1. Introduction With the emergence of "fieldbus" and the development of its application technologies, information exchange in industrial measurement and control is mainly accomplished through fieldbus and networks such as the Internet. To achieve information exchange between multiple sensors and controllers, it is necessary to connect the various sensitive units and functional units within the sensors, as well as the controller, and output digital signals conforming to a certain protocol format through software. This enables data exchange and sharing between sensors, between sensors and controllers, and between sensors and the system. Its future development direction is networked intelligent measurement and control devices. A networked intelligent measurement and control device is an independent node in a test network, capable of independently completing test and control tasks, and is the foundation for realizing networked measurement and control. The research goal of networked intelligent measurement and control devices is to enable sensors and controllers to implement a certain network protocol at the field level, allowing field measurement and control data to be accessed and shared in a timely manner within the network's reach. This is also one of the cutting-edge technologies that are currently being fiercely contested both domestically and internationally. 2. Introduction to Networked Intelligent Measurement and Control Devices Intelligent measurement and control devices consist of intelligent sensors and intelligent controllers. "Intelligent sensors" can process the raw signals of sensors and exchange data with the outside world in a standard format. Intelligent sensors have the following functions: ① detect input signals, make judgments and decisions based on the input signal values; ② can set and implement different functions through software; ③ can exchange information with the outside world and have standard input and output interfaces; ④ have self-detection, self-correction and self-protection functions. Intelligent sensors need to achieve temperature compensation, correction and calibration, and use A/D converters to convert analog signals into digital signals. Therefore, it is not a simple hardware structure, but a process that uses hardware and software integration technology to process signals and finally output digital signals. Under the control of intelligent chips, "intelligent controllers" can calculate the corresponding control quantities based on the measured values ​​and pre-programmed control algorithms, output analog signals after D/A conversion, and drive the actuator to control the measurement points. The essence of networked intelligent measurement and control devices is to realize networking and informatization on the basis of intelligent measurement and control devices. Its core is to enable measurement and control devices to realize network communication protocols. The main characteristics of networked intelligent measurement and control devices are: (1) flexible addressing communication. Each intelligent measuring and control device has an independent address and can be interconnected with other intelligent measuring and control devices through a standard interface. Sensors can communicate with each other and with the controller to exchange and share data information. (2) Flexible setting of status parameters. As a node on the network, users can send different commands through the network as needed to reprogram the status parameters and control algorithms stored in the EEPROM inside the intelligent measuring and control device to ensure that the intelligent measuring and control device works in the best state. 3. Introduction to Lonworks Technology LON (Local Operating Networks) bus was launched by Echelon Corporation in the United States in 1991. It has now become one of the most widely used fieldbuses. The open communication protocol LonTalk used by LonWorks has established a common standard for exchanging control status information between devices. Under the coordination of the LonTalk protocol, previously isolated systems and products are integrated into a network control system. It adopts the form of network variables, so that the data transmission between nodes can be completed simply by connecting the network variables. Furthermore, due to the support of hardware chips, the requirements of real-time performance and intuitive and simple interface of the bus are realized. The main performance characteristics of the LON bus include: • A Neuron chip with three processing units—one for link layer control, one for network layer control, and one for user applications—along with 11 I/O ports, allowing network and control functions to be completed on a single Neuron chip; • Support for various communication media (twisted pair, power line, net power line, fiber optic, infrared, wireless, etc.) and their interconnection; • LonWorks network topology allows for selection of various network topologies, including bus, star, ring, tree, and even combinations of several; • LonTalk is the communication protocol for the LON bus, supporting seven layers of network protocols and providing a network operating system embedded in the Neuron chip; • LonWorks technology improves the CSMA (Carrier Sense Multiple Access) communication protocol, enabling the network to maintain high performance even under heavy loads. LonWorks technology can achieve communication rates up to 1.25 Mb/s, with a maximum communication distance of 3.5 km for fiber optic media. Twisted pair media has a direct communication distance of 2.7 km at a communication rate of 78 kb/s. • Provides developers with a complete development platform, including the field debugging tool LonBuilder, protocol analysis, and the network development language Neuron C; • Supports object-oriented programming (network variables NV), making network interoperability easy to achieve. 4. Design of Intelligent Temperature Controller Nodes This article uses a temperature controller composed of K-type thermocouples as an example to specifically introduce the design principles and methods of a networked intelligent temperature controller based on Lonworks technology. 