How to choose the right PLC, remember these points is enough

PLC control system, Programmable Logic Controller, programmable logic controller, a digital operation operation electronic device designed for industrial production. It uses a kind of programmable memory for its internal storage program, performing logic operations, and sequence. User-oriented instructions such as control, timing, counting, and arithmetic operations, and control various types of mechanical or production processes through digital or analog input/output. It is the core part of industrial control.

PLC control system features

(1) From the development of switching quantity control to sequential control and arithmetic processing, it is from bottom to top;

(2) Logic control, timing control, counting control, step (sequence) control, continuous PID control, data control - PLC has multi-functions such as data processing capability, communication and networking;

(3) One PC can be used as the master station, and multiple PLCs of the same type are slave stations;

(4) It is also possible to use one PLC as the main station and multiple PLCs of the same type as slave stations to form a PLC network. This is more convenient than using a PC as the main station: when there is user programming, you do not need to know the communication protocol, just write it according to the format of the manual;

(5) The PLC network can be used as an independent DCS/TDCS or as a subsystem of DCS/TDCS;

(6) It is mainly used for sequential control in industrial processes, and the new PLC also has closed-loop control functions.

8 steps of PLC design selection

The level of system design will directly affect the performance of the control system and the reliability of the equipment. Among them, the selection of PLC is very important. How to choose the right PLC according to different control requirements, and design a control system with stable operation, reliable action, safe and practical, convenient debugging and easy maintenance? In the design of the PLC system, the system solution should be determined first, and the next step is the design and selection of the PLC. Select PLC, mainly to determine the specific model of the PLC manufacturer and PLC. For system solutions, there are distributed systems and remote I/O systems, and network communication requirements need to be considered. So how do you choose a PLC? The author believes that there should be the following aspects.

1, the choice of PLC manufacturers

To determine the manufacturer of the PLC, the main considerations should be given to the requirements of the equipment user, the familiarity of the designer to the PLC of different manufacturers, the design habits, the consistency of the supporting products, and the technical services. From the reliability of the PLC itself, in principle, as long as it is a product of a large foreign company, there should be no problem of poor reliability.

The author personally believes that, in general, for the control of independent equipment or a simple control system, supporting Japanese PLC products, the relative cost performance has certain advantages. For the system with large-scale network communication function requirements, open and distributed control system, remote I / O system, PLC produced in Europe and America has more advantages in network communication functions.

In addition, for some special industries (such as: metallurgy, tobacco, etc.), we should choose a proven and reliable PLC system in the relevant industry.

2. Estimation of input and output (I/0) points

The number of input/output points of the PLC is one of the basic parameters of the PLC. The determination of the number of I/O points should be based on the sum of all input/output points required to control the device. In general, the PLC's I/O points should have an appropriate margin. Usually, based on the number of input and output points of the statistics, an additional 10% to 20% of the expandable margin is added, and the data is estimated as the number of input and output points. In actual ordering, the number of input and output points must be adjusted according to the product characteristics of the manufacturer's PLC.

3. Estimation of PLC memory capacity

The memory capacity refers to the size of the hardware storage unit that the programmable controller itself can provide. The memory capacity of various PLCs can be found from the basic parameter table of the PLC. For example, the storage capacity of the user program of Siemens S7-314 PLC is The user program storage capacity of the 64KB, S7-315-2DP PLC is 128KB. The program capacity is the size of the memory unit used by the user program in the memory, so the memory capacity should be greater than the program capacity. In the design phase, since the user application has not yet been compiled, the program capacity needs to be estimated.

How to estimate the program capacity? Many literatures have given different formulas, which are generally 10 to 15 times the number of digital I/O points, plus 100 times the number of analog I/O points. This is the total number of words in memory (16 bits is One word), and then consider the margin by 25% of this number.

4, the choice of PLC communication function

Now PLC's communication function is more and more powerful. Many PLCs support multiple communication protocols (some need to be equipped with corresponding communication modules). When selecting, you should select the appropriate communication method according to actual needs.

The main forms of the communication network of the PLC system are as follows:

(1) PC is the main station, and multiple PLCs of the same type are slave stations, which constitute a simple PLC network;

(2) One PLC is the main station, and other PLCs of the same type are slave stations, which constitute the master-slave PLC network;

(3) The PLC network is connected to the subnet of the DCS as a DCS through a specific network interface;

(4) Dedicated PLC network (special PLC communication network of each manufacturer).

