Talking about the most popular network testing tec

2022-09-19
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Introduction

with the continuous improvement of the requirements of automatic control in the production process, the shortcomings of the traditional test system are becoming more and more prominent

① the matching between instruments and the measurement accuracy between instruments limit the improvement of the accuracy of the whole test system

② the traditional test system is composed of multiple measuring instruments, and the transmission speed of the signal is limited, which brings difficulties to the real-time analysis of the measured signal. In many cases, if the time is delayed, the measured signal is very different from the real-time signal, and the automatic control is difficult to achieve

③ the test system composed of multiple instruments is relatively scattered, large in size and difficult to carry, which limits the field measurement. In this regard, the transformation of the traditional test system is imperative

looking at the development of testing technology in recent years, modern testing technology, in addition to continuously improving sensitivity, accuracy and reliability, is mainly developing in the direction of miniaturization, non-contact, multi-function (multi parameter measurement), intelligence and networking. In recent years, the rapid development of computer technology, microelectronics technology, communication technology and networking technology has provided technical support for the development of networking testing technology based on PC and workstation. The application of networking technology in test system has become a major trend in the development of modern test technology

2 characteristics of networking testing technology

the biggest characteristic of networking is that it can realize resource sharing, make full use of existing resources, so as to realize the collaborative testing and diagnosis of multiple systems and experts. It solves the limitation of the existing bus on the number of instruments, makes a machine used by more users, realizes the sharing of measurement information, and realizes the high automation and intelligence of the whole testing process, At the same time, the hardware setting is reduced, and the cost of the test system is effectively reduced. In addition, the network can be free from geographical restrictions, which determines that the network test system can realize remote measurement and control, so that testers can get the required information anytime and anywhere without the limitation of time and space. At the same time, the network test system can also realize the remote test and diagnosis of test equipment, and improve the test efficiency. It is these advantages of the networking test system that make the networking test technology attract much attention

3 technical support of networking testing and networking instruments

the actual testing work is extremely complex. The whole testing process involves experimental design, model theory, sensor design, signal processing, error processing, control engineering, system identification and parameter evaluation. Networking testing requires not only these technologies, but also complete computer technology, microelectronics technology, communication technology and networking technology. The completion of these technologies provides strong material support for the production and application of networking testing technology, and the production of intelligent detection instruments accelerates the networking process of testing system. Various networking instruments that can be directly connected to the network have been applied in the field of practical measurement and control

in order to meet the needs, the networking instruments appearing in the market at present have standard specifications, such as the tcp/ip instrument protocol and interface transformation specification issued by VXI bus. This specification provides a method and standard for developing a general interface to realize the networking automatic test system. The standard specifies the transformation from this protocol to a specific interface. The formulation of the specification makes it possible to directly control the instrument through the network. As a part of the largest crack of the test system, the networking of the sensor is very important. Based on the intelligent sensor, the networking sensor embeds the tcp/ip protocol into the ROM of the field intelligent sensor, and uses local and wide areas to make the network sensor at the measurement and control point send the measurement and control parameter signals into the network after necessary processing. In addition, the specification of control area network (can) fieldbus has also been formulated as the international standard ISO 11898, which has been widely used in discrete control systems. At present, there are also networking oscilloscopes and networking logic analyzers with good user interface that can realize real-time remote measurement and control

the emergence of these networking instruments has accelerated the development of networking testing technology. A new generation of networking testing instruments with stronger versatility and more complete functions will continue to emerge in the market

4 Fieldbus Technology in networking testing technology

fieldbus is not only a new automation system, but also a low-level control network with low bandwidth. It can be connected with Internet and Intranet, and is located in the low-level of production control and network structure, so it is called low-level. As a network system, it has an open and unified communication protocol, and shoulders the unified task of measurement and control in the front line of production and operation

fieldbus technology has the following technical characteristics:

① openness of the system: open system refers to the open communication protocol, and the equipment of different manufacturers can be interconnected and realize information exchange. Fieldbus developers are committed to building a unified open system of the factory bottom network. Openness here refers to the consistency and openness of relevant standards, emphasizing the publicity and compliance with standards. An open system that can be connected to any other equipment or system that complies with the same standard. A fieldbus network system with bus function must be open. Open system gives the right of system integration to users. Users can form a system of arbitrary size with products from different suppliers according to their own needs and objects

② interoperability and interoperability: Interoperability here refers to the realization of information transmission and communication between interconnected devices and systems, and the implementation of point-to-point, point-to-multipoint digital communication; Interoperability means that equipment with similar performance from different manufacturers can be interchanged to achieve interoperability

