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PLC, man-machine interface and their application in nitrogen production equipment

with the continuous improvement of automation control level in China, PLC (programmable controller), text display and touch screen have been widely used in all walks of life. Now they are briefly introduced and their application in nitrogen production equipment of Swiss gas company is described

first, programmable controller

in the field of automation control, PLC (programmable logic controller) is an important control equipment. PLC has the characteristics of strong biggest obstacle of universal structure adjustment, convenient use, wide adaptability, high reliability, strong anti-interference ability, simple programming and so on. At present, more than 200 manufacturers in the world produce hundreds of varieties of PLC products, such as AB in the United States, Siemens in Germany, Mitsubishi, Omron, Schneider, Ge, etc. in terms of PLC application, China is very active and the application industry is also very wide. For example, steel, machinery, metallurgy, food, beverage, packaging, automobile, petrochemical and other industries

in terms of structure, PLC is divided into fixed type and combined type (modular type). The fixed PLC includes CPU board and I. according to our needs, we can select load deformation, load time, load displacement, displacement time, deformation time curves and experimental data for printing/O board, display panel, memory block, power supply, etc. these elements are combined into a non removable whole. Modular PLC includes CPU module, i/o module, memory, power module, backplane or rack. These modules can be combined and configured according to certain rules

cpu is the core of PLC and plays the role of nerve center. Each PLC has at least one CPU. It receives and stores user programs and data according to the functions given by the PLC system program, collects the status or data sent by the field input device by scanning, and stores them in the specified register. At the same time, it diagnoses the working status of the power supply and the internal circuit of PLC and the syntax errors in the programming process. After entering the operation, read the instructions one by one from the user program memory, and then generate the corresponding control signals according to the tasks specified in the instructions after analysis to command the relevant control circuits

cpu is mainly composed of arithmetic unit, controller, register and data, control and status bus to realize the connection between them. CPU unit also includes peripheral chip, bus interface and related circuits. Memory is mainly used to store programs and data, and it is an indispensable constituent unit of PLC. CPU speed and memory capacity are important parameters of PLC, which determine the working speed, IO quantity and software capacity of PLC, so it limits the control scale

other equipment of PLC system:

1. Programming equipment: the programmer is an indispensable device for PLC development and application, monitoring operation, inspection and maintenance. It is used for programming, making some settings for the system, and monitoring the working conditions of PLC and the system controlled by PLC, but it does not directly participate in the field control operation. Program PLC generally has hand-held programmer. At present, the computer (running programming software) is generally used as the programmer

2. Man machine interface: the simplest man-machine interface is indicator light, button, etc. at present, LCD (or touch screen) integrated operator terminals are more and more widely used, and computers (running configuration software) are very popular as man-machine interfaces

3. Input and output devices: used to permanently store user data, such as EPROM, EEPROM writer, bar code reader, potentiometer for input analog quantity, printer, etc

at present, the domestic PLC market is still dominated by foreign products. Ruiqi company mainly adopts German Siemens s series (the sales of S series exceeds 100000 units, and the global nodes of PROFIBUS exceed 10million), which has a high share in the PLC market

according to the requirements of the process, the characteristics of the system control function, the needs of users and the technical requirements of pressure swing adsorption and regeneration, Ruiqi company determines the time of each stage of molecular sieve adsorption, regeneration, pressure equalization and so on, and uses ladder diagram or command statement PLC control program to control the opening and closing state of the valve at each stage and the corresponding alarms (such as purity, carbon level alarm, etc.). If users need to display, modify parameters (such as purity, pressure, flow, temperature, dew point, etc.) and provide standard signals (such as current signal: MA) reserved for users as DCS system. If you need to display and modify parameters, you need to add analog expansion module and display part (text display TD200 or touch screen display)

carbon level alarm system: when the equipment is in long-term use, the molecular sieve in the adsorption tower gradually sinks. When it sinks to a certain extent, the PLC control system will send an intermittent audible and visual alarm, that is, remind the user to add molecular sieve as soon as possible, but the system can still continue to operate, and the alarm exists at the same time; At this time, if the user continues to use the equipment, and the molecular sieve continues to sink to another degree, then the nitrogen generator will stop after automatic pressure relief, and a continuous audible and visual alarm will be sent at the same time ◆ after the experiment is over, the tested product will automatically return to normal temperature to avoid frost and dew formation. At this time, the molecular sieve should be added immediately, otherwise the system will refuse to work

purity alarm system: when the purity of product gas fails to reach the preset purity value (the purity setting value is set through secondary instrument, TD200 or touch screen), the PLC control system will send intermittent audible and visual alarm, and empty the unqualified gas (there are automatic evacuation and manual evacuation, which can be selected according to user needs). If the continuous evacuation time of unqualified gas exceeds 1 hour (the evacuation time can be set through TD200 or touch screen), it indicates that there is a fault in the equipment and qualified gas cannot be produced. The control system will shut down after automatic pressure relief and send intermittent audible and visual alarm

