JPH0245135B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an earthquake sensor that detects vibrations caused by earthquakes and the like.

[Problems to be solved by conventional technology and invention]

First, we will explain the frequency of earthquakes.

It is generally said that the main component of seismic waves has a frequency of 1 to 10 Hz, and among these, the 1 to 5 Hz component is particularly prominent. Figure 2 shows 17:00 on June 12, 1978.
As an example, the power spectrum of the seismic waves observed in Ofunato is shown for the Miyagi Prefecture-Oki Earthquake that occurred on the 14th minute. The predominant frequency is 2-3Hz (2.4Hz), 1
-5Hz power is large (although not shown, the Fourier spectrum has almost the same shape and has many 1-5Hz components).

In addition, minute vibrations in the ground and buildings caused by various causes such as trains, dump trucks, construction work, and rotating machinery are different from seismic waves and constitute disturbance vibrations, but these disturbance vibrations are often over 20Hz, but also include vibrations around 10Hz. Therefore, in order to prevent malfunction, the Japan Elevator Association's technical standards for seismic design and construction guidelines state that the frequency characteristics of the sensor are ``a flat characteristic in the range of 1 to 5 Hz for normal grade, and a flat characteristic in the range of 0.1 to 5 Hz for precision grade. The sensitivity should be flat in the range exceeding 5 Hz.''

In response to the above-mentioned characteristics of earthquakes, conventional earthquake sensors are generally of an electrodynamic type, a strain gauge type, a piezoelectric type, or a mechanical weight drop type.

FIG. 3 shows an example of the structure of an electrodynamic earthquake sensor (vertical sensor). This electrodynamic earthquake sensor passes through the magnetic flux 5 generated by the permanent magnet 4.
When a coil 3 fixed to a weight 2 moves up and down due to vibration, a voltage is generated at both ends of the coil 3, and the magnitude of this voltage is proportional to the moving speed of the coil 3. This is used to detect earthquakes. It is. In addition,
1 is a spring system that supports the weight 2, and 6 is a yoke that forms a magnetic path. The natural frequency of this spring system 1 is normally set to about 4 Hz, but it is difficult to make the frequency characteristics fall above 5 Hz as mentioned above with this method (spring system problem), and it is usually 10 Hz.
If the temperature exceeds a certain level, it becomes a downward characteristic. Furthermore, since the natural frequency is greatly affected by the precision of the spring system 1 and the weight 2, the weight of the weight, etc. is actually adjusted by hand in the final process. That is, this electrodynamic seismic sensor has problems in terms of accuracy and the amount of effort required for adjustment.

In addition, in a strain gauge type earthquake sensor, strain gauges are installed in the X and Y directions, and their electrical outputs are vector-combined to obtain acceleration, but the frequency characteristics of the strain gauges themselves are Since it reaches up to KHz, an electric filter can be used to
It is designed to attenuate frequencies above Hz. Therefore, strain gauge type earthquake detectors are greatly affected by the characteristics of this filter, and also include many error factors such as the need for multipliers to perform vector synthesis, which poses problems in terms of reliability. be. In addition,
Piezoelectric earthquake sensors also use a vector synthesis method and have similar problems.

FIG. 4 shows an example of the structure of a falling weight type earthquake sensor. This is because in a stationary state, a weight 13 (magnetic material such as iron) is attracted to the permanent magnet 11 fixed to the case 10, but when vibrations above a certain level occur, the weight 13 falls. The lever 12 fitted into the weight 13 is the fulcrum 15
By rotating in the direction of the arrow around the center, the actuator 14' of the micro switch 14 is actuated to sense an earthquake.

Although this method is simple, the sensing level depends on the relationship between the attraction force of the magnet and the weight of the weight.
Adjustment is difficult and at the same time low frequency (1 Hz)
The following) have the disadvantage of being difficult to detect, and also have problems in terms of accuracy and reliability.