In order to alleviate the CPU communication task, according to the actual needs of the network composition, communication processors with different communication functions (such as point-to-point, fieldbus, industrial Ethernet, etc.) should be selected.

5, the choice of PLC models

PLC type: PLC is divided into two types according to the structure: integral type and module type; the integral type PLC has fewer I/0 points and is relatively fixed, so the user has less room for selection and is usually used in small control systems. Representatives of this type of PLC are: Siemens S7-200 series, Mitsubishi FX series, Omron's CPM1A series.

The modular PLC provides a variety of I/O modules that can be plugged into the PLC base, making it easy for the user to select and configure the I/O points of the control system as needed. Therefore, the configuration of the modular PLC is relatively flexible, and is generally used for large and medium-sized control systems. For example, Siemens' S7-300 series and S7-400 series, Mitsubishi's Q series, and Omron's CVM1 series.

6, the choice of I / O module

(1) Selection of digital input and output modules:

The choice of digital input and output modules should consider the application requirements. For example, for the input module, the application requirements such as the level of the input signal and the transmission distance should be considered. There are also many types of output modules, such as relay contact output type, AC120V/23V bidirectional thyristor output type, DC24V transistor drive type, DC48V transistor drive type, and so on.

Generally, the relay output-output type module has the advantages of low price and wide application voltage range, but has a short service life and a long response time, and needs to increase the surge absorbing circuit when used for an inductive load; the response time of the bidirectional thyristor output type module is fast. It is suitable for frequent switching, inductive low power factor load applications, but the price is more expensive and the overload capability is poor.

In addition, the input and output modules can be divided into 8 points, 16 points, 32 points, etc. according to the number of input and output points. When selecting, they should be properly equipped according to actual needs.

(2) Selection of analog input and output modules:

The analog input module can be divided into current input type, voltage input type, and thermocouple input type according to the analog input signal type. The current input type has a normal signal level of 4 to 20 mA or 0 to 20 mA; the voltage type input module usually has a signal level of 0 to 10 V, -5 V to +5 V, and the like. Some analog input modules are compatible with voltage or current input signals.

The analog output module is also divided into a voltage output module and a current output module. The current output signal usually has 0 to 20 mA and 4 to 20 mA. The voltage type output signal usually has 0 to 10V, -10V to +10V, and the like.

The analog input and output modules can be divided into 2 channels, 4 channels, and 8 channels according to the number of input and output channels.

7, function module

The function module includes a communication module, a positioning module, a pulse output module, a high-speed counting module, a PID control module, and a temperature control module. When selecting a PLC, the possibility of matching the function module should be taken. The selection of the function module involves both hardware and software.

In terms of hardware, first of all, it should be considered that the function module can be easily connected to the PLC. The PLC should have related connections, installation locations and interfaces, and connection cables. In the software, the PLC should have a corresponding control function, which can be easily programmed for the function module. For example, Mitsubishi's FX series PLC can easily control the corresponding function modules through the "FROM" and "TO" commands.

8. General principles

After the PLC model and specifications are generally determined, the basic specifications and parameters of each component of the PLC can be determined one by one according to the control requirements, and the model numbers of each component module are selected. The following guidelines should be followed when selecting a module model.

(1) Convenience: Generally speaking, as a PLC, there are many kinds of modules that can meet the control requirements. The selection should be based on the principle of simplifying circuit design, convenient use, and minimizing external control devices.

For example, for an input module, the input form that can be directly connected to an external detection component should be preferred to avoid the use of an interface circuit. For the output module, the output module that can directly drive the load should be preferred to minimize the components such as the intermediate relay.

(2) Generality: When selecting the type, it is necessary to consider the unity and generality of the PLC components, and avoid too many types of modules. This not only facilitates procurement, reduces spare parts, but also increases the interchangeability of various components of the system, providing convenience for design, commissioning and maintenance.

(3) Compatibility: When selecting the components of the PLC system, compatibility should be fully considered. In order to avoid problems with poor compatibility, the manufacturers of the main components that make up the PLC system should not be too much. If possible, try to choose the same manufacturer's product.

The most influential top ten domestic PLC brand

What is better done in China now is Taiwan's Delta, Yonghong, Fengqi and the mainland's Heli, Xinjie, Xiamen Haiwei, etc. The Taiwan brand has a history of more than ten years, so it has accumulated a certain number of customers. At present, the manufacturing industry is facing difficulties in reform and transformation. It is a good time for the development of domestic PLC. The following is a list of some domestically produced PLC brands.

