Abstract: Temperature control systems are widely used in industry, and the control software varies depending on the specific functional requirements. This paper presents the overall design scheme and development process of the field node of a temperature control system. Then, it introduces the temperature control node from both hardware and software perspectives. The hardware aspect mainly focuses on the design of the LonWorks control module and peripheral circuits, while the software aspect mainly focuses on the implementation of the data acquisition module and data control module of the field node. Keywords: Bus; Control System; Temperature; LonWorks [b][align=center]Design of Field Node in a Temperature Circular Control System based on Bus Technology[/align][/b] Abstract: The application of temperature control systems is popular in industrial fields, and it varies depending on the functional requirements. This paper provides the design method and development flow of temperature control systems, and then introduces the temperature system from both hardware and software perspectives. The hardware aspects include the LonWorks control module and the periphery circuit design, while the software aspects mainly focus on the data sample module and the data management module. Keywords: Bus; Control System; Temperature; LonWorks 1 Introduction As an interconnection and communication network between intelligent field devices in fields such as process automation, manufacturing automation, building automation, and transportation, fieldbus features openness, digitalization, and multi-point communication. Among numerous fieldbus standards, LonWorks stands out for its unique and superior performance. LonWorks is a complete, fully open, interoperable, and currently mature distributed control network technology. This paper designs a field node for a temperature cyclic control system using the LonWorks development platform. 2. Overall Hardware Circuit Scheme [align=center] Figure 1 Hardware Block Diagram of the Temperature Control System Node[/align] The hardware block diagram of the temperature control system node is shown in Figure 1. The temperature control node should include the following two main functional blocks: the LonWorks control module and the peripheral interface circuit. In this temperature control system design, it is necessary not only to acquire data but also to control the underlying devices. Based on this requirement, this design proposes an improved data acquisition node scheme, adding a D/A conversion circuit to the traditional design. This circuit can transmit the instructions issued by the node to the analog device, realizing the control of the data acquisition process. 3. Circuit Design of the LonWorks Control Module The LonWorks control module refers to a general-purpose node developed based on Neuron chips. It includes Neuron chips, memory, transceivers, I/O interfaces, and network ports, enabling plug-and-play operation in the field and achieving efficient and low-cost development. Neuron chips include two models: Neuron 3120 and Neuron 3150. The Neuron 3150 was chosen here due to its flexibility and suitability for this system's application. 1. Neuron Chip Communication Port: The Neuron chip supports various transmission media, most commonly twisted-pair and power line networks. Others include radio frequency (RF), infrared light waves, fiber optics, and cables. The Neuron chip has a multi-functional communication port; through different configurations, its five pins can connect to various transmission media interfaces, achieving a wide range of transmission rates. It has three operating modes: single-ended, differential, and dedicated operating mode. The FTT-10A twisted-pair transceiver provides a physical interface between the Neuron chip and the LonWorks network. The FTT-10A free-topology twisted-pair transceiver is suitable for various communication media and topologies. The FTT-10A free-topology twisted-pair transceiver supports star, bus, and ring topologies. Its speed reaches 78kbps, with a maximum communication distance of 2700m, which can be extended by repeaters. The connection between the Neuron3150 chip and the FTT-10A is shown in Figure 2. [align=center] Figure 2 Connection diagram of Neuron3150 chip and FTT-10A[/align] 2. External memory of Neuron chip In this design, we use the AT29C512 memory with a storage capacity of 64K bytes. It can ensure that the data is not lost when the power is off, and can also