【Abstract】Introducing a leakage current electrical fire monitoring system based on a 16-bit embedded microprocessor, the MSP430. The system is composed of electrical fire monitoring equipment and a network of various fire detectors. The detectors utilize an improved AC sampling algorithm and metering chip to carry out data collection of monitored lines, electrical fire early warning, and record fault and alarm notifications. It also allows for real-time monitoring and intelligent operation of the system through the monitoring equipment. The results indicate that the system meets national standard design requirements, featuring low energy consumption, high accuracy, safety and reliability, low false alarm rates, and ease of operation and maintenance, making it highly valuable for market applications.
Keywords: MSP430; Leakage Current; AC Sampling; Intelligent Monitoring
0 Introduction
With the rapid development of the national economy and the continuous improvement of people's living standards, the volume of electricity consumption has greatly increased. The demand for various electrical equipment and household appliances has surged, leading to a significant rise in electrical fire accidents. Over the past decade, electrical fires in China account for 30% of the total number of fire accidents, making it the primary disaster source among various types of fires domestically. The proportion of electrical fire accidents is increasing year by year, which is a cause for concern. As the importance of electrical fire prevention is increasingly recognized and with the introduction of new electrical fire detectors, the safety of the lives and property of the nation and its people is being safeguarded.
1 System Hardware Design
1.1 System Structure
The entire system, as shown in Figure 1, consists of a monitoring device networked with up to 255 detectors in a master-slave configuration. The electrical fire detector operates by independently monitoring and managing fire hazard parameters such as leakage current, overload and short-circuit current, over/under voltage, phase loss, and line temperature rise in the power distribution circuit and supply lines through a combination of external sensors, microcontrollers, and digital processing chips. In the event of leakage, overload, short-circuit, over/under voltage, phase loss, or overheating in the supply lines exceeding set thresholds, it can quickly and accurately emit audio-visual voice warning (alarm) signals, indicating the alarm location, recording the alarm time, displaying the alarm type, and reminding relevant personnel to handle the emergency situation promptly. The system, in conjunction with external input signals and circuit breakers, can isolate configured lines, initiate fire alarm联动, and input alarms. After networking via the RS485 bus, the monitoring device can perform real-time inspections, parameter settings, remote control, and data backup printing for the detectors, enabling remote measurement, control, adjustment, and signaling. The system's components are designed so that a fault in one part does not affect the normal operation of others, ensuring high stability and safety; it also facilitates centralized monitoring, rapid fault handling, and troubleshooting for operators.
The electrical fire detector in Figure 2 is designed based on the module classification according to the probe function, excluding the main control module with the microprocessor MSP430, it can be roughly divided into six parts: the signal acquisition module, clock and data storage module, human-machine interaction module, input/output module, communication module, and power control module.
1.2 Main Function Modules
1.2.1 Signal Acquisition Module
The primary application employs the交流采样algorithm to detect leakage current in circuits. Additionally, it utilizes temperature sensors and the electrical parameter DSP processor ATT7028 to real-time collect and process on-site temperature and main electrical parameters, such as voltage, current, phase, and power signals. Simultaneously, taking advantage of the gradual change in grid frequency, the ATT7028 completes frequency measurement of the circuit, providing the MCU with timer sampling interval settings. In terms of hardware, the MSP430F149 features a 12-bit precision analog-to-digital conversion module, with 1-bit non-linear differential error and 1-bit non-linear integral error, an integrated reference voltage source and temperature sensor (used to measure the chip's operating temperature), and 8 AD conversion channels. By repeatedly converting the leakage current and external temperature parameters through sequential channels, the ADC12 hardware automatically stores the conversion results in the corresponding ADC12MEM registers after appropriate settings.
1.2.2 Clock and Data Storage Module
The main components include the real-time clock chip DS1302 and the data storage chip 24CL0X, used for real-time recording and transmission of faults.
Information.
1.2.3 Human-Machine Interaction Module
Primarily composed of an LCD display, a 5-way LED indicator, and a 4x4 keypad, operators can check and configure the detector's status on-site via the screen and buttons.
