A brief analysis of the development of networked intelligent sensing technology

　　1. Introduction

　　Sensor technology, communication technology and computer technology constitute the three major foundations of modern information. They respectively complete the extraction, transmission and processing of measured information, and are an important symbol of the development of contemporary science and technology. With the development of science and technology, digitization, intelligence and networking have become the development trend of the times: the combination of computer technology and communication technology has produced computer network technology; the combination of computer technology and sensor technology has produced intelligent sensor technology; the integration of the three (the combination of computer network technology and intelligent sensor technology ) has produced networked intelligent sensor technology. Networked intelligent sensor technology has become a hot topic of concern. This article only briefly discusses the development status and development trend of networked intelligent sensor technology.

　　2. Networked intelligent sensing technology

　　The networked intelligent sensor is a new type of intelligent sensor with an embedded microprocessor as its core, integrating a sensing unit, a signal processing unit and a network interface unit, so that the sensor has self-inspection, self-calibration, self-diagnosis and network communication functions, thus realizing truly unified and coordinated information collection, processing and transmission.

　　Compared with other types of sensors, networked intelligent sensors have the following characteristics:

　　⑴ With intelligent sensing function. With the introduction of embedded technology, integrated circuit technology and microcontrollers, sensors have become a combination of hardware and software. On the one hand, the power consumption of sensors is reduced, the size is reduced, and the anti-interference and reliability are improved. On the other hand, sensors have self-identification and self-correction functions. At the same time, software technology is used to realize nonlinear compensation, zero drift and temperature compensation of sensors.

　　⑵ It has network communication function. The application of network interface technology enables the sensor to be easily connected to the industrial control network, which greatly facilitates the expansion and maintenance of the system.

　　3. Intelligent sensing technology based on fieldbus

　　Fieldbus technology is an emerging control technology that integrates computer technology, communication technology, integrated circuit technology and intelligent sensor technology. According to the standard definition of the International Electrotechnical Commission IEC61158: "The digital, serial, multi-point communication data bus between the field devices installed in the manufacturing and process areas and the automatic control devices in the control room is called fieldbus." It is generally believed that "fieldbus is a fully digital, two-way, multi-station communication system and an industrial bus for computer systems used in industrial control."

　　Fieldbus technology was born out of the need for intelligent instrumentation and full digital control systems. Fieldbus is a fully digital, open and bidirectional communication network that connects intelligent field equipment and the control room. With the emergence of various intelligent sensors, transmitters and actuators, a new industrial control system, the Fieldbus Control System (FCS), which is digitalized to the field, controls functions to the field, and manages equipment to the field, will inevitably replace the traditional distributed control system (DCS).　　3.1 The essential meaning of fieldbus

　　Fieldbus is not only a communication protocol, nor is it just replacing analog signal (4-20mA DC) transmission instruments with digital signal transmission instruments. The key is to replace the traditional distributed control system DCS with a new generation of fieldbus control system FCS to achieve the integration of field communication network and control system. Its essential meaning is reflected in the following six aspects:

　　⑴ Fully digital communication

　　Unlike the semi-digital DCS, the fieldbus system is a pure digital system. The fieldbus is a field digital communication network used to interconnect field devices or field instruments in process automation and manufacturing automation. It uses digital signals instead of analog signals, has strong transmission anti-interference and high measurement accuracy, and greatly improves the performance of the system.

　　⑵ Field equipment interconnection

　　Field devices or field instruments refer to sensors, transmitters, actuators, etc. These devices are interconnected through a pair of transmission lines. The transmission lines can use twisted pair cables, coaxial cables, and optical fibers.

　　(3) Interoperability

　　Interoperability means that field devices from different manufacturers can not only communicate with each other, but also be configured in a unified manner to form the required control loops and jointly implement control strategies.

　　⑷ Distributed functional blocks

　　FCS discards the input/output units and control stations of DCS, and distributes the functional blocks of the DCS control station to the field instruments in a decentralized manner, thus achieving complete decentralized control.

　　⑸ Communication line power supply

　　The commonly used transmission medium of fieldbus is twisted pair cable, and the communication line power supply method allows field instruments to directly absorb energy from the communication line.

　　⑹ Open interconnection network

　　The fieldbus is an open interconnected network that can be interconnected with similar networks or different networks, and can also realize network database sharing.

　　3.2 Deficiencies of Fieldbus

　　Since the emergence of fieldbus technology in the 1980s, it has always attracted great attention and is hailed as a revolution in the field of automatic control. Since the 1990s, fieldbus control systems have become a hot topic of research, and various fieldbus products have emerged. With the actual application of fieldbus control systems in production sites, intelligent sensing technology based on fieldbus is also facing many problems.

　　On the one hand, the formulation of international fieldbus standards has led to the coexistence of multiple standards due to technical and commercial interests. IEC 61158 stipulates 8 fieldbus standards such as FF and Profibus, plus the 3 fieldbus international standards (ICE 62026) that have been passed by IEC TC17, resulting in a total of 12 fieldbus international standards. Since the communication protocols adopted by each standard are completely different, there are compatibility and interchangeability issues of smart sensors, which affects the application of bus-type smart sensors. On the other hand, there are bottleneck problems in the fieldbus. It is manifested in: after the fieldbus is cut off, the system may have unpredictable consequences; the system group parameters are too complex, and the quality of their settings has a great impact on the system performance; production operation requires a large amount of human-machine data exchange, and the communication capacity of the fieldbus system is limited, which easily causes information flow blockage.