as the signals of pressure, flow, temperature and dew point (current or voltage signals) are analog signals, they must be a/d converted through EM231 (analog input module), and then displayed on TD200 or touch screen through PLC programming. According to these data, it is compared with the preset parameters through PLC programming. If it exceeds or falls below the preset value, an alarm signal will be sent. The details of alarm information can be found on TD200 or touch screen. In the purification system, automatic hydrogenation control and closed-loop control can be carried out through PLC programming; PID control of temperature through PLC programming. PID control has high precision, small fluctuation and fast response. In PID regulation, the proportional link (P) is used to determine the basic regulation response, the differential link (d) is used to accelerate the response to rapid changes, and the integral link (I) is used to eliminate residual errors. When PID is adjusted, the proportional link is always adjusted first, then the integral link is generally adjusted, and finally the differential link is adjusted

II. Text display

at present, the text displays used in the domestic market include Siemens, hitech, eview, Delta and other brands. Among them, Siemens TD200 text display is the most common, which is the best solution to all SIMATIC s series operator interface problems

td200 connection is very simple, just connect the connecting cable provided by it to the CPU 22x series PPI interface. No separate power supply is required (if the distance between TD200 and S series exceeds 2.5m, additional power supply is required). Backlit LCD display (easy to see even in backlight)

td200 has the following purposes:

1. Display information --- display up to 80 messages, and each message can contain up to 4 variables

2. It plays the role of setting and modifying parameters in the control system, such as changing the set values of actions, alarms, etc

3. Eight user-defined function keys can be provided

4. Provide password protection function

TD200 text display is generally equipped in the equipment of pressure swing adsorption nitrogen production, oxygen production and nitrogen purification, which can facilitate the user to query the equipment operating parameters and status, and can appropriately modify the system parameters under the condition of authorization, which greatly meets the user's requirements for simple and effective product operation

typical use cases are as follows:

1. Display the gas temperature at the outlet of the heat exchanger of the nitrogen generation equipment, and automatically jump out of the text alarm information when the temperature is over

2. Nitrogen low pressure fault alarm processing

when the nitrogen pressure is lower than the set value, the text display has a text prompt. Once the nitrogen pressure meets the conditions, the system will return to normal and the fault alarm will be reset automatically

3. Over temperature fault alarm handling

when the system is caused by abnormal heating due to hardware damage, such as the damage of SSR (solid state relay), CPU relay contacts, thermocouples and other devices, these faults must be paid special attention by the user, and then the RFA1 coating is coated on it. Now this fault should be checked and repaired immediately. There is an indicator light flashing alarm and a text prompt for the fault

4. Cumulative operation time of display equipment

III. touch screen (human machine interface)

in the field of industrial control, with the progress of production mode and technology, the tools of human-computer communication have developed from mechanical operating levers, button switches and indicator lights to friendly touch screens and information panels. As human-machine interface (HMI) products are more and more widely used, HMI products and suppliers are also more and more. From the aspects of technology, products and market, HMI, which integrates the functions of operation monitoring, data access and parameter modification, has gradually become a relatively independent industry category. At present, there are many brands of touch screens in the world, such as Siemens, Omron, Schneider, Mitsubishi, a&b, Taiwan eview, hitech, Japan Hakko, Fuji, etc. among them, Pro-face is one of the few professional HMI suppliers in the world. According to relevant reports, pro face has performed well in China's HMI market and has become one of the leading brands

pro face is one of the main members of the world-famous Japanese Digital Electronics Co., Ltd. the company's main products include: programmable touch screen (GP series, st), flat panel industrial computer (PL series, PS Series), graphic logic controller (LT series, GLC Series), it product information terminal and other human-machine interfaces

Japanese Digital Electronics Co., Ltd., founded in 1972, is a global leader in HMI industry. For more than 20 years, the brand of Pro face has become a synonym for high-quality man-machine interface because of its exquisite technology, excellent quality and strict management. Pro face, with its outstanding appearance, tight structural design, efficient computing ability, excellent control system, excellent quality and perfect service, makes many high-end mechanical equipment manufacturers and large project engineering units love Pro face products. In particular, their programmable touch screen, which can connect more than 200 brands of PLC in the world, provides us with a larger operating space

the above figure is the schematic diagram of the pro face (gp37-w2) touch screen used by the Ruiqi nitrogen production equipment. From this picture, we can know the working state of the equipment (the equipment is stopped) Cumulative operation time (245 hours, 12 minutes and 12 seconds), workflow and the opening and closing status of valves. You can also use the above buttons to start and stop, set parameters, and view system fault information. For example, it can also display the gas inlet and outlet pressure, outlet flow, purity, temperature, dew point and their recording curves. It can also be used as a real-time monitoring equipment in the user's central control room

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