1, Yonghong PLC

Yonghong PLC is the PLC product of Yonghong Motor Co., Ltd., and Yonghong Motor Co., Ltd. was founded in Taiwan in 1992 by a group of engineers who have been engaged in PLC design and development for many years. Yonghong focuses on the high-performance small and medium-sized PLC market, and its own brand “FATEK” has enjoyed a high reputation in the industry.

In recent years, in the face of competition from many large manufacturers and changes in client applications, only providing PLC products can no longer meet market demand. On the other hand, Yonghong has occupied a considerable economic scale in the market of micro PLCs. It is no easy task to grow up. Therefore, in addition to PLC products, providing more complete industrial automation solutions is a problem that Yonghong needs to face today.

At present, the specific development direction is still to develop a higher-performance PLC to stabilize the core competitiveness. At the same time, it is more active in motion controllers, human-machine interfaces, industrial power supplies, servo controllers, inverters and servo motors.

2, Delta PLC

Mr. Zheng Chonghua, the chairman of the godfather of Taiwan's electronics industry, founded Delta Electronics in 1972 and started his entrepreneurial journey with 15 people in order to open up the Japanese to build their own national brands. . When the small Delta Electronics was hard-pressed, it stood out from the fierce competition and emerged in the industry.

Delta Group not only "winned" Japanese manufacturers, but also defeated European and American manufacturers, becoming the world's number one power supply manufacturer, the world's largest component manufacturer, and the world's largest supplier of peripheral products for the computer industry, with 30 per year. The speed from % to 40% continues to grow.

Delta PLC Delta Group is an electronic device specially designed for industrial automation and digital computing operation. Delta PLC uses a program-programmable memory to store instructions for performing operations such as logic operations, sequential operations, timing, counting, and arithmetic operations, and can control various inputs through digital or analog inputs and outputs. Type of mechanical or production process.

Delta PLC is known for its high speed, robustness and high reliability, and is widely used in various industrial automation machines. In addition to features such as fast execution of program calculations, rich instruction set, multi-expansion function card and high cost performance, Delta PLC supports a variety of communication protocols, making the industrial automation system integrated into one.

Delta's full range of hardware devices can form a control system that can meet various requirements. Users do not have to design and manufacture hardware devices themselves. After the hardware is determined, the user does not have to change the hard device of the PLC in the case of production process change or production equipment update, and only needs to adapt the program to meet the requirements. Therefore, in addition to being applied to stand-alone control, PLC is also widely used in factory automation.

3, Hollysys PLC

Founded in 1993, Beijing Hollysys Group is a high-tech enterprise group engaged in independent design, manufacturing and application automation control system platforms and industry solutions. The Group has national level qualification for system integration and is a national enterprise technology center. The company has more than 3,000 employees.

In the field of factory automation and machine automation, Hollysys has launched its own LM small PLC, LK large PLC, MC series motion controller since 2003. The products have passed CE certification and UL certification. Among them, LK large PLC is the only large PLC with independent intellectual property rights in China, and has obtained the “National Key New Product” certificate jointly issued by the four ministries. Hollysys PLC and motion control products have been widely used in subway, mine, oil field, water treatment, machine equipment control industries.

In the domestic PLC market, Heli Time is still in a disadvantaged position regardless of the product's wide range of products, brand influence and industry application experience. To this end, from the very beginning, Lishi has formulated a strategy of “urban encircling the city”. The company's business blind spot for large companies can quickly increase the business volume of Hollysys PLC and also test the performance of PLC.

Hollysys not only provides PLC products for customers, but also provides integrated solutions for motion controllers, man-machine interfaces, inverters, motors and drives, and machine control. It also provides customers with pre-sales solution configuration and system optimization. , the sale of technical advice, programming guidance, system complete sets, after-sales product repair, spare parts to provide a full range of services, and truly to "customize" for customers.

4, security control PLC

Established in 1998, Ankong Technology is located in Shangdi Information Industry Base, Haidian Park, Zhongguancun Science and Technology Park, Beijing. It is a high-tech enterprise specializing in R&D, production, sales, after-sales and system integration of industrial grade RTU products. Based on RTU technology, we have developed a variety of specialized classic products in the oil and gas and environmental online monitoring industry. The products are widely used in oil and gas mining, processing, pipeline transportation, storage and distribution, as well as environmental online monitoring, city gas, water supply and heating, etc. In the field of pipe network monitoring, it has been exported to the United States, Canada, Mexico, Turkey, Kazakhstan, Turkmenistan, Iraq, Iran, South Korea, Thailand, Malaysia and other countries.

