JPS6364753B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a photoelectric rain gauge that counts raindrops passing through a light beam between a projector and a light receiver.
Specifically, it can be used as a rainfall intensity determination sensor to control the operation of equipment depending on the intensity of rainfall, for example to control the operation of vehicle windshield wipers, and also to quantitatively measure rainfall to obtain weather information. The present invention relates to a photoelectric rain gauge that is used as a sensor for measuring rainfall intensity or precipitation amount, and is characterized by a fast response speed. Conventionally, rain gauges commonly available on the market include:
For example, there is a rain gauge that can be tipped over, but this has the disadvantage of slow response speed. In this case, if one fall is 0.1mm
Even if you use a measuring meter (regular rain gauges are certified by the Japan Meteorological Agency and have a capacity of 0.5 mm per fall), it takes 12 seconds to fall once in the face of heavy rain of 30 mm/hr (as mentioned above).
60 seconds is required for a one-turn type with a 0.5 mm measuring square).
In addition, some optical rain gauges utilize the fluctuation of the received light due to the multiple scattering effect of the light propagated by raindrops, but in this case the sensor must have an extremely long optical path length of several hundred meters or more. The disadvantages were that the propagation loss of the light inside was large, the signal processing was complicated, the equipment became large, and the installation location was restricted to ensure visibility. In order to overcome the above-mentioned drawbacks, the present invention reduces the optical path length to approximately
The objective is to provide a rain gauge that is short, less than 2 meters long, and has a high response speed by taking advantage of its photoelectric features. When shortening the optical path length, the raindrops do not scatter a large amount of the propagating light, so in this case, the effect of blocking the propagating light by the raindrops, that is, the attenuation of the amount of received light due to the absorption or single scattering effect by the raindrops can be used. become. Hereinafter, the present invention will be explained with reference to the drawings of one embodiment. Note that the principle of the present invention applies equally to visible light and invisible light, so in the following description, visible light and invisible light will be collectively referred to as "light." FIG. 1 shows the basic structure of the photoelectric rain gauge of the present invention together with its peripheral structure. 1 is a light source, and the light source 1 is electrically or mechanically modulated by a modulator 2 in order to distinguish it from background light. Reference numeral 3 denotes a condensing optical element disposed in front of the light source 1. The condensing optical element 3 is made of, for example, a convex lens or a concave mirror, and condenses the light beam into a light beam 13. In this case, when the light source 1 itself is condensed and becomes a light beam 13 in advance, for example, in the case of a laser beam, the condensing optical element 3 can be omitted. The light source 1, modulator 2, and condensing optical element 3 are collectively referred to as a light emitting optical system 4. Reference numeral 5 denotes a light-receiving optical element consisting of a convex lens, a concave mirror, etc., arranged at a finite distance (approximately 2 m or less) away from the light-receiving optical element 3, and a photoelectric conversion element 6 and a preamplifier are placed behind the light-receiving optical element 5. 7, and the light receiving optical element 5, photoelectric conversion element 6, and preamplifier 7 constitute a light receiving optical system 8. Here, the light beam 13 emitted from the light source 1 is modulated by raindrops while propagating through a space of about 2 m or less. This change in light amount is extracted as an electrical signal by the light receiving optical element 5, the photoelectric conversion element 6, and the light receiving optical system 8 of the preamplifier 7. Note that if it is guaranteed that the photoelectric conversion element 6 has a large area and high sensitivity, the light receiving optical element 5 may be removed from the light receiving optical system 8. Furthermore, if the output from the photoelectric conversion element 6 is sufficiently large, the preamplifier 7 can be placed away from the light receiving optical system 8 and closer to the signal processing circuit. The electric signal converted in this way is subjected to a detection circuit 9 connected to a light receiving optical system 8, in which only the variation is extracted, and is further guided to a square detector 10, where the magnitude of the variation is detected by the output I. This will be output as . The signal waveforms after this detection circuit 9 are shown in FIGS. 2A and 2B. Figure 2A is a typical signal waveform for light rain, and Figure 2B is a signal waveform for heavy rain.It is clear that the heavier the rain, the larger the fluctuation, that is, the larger the effective value of the detection output. be. This effective value can be divided into several levels and the rainfall intensity can be determined accordingly. In addition to arranging the light-emitting optical system 4 and the light-receiving optical system 8 in a straight line as shown in FIG.