③ intellectualization and functional autonomy of field equipment: it disperses the functions of sensing measurement, compensation calculation, engineering quantity processing and control into the field equipment. Only the field equipment can complete the basic functions of automatic control, and can diagnose the running state of the equipment at any time

④ highly decentralized system structure: because the field equipment makes the speed regulation ratio reach 500000 times (0.001mm/min - 500 mm/min), it can complete the basic function of automatic control, so that the field bus has formed a new architecture of fully distributed control system, which fundamentally changes the existing DCS centralized and decentralized distributed control system, simplifies the system structure, and improves the reliability

⑤ adaptability to the field environment: working in the front end of the field equipment, as the field bus at the bottom of the factory network, it is specially designed for working in the field environment. It can support double glue line, coaxial cable, optical cable, RF, infrared, power line, etc., has strong anti-interference ability, can adopt two-wire system to realize power transmission and communication, and can meet the requirements of intrinsically safe explosion-proof, etc

because of this, especially the simplification of the fieldbus system structure, the entire networking test system shows great advantages from design, installation, operation to normal production and operation and its maintenance. Its advantages are mainly reflected in the following aspects:

① saving hardware quantity and Investment: because the intelligent devices scattered in the front end of the equipment in the fieldbus system can directly perform a variety of sensing, control Alarm and calculation functions, so the number of transmitters can be reduced. There is no need for separate controllers, calculation units, etc., nor for functional units such as signal processing, conversion, anti-corrosion technology and their complex wiring of DCS system. Industrial control PC can also be used as the operation station, which saves a lot of hardware investment. Due to the reduction of control equipment, the floor area of the control room can also be reduced

② save installation costs: the wiring of the fieldbus system is very simple. Because a pair of double glue wires or a cable can usually be connected to multiple devices, the consumption of cables, terminals, slots and bridges is greatly reduced, and the workload of connection design and joint calibration is also greatly reduced. When it is necessary to add field control equipment, there is no need to add new cables, which can be connected to the original cables nearby, which not only saves investment, but also reduces the workload of design and installation. According to the budget data of typical test projects, the installation cost can be saved by more than 60%

③ save maintenance costs: because the field control equipment has the ability of self diagnosis and simple fault handling, and sends the relevant diagnosis and maintenance information to the control room through digital communication, users can query the operation, diagnosis and maintenance information of all equipment, so as to analyze the cause of the fault early and eliminate it quickly. The maintenance downtime is shortened, and the maintenance workload is reduced due to the simplified system structure and simple connection

④ users have a high degree of system integration initiative: users can freely choose the equipment provided by different manufacturers to integrate the system, so as to avoid the selection range of equipment being "blocked" due to the selection of a certain brand of products, and will not be helpless for incompatible protocols and interfaces in system integration, so that the initiative in the process of system integration is completely in the hands of users

⑤ improve the accuracy and reliability of the system: due to the intellectualization and digitization of the fieldbus equipment, compared with the analog signal, it fundamentally improves the accuracy of measurement and control and reduces the transmission error. At the same time, due to the simplified structure of the system, the equipment and wiring are reduced, the internal function of the field instrument is strengthened, the round-trip transmission of the signal is reduced, and the working reliability of the system is improved. In addition, because of its standardized equipment and modular functions, it also has the advantages of simple design and easy reconfiguration

fieldbus technology meets the requirements of networking test system, and has been widely used in it

the overall design scheme of the networking test system

the actual test process requires us to consider the test scheme, stimulate the required information to the greatest extent, and show it in the form of obvious information, use the most agile and reasonable method to obtain the most useful and highly expressive relevant information, and design and implement it with effective experimental methods. The composition of the general test system is shown in Figure 1

Figure 1 structure block diagram of general test system

networking test system is faced with a test system with scattered space, complex test tasks and large amount of information exchange. The whole test system should have the functions of comprehensive information collection, information processing, storage, transmission and control, and data analysis at the same time. To build a powerful and complete networking test system, we must consider and focus on solving the following problems:

① in order to make full use of existing resources, the measurement device of the test system can be redefined

② data acquisition is an important link in the networking test process, so the commonly used data acquisition hardware must be compatible

③ data analysis and signal processing are the last link in the test process, and also a key step in the whole test process. Therefore, the signal processing process of the test analysis system must be redefined

④ for the whole test system, its basic functional unit must be intelligent, with local microprocessor and memory, and with networking interface

the openness and interoperability of a fully functional networking test system are also very important. The system should also follow the principles of scalability, security and server distribution. Accordingly, the basic block diagram of the networking test system is shown in Figure 2

Figure 2 networking test system structure

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