Abstract: A gearbox status monitoring substation with PROFIBUS-DP bus was implemented using MSP430F149 and SPC3 chips. It can monitor vibration, shaft temperature, speed, motor voltage and current, and also features LCD display and parameter storage functions. Online intelligent monitoring of the gearbox was achieved. Keywords: PROFIBUS; MSP430; SPC3 Introduction In industries such as power, steel, petroleum, and chemical engineering, there are numerous mechanical equipment such as gearboxes, fans, and pump stations. If these devices operate in a faulty state, their service life will be significantly reduced, affecting production and causing economic losses to enterprises. Traditionally, relying on workers' listening and touching methods to detect potential problems is limited by the on-site environment and the experience of the diagnosticians, often resulting in missed or misdiagnosed cases. The long interval between two inspections of the same equipment is also not conducive to the timely detection of abnormalities. Therefore, online monitoring in factories is crucial. Gearboxes are one of the most common drive devices, and important parameters for their abnormal operation include: vibration, bearing temperature, output shaft speed, motor current, and voltage. Vibration signals can indicate whether gear meshing and dynamic balance are normal; bearing temperature can indicate whether bearing clearance and lubrication are adequate; and output shaft speed and motor current can indicate overload. The main functions of the substation are monitoring, processing, data uploading, and over-limit alarms. 1. Overall Structure A distributed monitoring system typically deploys a master station at the monitoring center and substations at various monitoring points, connected via a bus structure (Figure 1). After collecting and processing information from various sensors, the substations display some important data on their display devices and simultaneously upload all data to the master station via the bus. The master station analyzes and processes the information uploaded by each substation and displays it to the operation monitoring personnel, achieving online monitoring of a large area of ​​operating equipment. Figure 1 Network Structure. The system uses Texas Instruments' MSP430F149 as the controller and connects to the PROFIBUS-DP bus via Siemens' SPC3 chip. Vibration sensors with standard 4–20mA current signal output are selected, and the motor current and voltage are converted to achieve 0–3V output. A DS18B20 temperature sensor is installed at the bearing location to monitor the shaft temperature (the normal operating temperature of the reducer is 50-60℃, and the operating temperature of rolling bearings should not exceed 95℃). A pulse-output speed sensor is installed on the output shaft. The MSP430F149 collects and processes the above operating signals, displays them on the LCD, and simultaneously uploads them to the bus to report the operating status of the substation to the master station. 2. Related Introduction 2.1 MSP430F149 Microcontroller The MSP430F149 is an ultra-low power, mixed-signal 16-bit controller manufactured by TI, with an operating voltage of 1.8-3.6V. This microcontroller has rich peripheral functions, internally integrating a multi-channel 12-bit A/D converter, hardware multiplier, 60KB Flash and 2KB RAM. The operating temperature range is -40℃ to +85℃, which can adapt to various harsh environments, making it very suitable as a terminal controller for field monitoring. 2.2 PROFIBUS-DP Fieldbus PROFIBUS is a manufacturer-independent, open fieldbus and one of the most widely used fieldbus standards internationally. With its unique technical characteristics, strict certification specifications, open standards, support from numerous manufacturers, and continuously evolving application standards, it has been incorporated into the international fieldbus standard IEC61158 and the European standard EN50170, and was designated as my country's national standard JB/T10308.3-2001 in 2001. PROFIBUS-DP (Decentralized Periphery) is mainly used for unit-level control systems and distributed communication in automation systems. It uses Layer 1, Layer 2, and the user interface layer, leaving Layers 3-7 unused. This streamlined structure ensures high-speed data transmission. 2.3 SPC3 Protocol Dedicated Chip The PROFIBUS-DP physical layer is RS-485, but the communication protocol is relatively complex. SPC3 is a dedicated protocol chip from SIEMENS, which allows bypassing the complex protocol. The SPC3 integrates the FDL layer of the DP protocol. Because the SPC3 integrates the complete DP bus protocol, when communicating with the master station, the microcontroller uses the SPC3 chip as if operating internal RAM, greatly reducing the programming workload of the slave controller. The SPC3 ensures the validity of messages and can meet the consistency of data exchange throughout the message. The bus interface is a parameterizable synchronous/asynchronous 8-bit interface, internally integrating 1.5K dual-port RAM. The entire RAM adopts an 8-byte segment structure, and all BUF pointers that require address allocation must point to the beginning of the segment. The service access point for DP communication is automatically established by the SPC3, and various message information is presented to the user as the internal data of different BUFs. 3. System Hardware Design The system hardware mainly consists of a keyboard, display module, communication module, and system measurement module (Figure 2). The use of a 3×3 row and column