1.2.4 Input/Output Module
Primarily designed to complement other equipment and products to enhance system functionality, it includes 5 digital switch input signals: fire alarm联动 signal input, circuit breaker status feedback input, remote disconnection signal input, and 2 smoke alarm signal inputs. The output section mainly consists of speaker control signals, auxiliary alarm signals, and multi-functional relay control signals.
1.2.5 Communication Module
Design selects the RS485 bus for networking applications. The RS485 interface transmits signals differentially, suitable for half-duplex communication in master-slave mode, and its bus topology ensures the master-slave communication mode required by the detector applications. The transmission line employs differential channels, requiring only a pair of balanced twisted-pair cables, offering strong common-mode interference rejection. Furthermore, due to its low impedance and no grounding issues, its theoretical transmission distance can reach 1200m with a transmission rate up to 1Mb/s. However, signal quality can degrade in practical applications due to common-mode voltage ranges among detector nodes, EMI interference, and an excessive number of nodes on the bus or overly long node branches. Therefore, attention must be given to hardware anti-interference design.
2 System Software Design
The electrical fire monitoring system software design is mainly divided into two parts: detector software design and remote control software design for the monitoring system. Data transmission is achieved through the establishment of a unified networking communication protocol. For electrical fire detectors, the 16-bit microcontroller MSP430's powerful timing, interrupt, and peripheral module functions are fully utilized through reasonable programming, along with synchronous communication between internal devices and the implementation of module functions. For the electrical fire monitoring equipment, after installing remote monitoring software with technologies such as application login passwords, MFC function extension classes, ActiveX controls, database access, and hooks, the networking with detectors can directly perform a series of tasks such as system monitoring host-based inspection of all controlled points, real-time monitoring, data backup printing, and remote control. This not only facilitates operation and management but also ensures high security and stability.
2.1 Communication Sampling Algorithm
For the basic AC sampling algorithms for power parameter measurement, they can be divided into sine function model algorithms and non-sinusoidal periodic function algorithms. According to the application requirements of the project, the primary target is to collect current parameters within the power frequency range. The ideal single-cycle sampling signal is a sine wave with a frequency of 50Hz. For the main algorithms, experimental simulations were conducted using the sine function model algorithm, introducing an ideal AC function model:
Its fundamental wave amplitude A1=138, respectively for various algorithms under ideal conditions A3=A5=A7=A9=0 and the Introduction of Odd Harmonics into the Power Grid3=22.3，A5=6.4，A7=3.2，A9=0.5 Simulations were conducted for two cases. Current amplitude Im=138mA, RMS current I = 97.581mA. Tables 1 and 2 present the AC sampling simulation results of the sine function model algorithm and the non-sinusoidal periodic function model algorithm at f = 50Hz, respectively.
Through experimental comparisons, it can be observed that applying non-sinusoidal periodic function algorithms in real-world environments effectively removes harmonic interference by collecting a complete cycle of signals, thus yielding a more ideal electrical parameter signal.
2.2 Detector Software Design
Figure 3 is the main program flowchart of the fire detector. Based on the main function loop and program design logic, the main program can be divided into initialization module, data processing module, fault handling module, main display module, and communication module. After the system is initialized correctly upon power-up,
AD conversion data and on-chip communication data are processed together, with fault and loop interface display decisions made based on the processing results. Additionally, user operations involving communication, key presses, and other interrupts trigger program calls and parameter setting functions.
2.3 Monitoring Equipment Software Design
The electrical fire monitoring equipment software utilizes Visual C++/MFC and follows an object-oriented design approach (OOP) for the development and design of the system and its interface. The system defaults to a Win32-based PC platform. MFC, with the help of AppWizard, frees developers from writing basic code repeatedly. Using ClassWizard and message mapping, it eliminates the confusion and redundancy of message handling code. Leveraging C++'s encapsulation features, developers are freed from the hassle of various handles in Windows, allowing them to deal with C++ objects, thus making development closer to the programming language and further from the system. In the design process of the control software for RS485 networking, in addition to calling the encapsulated API functions with MFC, it also primarily utilizes communication ActiveX controls, hooks, and database access technology to ensure timely response and processing of transmitted data.
3 Test Results
Electrical fire detector testing methods are in accordance with the current national standards, which have conducted tests on a series of indicators, including insulation, voltage resistance, and vibration of the detector samples.