perform a limited number of data write operations when the power is on. 4 Peripheral interface circuit design The peripheral interface circuit of the temperature control node mainly includes temperature acquisition circuit, A/D conversion, D/A conversion circuit and power supply circuit. (1) Temperature acquisition circuit The temperature acquisition circuit mainly uses the integrated temperature sensor AD590 to convert the temperature value on site into a voltage value. The specific temperature-voltage conversion circuit is shown in Figure 3. [align=center] Figure 3 Schematic diagram of temperature acquisition circuit[/align] AD590 is a single-chip integrated two-terminal temperature sensing current source produced by Analog Devices. In the temperature acquisition circuit, potentiometer R14 is used to adjust the zero point, and R15 is used to adjust the gain of operational amplifier LM324. The adjustment method is as follows: Adjust R14 at 0℃ to make the output A1N1=0V, and then adjust R15 at 100℃ to make AIN1=5V. Repeat this adjustment many times until AIN1=0V at 0℃ and AIN1=5V at 100℃. Finally, verify at room temperature. (2) A/D conversion circuit The main function of the A/D conversion circuit is to convert the acquired voltage value into a digital signal. The A/D conversion is mainly implemented using the MAX186 chip from MAXIM Corporation of the United States. It contains an 8-channel multiplexer, a high-bandwidth track/hold circuit, a 12-bit successive approximation A/D converter, a serial interface circuit, etc. The MAX186 has a built-in 4.096V reference source and is itself a complete single-chip 12-bit data acquisition system. Of the 11 I/O ports of Neuron 3150, IO0 to IO3 have high current sinking capability and can directly drive some low-power devices; IO0 to IO7 have low-level detection and latching function; in addition, all pins have TTL level input function. These pins can be flexibly configured into 34 different I/O objects to meet different user needs. The Neuronwire I/O object is selected in this system. This object uses any one of the IO8, IO9, IO10 and IO0 to IO7 pins of the Neuron chip to realize up to 255 bits of bidirectional serial data transmission. The Neuronwire master mode uses the Neuron chip pin IO8 as clock input, and IO9 and IO10 as serial data input and output respectively, thus forming a simple three-wire bus structure. (3) D/A conversion circuit The main function of the D/A conversion circuit is to process the data collected on site at the temperature control node and feed the processed information back to the field device. The D/A conversion is mainly implemented using the MAX522 chip. The MAX522 chip has two 8-bit voltage buffered output D/A converters (DAC A and DAC B), 8-pin energy-saving package and DIP package. The buffer current of DAC A can reach 5mA and the buffer current of DAC B can reach 500μA. The MAX522 operates at a unidirectional voltage of +2.7V to +5.5V. The MAX522 has a 3-wire serial interface and can operate at a voltage of 5MHz. It is directly compatible with SPI™, QSPI™ and Microwire™. It has an I6-bit input shift register containing 8 bits of DAC input data and 8 bits of DAC select and shutdown control. Data can be stored in the DAC register on the positive edge of /CS. IO7 is used as the chip select terminal, IO8 is used as the clock input, and IO9 is used as the serial data input. (4) Power supply circuit The power supply circuit of the temperature control system is shown in Figure 4. This system uses an external 220V AC power supply. After transformer transformation, bridge rectification and capacitor filtering and adjustment by adjustable three-terminal regulator CW317, it can output a continuously adjustable DC voltage with an adjustable range of 3 to 9V. [align=center] Figure 4 Power supply circuit diagram of temperature control system[/align] As shown in Figure 4, the adjustable three-terminal regulator CW317 has the following characteristic parameters: Vo = 1.2V～3.7V, Iomax = 1.5V, minimum input-output voltage difference (Vi-Vo)min = 3V, and maximum input-output voltage difference (Vi-Vo)max = 40V. R1 and RP1 form a voltage output regulation circuit, and the output voltage Vo is: (1) The value of R1 is 120Ω-240Ω, the ripple current flowing through R2 is 5mA～10mA, RP1 is a precision adjustable potentiometer, capacitor C3 and RP1 are connected in parallel to form a filter circuit to reduce the output ripple voltage, and diode D5 is used to prevent damage to the