[Means for solving problems]

The present invention includes a container with a sealed structure that blocks light from the outside, and at the bottom of the container there is a first liquid with a large specific gravity and a high surface reflectance, and a second liquid with a small specific gravity and a low surface reflectance. is included, and the first
above the liquid and the second liquid is a light source that irradiates the inside of the container, and a light source that receives reflected light from the surface of the first liquid among the light emitted by the light source and converts the amount of light into an electrical signal. a photoelectric conversion element, which detects the inclination of the liquid level of the first liquid as a change in the amount of reflected light from the first liquid surface, and outputs an output when an output electric signal of the photoelectric conversion element is larger than a predetermined value. It is equipped with a signal processing section that emits a signal.

[Effect]

If the surface of the first liquid changes into an uneven shape in response to the vibration while being damped by the second liquid, this change is taken as a change in the amount of reflected light on the liquid surface, and the level of vibration caused by the earthquake is detected.

[Principle of the present invention]

That is, the basic principle of the present invention is as follows.

For simplicity, when a small cylindrical container containing a liquid is vibrated in the horizontal direction with a constant vibrational acceleration, the movement of waves on the surface of the liquid is expressed as follows: the magnitude of the vibrational acceleration is A, the acceleration of gravity is g, and the amplitude of the wave. and the wavelength a
and λ, and if the X-axis is taken along the wave path, then as shown in Figure 10, the vibration of a 1/2-wavelength sine wave that appears at various peaks or troughs on the side wall of the small cylindrical container is generated. The main component vibrates. When the angle of inclination θ of the liquid level is small, it is given by the following equation.

θ=A/g=2πa/λcos2πχ/λ...In other words, since the magnitude A of the vibrational acceleration is proportional to the inclination angle of the liquid surface, in order to detect the vibrational acceleration, it is sufficient to detect the inclination angle of the liquid surface. become.

Waves in a cylindrical container like this require the liquid to move vertically at the side wall, and the wave pattern has peaks or troughs that are large enough to be located at the side wall. The fundamental wave mode is shown in FIG. 10, and the fundamental wave mode is shown in FIG. 11 during vertical vibration.

Next, the basic optical system for detecting the angle of inclination of the liquid surface is as shown in FIG.

That is, the incident light beam on the liquid surface is φ ₁ , the reflected light beam on the stationary liquid surface is φ ₂ , the reflected light beam on the tilted liquid surface is φ ₃ , and the photoelectric conversion element when the liquid surface changes by the tilt angle θ If the amount of change in the luminous flux incident on is φ ₄ , then
As is clear from the figure, when the liquid surface is tilted by an angle of θ, the moving angle of the reflected light flux becomes 2θ, so the amount of change in the light flux incident on the photoelectric conversion element is φ ₄ (the amount of change in the light flux reflected from the liquid surface) ) is proportional to θ.

Now, when we use something like a photodiode as a photoelectric conversion element, its output is proportional to the incident luminous flux (light amount), so when the cylindrical container is accelerated,
The output u at that time can be expressed by the following equation if the equations are considered.

u=K ₁ ·θ=K ₂ A... However, K ₁ and K ₂ are constants. In other words, the output of the photoelectric conversion element is proportional to the vibration acceleration.

〔Example〕

FIG. 5 is an example of a block diagram showing the configuration of an earthquake sensor according to the present invention. In the figure, 20 receives reflected light from different types of liquids contained in a container, and receives an electrical signal according to the amount of received light. a sensing unit that outputs 20a, 2;
Reference numeral 1 denotes a signal processing section that outputs an output when the electric signal 20a exceeds a predetermined value. In this example, the signal processing unit 21 has two levels of set values, and when the output of the preamplifier (AC amplifier) 22 is larger than the first set value, the first comparator 23 and output circuit 24 output a signal. 24a is output, and if it is larger than the second set value, the second comparator 25 and output circuit 26 output a signal 26a.
Note that a filter for noise removal may be provided after the preamplifier 22, and the setting values are not limited to two stages as described above, but may easily be set to any plurality of stages.

