JPH0245133B2 - - 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 1 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.

Figure 2 shows an example of the structure of an electrodynamic seismic sensor (vertical sensor). In this electrodynamic earthquake sensor, when a coil 3 fixed to a weight 2 moves up and down due to vibration in a magnetic flux 5 generated by a permanent magnet 4, a voltage is generated at both ends of the coil 3. Earthquakes are sensed by utilizing the fact that the size is proportional to the moving speed of the coil 3. In addition, 1
6 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 about 10 Hz. The above results in a descending 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. Note that piezoelectric earthquake sensors also use a vector synthesis method and have similar problems.

FIG. 3 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 is affected by the relationship between the attraction force of the magnet and the weight of the weight, and it is difficult to adjust, and at the same time, it has the disadvantage that it is difficult to detect at low frequencies (1 Hz or less). However, there are still problems with accuracy and reliability.

[Means for solving problems]

The present invention includes a container with a sealed structure that blocks light from the outside, the container contains a liquid that reflects light, and above the liquid there is a light source that illuminates the inside of the container, and a light source that emits light from the light source. A sensing section equipped with a photoelectric conversion element that receives reflected light from the surface of the liquid and converts the amount of light into an electrical signal is provided, and the inclination of the liquid surface is detected as a change in the amount of reflected light from the liquid surface. The photoelectric conversion element includes a signal processing section that outputs an output when the output electric signal of the photoelectric conversion element is larger than a predetermined value.

[Effect]

With the configuration as described above, the detection of the vibration level due to an earthquake can be detected as a change in the amount of reflected light on the liquid surface.

[Principle of the present invention]

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. If a is the wavelength of the wave, and λ is the wavelength of the wave, and the x-axis is taken along the course of the wave, then the 10th
As shown in the figure, the main component of the vibration is a 1/2-wavelength sine wave that forms peaks or valleys on the side wall of the small cylindrical container. And the inclination angle θ of the liquid level
If the value is small, it is given by the following formula.

θ=A/g=2πa/λcos2πx/λ...In other words, the magnitude A of the vibrational acceleration is proportional to the inclination angle of the liquid surface, so 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 basic mode is shown in FIG. 10, and the basic 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= _K1・θ= _K2・A... However, _K1 and _K2 are constants. In other words, the output of the photoelectric conversion element is proportional to the vibration acceleration.

Therefore, the sensing unit converts the luminance distribution of reflected light from the liquid surface, which changes as the liquid in the container is shaken by seismic waves and the shape of the liquid surface changes, into an electrical signal and outputs it. , the signal processing section identifies the vibration level based on the magnitude of this output signal. This provides a highly reliable earthquake sensor with a simple configuration and high accuracy that can detect both horizontal vibration waves (hereinafter referred to as S waves) and vertical vertical vibration waves (hereinafter referred to as P waves). be.

〔Example〕

FIG. 4 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, 20 receives reflected light from a liquid in a sealed container containing liquid, and a signal 20a corresponding to the amount of light received. The sensing section 21 outputs the signal 2.
This is a signal processing section that generates an output when 0a exceeds a predetermined value. In this example, the signal processing unit 21 has two stages of setting values, and the preamplifier (AC amplifier)
If the output of 22 is larger than the first set value, the first
The comparator 23 and output circuit 24 output the signal 24a, and if the signal 24a is larger than the second set value, the second comparator 25 and output circuit 26 output the signal 24a.
A signal 26a is output. Note that a filter for noise removal may be provided after the preamplifier 22, and the set value is not limited to two stages as described above, but may be set to any number of stages.

FIG. 5 is a cross-sectional view showing the structure of one 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 oil or mercury contained in the container 31 that reflects light. 33 is a power source, 34 is a light source such as a light emitting diode that illuminates the inside of the container 31, and 35 is a photoelectric conversion element that receives light. In FIG. 5, when the container 31 is placed in a stationary state, the liquid 32 is also in a stationary state, so the distribution of reflected light from the liquid 32 is constant, and the output 20a of the photoelectric conversion element 35 is also constant. However, when the liquid 32 shakes due to vibrations such as earthquakes, the shape of the liquid surface changes, and in particular, the form of reflection and scattering of light from the liquid 32 changes, causing the brightness distribution inside the container 31 to change as well. The output 20a of the photoelectric conversion element 35 also fluctuates.

