Abstract: This paper presents a design scheme for a multi-parameter measurement and control system of intelligent circuit breaker based on Profibus-DP fieldbus, and elaborates on the design method of power signal and temperature detection circuit and Profibus-DP bus interface module. The scheme adopts an advanced frequency adaptive synchronous fast AC sampling algorithm to design the multi-parameter measurement and control software, providing an effective way to realize the data acquisition and communication of intelligent circuit breaker. Keywords: intelligent low-voltage circuit breaker; fieldbus; intelligent controller 1 Introduction In the field of low-voltage electrical appliances, circuit breaker is a very important device. Intelligent low-voltage circuit breaker has the advantages of automation, intelligence and modularity that traditional circuit breaker does not have. It is based on intelligent controller and is a high-tech product that integrates microprocessor technology, network technology and information technology. The intelligent controller based on microprocessor has a variety of detection and communication functions. Using bus function to realize power quality monitoring is an economical and effective solution [2]. The circuit breaker measurement and control system presented in this paper adopts Profibus-DP fieldbus. Profibus-DP is designed for high-speed data transmission at the field level. At this level, the central controller communicates with the distributed field devices through high-speed serial lines [3]. This paper presents the design of a multi-parameter measurement and control system for intelligent circuit breakers based on the PROFIBUS-DP bus. The design uses the Philips LPC2114 microprocessor as the core of the field control, and the 51 microcontroller LPC932A1 is used for PROFIBUS bus communication. The LPC2114's built-in A/D converter and the single eight-channel analog switch CD4051 work together to complete the acquisition of multiple signals. The high-precision real-time clock chip SD2304FLP effectively realizes temperature detection and real-time clock functionality. Finally, the paper also presents the design of advanced measurement and control software algorithms and communication interface software. 2. Control Circuit Hardware Design The intelligent controller mainly consists of a microprocessor, signal acquisition circuit, clock and temperature detection circuit, power supply, keyboard and LCD display circuit, actuator, and PROFIBUS-DP bus interface circuit, as shown in Figure 1. The intelligent controller system can realize functions such as temperature acquisition, processing control, and field communication. It can independently complete field measurement and control, or it can be combined with multiple slave stations and master stations to build a large system to complete the overall measurement and control tasks. [align=center]Figure 1 Block Diagram of Intelligent Controller[/align] 2.1 Microprocessor Selection This design task selected the Philips LPC2114 microprocessor as the core of the field control. This processor has sufficient I/O interfaces and fast data processing capabilities, meeting the requirements of real-time monitoring and alarm for multi-parameter systems. The LPC2114 has 128K of on-chip FLASH program memory, with ISP and IAP functions, bringing great flexibility to system development and maintenance; the prefetch instruction method makes the CPU execution speed four times faster than the highest speed of ordinary FLASH, with an instruction execution speed of up to 18ns; 4-channel 10-bit A/D converters with a conversion time as short as 2.44μs; multiple serial ports, up to 46 general-purpose I/O ports, and 12 independent external interrupt pins. With careful software design, the required performance can be achieved with the fewest components, improving reliability. 2.2 Temperature Detection and Real-Time Clock Circuit Traditionally, temperature detection and real-time clocking are handled by separate chip circuits. This decentralized processing often reduces the microprocessor's efficiency and increases circuit complexity. Therefore, this design uses the high-precision real-time clock SD2304FLP. The SD2304FLP is a high-precision real-time clock chip with a built-in crystal oscillator and a two-wire serial interface. This chip guarantees a clock accuracy of ±5ppm (from -10ºC to 50ºC). It has a built-in clock accuracy adjustment function; through the built-in digital temperature sensor, an adjustment value can be set to adapt to temperature changes, achieving high-precision timing over a wide temperature range. It also has a built-in 2K serial E2PROM for storing clock accuracy compensation data at various temperature points. Because of the built-in I2C bus digital temperature sensor, temperature data can be easily read via the I2C interface. Temperature compensation of the SD2304FLP is crucial to the application. The clock accuracy compensation data for temperature changes is stored in the 2K capacity E2PROM before leaving the factory; therefore, the current temperature value can be determined simply by reading the on-chip temperature sensor. The address of the compensation data stored in the E2PROM is determined based on the high eight bits of the temperature value. This compensation data is then read and written to the clock adjustment register. It is important to note that the pull-up voltage of the I2C bus must always be present when the bus needs to operate, and it should be the first to be powered on and the last to be powered off in the system. 