FIG. 1 is a cross-sectional view showing the structure of an embodiment of the sensing unit 20, in which 31 is a container with a closed structure that blocks light from the outside, and 32 is a liquid contained in the container 31, which has a specific gravity such as mercury. The liquid 33 has a large, low viscosity and high surface reflectance, and is a liquid such as oil, which has a lower specific gravity, higher viscosity, and lower surface reflectance than the liquid 32, and constitutes a double layer liquid 34. 35
is a power source, 36 is a light source such as a light emitting diode,
37 is a photoelectric conversion element that receives light. In FIG. 1, when the container 31 is in a stationary state, the double layer liquid 34 is also in a stationary state, so the distribution of reflected light from the liquid 32 is constant and the output 37a of the photoelectric conversion element 37 is also constant. However, when the double layer liquid 34 is shaken due to vibrations such as earthquakes, the shape of the surface of each liquid 32 and 33 making up the double layer changes, and in particular the reflection and scattering of light from the liquid 32 changes. As the shape changes, the luminance distribution inside the container 31 also changes, and correspondingly, the output 37a of the photoelectric conversion element 37 (however, the output after passing through the preamplifier 22).
Based on the above-mentioned principle, the output voltage of the sensor 20 (hereinafter referred to as the output voltage of the sensor 20) is calculated as shown in Fig. 6 (a) when the frequency of the earthquake is low.
b indicates the case where the earthquake frequency is high). The output level in this case is determined by the frequency characteristics.

If the vibration frequency of the earthquake changes, the way the liquid 34 oscillates will differ between P waves and S waves, so the brightness distribution inside the container 31 will also change slightly, and this effect will appear on the output voltage.

Here, the reason why the double layer liquid 34 composed of different types of liquids 32 and 33 is placed in the container 31 will be explained in detail below. Figure 7 shows a liquid 32 with high specific gravity, low viscosity, and high surface reflectance.
JISI grade mercury only 1g and 2g in diameter 30mm and depth
The experimental results of the output characteristics with respect to the vibration frequency of the sensor 20 when placed in an inverted conical container 31 having a diameter of 12.6 mm and an apex angle of 100° are shown. FIG. 7a shows the case of horizontal vibration (hereinafter referred to as horizontal vibration; the solid line indicates 2 g and the broken line represents 1 g), and FIG. 7 b shows the case of vertical vertical vibration (hereinafter referred to as vertical motion). As can be seen from Figure 7, at a specific frequency, for horizontal motion, an extreme peak A occurs around 5 Hz for 2 g of mercury, a peak around 8 Hz for 1 g of mercury, and a peak B for vertical motion. It has also been found through experiments that the frequency at which this peak occurs changes depending on the amount of liquid 32.

On the other hand, Fig. 8 shows JIS2232 aircraft hydraulic oil as a liquid 33 with low specific gravity, high viscosity, and low surface reflectance.
The experimental results of the output characteristics with respect to the vibration frequency of the sensor 20 when placed in an inverted conical container 31 with an apex angle of 100° are shown. FIG. 8a shows the case of horizontal movement, and FIG. 8b shows the case of vertical movement. In this case, for horizontal motion, when 1.5 g of aircraft hydraulic oil is used, peak A occurs as shown by the dotted line in the figure, but when 0.5 g of aircraft hydraulic oil is used, the low frequency is maximized as shown by the solid line in the figure. It was found that the characteristic decreases as the frequency increases. It was also found that in the case of 0.5 g of aircraft hydraulic oil, the low frequency increases slightly with respect to vertical motion, and as the frequency increases, the characteristics become approximately flat.

Next, a double layer liquid 34 is made in the same shape using an amount of liquid 32 having the characteristics shown in FIG. 7, that is, 1 g of mercury, and an amount of liquid 33, that is, 0.35 g of hydraulic oil having the characteristics shown by the solid line in FIG. FIG. 9 shows the experimental results of the output characteristics of the sensor 20 with respect to the vibration frequency when the sensor 20 is placed in a container. FIG. 9a shows the case of horizontal movement, and FIG. 9b shows the case of vertical movement. Here, the parameters (g ₁ , g ₂ , g ₃ , g ₄ ) shown in FIG. 9a are horizontal vibration accelerations v ₁ to v ₄
is the output voltage at 5 Hz of each vibration acceleration, and it was found that the magnitude of the acceleration and the output voltage are approximately proportional. Incidentally, Fig. 9 a ₁ shows a case where the amount of hydraulic oil is changed to 0.25 g while keeping the amount of mercury at 1 g, and Fig. 9 a ₂ shows a case where the amount of hydraulic oil is changed to 0.45 g. or,
The parameters (g ₅ , g ₆ ) shown in FIG. 9b are vertical vibration accelerations, and v ₅ , v ₆ are the vibration accelerations of the sensor 20 at 5 Hz for each vibration acceleration in the case of 1 g of mercury and 0.35 g of hydraulic oil.
The output voltages v ₅ and v ₆ are proportional to the magnitude of vibration acceleration. As is clear from Fig. 9, if appropriate amounts of liquids 32 and 33 are selected, the frequency characteristics for each vibration acceleration will be approximately flat in the range of 1 to 5 Hz for both horizontal and vertical motions, and will have a falling characteristic above 5 Hz, resulting in the frequency of the seismic wave. It was confirmed that the characteristics match the characteristics and are ideal for an earthquake sensor.