The main electrical parameter performance test results for the probe samples are as follows: Voltage: 172-268VAC, Accuracy: 1; Current: 200-800AAC, Accuracy: 1; Frequency: 45-55HzAC, Accuracy: 0.1Hz; Communication Protocol: MODBUS, RS485 Interface, 4800/9600/19200 bits/s; Power Supply Voltage: 220VAC; Protection Functions: Leakage Protection, Overload and Short Circuit Protection, Phase Loss and Open Circuit Protection, Overvoltage and Undervoltage Protection, Temperature Protection, Fire Alarm Linkage, Digital Switch Signal Input Protection; Protection Methods: Shutdown/Alarm/Tripping.
1) Under identical conditions, the CTcP process provides more uniform, stable, and accurate imaging than the CTF process.
The higher the imaging resolution, the better the reproduction effect of the printing plate dots.
Increasing the screen line count will reduce the image's grayscale level, causing severe dot expansion and increasing the difficulty of the printing process.
4) Solutions 1 and 3, widely used in the industry, both exhibit good performance in the reproduction of dot gain in printing plates. However, Solution 1 falls slightly short in its ability to manage pixel transitions and the gradation of tone levels.
Ankorree Electric's Fire Monitoring System 4
(1) Overview
The Acre1-6000 Electrical Fire Monitoring System has been certified by the central fire product testing and certification center, and all have passed rigorous EMC electromagnetic compatibility tests, ensuring safe and normal operation of the series in low-voltage distribution systems. It is now in mass production and widely applied across the country. The system monitors and collects signals such as residual current, overcurrent, overvoltage, temperature, and fault arcs to prevent and alarm electrical fires early. It can also disconnect distribution circuits with excessive residual current, temperature, and fault arcs upon need. Additionally, it can meet the requirements for data exchange and sharing with the AcreIEMS corporate microgrid management cloud platform or fire automatic alarm systems, as per user needs.
(2) Application Scenarios
Applicable to intelligent buildings, high-rise apartments, hotels, restaurants, commercial buildings, industrial and mining enterprises, key fire protection units of the state, as well as the fields of petrochemical, cultural and educational health, finance, and telecommunications.
(3) System Architecture
(4) System Features
Monitoring equipment can receive residual current and temperature information from multiple detectors. When an alarm is triggered, it emits both audio and visual alarm signals. Simultaneously, the red "ALARM" indicator light on the device illuminates, the display indicates the location and type of the alarm, records the alarm time, and the audio-visual alarm persists until the "RESET" button on the device or the "RESET" key on the touch screen remotely resets the detector. The audio alarm signal can also be manually canceled using the "Mute" key on the touch screen.
When the monitored loop triggers an alarm, the control output relay closes to control the protected circuit or other equipment. Once the alarm is cleared, the control output relay releases.
Communication Fault Alarm: In the event of a communication failure between monitoring equipment and any connected detector, or if the detector itself fails, the corresponding detector on the monitoring screen will display a fault alert, and the yellow "Fault" indicator on the device will light up, along with an alarm sound. Power Supply Fault Alarm: If the main power supply or backup power supply fails, the monitoring equipment will emit an audio-visual alarm signal and display fault information. Detailed information can be viewed on the corresponding interface, and the alarm sound can be deactivated.
In the event of residual current, over-temperature alarms, communication, or power supply failures, the alarm location, fault information, and alarm time are stored in the database. Similarly, records are made when the alarm is lifted and the fault is resolved. Historical data offers various convenient and quick search methods.
5 Conclusion
The electrical fire monitoring system, composed of independent electrical fire detectors and fire monitoring equipment, is an intelligent integrated protection product for online real-time monitoring of low-voltage power supply systems. This system effectively prevents electrical fires caused by leakage-induced ground arc faults, while also monitoring parameters such as voltage, current, power, electricity, and environmental temperature of the protected circuits. It features multi-channel fire alarm联动 and alert functions; utilizes standard RS485 communication, and offers an optional Ethernet communication interface. Paired with intelligent remote control software, it fully meets the requirements for remote monitoring and comprehensive management, and holds significant market application value.
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Ankorri Corporation Microgrid Design and Application Handbook, 2022.05 Edition.