regulator when the output terminal is short-circuited to ground. The output voltage Vo of the integrated voltage regulator is the same as the output voltage of the regulated power supply. The maximum allowable current ICM of the voltage regulator is given by equation (2). In the equation, Vomax is the maximum output voltage, Vomin is the minimum output voltage, (Vi-Vo)min is the minimum input-output voltage difference of the voltage regulator, and (Vi-Vomax) is the maximum input-output voltage difference of the voltage regulator. From equation (1), we can get Vo≈1.25(1+RP1/R1). Taking R1=240Ω, then RP1max=1.49KΩ. Therefore, RP1 is taken as a 4.7KΩ precision wire-wound adjustable potentiometer. From equation (2), the range of input voltage Vi is (3). Secondary voltage V2≥Vimin/1.1=12/1.1 V, take V2=11V, secondary current I2>Iomax=0.8A, take I2 = 1A, then the secondary output power P2≥I2V2=11W. After looking up the table, we know that the efficiency of the transformer η=0.7, then the primary input power P1≥P2/η=15.7W. To leave room for error, a power transformer with a power of 20W is selected. Rectifier diodes D1, D2, D3 and D4 are selected as IN4001, and filter capacitors C1 and C2 can be 2200μF/25V electrolytic capacitors. A fuse FU should be connected to the secondary side of the transformer to prevent short circuit damage to the transformer or other devices. 5 Software design of temperature control system node In terms of software, the function of temperature control system node is mainly realized by two parts of software: data acquisition and data control. The node, based on the Neuron 3150 chip, is entirely written in Neuron C. Its overall structure typically involves first defining variables, functions, and I/O port usage, then writing subroutines and `when` statements to schedule the program. According to project requirements, this node needs to implement two functions: 1. Acquiring analog data via the I/O interface, performing A/D conversion, and transmitting it to the upper-level PC for monitoring; 2. Receiving control information from the upper layer, performing D/A conversion via the I/O interface, and then transmitting it to the lower layer to control field devices. Therefore, the software design and implementation of this node mainly includes two parts: data acquisition and control. The I/O objects used for data acquisition and data control are the same, both applying Neurowire I/O objects. By defining Neuron I/O objects, the Neuron chip can achieve synchronization with peripherals and complete full-duplex serial communication. Neuron I/O objects can be configured in master or slave mode. In master mode, the Neuron chip can simultaneously power multiple peripherals conforming to Motorola's SPI interface. The innovative aspects of this paper are as follows: This paper proposes a research on a field node for a temperature cyclic control system based on bus technology, and completes the design and software development of the LonWorks control module. This node scheme, tailored to a specific temperature acquisition circuit, integrates A/D and D/A conversion modules, accomplishing both routine data acquisition and facilitating on-site control by monitoring personnel. References: [1] Ma Li. Intelligent Control and Lon Network Development Technology [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2003, 2: 63-67. [2] Liu Bo, Guan Shuo. Design of LonWorks Fieldbus and Analog Device Interface Circuit [J]. Fieldbus Technology, 2003, 3: 22-24. [3] Ren Qingzhen, Wang Ningfang. Implementation of High-Speed ​​Data Acquisition Node Based on LonWorks Bus [J]. China Instrument and Meter, 2003, 4: 10-12. [4] Yang Caibiao, Zhao Jianlong. Research on Chip Temperature Control System Based on 812 [J]. Microcomputer Information, 2007, 9-1: 43-44. About the author: Liu Yanju (1965.10-), female, Benxi City, Liaoning Province, Associate Professor, Master, research direction: engaged in the research of process parameter acquisition and detection and networked measurement and control. Zhang Jingyi (August 1965 -), male, from Dalian, Liaoning Province, is a professor at the Academic Affairs Office of Shenyang University of Technology, holding a master's degree. His research interests include information systems and process control. Wang Minliang (June 1968 -), male, from Shenyang, Liaoning Province, is an engineer at the Research and Development Department of Shenyang University of Technology. His research interests include computer applications.