Pneumatic valves are widely used in various industrial productions, such as electrical, mechanical, hydropower, petrochemical, etc. The traditional control methods of pneumatic valves have many disadvantages, such as high control costs and easy to cause safety problems. Therefore, the author proposes to control pneumatic valves. The use of fieldbus technology can improve overall control stability and safety, and reduce control costs.
1. Traditional pneumatic valve control methods and control systems
The traditional switch control of pneumatic valve mainly adopts local control and remote control. When the automation requirements are not high, the local control method is mainly used. When performing local control, the technician operates the relevant control buttons to realize the on and off of the solenoid valve coil, and the solenoid valve also realizes the reversal, so that the cylinder starts to move. Finally realize the opening or closing of the valve. The technician judges the switch state of the valve mainly by the indicator light around the switch button. With the continuous improvement of the level of automation, the requirements for automation of pneumatic valve control are getting higher and higher, and the application of remote control methods is gradually being widely used. In the early remote control, the technicians are mainly in the remote control room, or use some remote control equipment such as programmable controllers to control. Under the media of the transmission cable, the valve switch control signal sent by the remote control room passes through The transmission cable can be threaded to the position of the remote pneumatic valve to realize the on-off control of the valve. The technician judges that the on-off state of the valve is consistent with the local operation, which is determined by the indicator light around the switch button.
The connection methods of traditional valve control systems are almost always one-to-one, point-to-point physical connections, requiring a large number of transmission cables and connection equipment to be laid, and if the number of valves is very large, a very large number of interface devices are required, resulting in the cost of the entire valve system The cost has risen sharply. In addition, the transmission of control signals are standard analog signals. When remote control of long-distance transmission occurs, once a signal interference source occurs, it will cause the valve to be miscontrolled or out of control, which greatly reduces the stability and reliability of the entire control system. In addition, the control accuracy of the traditional control system is not high, the realization of information sharing is difficult, and the ultra-long distance information transmission cannot be realized. Although the later DCS control system uses a layered structure to solve some of the shortcomings of one-to-one control and realizes the mixing of digital and analog signals, it still cannot completely solve the problems caused by the analog signal itself, and it will still lead to the existence of valve control. Hidden dangers, and each manufacturer’s products have their own characteristics and cannot be universal.
2 Control system characteristics of fieldbus technology
Fieldbus technology is a new type of automation control technology that has developed rapidly in the past ten years. It integrates computer, communication technology and control technology, which directly promotes the emergence of FCS (Field Control System) control systems. Fieldbus technology breaks the traditional one-to-one, point-to-point physical connection, and is a digital revolution in industrial field-level device communication. The application of fieldbus technology makes the connection between the valve control system and the valve equipment control simpler and more convenient. Compared with the analog signal control system of traditional local control and remote control, the valve control system based on fieldbus technology has very significant advantages.
2.1 Simple structure and low development cost
Fieldbus control system can realize one-point-to-multipoint control means, which can ensure that a bunch of lines are connected to multiple devices, and digital signals are transmitted in both directions. This connection method breaks through the traditional point-to-point connection method and the problems existing in analog signal output, thereby saving a lot of wiring and space, reducing wiring points, reducing anti-interference factors, and making installation and maintenance very convenient. Intercommunication between multiple devices can be realized by using only two cables and four wires.
2.2 has very good stability
The fieldbus technology is used to control the pneumatic valve, and the output signals are all digital signals. It can effectively reduce the signal loss in the conversion process, greatly enhance the anti-interference ability, and due to the characteristics of the digital signal itself, the quality of the signal under the bed is also very stable. At the same time, it also reduces the use of many auxiliary equipment, which can effectively reduce the probability of manual control of pneumatic valves.
2.3 Simple operation and convenient maintenance
The use of fieldbus technology realizes the functions of two-way communication and two-way signal transmission. The technicians can not only perform corresponding serial number calibration, parameter setting and function configuration on the valve device of the pneumatic valve control field in the control room, but also can observe in real time The working status of the on-site valve facilitates equipment maintenance. At the same time, remote programming control and diagnosis can be carried out, and the valve status can be detected in real time. Once any problem occurs, self-diagnosis can be carried out, and then remote control consultation can be realized through remote programming to solve the fault.
3 Pneumatic valve control example analysis based on fieldbus technology
Fieldbus technology is generally used for group-scale valve control, and each group of valves is called a valve island. The following introduces an example of using fieldbus technology to control pneumatic valves when a research institute is carrying out material transportation. The system diagram is shown in Figure 1.
Figure 1 Control system diagram using fieldbus technology
As shown in Figure 1, the main structure of this control system includes PC master control machine, PLC and field bus technology. PC master control machine uses industrial control computer, PLC uses Siemens S7-300 series, which is one of PC and PLC. The communication connection between the two is completed through Ethernet, and the communication medium is Category 5 UTP. Fieldbus technology uses PROFIBUS-DP protocol to connect PLC and local control equipment, and the peak output rate can reach 12Mbps. The on-site valve control relies on an intelligent valve island based on FESTO CPV10, which is attached with a field bus interface, and is equipped with on-site operation buttons, indicator lights and valve position feedback information modules.
Combining the effect of the system to control the pneumatic valve and the actual situation of the entire project operation, it can be found that the application of fieldbus technology has very significant advantages, greatly reducing the number of transmission cables, and other erection materials such as steel pipes, beams, and profiles The amount of use has also decreased. The reduction in the use of engineering materials and equipment has shortened the construction period for the implementation of the system, further reducing the overall manufacturing cost. At the same time, the debugging process is very simple. As long as the fieldbus communication is turned on, the valve pneumatic debugging can be realized. The control system has stable signal transmission during control operation, strong anti-interference ability, and no miscontrol or out-of-control conditions of the pneumatic valve. Further strengthening the control instructions and functions can facilitate the debugging and maintenance of the process system.
Fieldbus technology is applied to the control of pneumatic valves. It is not suitable for all occasions. Generally, fieldbus is used for group-controlled valves, which can effectively reduce the number of wiring and ensure the reliability of system operation. However, for some occasions with few valves and scattered Not applicable, because the cost of fieldbus interface is much higher than that of ordinary cables. Therefore, when using the fieldbus technology to control the valve, it is necessary to distinguish the occasion and choose the most economical control method.