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th The 14 World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China SEISMOMETERS AND THEIR ROLE IN PREVENTING SECONDARY EARTHQUAKE DISASTERS Biao Sun1 and Kunimitsu Kanai2 1 Senior Engineer, UBUKATA INDUSTRIES CO., LTD (Japan) 2 UBUKATA INDUSTRIES CO., LTD (Japan) Email: [email protected], [email protected] ABSTRACT: Immediately following an earthquake, secondary earthquake disasters, such as explosions or fires due to ruptures in gas piping or leakage of electrical wiring, destroy lifelines in the quake-stricken area, causing immeasurable damage to lives and properties. Ubukata Industries Co., Ltd. of Japan has developed a compact seismometer that detects the occurrence of large-scale earthquakes in real-time, thereby actively helping to prevent the destruction of important infrastructures that sustain the lives of many people. This seismometer is characterized by its consumption of no power at normal times in order to respond to user requests for a broader operational temperature range. When an earthquake of the 5th degree on the seismic scale occurs, the seismometer outputs alternating continuous ON and OFF signals that last longer than a set period of time, which is predetermined according to the intensity of the vibrations. The control circuit can detect an earthquake using these easy-to-process digital signals. This seismometer can be surface-mounted onto a substrate and is equipped with an automatic leveling function, which allows for easy installation on devices. Under Japanese law, inexpensive and accurate seismometers of this kind must to be installed in intelligent gas meters. KEYWORDS: compact seismometer, high reliability, low power consumption, secondary disaster prevention 1. INTRODUCTION OF THE SEISMOMETER 1.1. Structure of the Seismometer The seismometer is comprised of a seismic element and an automatic leveling mechanism. 1 th The 14 World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China 1.1.1 Seismic Element As described in Figure 1, the seismic element is comprised of an air-tight conductive housing, a metal ball, lead pins and umbrella-shape blade electrodes connected to them electrically. The lead pins and the housing are insulated by means of the insulators that lie between them. Lead pin Insulator Electrode Metal ball Housing Figure 1 Seismic element structure 1.1.2 Automatic Leveling Mechanism As described in Figure 2, the seismic element is immersed in oil and maintains a level state even if the seismometer is tilted; therefore, it can continue to operate properly. Even if the seismometer tilts 10 degrees in any direction, it can still function properly. The oil viscosity has been specifically selected so as not to disturb the detection of vibration. This seismometer, which can be surface-mounted onto a substrate, can be easily installed on devices due to this automatic leveling mechanism. Oil At inclination (10 degrees) Figure 2 Schematic drawing of the automatic leveling mechanism 2 th The 14 World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China 1.1.3 Operating Principle There is a depression in the central part of the bottom of the housing that holds the metal ball in place until the predetermined amount of vibration is provided. If this stationary part does not exist, the metal ball will easily roll from even the slightest vibration, making the characteristics near the response threshold unstable. This can cause chattering, etc., between contacts. The size of the depression in the central part of the housing is determined by the diameter of the metal ball and the predetermined vibration acceleration that is to be detected. When the radius of the metal ball is denoted by R, and the radius of the depression is denoted by r, the vibration acceleration α at which the metal ball begins its rolling motion is mostly determined using the following formula: α= r⋅g R2 − r 2 (g is the gravitational acceleration) (1.1) If the metal ball radius R and the depression radius r are set appropriately, the vibration acceleration will be around 100 gal or 250 gal, which closely corresponds to the range of the vibration acceleration during an earthquake of the 5th degree on the seismic scale, which is from 80 gal to 250 gal. As described in Figure 3, normally, the metal ball is in a stationary state in the depression in the central part of the housing bottom. At this time, the blade electrodes and the metal ball are not in contact with each other, and therefore no electricity flows between the terminals. When an earthquake of the 5th degree or greater on the seismic scale occurs, the metal ball will roll due to the quake and will repeatedly come into contact with and separate from the blades, and the electrical flow in the circuit will automatically turn on and off, sending out alternating ON and OFF signals. By inputting these signals into various alarm systems or controllers, safety devices for devices such as combustors or intelligent gas meters can begin working in order to prevent secondary earthquake disasters. 3 th The 14 World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China Terminal Terminal Terminal Terminal Electrode Electrode Metal ball Metal ball In vibration Stationary state Since the metal ball is not touching the electrodes Since the metal ball repeatedly comes into contact with (thin blades), the power between the terminals is OFF. and separates from the electrodes, the power between the terminals repetitively turns ON and OFF. Figure 3 Operation of the seismometer 1.2. Features of the Seismometer 1.2.1 Low Power Consumption As described in Figure 3, the blade electrodes and the metal ball of the seismometer do not come into contact with each other when there is no vibration due to earthquake; therefore, no electricity flows through the seismometer and there is no power consumption. This seismometer can be very effective in devices using dry-cell batteries, etc., as their power source, since it is difficult to use a device such as a semiconductor acceleration sensor, which constantly consumes power, in such devices. In Japan, seismometers are used in all household intelligent gas meters. 1.2.2 High Reliability Taking a case in which the seismometer is employed in a intelligent gas meter used for manufactured gas or propane gas cylinders as an example, earthquakes and vibrations caused by disturbances other than earthquakes must be differentiated from each other, in order to avoid unnecessary activation of the safety device. In this seismometer, time degradation of components is less likely to occur due to its sealed structure. Moreover, since it is placed in oil, it does not react to vibrations from daily life of several tens of hertz or greater, but reacts to seismic waves of 5 hertz or smaller. 