The optical path of the light beam 13 may be reflected in several stages using a reflector 21 as in another embodiment shown in FIG. In FIG. 3A, a reflector 21 is attached to a part of the light beam 13, and the reflector 2
1 is inserted together with a cover member 22 to protect it from rain, and the light beam 13 is reflected once and guided to the light receiving optical system 8 installed in parallel with the light emitting optical system 4, thereby reducing the size of the entire device. In FIG. 3B, a cover member 22 having three reflectors 21 is interposed in a part of the light beam 13, and the light beam 13 is reflected three times to make the optical path reciprocate and be guided to the light receiving optical system 8. This reduces the size of the entire device. To explain quantitative rainfall intensity measurement in more detail, first, the output of the detection circuit 9 is converted into a pulse shaping circuit 11.
The pulse shaping circuit 11 is adjusted so that the passage of one raindrop in the light beam 13 generates one pulse, and the number of output pulses per unit time is counted by the counting circuit 12. This is Pc〔/sec〕
This is extracted from the output as . Now, the counted pulse number Pc and rainfall intensity h
[mm/hr] is related as follows. FIG. 4 is an explanatory diagram showing the concept of the light beam 13 for explaining this rainfall intensity measurement. Although the light beam is drawn in a cylindrical shape in this figure, the light beam does not necessarily have to be cylindrical. At this time, if the diameter of the condensing optical element 3 and the light receiving optical element 5 is d [m], and the distance between them, that is, the optical path length, is L [m], then the cross-sectional area of the light beam 13 in the vertical direction is S [m ² ].
is given by S=d・L[m ² ]...(1). However, it is assumed that the rain 14 falls vertically. When the rainfall intensity is h [mm/hr], the total volume v of raindrops passing through the cross-sectional area S [m ² ] in one second is expressed by the following formula. v=10 ^-3 /3600h s [m ³ /sec] ...(2) On the other hand, if the number of output pulses per second is Pc and the average volume of raindrops at that time is v _r [m ³ ], then the formula (2) ) is also expressed by the following equation. v=Pc v _r [m ³ /sec] …(3) The average volume of raindrops v _r is the volume probability density function P of raindrops
(h, a), v _r (h) = ∫ ^∞ _p 4/3πa ³ p (h, a) da … (4) where a: given by the radius of the raindrop, and the average volume of the raindrop is determined only by the rainfall intensity h becomes a function of Also, the volume probability density function of raindrops is
It is a function of rainfall intensity h [mm/hr] and raindrop radius a [m], and from the raindrop size distribution n [h, a) da, that is, the number of raindrops with radius a to a + da in a unit volume, the following It can be defined by Eq. P(h,a)da=4/3πa ³ n(h,a)da/∫ ^∞ / ₀
4/3πa ³ n (h, a) da = a ³ /6 α ⁴ e ^- 〓 ^a da …(5) where n (h, a) da = n ₀ e ^- 〓 ^a da … (5′) n ₀ =8×10 ⁶ [m ^-4 ] α=8200h ^-0.21 [m ^-1 ]. Substituting equation (5) into equation (4) and further substituting into equation (3), v=160π/8200 ³ Pch ^0.63 [m ³ /sec] ...(6), and the above equation (6) and equation ( 2) are equal, we get h=(3.28×10 ^-3 /S) ^2.7 Pc ^2.7 [mm/hr] …(7). In other words, the rainfall intensity is 2.7 of the pulse number Pc
Since the proportionality constant includes only the sensor specifications S, it can be easily given, and the rainfall intensity can be quantitatively calculated. Figure 5 shows the distance between transmitting and receiving light, that is, the optical path length.
= 2 m, optical beam diameter d = 4 × 10 ^-2 m, GaAs
It is a graph showing the relationship between the number of output pulses Pc obtained using a light beam emitted by modulating an LED at 30 KHz and the rainfall intensity h. In this case, the rainfall intensity was measured using a normal rain gauge, and the solid line in the figure shows the calculated value using Equation 7, and a good agreement between the theoretical value and the measured value was obtained. However, there are some differences in light rain. Correction in this case will be described below. 6th
The figure shows the volume probability density function expressed by Equation (5), and it can be seen from the figure that as the rainfall intensity decreases, the ratio of raindrops with small radius to the unit volume increases. As the radius of a raindrop becomes smaller, the change in light intensity when the raindrop passes through the light beam becomes smaller, and if that change becomes smaller than the noise of the electrical signal processing circuit of the light receiving optical system, the raindrop will not be detected. In other words, the lower limit value amin is applied to the raindrop that generates one pulse in the pulse shaping circuit 11.
It means that there is. This lower limit value is the electric signal processing circuit (in Fig. 1, the photoelectric conversion element 6,
Preamplifier 7, detection circuit 9, pulse shaping circuit 11
and counting circuit 12), and in the apparatus used in the experiment shown in FIG. 5, amin=3.1.
