Hollysys PLC - the six application functions of PLC

1. It is used for switching control

The ability of PLC to manipulate switching quantities is very strong. The number of points in and out of the control, less than a dozen points, dozens of points, more can be hundreds, thousands, and even tens of thousands of points, because it can be networked, the number of points is almost unlimited, no matter how many points can be controlled, the logical problems manipulated can be so varied: combination, timing, immediate, delayed, no need to count, demand counting, fixed order, random operations, etc., can be carried out.

The hardware structure of the PLC is variable, and the software program is programmable, which is very sensitive when used for control. If necessary, multiple sets or groups of programs can be written and called according to requirements. It is very suitable for the needs of multi-working conditions and multi-state changes in industrial sites.

There are many examples of switching quantity control with PLC, metallurgy, machinery, light industry, chemical industry, textile, etc., almost all industrial occupations need to use it. Today, the first goal of PLCs, which cannot be compared with other controllers, is that they can be used easily and reliably for the control of switching quantities.

2. It is used for analog control

Analog quantities, such as current, voltage, temperature, pressure, etc., change in size one after another. Industrial production, especially in successive production processes, often requires the manipulation of these physical quantities.

As an industrial control electronic equipment, if PLC cannot control these quantities, it is a big shortage, so PLC manufacturers have carried out a lot of development in this regard. Now, not only large and medium-sized machines can be operated in analog quantities, but also small machines. The PLC is used for analog control, and it is necessary to be equipped with A/D, D/A units that convert analog and digital to each other. It's also an I/O unit, but it's a special I/O unit.

The A/D unit converts the analog quantity of the external circuit into a digital quantity, and then feeds it into 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 the characteristics of I/O circuit anti-interference, surface and back circuit blocking, and communication information with input and output relays (or internal relays, which are also an area of PLC operating memory, which can be read and written).

The A in A/D here is mostly current, or voltage, and also has temperature. A in D/A is mostly voltage, or current. The scale of voltage and current change is mostly 0-5V, 0-10V, 4-20mA, and some can also deal with positive and negative values. The D here, the small computer is mostly 8-bit binary numbers, and the medium and large computers are mostly 12-bit binary numbers. A/D AND D/A are available in single and multi-way. There are many input and output relays that are accounted for by multiple channels. With A/D, D/A units, the rest of the processing is digital, which is not difficult for PLCs with information processing talents. Medium and large PLC processing can be stronger, not only can be added, subtracted, multiplied, divided, but also squared, interpolated, floating-point operations, and some have PID instructions, can be proportional, differential, integral operations on the deviation system, so as to produce the corresponding output, the computer can calculate almost all of it.

In this way, it is completely possible to complete analog control with a PLC.

PLC for analog control, as well as A/D, D/A combined units, and can be controlled by PID or fuzzy control algorithm, can get high control quality. The advantage of using PLC for analog control is that the switching quantity can also be controlled while the analog quantity is controlled. This advantage is not available in other controllers, or the completion of control is not as convenient as PLC. Of course, if it is a purely analog system, the use of PLC may not be as good as the use of regulators in terms of performance-to-price ratio.

3. It is used for sports control

The actual physical quantity, in addition to the switching quantity, the analog quantity, and the motion control. For example, the displacement of machine tool components is often expressed as a digital quantity. The effective way to control the movement is NC, which is the digital control skill. This is a computer-based control skill born in the United States in the 50s. Nowadays it is very popular and perfect. At present, the proportion of metal cutting machine tools in advanced countries has exceeded 40%-80%, and some are even higher. PLC is also based on computer skills and is becoming more and more perfect. The PLC can accept counting pulses with frequencies up to a few ks to tens of kHz, and can be accepted in a variety of ways, as well as in multiple ways. Some PLC also has pulse output function, pulse frequency can also reach tens of k, with these two functions, plus PLC has data processing and computing ability, if equipped with the corresponding sensor (such as rotary encoder) or pulse servo equipment, it can be completely according to the principle of NC to complete all kinds of control. The high- and mid-range PLCs are also equipped with NC units or motion units to complete point control. The motion unit can also complete curve interpolation and manipulate curve movements. 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 the programming language of NC skills have been released, making it easier to use the PLC for digital control.

4. For data collection

As PLC skills develop, their data storage areas are getting bigger and bigger. For example, the PLC of Devison company can reach 9999 words in its data storage area (DM area). With such a large data store, a large amount of data can be stored. Data collection can be recorded with a counter to record the number of collected pulses and transfer them to the DM area on time. Data collection can also be done in A/D units, where analog quantities are converted into digital quantities and then transferred to the DM area on time. The PLC can also be equipped with a small printer to type out the data in the DM area regularly.

The PLC can also communicate with the computer, and the computer will read out the data in the DM area, and the computer will process the data. At this point, the PLC becomes the data terminal of the computer.

Power users have used PLC to record the user's electricity consumption in real time, so as to complete the charging method of different electricity consumption times and different pricing, and encourage users to use more electricity when the electricity consumption is low, so as to achieve the intention of reasonable electricity consumption and electricity saving.

5. It is used for signal monitoring

There are many PLC self-test signals and many internal equipment, but most of the 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 control object. For a complex control system, especially the automatic control system, it is necessary to monitor and further self-diagnosis, which can reduce the problems of the system, find the faults, improve the cumulative average fault-free operation time, reduce the fault correction time, and improve the reliability of the system.

6. It is used for networking and communication

PLC networking and communication capabilities are very strong, and new networking structures are constantly being introduced.

The PLC can be connected with the personal computer for communication, and the computer can be used to participate in the programming and control of the PLC, making the PLC more convenient.

In order to give full play to the effect of the computer, one computer can be implemented to control and handle multiple PLCs, up to 32 sets. It is also possible to communicate with two or more computers with one PLC to exchange information to complete the monitoring of the PLC control system. PLC and PLC can also communicate, 1-to-1 PLC communication, several PLC communication, more than tens, hundreds.

PLC and intelligent instruments and intelligent actuators (such as frequency converters) can also communicate with each other on the Internet, exchange data, and operate with each other. It can be connected into a long-distance control system, and the system scale can be as large as 10 kilometers or more. It can be integrated into the network, not only PLC, but also high-end computers and various intelligent devices can also be connected to the network. Bus networks can be used, or ring networks can be used. The net can also be set up. Net-to-net can also be bridged. Networking can arrange thousands of PLCs, computers, and smart devices in one network. Nodes between networks can communicate and exchange information directly or indirectly.

Networking and communication are adapting to the needs of today's computer-integrated manufacturing system (CIMS) and intelligent factory development. It can make the industrial control from point (point) to line (Aero), so that the control of the equipment level, the control of the production line, and the control of the factory management layer are connected into a whole, so as to create higher efficiency. This infinitely bright future is becoming clearer and clearer for our generation.

The above points are applied in a qualitative manner. In terms of quantity, PLC has large and small, so its control scale can also be large and small, and the small one only controls a piece of equipment, or even a component and a station; Large ones can operate multiple machines, a production line, or even an entire plant. It can be said that the large and small occasions of industrial control are inseparable from PLC.

Hollysys PLC - the six application functions of PLC

Hollysys PLC - the six application functions of PLC

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