After the success of the RTU dedicated to remote measurement and control, in 2004, the control of the RockE series PLC came out. From RTU to PLC, as from oil and gas to many industries and fields, for security control, this is a development idea, from point to line, and then from line to face. Ankong has the development foundation and project experience of RTU. The development and production of PLC seems to be no longer a problem.

Ankong Technology has introduced a number of communication technologies into the RockE40 series PLC products, which has greatly improved its communication capability compared with general PLC. RockE40 series PLC products can provide a variety of communication interfaces, such as: network, RS232, RS485, dialing, radio, etc., coupled with the corresponding communication equipment, can achieve the various communication methods mentioned above. Since the communication expansion module is provided, there is no limit to the number of communication interfaces in theory.

In addition to the communication interface, RockE40 series PLC products also support a variety of standard communication protocols, such as: ModbusRTU, ModbusASCII, ModbusTCP, DNP3 and so on. Because RockE40 supports C and C++ programming, users can also easily implement custom communication protocols, or provide customized communication protocols by our company.

At present, the safety control PLC products have been widely used in urban water supply and water treatment automation control, thermal network pipeline automation control, general industrial data acquisition and process control, hot water boiler, industrial steam boiler monitoring, open channel, sluice and water level detection and control , atmospheric environment and water quality monitoring, power system parameters telemetry remote control and many other fields.

5, Taian PLC

Taian Technology (Wuxi) Co., Ltd. is a wholly foreign-owned enterprise established in mainland China on July 1, 2000 by a well-known multinational company in Taiwan, Antai International Investment (Singapore), a subsidiary of Dongyuan Group. The company is located in the National High-tech Industrial Development Zone of Wuxi City, Jiangsu Province, with a total investment of 24 million US dollars and a registered capital of 16.5 million US dollars. The company has international standard factory buildings, first-class product quality and employees with professional knowledge. The target annual output value is expected to reach 2.5 billion yuan in the future.

At present, the company has a high-quality production, sales and R&D team of nearly 1,000 people. It produces, sells and develops a series of industrial control and low-voltage electrical and distribution products, subordinate components and electronics. The Component Division has a well-established production management level, high-level engineering automation technology, high-performance manufacturing equipment and a high-quality sales force. It produces and sells low-voltage electrical appliances and produces power distribution products. Low-voltage electrical products have complete categories, reliable quality and reasonable price, and are well received by users. Power distribution products have excellent performance and reasonable price, which are widely recognized by the market. In order to meet the needs of the market, new products are being continuously developed to ensure strong competitiveness.

AP is a new generation of high-speed, high-quality programmable controller (PLC) newly developed by Taian Technology. The small universal PLC is suitable for small-scale equipment control. It can connect the high-speed counter and pulse output positioning control function directly to the computer through the USB communication port. In addition, Taian also has TP03 series PLC, which is suitable for conveying equipment, electronic equipment and other socks machines, flat knitting machines, weft feeders, water jet loom, winder, FAN and other occasions.

Taian Technology has the most advanced complete sets of equipment and flow lines, and realizes decentralized control and centralized management centered on the latest control system. Its technical personnel have high-level electronic technology and rich experience, and are based on the latest electronic technology. A more flexible flexible production system unit can be provided according to the requirements of various production sites. The industrial control products produced by it have won the industry recognition, and both production and sales are booming.

6, Feng Wei PLC

Fengqi Technology Enterprise Co., Ltd., established in 1995 in Danshui Town, Taipei County, is one of the largest PLC manufacturers in Taiwan and one of the most widely used PLCs in Taiwan. Since its inception, Fengqi R&D team has been dedicated to the development and manufacture of programmable controller (PLC) products. Since its establishment, although it has faced the threat of competition from imported PLC products and the development of PLCs with strong financial resources in the country, but under the strong enemy of all parties, Fengqi is still supported by many users, performance, sales year Years of continuous growth.

In addition, Feng Wei has a technical support department to provide product technology consulting services. In 2005, the establishment of Fengzhang International Trading (Shanghai) Co., Ltd. provided Fengshun PLC product sales and technical support services in the mainland. At the same time, the expansion of overseas markets will also be a key focus of the work. The Fengqi team upholds the love and dedication of PLC, in addition to enhancing the functions on the original system.