2.3 Signal Acquisition Circuit This design acquires four-phase current and three-phase voltage signals. Both voltage and current signals are induced voltages on the secondary side of the transformer. After filtering, isolation, and amplification, a voltage range suitable for A/D conversion is formed. The seven signals are processed and sent to a multi-channel electronic switch. Since the LPC2114 itself has an A/D converter, the acquisition of multiple signals can be completed by controlling the electronic switch to select the required signals using the LPC2114. This design uses a single eight-channel analog switch, the CD4051. The CD4051 has a channel conversion frequency of up to 10MHz, is easy to control, has a range of up to 10V, and an operating temperature range of -55ºC to +125ºC, featuring a wide range and real-time signal acquisition. The LPC2114's A/D conversion frequency can reach a maximum of 4.5MHz, with a conversion accuracy of 2-10, fully meeting the requirements for real-time acquisition and high precision. The A/D initialization and conversion of the CD4051 and LPC2114 are completed by the main program. The design uses a timer interrupt method, requiring one data acquisition point from each of the three voltage and four current signals every 1ms. The LPC2114 stores the acquired and converted data in ADDR (A/D data memory). 2.4 Profibus-DP Bus Interface Module During Profibus-DP bus communication, the master station cyclically reads the input information from the slave station and periodically sends output information to the slave station. Simultaneously, data communication is monitored through the master and slave station monitoring functions. This system uses the 51 microcontroller LPC932A1 specifically to implement Profibus bus communication. Since the LPC932A1 microcontroller has an enhanced UART installed, the Profibus fieldbus protocol can be simulated using software. The LPC932A1 operates at a frequency six times faster than standard 80C51 devices, with an instruction execution time of only 167 ns. Its enhanced UART baud rate allows data transmission up to 500 Kb/s on the Profibus-DP bus, enabling high-speed periodic data communication, making it particularly suitable for time-critical applications. The Profibus-DP interface module, shown in Figure 2, consists of four main parts: a microcontroller LPC2114, an analog bus protocol processing microcontroller LPC932A1, a high-speed optocoupler 6N137, and an RS485 transceiver SP3485. The Profibus-DP interface module design only requires four pins on the LPC2114, significantly saving port resources. To enhance the anti-interference capability of the Profibus-DP bus nodes, the TXD and RXD of the LPC932A1 are not directly connected to the TXD and RXD of the RS-485 transceiver SP3485. Instead, they are connected to the SP3485 through a high-speed optocoupler 6N137. This effectively achieves electrical isolation between the Profibus-DP nodes on the bus. The two power supplies, VCC and VPP, used in the optocoupler circuit must be completely isolated. Although this increases the complexity of the node, it improves its stability and security. The pull-up resistor connected to pin A of the SP3485 and the pull-down resistor connected to pin B ensure that the SP3485 chip is in an idle state when there is no connection, providing network failure protection and improving the reliability of the RS-485 node and the network. 3 Software Design 3.1 Algorithm of Measurement and Control Software The software algorithm adopts the integral method used in small current grounding systems for protection, based on the fact that the integral of the absolute value of the half-cycle of a sinusoidal quantity is proportional to the amplitude Ѕ[sub]m[/sub]. The algorithm is expressed as follows: M is the number of samples in each cycle, S(j) is the j-th sample value, and K(α) is the proportionality coefficient, which is related to the angle of the initial sampling point S(0). This algorithm has a large error only due to the different initial sampling points, but the impact of individual sample values ​​on the total value after interference is small, and some harmonics are canceled out during the half-wave integral process. The algorithm formulas for voltage, current and three-phase active power are as follows: U(l) and i(l) are the voltage and current sample values ​​at the i-th point. U[sub]AB[/sub], U[sub]CB[/sub] and I[sub]A[/sub], I[sub]C[/sub] can be calculated from the above algorithm. Other quantities such as cosφ can also be derived from this. In ordinary algorithms, the Q formula is usually derived from the P formula, while in the algorithm used in this design, the Q formula is directly derived from the current and voltage, which greatly improves the calculation accuracy. 