relays, which are also an area of PLC job memory, readable and writable), etc. Features.
The A in A/D here is mostly current, or voltage, but also temperature. The A in D/A is mostly voltage or current. The voltage and current change scales are mostly 0～5V, 0～10V, 4～20mA, and some can handle positive and negative values. Here D, minicomputers are mostly 8-bit binary numbers, and medium and large-sized computers are mostly 12-bit binary numbers. A/D and D/A have single channel and multiple channels. There are many input and output relays occupied by multiple channels. With A/D and D/A units, the remaining processing is digital, which is not difficult for PLCs with information processing capabilities. The processing of medium and large PLCs can be more powerful. It can not only add, subtract, multiply, and divide numbers, but also square, interpolate, and perform floating-point operations. Some also have PID instructions, which can share the error control amount. , Differential and integral operations, so as to generate the corresponding output, it can be calculated by the calculation function.
In this way, it is completely possible to complete analog control with PLC.
The PLC performs analog control, and there are units that combine A/D and D/A, and can be controlled by PID or fuzzy control algorithms, which can achieve high control quality. The advantage of using PLC for analog control is that while the analog control is being carried out, the switch can also be manipulated. This advantage is not available in other manipulators, or the completion of the control is not as convenient as PLC. Of course, if it is purely an analog system, using PLC may not be as good as using a regulator in terms of performance and price ratio.
Used for motion control The
actual physical quantity, in addition to the switch quantity, analog quantity, and movement control. For example, the displacement of machine tool parts is often expressed in digital quantities. A useful method for motion control is NC, which is digital control skills. This is a computer-based control technique that was born in the United States in the 1950s. Nowadays, it is very popular and perfect.
At present, the rate of numerical control of advanced metal cutting machine tools has exceeded 40% to 80%, and some are even higher. PLC is also based on the skills of accounting machines, and is becoming more and more perfect. PLC can accept counting pulses, the frequency can be as high as several k to tens of k Hz, and this pulse can be received in a variety of ways, and it can also be received in multiple ways. Some PLCs also have pulse output function, and the pulse frequency can reach tens of k. With these two functions, plus PLC has data processing and calculation capabilities , if it is equipped with corresponding sensors (such as rotary encoders) or pulse servos The equipment can be completely controlled according to the principle of NC.
For high- and mid-range PLCs, NC units or motion units have also been developed to complete point control. The motion unit can also complete curve interpolation and control curve movement. Therefore, if the PLC is equipped with this kind of unit, it can completely use the NC method to carry out digital control. The newly developed motion unit and even the NC skill programming language has been issued, which provides convenience for better digital control with PLC.
For data collection
With the development of PLC skills, its data storage area is getting bigger and bigger. Such as the PLC of Deweisen company, its data storage area (DM area) can reach 9999 words. Such a huge data storage area can store a large amount of data. Data collection can use a counter to accumulate the number of pulses collected and transfer them to the DM area on time. A/D unit can also be used for data collection. When the analog quantity is converted into a digital quantity, it will be transferred to the DM area on time. The PLC can also be equipped with a small printer to print out the data in the DM area regularly.
The PLC can also communicate with the accounting machine. The accounting machine reads out the data in the DM area, and the accounting machine processes these data. At this time, PLC becomes the data terminal of the computer.
Electricity users have used PLC to record the user's electricity consumption in real time, to complete different charging methods at different times of electricity use, and to encourage users to use more electricity when the electricity is low, to achieve the purpose of reasonable electricity use and electricity saving.
There are many PLC self-checking signals used for signal monitoring , and there are many internal devices, and most users do not give full play to their effects. In fact, it can be used to monitor the operation of the PLC itself, or to monitor the controlled objects. For a complex control system, especially an automatic control system, monitoring and even further self-diagnosis is very necessary. It can reduce system faults, make it easier to find faults, increase the cumulative average fault-free operation time, and reduce fault repairs. Improve the reliability of the system at all times.
Used for networking, communication
PLC networking, strong communication ability, and new networking structures are constantly being introduced.
The PLC can be connected to the personal accounting machine for communication, and the accounting machine can be used to participate in the programming and control of the PLC, which makes the use of the PLC more convenient.
In order to give full play to the effect of the accounting machine, one accounting machine can be implemented to control and manage multiple PLCs, up to 32. One PLC can also communicate with two or more accounting machines to exchange information to complete multiple monitoring of the PLC control system. PLC and PLC can also communicate, one-to-one PLC communication, several PLC communication, which can be as many as tens or hundreds.
PLC and smart meters, smart execution equipment (such as frequency converter), can also communicate with each other, exchange data, and operate with each other. It can be connected to the long-distance control system, and the system scale can be as large as 10 kilometers or more. It can form a local network, not only PLC, but also advanced computers and various intelligent devices can be connected to the network. A bus network or a ring network can be used. The net can also be set with a net. Net and net can also be bridged. Networking can arrange thousands of PLCs, computers, and smart devices in one network. The nodes between the networks can communicate and exchange information directly or indirectly.
Networking and communication have become accustomed to the needs of today's computer integrated manufacturing system (CIMS) and the development of intelligent factories. It can make the industrial control from point (Point), to line (Line) to surface (Aero), so that equipment-level control, production line control, and factory management layer control are connected into a whole, so as to invent higher Benefits. This infinitely beautiful vision has become more and more clearly displayed in front of our generation. The
above applications are focused on quality. In terms of quantity, PLC has large and small. So its The scale of control can also be large or small. The small one can only control one device, or even one part, one site; the large one can control multiple devices, one production line, and even the entire factory. It can be said that industrial control is inseparable from all occasions. Open the PLC.
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