　　4. Intelligent sensing technology based on IEEE P1451 interface standard family

　　The IEEE P1451 family of standards is proposed based on the fact that the current fieldbus standards are different, and each fieldbus standard has its own prescribed communication protocol, which is incompatible with each other, thus bringing adverse effects on the application, expansion and maintenance of intelligent sensor technology. The purpose is to greatly simplify various network control systems composed of sensors/actuators by defining a set of universal communication interfaces, solve the compatibility problems between different networks, and ultimately achieve interchangeability and interoperability between products of various manufacturers.

　　4.1 Introduction to the IEEE P1451 Smart Transmitter Interface Standard Family

　　The IEEE P1451 proposed standard family defines the hardware and software interface of the transmitter (sensor or actuator). All standards in this group support the concept of electronic data sheet (TEDS), which provides self-identification and plug-and-play functions for the transmitter. The following is a brief introduction to the IEEE P1451 family of standards.

　　⑴ IEEE P1451.0

　　IEEE P1451.0 proposed standard, namely Common Functions, Communication Protocols, and Transducer Electronic Data Sheet (TEDS) Formats. The IEEE P1451 proposed standard family consists of several standards. Although they have common features, there is no common setting of functions, communication protocols and electronic data sheet formats, which affects the interoperability between these standards and hinders the widespread use of these standards among the user community. The IEEE P1451.0 proposed standard is proposed to solve this problem. By defining a physical layer that is independent of the NCAP to transmitter module interface and includes basic command settings and communication protocols, it provides a common and simple standard for different physical interfaces to enhance the interoperability between these standards.

　　⑵ IEEE Std 1451.1

　　IEEE Std 1451.1, Network Capable Application Processor (NCAP) Information Model for smart transducer, was approved by IEEE in July 1999. This standard uses an object-oriented approach to accurately define a general smart sensor information model, covering various applications of networked transducers, and uses a standard application programming interface (API) to achieve the mapping from the model to the network protocol , and uses a series of functional modules such as I/O driver hardware abstraction to support a variety of transducers.

　　⑶ IEEE Std 1451.2

　　IEEE Std 1451.2, Transducer to Microprocessor Communication Protocols and Transducer Electronic Data Sheet (TEDS) Formats, was approved by IEEE in September 1997. This standard specifically defines the electronic data sheet format TEDS and a 10-wire digital interface TII (Transducer Independent Interface) as well as the communication protocol between the transmitter and the microprocessor (as shown in Figure 4), which enables the intelligent sensor/actuator module to have plug-and-play capabilities, and the measurement and control network can also monitor and configure the sensor/actuator channel by accessing TEDS. (⑷) IEEE Std 1451.3

　　IEEE Std 1451.3, Digital Communication and Transducer Electronic Data Sheet (TEDS) Formats for Distributed Multidrop System, was approved by IEEE in October 2003. This standard uses spread spectrum technique to achieve simultaneous data acquisition, communication and power supply for electronic devices connected to the transmitter bus on a single signal cable.

　　⑸ IEEE P1451.4

　　IEEE P1451.4 proposed standard, namely Mixed-mode Communication Protocols and Transducer Electronic Data Sheet (TEDS) Formats. IEEE 1451.1, IEEE 1451.2 and IEEE 1451.3 standards are mainly aimed at digitally readable sensors and actuators with network processing capabilities. The IEEE P1451.4 standard is mainly committed to proposing a mixed-mode smart transmitter communication protocol based on the existing analog transmitter connection method: the mixed-mode interface supports the reading and writing of TEDS by the digital interface on the one hand, and the measurement of field instruments by the analog interface on the other hand; at the same time, the compact TEDS is used for simple and low-cost connection of analog sensors.

　　⑹ IEEE P1451.5

　　IEEE P1451.5 proposed standard, namely Wireless Communication and Transducer Electronic Data Sheet (  TEDS) Formats. This proposed standard was newly launched in June 2001. It aims to build an open standard wireless sensor interface under the existing IEEE P1451 framework to meet the needs of different application fields such as industrial automation.

　　4.2 IEEE P1451 Smart Transmitter Interface Standard Family Architecture

　　The IEEE P1451 standard can be divided into two parts: software-oriented interface and hardware-oriented interface. The software interface part uses an object-oriented model to describe the behavior of networked smart transmitters and defines a set of software interface specifications that enable smart transmitters to smoothly access different measurement and control networks; at the same time, by defining a common function, communication protocol and electronic data sheet format, it aims to enhance the interoperability between the IEEE P1451 family of standards. The software interface part is mainly composed of IEEE 1451.1 and IEEE P1451.0. The hardware interface part is composed of IEEE 1451.2, IEEE 1451.3, IEEE P1451.4 and IEEE P1451.5, which are mainly proposed for the specific application of smart sensors. Figure 7 describes the overall framework of the IEEE P1451 standard family and the relationship between its members.

　　It should be noted that although 1451.X work together, they can also work independently of each other. 1451.1 can be used without any 1451.X hardware interface, and 1451.X hardware interface can also be used without 1451.X software interface, but its software must provide corresponding functions such as network transmission of sensor data or information.

　　5. Conclusion

　　The research on networked intelligent sensor technology is in the ascendant, and the establishment and development of intelligent sensor interfaces suitable for industrial control systems will become the main task of the International Organization for Standardization in the future. There is no doubt that with the establishment and improvement of the IEEE P1451 intelligent transmitter interface standard family system, the networked intelligent sensor technology defined by the IEEE P1451 standard family represents the development direction of future measurement and control systems and will surely be more and more widely used.