3.2 Real-time Clock and Temperature Detection Software Design When the measurement and control system is running, clock calibration and temperature detection are performed periodically. The main program reads the temperature detection value in the self-diagnosis module to determine if the ambient temperature is abnormal. The master station sends the standard time to each intelligent slave station via the Profibus bus, and then each slave station calibrates its own clock. When a slave station experiences a fault or alarm, it reads and writes its own D2304FLP to obtain the clock and temperature values ​​at the time of the fault or alarm. The D2304PLP initialization program is shown in Figure 3. [align=center] Figure 3 D2304FLP Initialization Program Flowchart[/align] To optimize the software design and balance development efficiency and code execution speed, some modules in the measurement and control program with high real-time or computational requirements are programmed in assembly language, such as real-time parameter control, floating-point arithmetic, data acquisition, sensor calibration, timing display, and EEPROM access. These are then embedded into the C program for processing. To address the cumbersome calibration procedures of general parameter measuring instruments, an AT24C02 serial EEPROM was used to develop a parameter calibration module. This avoids calibration every time the instrument is powered on and allows for automatic calibration based on usage, improving the instrument's measurement accuracy and execution precision. 3.3 Communication Interface Software Design The software design of the Profibus-DP interface module mainly includes three parts: SAPs cache initialization for LPC932A1, the main program for communication with the master station (see Figure 4), and SPI communication between LPC2114 and LPC932A1. [align=center] Figure 4 Flowchart of the main program for communication with the master station[/align] LPC932A1 embeds a program that can simulate a simple Profibus-DP fieldbus protocol. LPC932A1 initialization includes: setting the UART interrupt and transmission baud rate according to the Profibus-DP communication protocol requirements, setting up SPI communication, and setting up the parameter buffer, diagnostic buffer, address buffer, and data exchange buffer. Communication between the LPC932A1 and the PROFIBUS-DP master occurs before the slave station begins receiving messages from the master. The slave receives messages by responding to UART interrupts. It then determines if the received message is intended for the local station; if not, the interrupt ends, and it waits for the next message. If it is, it checks if the local address needs to be changed; if not, it transmits data with the LPC2114 via SPI communication. Finally, it sends the processed PROFIBUS-DP compliant message to the master station. After successful transmission, it waits for the next cycle. The LPC932A1 and LPC2114 communicate via SPI. The LPC2114 responds to SPI interrupts and begins receiving protocol-converted messages from the LPC932A1. Because the message format received by the LPC2114 is relatively simple, it does not require excessive resources from the LPC2114. It is important to note that in SPI communication, the LPC932A1 should be set as the master, and the LPC2114 as the slave. 4. Conclusion This paper describes the design of a novel intelligent circuit breaker multi-parameter acquisition system from a development perspective. The intelligent low-voltage circuit breaker controller, composed of two microprocessor chips (LPC932A1 and LPC2114) with Profibus-DP communication capability, has its own advantages and can effectively improve control real-time performance. In industrial, building, and infrastructure projects, this new generation of circuit breakers with communication capabilities opens up entirely new application possibilities in initialization parameters, configuration, diagnosis, testing, maintenance, and energy management. The innovations of this paper are as follows: 1. The intelligent circuit breaker is controlled using a PROFIBUS-DP bus network, and the LPC932A1 51 microcontroller is selected to realize PROFIBUS bus communication; 2. The microprocessor of the intelligent circuit breaker is the LPC2114 microprocessor with ISP and IAP functions. It has the characteristics of high speed and multiple interfaces. With careful software design, the required performance can be achieved with the fewest components; 3. The measurement and control system uses the high-precision real-time clock chip SD2304FLP with temperature compensation function to realize temperature detection and real-time clock; 4. An advanced frequency adaptive synchronous fast AC sampling algorithm is adopted. References [1] Yang Xianhui. Fieldbus Technology and Its Application [M]. Tsinghua University Press, 1998 [2] Jin Shengfu. Research on Intelligent Controller of Universal Circuit Breaker [J]. Journal of East China Shipbuilding Industry Institute, 2003, 17 (5): 75-79 [3] Zhang Zhifeng, Wang Jian. Discussion on PROFIBUS-DP Master-Slave Communication of Fieldbus [J]. Microcomputer Information, 2004, 20 (7): 7-8, 60 [4] Huang Yicheng. Application of Intelligent Slave Based on Profibus [J]. Instrumentation Standardization and Metrology, 2004, (4): 22-25 [5] Zhou Tong. Protocol Analysis and Software Design of Slave Development Based on Profibus-DP [J]. Information and Control, 2005, 31 (1): 115-118