4.1 ADR-120 Module The ADR120 is an intelligent control module using Lonworks technology, employing the MC143150 neuron chip, with external ROM, RAM, and FLASH chips as memory. The ADR-120 integrates 8-channel A/D converters and 4-channel D/A converters, and can be used as a standalone loop controller. Its external diagram is shown in Figure 1. The main technical features of the ADR-120 include: • 8-channel single-ended or 4-channel differential signal 12-bit A/D conversion circuit, with 0-5V voltage or 0-20mA current input; • 4-channel 12-bit D/A conversion circuit, configurable 0-5V, 0-10V, -5-+5V voltage or 4-20mA current output; • Uses Echelon's FTT-10 transceiver, supporting free topology; • Overvoltage protection, spike voltage protection, reverse power supply protection, EMI/RFI filtering; • EEPROM memory ground voltage detection protection; • Power and status indicator lights, SERVICE button for easy user installation and maintenance; • Pluggable terminals for convenient and quick installation and maintenance. [align=center]Figure 1 ADR-120 Outline Diagram[/align] 4.2 Hardware Design of the Temperature Controller Node The hardware schematic diagram of the K-type thermocouple intelligent temperature controller node is shown in Figure 2. It mainly consists of the ADR-120 intelligent control module, thermocouple, signal conditioning circuit, thyristor power regulator, and alarm circuit. Among them: [align=center]Figure 2 Hardware Schematic Diagram of the K-type Thermocouple Intelligent Temperature Controller Node[/align] The signal conditioning circuit uses the AD595 dedicated circuit for K-type thermocouple signal conditioning. In actual thermocouple temperature measurement, relatively tedious work such as cold junction compensation, zeroing, voltage amplification, and linearization must be performed, otherwise, it will cause a large error. The AD595 is a dedicated chip designed by AD to address the above problems. It has circuits for amplification, cold junction compensation, freezing point reference, and thermocouple fault alarm. The relationship between the measured temperature and the output voltage of the AD595 is 10mV/℃. The chip can work normally within the range of +5V to +30V. As the measured temperature range increases, the power supply voltage should be increased accordingly. Note that pin 1 of the AD595 must be connected to the positive terminal of the thermocouple and grounded. Potentiometer W in Figure 1 is used for fine-tuning the cold junction compensation voltage. Pin 7 of the AD595 is the negative power supply terminal. If temperatures below 0°C are not measured, negative voltage power supply is not required, and pin 7 can be grounded in this case. Pins 12 and 13 of the AD595 are the output terminals of the thermocouple fault alarm circuit. After pin 13 is grounded, pin 12, which has an open collector, is connected to a pull-up resistor. The output is high when the thermocouple is normal and low when there is a thermocouple failure. This logic level is introduced to terminal 11 of the ADR-120 for correct determination of the thermocouple voltage Vo. The intelligent control module processes the measured temperature value and publishes the data to the LON bus via the network interface for processing and monitoring by the host computer. Simultaneously, it derives the control quantity based on a pre-programmed control algorithm, converts it into a 0-5V voltage signal or a 4-20mA current signal after D/A conversion, and outputs it to the thyristor power regulator to drive the actuator to adjust the temperature at the measurement point. 4.3 Node Software Design The ADR-120 intelligent control module can be programmed using Neuron C language or the OnLon graphical programming language. The node software consists of two parts: system software and application software, both of which must be embedded in the ADR-120's internal EEPROM. The system software mainly implements the LON network protocol, while the application software mainly implements the user-required functions, such as A/D conversion and timing. In the LonWorks system, network variable data communication simplifies the programming of distributed applications. Programmers do not need to worry about the underlying details; they only need to reassign the network variable, and the value of the network variable will be automatically sent to the designated node. The node software structure flowchart is shown in Figure 3. The following is a partial Neuron C language source code, taking the data acquisition (i.e. A/D conversion) program as an example: IO_0 output bit ADC_CS=1; // Defined as a bit output object, used as a chip select signal IO_8 neurowire master select (IO_0) ADC_IO; // Defines a neuron I/O object, used as a bidirectional serial interface unsigned short C[8]=｛0,4,1,5,2,6,3,7｝; // Sequentially defines the channel selection address of the ADC metimer tmAD="500"; // Defines a millisecond timer, with a data acquisition interval of 500ms msg_tag mess_out; // Defines the message tag…… when(timer_expires(tmAD)) // Drives the event processing when the timer interval expires { int i,temp; unsigned int adc_info; unsigned long ADH; unsigned long ADL unsigned long ADV[8]; for (i=0;i<8;i++) // Collect data from 8 channels sequentially { adc_info = (C[i] + 8) * 16 + 14; // Set ADC conversion control word TB1 io_out(ADC_IO, &adc_info, 8); // Send TB1, ignoring the first byte RB1 adc_info = 0x00; // Set all-zero bytes io_out(ADC_IO, &adc_info, 8); // Send all-zero bytes ADH = adc_info; // Receive the second byte RB2 adc_info = 0x00; // Set all-zero bytes io_out(ADC_IO, &adc_info, 8); // Send all-zero bytes ADL = adc_info; // Receive the third byte RB3 ADV[i] = ADH * 32 + ADL / 8; // Convert the collected data tmAD = 500; // Set a 500ms interval } } [align=center] Figure 3 Flowchart of K-type thermocouple intelligent temperature controller node[/align] 4. Conclusion Fieldbus technology is maturing rapidly, and manufacturers are developing more and more fieldbus-based modules. Among these, many intelligent and low-cost field measurement and control products have emerged with the support of the LON bus. To support the LON bus, Echelon developed Lonworks technology, which provides a complete development platform for LON bus design and commercialization. The intelligent temperature controller designed in this paper can simultaneously connect to four external K-type thermocouple measurement channels, correspondingly driving four thyristor power regulators for temperature adjustment. Furthermore, by programming different programs according to the needs of practical applications, it can not only achieve multi-point temperature measurement and control, but also perform corresponding control based on the temperature difference and average temperature between different measurement points. Compared with traditional temperature controllers, it is more flexible and convenient to use. The author's innovation points: References [1] Ling Zhihao. From Neuron Chips to Control Networks [M]. Beijing University of Aeronautics and Astronautics Press. 2002 [2] Zhi Chaoyou, Gao Yakui. Design and Implementation of CAN Networked Intelligent Sensors [J]. Measurement and Control Technology, 2006, 25(3): 21-23 [3] Bao Jilong, Ye Ping. Networked Development of Industrial Monitoring Systems [J]. Microcomputer Information, 2006, 6-1: 66-68