Construction of Wireless Fire Alarm System Based on ZigBee Technology

Transcription

1 Available online at Procedia Engineering 11 (2011) The 5 th Conference on Performance-based Fire and Fire Protection Engineering Construction of Wireless Fire Alarm System Based on ZigBee Technology MA Shu-guang Department of Fire Commanding, The Armed Police Academy, Langfang, , China Abstract This paper points out the defect of wired automatic fire alarm system in used, and the necessity and possibility of constructing wireless fire alarm system. ZigBee technology based on IEEE and its characteristics are introduced. We also give out a method of constructing wireless fire alarm system based on ZigBee, including the design of construction, hardware and software Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Keywords: ZigBee; wireless sensor; automatic fire alarm 1. Introduction Most fire sensor networks are built based on CAN bus in currently used automatic fire alarm system, in which signals and data are transferred through cable. Compared to traditional distributed cable network, bus network have greatly improved in expansibility and difficulty of construction and maintenance. But there are still some defects. The cables are easily to be eroded, bitten by rats, frayed, causing to high fault rate and high false alarm rate. The cable transmission distance is limited, usually no more than 1km, otherwise the attenuation and interference will lead to failure of system. We may conceive that, constructing automatic fire alarm system in wireless transmission way, can avoid above problems. A new way of wireless signal relay also can increase alarm signal transmission distance. With microelectronics and wireless communication technology development in recent years, this can become a reality. This paper introduces a method of constructing automatic fire alarm system based on ZigBee technology. 2. ZigBee Technology ZigBee is an alternative name of IEEE , a wireless network protocol released in ZigBee technology is a two-way radio communication technology, mainly suitable for automatic control and remote control * Corresponding author. Tel.: address: aurorama@163.com Published by Elsevier Ltd. doi: /j.proeng Open access under CC BY-NC-ND license.

2 MA Shu-guang / Procedia Engineering 11 (2011) based on wireless communication. It can be embedded in various consuming electronics, family and building automation equipment, industrial control equipment, various sensors equipment, also supporting the geographical location function. ZigBee has the following features: Low power dissipation. Due to short working cycle, it has low power dissipation in sending and receiving messages, and adopts a sleep mode. Two 5# dry batteries can support a node work for 6 to 24 months, or even longer. Low cost. Dramatically simplifying the protocol and reducing the requirement of communication controller, causes very low cost. The modules are cheap, and ZigBee protocol patent is free. Low transmission rate. It works at 250kbps rate, satisfying the application requirements of low data transmission rate. Short distance. The transmission distance between adjacent nodes is usually 10 ~ 100m. If increase transmitting power of RF, the distance can be 1-3km. If through the routing and communication relay, the distance will be even more. Short time delay. ZigBee has optimization in time delay sensitive application, the communication delay and activated delay from dormancy is very short. Generally, from sleeping to working, just needs 15ms, and the nodes connecting to network needs only 30ms. High capacity. ZigBee network can be constructed in different types. A master node can manage 254 nodes, still can extend to bigger network by each node. Total network can have nodes in theory. High security. ZigBee provides a three-level safe mode, including data integrity checking and authenticating, using Access Control List (ACL) to prevent illegal data acquisition, using Advanced Encryption Standard (AES128) symmetrical passwords to determine the security attribute flexibly. Free frequency band. It uses direct sequence spread spectrum technology, working at global free ISM 2.4GHz frequency band. Usually, application accord with the following conditions can consider using ZigBee technology: [2] the equipment cost low, transmitting data volume is small equipment is small in size, unfit to place big battery or power module unfit to replace batteries frequently or inconvenience for charging repeatedly cover a wide range of communication, many equipment in network, but only for monitoring and controlling Automatic fire alarm system has almost all of the above characteristics, so it s very suitable to be built based on ZigBee technology. 3. System Designing 3.1. System Structure Fig.1 System structure The system uses ZigBee wireless network to achieve fire monitoring and automatic alarming, mainly includes three parts: the data acquisition nodes, data sink nodes and fire control center, [3] as shown in Fig. 1. Data acquisition node is an embedded wireless sensor module integrating sensors, main control unit (MCU) and radio frequency (RF) communication functions. After preprocessing the fire signals detected by the sensors, it

