Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1991-11-06
1995-03-07
Peng, John K.
Communications: electrical
Condition responsive indicating system
Specific condition
73654, 2006147, G08B 2100, H01H 3502
Patent
active
053962230
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an earthquake detecting apparatus having a vibration sensor for sensor earthquake vibrations and a signal processing means for processing a signal from this vibration sensor.
TECHNICAL BACKGROUND
Conventionally, a vibration sensor for sensing earthquake vibration, combines two vibration systems having natural vibration frequencies in two frequency bands. The two system vibration sensor can detect frequencies higher than that of earthquake vibration to distinguish earthquake vibration from shock vibration caused by a collision of an object with equipment incorporating a vibration sensor.
FIG. 10 shows an example thereof. A vibration sensor 20 has a cone-shaped vibrating surface 23. Vibrating surface 23 has a recess 22 whose top end part is small in diameter, and is formed at the central part of the inner bottom surface of a case 21. A comparatively large steel ball 24 (i.e., vibrating member) reciprocates by rolling on this vibrating surface 23. A sliding piece guide 25 moves upwards in response to the rolling of the steel ball 24. Sliding piece guides 25a and 25b support the sliding piece 25 in a vertically slidable manner. A movable contact 26 is pushed up by the sliding piece 25, and a fixed contact 27 contacts the movable contact 26 when it is pushed up.
In the above-mentioned vibration sensor 20, when the steel ball 24, bound in the central recess 22 of the cone-shaped vibrating surface 23, is subject to vibration above a certain value in Gal, it moves out of the recess 22 and reciprocates on the vibrating surface 23. At this time, the movable contact 26 is moved upward by the rolling motion of the steel ball 24, and contacts the fixed contact 27. As a result, an ON/OFF signal is generated from leads 28.
The vibration system dominating the movement of the steel ball 24 of this conventional vibration sensor 20, as shown in FIG. 11, has a vibration system A and B. The vibration system A has a comparatively low natural frequency (for example, about 4 Hz) which is determined from the curvature of a spherical surface replaced by the vibrating surface 23 and the size of the steel ball 24. The vibration system B has a comparatively high natural frequency (for example, about 12 Hz) which is determined from the diameter of the top end part of the central recess 22 of the vibrating surface 23 and the size of the steel ball 24. Accordingly, when operating in the earthquake wave band (1-4 Hz), the steel ball 24 moves out of the recess 22 at the level of the vibration system B, and thereafter moves to system A operation because of the lower operation level of the vibration system A. The steel ball reciprocates on the vibrating surface 23. Also, when the steel ball 24 operates in the shock wave band (for example, 5 Hz or more) i.e., other than earthquake vibration, it moves out of the recess 22 at the level of the vibration system B and approaches the vibration system A. However, unless a vibrating force above the operation level of the vibration system A is applied, no reciprocating motion on the vibrating surface 23 occurs. This is because the operation level of the vibration system A is higher than the applied vibrating force.
However, the actual vibration at a shock or the like sometimes has a frequency close to the earthquake wave band, and even a frequency above 5 Hz sometimes causes a vibrating force exceeding the operation level of the vibration system A. Therefore, as shown in FIG. 12, a signal processing means 29 is connected to the leads 28 of the vibration sensor 20 to process an ON/OFF signal of the vibration sensor. When ON-time pulses above a predetermined time width (for example, 30 ms) are generated a predetermined number of times (for example, five times) within a predetermined time (for example 3 sec) and an OFF-time is above a predetermined time length (for example, 40 ms) the vibration is judged to be an earthquake vibration. The predetermined time width of each ON-time and OFF-time are set to a value which will not produce detection of shock
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Iwabuchi Hiroo
Koga Ryoichi
Uno Takashi
Matsushita Electric - Industrial Co., Ltd.
Mullen Jr. Thomas J.
Peng John K.
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