Download seismometers and their role in preventing secondary earthquake

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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.
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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
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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.
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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.
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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.
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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.
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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.
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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.
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