3 310 MA Shu-guang / Procedia Engineering 11 (2011) chooses an optimal path to send them to the data sink node. The data sink nodes sends the data from the sensor network to the fire control center. When necessary, the data may also be sent to the fire control center by external network, such as Internet. Fire control center consists of supervision host and server. The server is used to store fire control data, electronic map, etc. The supervision host is used for data processing and statistical evaluation, displaying alarm information through peripheral equipment, and for data management, data query and interaction with the user System hardware The system hardware mainly consists of data collector and data receiver. Data collector consists of sensors, MCU, RF chips, etc. MCU and RF chips are connected by PCI bus, they constitute the wireless transmission module. With the same kind of wireless module, data receiver communicates with the PC through RS232 asynchronous serial interface. In one direction, the control signals are emitted from the host to the data collector in wireless way, in another direction, the collected data is uploaded to the host. When fire signal is detected by the sensors, the fire control center will process and statistically evaluate the data, and convert it to suitable alarming indicator according with the pre-set rules, then send out alarm signals. Diagram of the system hardware structure is shown in Fig. 2. Fig.2 System hardware structure

4 MA Shu-guang / Procedia Engineering 11 (2011) MCU can choose 8 or 16-bit single-chip microcomputer with on-chip integrated ROM, such as MCS51 series, HCS08 series or MSP430 series MCU., Taking MC9S08GT60 for example, one type of HCS08 series, it works at 1.8V voltage, integrated 4KB RAM and 60KB Flash ROM, and integrated 8 channels 10-bit ADC, 2 SCI interface and 1 SPI interface. It also has corresponding internal clock module and background debug interface. [4] The MCU of the data collector receives the signal sent by the sensor, then sends it to RF chip after A/D conversion. While the MCU of the data receiver receives the data sent from the RF chip, and send it through RS232 interface to the up computer for further analysis. When necessary, it may also directly drive simple audible or visual alarm devices such as buzzer, LED, etc. RF chip can choose ZigBee wireless transceiver series, CC series of TI or MC series of Freescale. They both work at 2.4 GHz band. Taking MC13192 for example, it is a low cost, low power consumption, high performance RF chip accord with ZigBee standard. It mainly consists of analysis receiving-transmission unit, digital modems, onchip frequency synthesizer, power manager and MCU interface. It s working band is ~ GHz, data transfer rate is 250kbps, working frequency band can be divided into 16 channels, each channel bandwidth 5MHz. Due to the low transmission rate and the large bandwidth of the channel, so the SNR is very high, anti-jamming capability is strong. External crystal provides the clock needed by MC13192, and the on-chip frequency synthesizer output signals provide the clock for MCU. Read-write operation on MC13192 is achieved through a standard four-wire SPI by the MCU. It should be pointed out that, most MCUs and RF chips produced by different companies can be collocated flexibly, but in practical engineering, it is suggested to use the products from same company in order to ensure the stability of the system. Also, embedded chips integrated MCU and RF chip can be adopted System software System software includes three parts: wireless sensor node procedures, data sink node procedures and center monitoring procedures. [5] Wireless sensor nodes periodically detect environmental parameters. When the system begins to work, MCUs and RF chips are initialized firstly, then chooses the channel, opens interrupt for receiving data. Then initialize ADC and collect data to process. If there is an alarm signal, the signal, sensor node address and the collected data will be combined as alarm data, and translated into ZigBee communication protocol packets. Selecting an optimal communication path, the packets are sent to the data sink node, and waiting for the returned confirmation. Thus, a whole ZigBee wireless communication is completed. After receiving the confirmation returned from the sink node, the sensor node will stay at low power mode automatically. In addition, when the sensor node receiving a request from the sink node, it can collect data immediately, in order to realize real-time, active monitoring. The sensor node procedure is shown in Fig.3. The sink node procedure is mainly to receive data from wireless sensor, confirming, then send it to the supervision host through RS232 interface. Located in the fire control center, the supervision host is used for receiving the data sent by the sink nodes, monitoring, alarming, and controlling working condition of the sensor nodes. The monitoring procedure in upper computer is designed based on serial communication. VC++ provides serial communication ActiveX can easily operate on serial port. Software sends request through serial port, indicating the data receiving process by a progress bar, and can display the data waveform through a display interface instantly, and save data to database for further analysis or inquiry at the same time.

5 312 MA Shu-guang / Procedia Engineering 11 (2011) Fig. 3 Flow chart of sensor node procedure 4. Conclusion The wireless automatic fire alarm system constructed based on ZigBee overcomes the limitations of the cable alarm system and avoids high power consumption of the other wireless communications technology. Compared with existing wireless sensor network, it has some advantages such as low cost, high network capacity, long life. And system installation does less damage to buildings, conveniently to place nodes and maintenance. Avoiding the unsafe factors of fire, lightning strike in cable systems, it is suitable for various occasions, especially for fire control in museums, ancient building group, with a wide application prospect.

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