Fengqi products are close to the market, innovative and practical, and have won praises from customers for their complete functions and performance stability. The use of Fengqi PLC is similar to that of Mitsubishi Plc, and it is very convenient to learn. It has various special functions that are practically needed, and has the function or price advantage compared to other Taiwan PLCs. Each Fengqi PLC is equipped with the industry's first multi-function display screen, which can tell the operator the operation status of the machine in a timely manner. No additional cost is required. Fengqi offers innovative connector type PLCs, which can reduce wiring man-hours, reduce wiring errors, and make machine maintenance simple and convenient compared to terminal block type PLCs. The effect is especially noticeable when used in large quantities. VH, VBO, VB2 three series of PLC.

7, Nanda proud of PLC

Nanda Aotuo Technology Jiangsu Co., Ltd. was established in October 2008 and entered the National University Science Park of Nanjing University-Drum Tower University. It is committed to independent research and development of cutting-edge industrial control products with reliable performance, excellent quality and advanced technology. Products with completely independent intellectual property rights cover programmable controllers, man-machine interfaces, inverters, servo systems, configuration software, etc., providing customers with comprehensive solutions for automation products. At the same time, the company actively cooperates with research institutes and industry users to jointly develop enterprise management information systems based on industry automation solutions.

8, Xinjie PLC

As one of the earliest participants in the industrial control market in China, Xinjie Electric has long been focused on improving the automation level of the mechanical equipment manufacturing industry. Wuxi Xinjie PLC products now have XC series and XD series, mainly used in textile industry, machine tool industry, packaging machinery industry, food machinery industry, HVAC industry, rubber industry, mining industry, plastic machinery industry, printing industry, automobile. Manufacturing industry, etc. Each series of products covers standard, economical, enhanced, basic, motion control, high performance and other products for users to choose.

As a representative enterprise of domestic PLC, Xinjie has the advantage of PLC. It can apply C language to trapezoidal en route and integrate motion control. It has more secure program security function and rich device capacity and type, and it can be processed quickly. Speed ​​and I/O switching are more user friendly.

9, Huangshi Kewei PLC

Huangshi Kewei Automatic Control Co., Ltd. is a provincial high-tech enterprise and software enterprise that develops, produces and sells embedded PLC, servo drive and automation system.

The embedded PLC embeds the PLC ladder programming language into a specific control device, so that the device has the basic functions of the PLC. On the software platform, the developer can easily and quickly design the general PLC, the guest PLC and each Kind of control panel. Embedded PLC is based on the original automation instrument technology, fieldbus technology and more than 10 years of automation engineering project experience. Under the cooperation of Huazhong University of Science and Technology and Wuhan University of Technology, after more than three years of hard work, the first successful . Due to the huge social and economic value of embedded PLC, it was listed as a national research plan in 2005.

The embedded PLC software for the national project results, the customized PLC for textile machinery, was funded by the National Innovation Fund in 2007; the elevator controller based on embedded PLC software was developed, and the software special fund of Hubei Province was obtained in 2008. stand by. So far, Kewei's embedded PLC products - general PLC, custom PLC, control board, have been in textile machinery, elevators, industrial furnaces, plastic machinery, printing and packaging machinery, food machinery, CNC machine tools, constant pressure water supply Successful application in industries such as equipment and environmental protection equipment.

10, Zhenghang PLC

Shanghai Zhenghang Electronic Technology Co., Ltd. is a high-tech enterprise dedicated to product development, production, sales and service in the field of industrial control. The company is a leading technology and service provider in industrial automation and process automation, and one of the fastest growing control system manufacturers.

Zhenghang PLC is a high-quality small PLC produced by Shanghai Zhenghang Electronic Technology Co., Ltd. It belongs to the high-quality PLC in domestic PLC. The product performance is safe, stable, reliable and cost-effective. In order to meet the higher requirements of customers for product performance, Zhenghang has launched CHION-Chin series PLC. CHION Chien series PLC is a high-quality PLC produced by Zhenghang Company with German technology and domestically produced. It is fully compatible with Siemens S7-200 series PLC products. It can be programmed and debugged with Siemens S7-200 software STEP7-MicroWin, and its CPU and modules can be fully compatible and used interchangeably.

At present, the company's main products include PLC, HMI, servo, special control system, remote I / O and field bus products, its high-performance automation products and control solutions are widely used in plastic machinery, electronic equipment, textile machinery, new energy, refrigeration Heating, medical equipment, packaging equipment, CNC equipment and many other industries. After years of development, Zhenghang PLC has developed into a well-known brand of domestic PLC.

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