4 th The 14 World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China 1.2.3 Broader Operational Temperature Range The characteristics of the seismometer do not change due to temperature changes. Unlike a semiconductor acceleration sensor, it functions outdoors, without being affected by ambient temperature. 2. THE ROLE OF THE SEISMOMETER IN THE PREVENTION OF SECONDARY EARTHQUAKE DISASTERS 2.1. Development of Laws Concerning the Prevention of Secondary Earthquake Disasters in Japan Japan is referred to as an earthquake archipelago, and suffers greatly from earthquakes. Especially in densely-populated, larger modern cities, secondary disasters from earthquakes are among the major disasters that threaten the lives and properties of humans. Approximately 105,000 lives were claimed in the Great Kanto Earthquake of the 1920’s during the 20th century, which had a magnitude of 7.9, and most of these fatalities were due to fires. The Japanese government places a great deal of importance on the prevention of secondary earthquake disasters. In regard to gas systems and power supply systems that can easily cause secondary disasters during earthquakes, the Japanese government has enacted related laws and regulations under 2 categories, industry and private, and has established technical standards for corresponding facilities. Among the laws and regulations for private systems, there is the “Gas Utility Industry Law” and “Liquefied Petroleum Gas Safety Regulations”. The government sector and related departments have issued reasonable compulsory laws and regulations regarding power grids, etc. Power supply systems must be equipped with earthquake emergency response systems, and it is a requirement that earthquake-sensing auto-shutoff devices be installed in these systems. It is required that gas companies install gas meters with auto-shutoff functions equipped with seismometers. Products for secondary earthquake disaster prevention must be approved by the Ministry of Economy, Trade and Industry, as well as related associations. For example, gas meters equipped with seismometers require approval by the Japan L.P. Gas Instrument Inspection Association, the High Pressure Gas Safety Institute of Japan, the Japan Community Gas Association, and the Japan Gas Association. 5 th The 14 World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China 2.2. Example of an Application of the Seismometer in Intelligent Gas Meters In Japan, the seismometer previously introduced is widely used in intelligent gas meters, taking advantage of its low power consumption, which is the most significant feature of the seismometer. When an earthquake of the 5th degree or greater on the seismic scale occurs, the seismometer outputs alternating continuous ON and OFF signals that last longer than a set period of time, which is predetermined according to the intensity of the vibrations. The control circuit of the microcomputer can detect the earthquake using these easy-to-process digital signals, and it activates the shutoff valve of the gas meter in real time. Since its application in intelligent gas meters began, there have been no reports of malfunctions of this seismometer due to vibrations other than those from earthquakes. After an earthquake ends, intelligent gas meters can easily be reset to normal conditions using the reset button on the gas meters. Unlike semiconductor acceleration sensors, this seismometer is not easily affected by ambient temperature, and can therefore be used in gas piping outdoors, where the temperature varies widely. External signal Gas inlet Gas outlet Pilot lamp Seismometer Reset button Microcomputer Shutoff valve Battery Measuring part Figure 4 Example of an application of the seismometer to intelligent gas meters The penetration rate of intelligent gas meters in which these seismometers are installed has already reached 100%, including both new and old houses in Japan. 6 th The 14 World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China 2.3. Effects of the Application of the Seismometer to Intelligent Gas Meters Positive effects have been achieved by applying this seismometer to intelligent gas meters. According to material issued by the Japan L.P. Gas Association, only 6434 lives were claimed in the Great Hanshin Earthquake of the 1990’s in one large Japanese city, which had a magnitude of 7.3. It was uncommon that loss of life could be prevented to such an extent, and this surprised the world. Although 175 cases of fires occurred in Kobe City within 10 days of the earthquake, none of these were caused by gas leaks. An expert analyzed that if gas shutoff valves had not been shut off in real time due to a failure in installing seismometers to intelligent gas meters, tens of thousands, or even hundreds of thousands of lives would have been claimed in such an earthquake in a large city. Ubukata Industries Co., Ltd. was commended by the Japanese government for the fine effects achieved by its seismometers during the earthquake. 3. CONCLUSION While we were preparing the presentation to be given at the 14th World Conference on Earthquake Engineering on May 12th, 2008, a magnitude 8 earthquake known as the Great Wenchuan Earthquake, occurred in the Sichuan Province in China. As of July 13th, 69,197 lives have been claimed, 374,176 people have been injured, and 18,289 people have been reported missing. We sincerely pray for the victims of this earthquake. We would also like to express our heartfelt sympathy to those injured by this earthquake. Earthquakes are the greatest natural disaster threatening the safety and existence of humans. Since perfect earthquake prediction is difficult even now, preventing secondary earthquake disasters to the maximum extent is of the utmost importance. We at Ubukata Industries Co., Ltd., would like to continue in our efforts to improve our seismometers and to develop new products, since we provide safety to society through our products and services. 7 th The 14 World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China REFERENCES 1. Japan. Unexamined Patent Publication No.6-94510 [Seismometer] (Ubukata Industries Co., Ltd.). 2. Japan. Unexamined Patent Publication No. 7-72004 [Seismometer] (Ubukata Industries Co., Ltd.). 3. China. Patent No. ZL 97109796.8 [Acceleration response switch] (Ubukata Industries Co., Ltd.). 4. Tong Zhenhuan and Sun Biao. (2008). To carry out seriously “Legislation for Urban and Rural Planning”; to do good job about public security and disaster prevention and disaster mitigation. Development of small cities and towns (Monthly magazine by the Ministry of Construction, China) No.6(Serial 228), 30-31. 8