scanning keyboard can greatly save I/O port usage. The 128×64 dot matrix graphic LCD can display a large amount of information. To store set parameters and operational data, the Microchip 24LC02B serial memory chip was selected. It uses an I²C bus interface, is organized into 256-byte blocks, has an 8-byte page write buffer, and supports 1 million erase/write cycles. The communication module consists of an SPC3 chip and peripheral circuitry. Since the SPC3 operates on 5V while the MSP430F149 operates on 3.3V, the hardware design must consider the coexistence of 3.3V and 5V logic systems. Devices typically have limited voltage applied to their input and output pins, which are connected to Vcc via diodes or discrete components. To prevent component damage and data loss, a dedicated level converter chip, SN74LVCC4245A, is used. This is an 8-bit bidirectional I/O level converter. Bus B is for 3.3V data, and Bus A is for 5V data, connected to the SPC3 chip. DIR determines the data direction. The SPC3 interrupt signal X/INT is level-converted and sent to P1.6, providing a communication interrupt signal for the microcontroller. To improve the anti-interference capability of communication, the internal circuitry of the SPC3 must be electrically isolated from the physical interface. High-speed optocouplers HCPL7101 and SN75ASL176D transceivers ensure high reliability of PROFIBUS bus communication. Shaft temperature measurement uses the DS18B20 single-bus digital temperature measurement chip manufactured by Dallas Semiconductor, with an operating voltage of 3.0V～5.5V and a temperature measurement range of -55℃～+125℃. It has a bus structure, and signals from eight temperature sensors can be acquired through P2.0. Figure 2 shows the system interface circuit diagram. 4. System Software Design After the system is powered on, the SPC3 and LCD must first be initialized, and the registers configured. The main program calls the signal acquisition, keyboard display, and communication programs according to interrupt requests. 4.1 Status Signal Acquisition The signal acquisition program is called by a timer interrupt. Since the monitoring system does not participate in real-time control, and to avoid the transmission of large amounts of data on the bus, an interrupt is generated every 2 seconds to execute signal acquisition. After the status signals are converted by the external circuit, they are all analog voltage signals when they enter the MSP430 microcontroller. The program mainly involves A/D conversion and filtering. For the temperature sensor, since it is connected via a bus, it calls the temperature reading subroutine eight times for different addresses, refreshing the value in the temperature buffer, and waiting for calls from the display and communication programs. Rotational speed measurement uses a timer and interrupt counting method. 4.2 Keyboard Display The keyboard uses a row-column scanning method. When a key is pressed, an interrupt signal is generated, executing parameter setting, display, page turning, and other programs. The LCD display module has an internal character library, so character model writing is not required. After initialization, the data to be refreshed is periodically sent to the display buffer. 4.3 Communication Interface The communication interface software is quite important in the system, including three parts: SPC3 initialization, input processing, and output processing. After the SPC3 is powered on, it must first be initialized, setting the SPC3 register variable names, hardware mode, address and identifier, the addresses and lengths of each BUF, and obtaining the BUF pointer. When SPC3 generates a signal to P1.6, the CPU generates an interrupt, executes the input processing program, and obtains instructions and data from the bus. After acquiring the status signal, the substation performs a data output process and sends its status parameters to the bus. 4.4 GSD File After writing a standard GSD file, the substation can be used as a standard PROFIBUS device, recognized by various manufacturers (the system master station is SIEMENS PLC-300). The GSD file includes the manufacturer and device name, software and hardware version number, baud rate, monitoring time interval, and the number and type of slave device channels, etc. 5. Conclusion The online monitoring system for reducers based on MSP430F149 and PROFIBUS-DP bus has advantages such as multiple measurement parameters, high accuracy, flexible display, long transmission distance, and strong anti-interference ability. Under the same monitoring standards, the cost is much lower than other monitoring systems. This article uses a reducer as an example to illustrate the construction of a distributed status monitoring substation with a bus structure, which has promotional value in the fields of power, petroleum, and chemical industries. This paper presents an innovative approach to factory online monitoring, combining MSP430 and PROFIBUS-DP bus technologies. It features a standard bus interface, high versatility, and suitability for long-distance, high-speed transmission. The system is convenient and simple to use, displaying data and information directly on an LCD screen, and has broad application potential in remote monitoring. References: 1. SPC3 Siemens PROFIBUS Controller User Description. Siemens, 1996. 2. SIEMENS. SPC3 User Description [R]. 1996. 3. Su Tiannuo, Fang Yanjun. Research on PROFIBUS-DP and HART Protocol Conversion and Gateway Design [J]. Microcomputer Information, 2005, 10-1: 12-14. 4. 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