×10 ^-4 m. Once the minimum detectable raindrop radius is determined in this way, the volume probability Pmiss that the photoelectric rain gauge will miscount raindrops is given by the following equation from equation (5). Pmiss=∫ ^amin _p P(h,a)da=1−e ^- 〓 ^amin [(αamin) ³ /6+(αamin) ²
/2+ (αamin)+1] …(8) Therefore, from equation (3), if the number of pulses counted with miscount is Pcmiss, then Pcmiss=Pc(1−Pmiss) …(9) , the actually measured number of pulses Pcc is 1/(1
−Pmiss) will give Pc.
Therefore, to calculate the rainfall intensity h from Pcc, use the formula
Substitute into (7) and get h=(3.28×10 ^-3 /S) ^2.7 (Pcc/1−Pmiss) ^2.7 …(1
0). The value corrected by amin=3.1×10 ^-4 m is the seventh
Indicated by dotted lines in the figure. In the figure, the solid line is the value of equation (7), and it can be seen that the correction value matches the actual measured value marked O very well. Next, we will consider the observation field volume. In the example shown in FIG. 4, the observation field volume V is a cylinder and is defined as V=π(d/2) ² L (11) (the observation field volume does not necessarily have to be a cylinder). The principle of the present invention is based on the premise that the number of raindrops existing within this observation field volume V is one or less. This is because when there are two or more raindrops, miscounts occur due to overlapping of raindrops within V. Now, the number n _r of raindrops within this observation field volume is calculated by formula (5') as n _r = V∫ ^∞ _anio n(h, a) da = Vn ₀ /αe ^- 〓 ^amin ...(12) . Using the device that obtained the measured values shown in Figure 5 as an example, when these values are calculated for rainfall intensity, the results are as shown in the table below.

[Table] The above table also shows the correction coefficients shown in Figure 7. From the same table, assuming n _r 1, rainfall intensity is 15 mm/
It can be seen that the principle of the present invention is applicable up to hr. When measuring rainfall intensity greater than 15 mm/hr, the observation field volume may be reduced so that the n _r value within that volume is 1 or less. Incidentally, this means that the folding structure shown in FIGS. 3A and 3B is applied to the quantitative calculation of rainfall intensity by counting the number of pulses per unit time as set forth in claim 2. However, the overlapping portion of the light beams must be excluded from the cross-sectional area S in the calculation. In addition, in the above example, Pc is the number of output pulses per second, but by adjusting the integration time of the counting circuit 12, the average rainfall intensity for that time can be calculated from the average number of output pulses for 10 seconds or 1 minute. By increasing the integration time and increasing the integration time, for example, 1
It goes without saying that it is possible to obtain daily rainfall amounts. Furthermore, to explain other embodiments, first, the principle of the present invention is derived from the assumption that rain falls perpendicularly to the light beam, as described above. In general, most rainfall can be thought of as falling vertically, but when accompanied by strong winds, such as during typhoons, the direction of the rainfall must be considered. That is, the explanatory diagrams shown in FIGS. 8A and 8B show the case where the direction of rainfall is taken into account in the explanatory diagram of FIG. 4. As is clear from FIG. 8A, if the direction of the light beam 13 is perpendicular to the rain direction and the light beam 13 is cylindrical, the cross-sectional area crossed by the raindrop is S, which is the same as the shaded area in FIG. be. In this case, no correction is required for the counted number of pulses. However, if the direction of rainfall is within a plane that includes the axis of the light beam and forms an angle α with the light beam, that is, in the case of Figure 8B, the counted pulse number Pco is There is a relationship between the number of pulses Pc passing through the same cross-sectional area S and Pc=Pco/cosα (13). This cosα is called the rainfall direction correction coefficient. FIG. 9 shows the system diagram shown in FIG. 1 in which the light-emitting optical system 4 and the light-receiving optical system 8 are integrated into an integrated structure 31 by a connecting body 34 having a pivot portion 33 in the center. Furthermore, it is only necessary that the axis of the light beam 13 be automatically adjustable so that it is perpendicular to the wind direction, that is, the direction of rainfall. In this way, the cross-sectional area S will be constant, and the rain intensity will always be calculated correctly regardless of the rain direction. In the example shown in FIG. 9, this adjustment mechanism uses a wind direction plate 32 to adjust the direction. Apart from this, it goes without saying that the direction of the light beam may be adjusted by detecting the direction of the wind or the direction of rainfall. Next, three integrated light emitting optical systems 4 and light receiving optical systems 8 may be prepared, as shown in FIG. 10, and arranged so that the axes of the respective light beams 13 are orthogonal to each other. That is, in the case of FIG. 10, a three-dimensional reflector 41 is provided in the center, and light beam splitters 42 are installed in three directions orthogonal to the three-dimensional reflector 41. The light-emitting optical system 4 and the light-receiving optical system 8 are positioned so that the light-emitting beam and the light-receiving beam are on the same optical axis, thereby eliminating errors caused by the optical axis difference between the light-emitting beam and the light-receiving beam. However, the optical path length L in this case is the distance from the light receiving optical system 4 to the three-dimensional reflector 41. It is necessary to attach a cover member 22 to the three-dimensional reflector 41 to protect it from rain, as in FIG. 3. In consideration of this cover member 22, each cross-sectional area must be kept the same. Generally, if the direction of rainfall is θ from the Z axis and φ from the x axis, the respective correction coefficients cosαi