FIG. 6 is a diagram showing how the liquid 32 oscillates within the container 31 when horizontal vibration occurs. In the case of a relatively low frequency, as shown in a,
The liquid 32 moves largely in the direction of the arrow, and when the frequency is relatively high, as shown in b, the surface of the liquid 32 shakes little by little (there is no movement of the liquid), and the inclination angle of the surface of the liquid changes from moment to moment.

In this way, the manner in which the liquid oscillates differs depending on the vibration frequency, and as a result, based on the above-mentioned principle, the fluctuation in the output of the photoelectric conversion element 35 also differs depending on the vibration frequency.

FIG. 7 shows the experimental results for the output 20a of the photoelectric conversion element 35 (output after passing through the preamplifier 22), where a indicates the case where the frequency is low and b indicates the case where the frequency is high. Each case is shown.

FIG. 8 is a diagram showing the experimental results of the output characteristics of the output voltage shown in FIG. 7 with respect to the vibration frequency when engine oil is used as the liquid.
Here, the parameters (a1, a2, a3, a4) are vibration accelerations, and as an example, a1=30gal, a2=
80gal, a3=120gal, a4=150gal, 5Hz
The output voltages when are b1=0.45V and b2=
1.2V, b3 = 1.85V, b4 = 2.3V, and the ratio of the magnitude of acceleration and output voltage is almost proportional.

In this way, the relationship between acceleration and output voltage is linear, and as is clear from FIG.
Hz is almost a flat characteristic, and above 5Hz it is a falling characteristic, matching the frequency characteristic of seismic waves, making it an ideal characteristic for earthquake detectors (in the case of mercury, it is 3~3Hz).
It shows particularly sharp output characteristics at 4Hz).

In addition, although the above has been described for the case of S waves, P
In the case of waves, the liquid oscillates as shown in Figure 9, and changes in the brightness distribution of the reflected light from the liquid,
That is, by capturing changes in the output voltage of the sensing section, P waves can be sensed in the same way as S waves.

Also, as the liquid in the container, mercury that reflects light or oil that has an appropriate viscosity is suitable.
Oil is better in terms of accuracy in capturing only seismic waves.
Mercury is slightly better in cases where it is necessary to detect frequencies as low as 0.1 Hz in high places such as high-rise buildings.

〔Effect of the invention〕

According to the present invention, as mentioned above, the sensing part itself matches the frequency of seismic waves, and malfunctions can be almost eliminated, and installation adjustment requires almost no effort (no need for strict leveling). , its configuration is very simple (low cost). 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 drawings]

Figure 1 shows an example of the power spectrum of seismic waves, Figure 2 shows an example of the structure of an electrodynamic earthquake sensor, and Figure 3 shows an example of the structure of a falling weight earthquake sensor. , FIG. 4 is a block diagram showing the structure of an embodiment of the present invention, FIG. 5 is a sectional view showing the structure of an embodiment of the sensing section, and FIG. Figure 7 is a diagram showing the experimental results regarding the output of the sensing section, and Figure 8 is a diagram showing the
Figure 9 shows the experimental results of the output characteristics of the output voltage versus vibration frequency; Figure 9 shows how the liquid in the container oscillates in response to P waves; Figures 10 to 12 illustrate the basic principle of the present invention. It is an explanatory diagram for explanation. 20... Sensing section, 21... Signal processing section, 22...
...Preamplifier, 23, 25...Comparator, 2
4, 26... Output circuit, 31... Container, 32...
Liquid, 34...Light source, 35...Photoelectric conversion element.

Claims (1)

[Claims] 1. A container having a sealed structure that blocks light from the outside, the container containing a liquid that reflects light,
A sensing device is provided above the liquid, and includes a light source that illuminates the inside of the container, and a photoelectric conversion element that receives reflected light from the surface of the liquid among the light emitted by the light source and converts the amount of light into an electrical signal. and a signal processing unit that detects the inclination of the liquid level as a change in the amount of reflected light from the liquid surface and outputs an output when the output electric signal of the photoelectric conversion element is larger than a predetermined value. Features an earthquake sensor. 2. The earthquake sensor according to claim 1, wherein the liquid is a liquid with high surface reflectance. 3. The earthquake sensor according to claim 2, wherein the liquid is mercury. 4. The earthquake sensor according to claim 1, wherein the signal processing section includes a comparator for comparing with a plurality of predetermined values. 5. Claims characterized in that 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 as a change in the amount of light reflected from the liquid surface. Earthquake sensor according to paragraph 1.