As mentioned above, it is extremely difficult to obtain flat characteristics in the frequency range of 1 to 5 Hz using only either liquid 32 or 33, but a double layer liquid containing different types of liquids 32 and 33 as in the present invention If 34 is used, the peak (resonance point), which is the characteristic of only the liquid 32, is suppressed by the damping effect of the liquid 33, and at low frequencies, the characteristics of the liquid 33 work to increase the characteristics of the liquid 33, which decreases, resulting in stability. The sensor 20 itself can have flat characteristics within the ideal range of 1 to 5 Hz.

〔Effect of the invention〕

According to the present invention, by using different types of liquids as described above, the sensing section itself can be made to match the frequency characteristics of seismic waves, so signal processing in the signal processing section 21 can be easily performed and malfunctions can occur. There is no fear of this, there is almost no need for installation adjustment (no need for strict leveling), and the configuration is very simple (low price). Furthermore, since the output voltage of the sensing section is linear with respect to the magnitude of acceleration, the set value can be set in any number of stages, and it is possible to detect both P-wave and S-wave seismic waves. It has many excellent features that have not been seen before.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a sensing section according to the present invention, FIG. 2 is a view showing an example of the power spectrum of seismic waves, FIG. 3 is a view showing an example of the structure of an electrodynamic seismic sensor, and FIG. Figure 5 is a diagram showing an example of the structure of a falling weight type earthquake sensor, Figure 5 is a block diagram showing the configuration of an embodiment of the present invention, Figure 6 is a diagram showing experimental results regarding the output of the sensing section, Figures 7 and 8 are diagrams showing experimental results of output characteristics versus vibration frequency for output voltage for different types of liquids, and Figure 9 is output characteristics for output voltage versus vibration frequency for double-layer liquids. 10, 11, and 12 are explanatory diagrams for explaining the basic principle of the present invention. 20... Sensing section, 21... Signal processing section, 22...
...Preamplifier, 23, 25...Comparator, 2
4, 26... Output circuit, 31... Container, 32, 3
3...Liquid, 34...Double layer liquid, 36...Light source, 37...Photoelectric conversion element.

Claims (1)

[Scope of Claims] 1. A container with a closed structure that blocks light from the outside is provided, and a first liquid having a large specific gravity and a high surface reflectance and a second liquid having a small specific gravity and a low surface reflectance are provided at the bottom of the container. A light source that irradiates the inside of the container is provided above the first liquid and the second liquid, and among the light emitted by the light source, reflected light from the surface of the first liquid is contained. and a photoelectric conversion element that receives light and converts the amount of light into an electrical signal, and detects the inclination of the liquid level of the first liquid as a change in the amount of reflected light from the surface of the first liquid, and converts the amount of light into an electric signal. An earthquake sensor characterized by comprising a signal processing section that emits an output when an output electrical signal is larger than a predetermined value. 2. The earthquake sensor according to claim 1, wherein the first liquid is mercury. 3. The earthquake sensor according to claim 1, wherein the second liquid is a liquid that damps the movement of the first liquid. 4. The earthquake sensor according to claim 1, wherein the second liquid is aircraft hydraulic fluid. 5. The earthquake sensor according to claim 1, wherein the signal processing section includes a comparator for comparing with a plurality of predetermined values. 6. The signal processing unit includes an AC amplifier that receives the output electric signal of the photoelectric conversion element as input and detects the inclination of the liquid level of the first liquid as a change in the amount of light reflected from the first liquid surface. An earthquake sensor according to claim 1.