(i = x, y, z) with reference to Figure 11 becomes. Therefore, the number of output pulses for each
If Pci (i = x, y, z), Pcx ² + Pcy ² + Pcz ² = (Pccosα _x ) ² + (Pccosα _y ) ² +
(Pccosα _z ) ² = 2Pc ² ...(15) The number of pulses Pc passing through the same cross-sectional area S in the plane perpendicular to the direction of rainfall is Pc can be determined regardless of the direction of rainfall. The rainfall intensity is calculated from this Pc using equation (7). As described above, the rain gauge of the present invention converts the light from the light emitting light source into a focused light beam, receives the light beam by a light receiving element placed a certain distance away (a finite distance such as 2 m or less), By using a photoelectric method that detects changes in the intensity of light when raindrops pass through a light beam, it is possible to quickly respond to rainfall intensity and precipitation measurement, and in this case, the raindrops are counted by converting them into electrical signal pulses. It is possible to measure the amount of rainfall instantaneously. Furthermore, since the optical path of the light beam can be set extremely short in the present invention, the light emitting part and the light receiving part can be integrated into an integrated structure, so that the entire device can be made compact, and can be installed, for example, in the windshield wiper part of an automobile. This has the advantage of being able to be attached to various devices, such as automatically driving the wipers when it starts to rain while driving.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention. Fig. 1 is a system diagram, Fig. 2 A and B are signal waveform diagrams during light rain and signal waveform diagrams during heavy rain, and Fig. 3 A and B are other diagrams. 4 is an explanatory diagram of the light beam section, FIG. 5 is a relationship curve diagram between the number of output pulses and rainfall intensity, and FIG. 6 is a volume probability density function diagram of raindrops. 7th
The figure is a relationship curve diagram showing the actual measured value, calculated value, and correction value of the number of output pulses and rainfall intensity. Figures 8A and B are explanatory diagrams when the light beam has a direction of rainfall. Figure 9
The figure is a perspective view of an embodiment in which the light-emitting optical section and the light-receiving optical section are integrated, FIG. 10 is a perspective view of an embodiment in which three integrated structures are combined, and FIG. 11 is the correction relationship in the direction of rainfall. FIG. DESCRIPTION OF SYMBOLS 1... Light source, 2... Modulator, 3... Condensing optical element, 4... Emitting optical system, 5... Light receiving optical element, 6
... Photoelectric conversion element, 7 ... Preamplifier, 8 ... Light receiving optical system, 9 ... Detection circuit, 10 ... Square detector, 11 ... Pulse shaping circuit, 12 ... Counting circuit, 13 ... light beam.

Claims (1)

[Scope of Claims] 1. A light emitting optical system that emits a light beam formed by a light source equipped with a modulator and a condensing optical element, and a light receiving optical element and a photoelectronic device installed at a finite distance from the light emitting optical system. A light receiving optical system consisting of a conversion element and a preamplifier is provided, and a detection circuit and a square detector are connected to the preamplifier to electrically detect changes in light intensity caused by one raindrop passing through the light beam. In addition to converting the electrical signal into a signal, a pulse shaping circuit and a counting circuit are connected to the detection circuit to convert the electrical signal into one pulse, and the number of pulses per unit time is calculated to quantitatively calculate the rainfall intensity. Features a photoelectric rain gauge. 2. A light emitting optical system that emits a light beam formed by a light source equipped with a modulator and a focusing optical element, and a light receiving optical element, a photoelectric conversion element, and a preamplifier installed at a finite distance from the light emitting optical system. In the photoelectric rain gauge equipped with a light-receiving optical system, three detecting means are formed in which the light-emitting optical system that emits a light beam from the modulated light-emitting light source and the light-receiving optical system that receives the light beam are integrated. , a photoelectric rain gauge characterized in that each detection means is arranged in three directions where the respective light beams are orthogonal to each other, and the rainfall intensity is measured regardless of the rainfall direction by calculating the square sum of the respective output pulse numbers. Total.