CA1141191A - Forward-scatter visibility meter - Google Patents
Forward-scatter visibility meterInfo
- Publication number
- CA1141191A CA1141191A CA000361226A CA361226A CA1141191A CA 1141191 A CA1141191 A CA 1141191A CA 000361226 A CA000361226 A CA 000361226A CA 361226 A CA361226 A CA 361226A CA 1141191 A CA1141191 A CA 1141191A
- Authority
- CA
- Canada
- Prior art keywords
- light
- visibility meter
- partition
- meter defined
- visibility
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/47—Scattering, i.e. diffuse reflection
- G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
- G01N21/53—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke
- G01N21/538—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke for determining atmospheric attenuation and visibility
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- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
- Photometry And Measurement Of Optical Pulse Characteristics (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Two embodiments of the visibility meter are disclosed.
In the first embodiment, light transmitted from the light trans-mitter and light received by the light receiver is propagated in a conical beam. The beams are so oriented that they include an obtuse angle. In the first embodiment, a partition blocks all direct transmission of light from the light transmitter to the light receiver. In the second embodiment, direct transmission of light from the light transmitter to the light receiver takes place through the partition, but is limited to a predetermined level.
Two embodiments of the visibility meter are disclosed.
In the first embodiment, light transmitted from the light trans-mitter and light received by the light receiver is propagated in a conical beam. The beams are so oriented that they include an obtuse angle. In the first embodiment, a partition blocks all direct transmission of light from the light transmitter to the light receiver. In the second embodiment, direct transmission of light from the light transmitter to the light receiver takes place through the partition, but is limited to a predetermined level.
Description
This invention pertains to visibility meters, such as are used in meteorology, aeronautics and in automotive traffic-control systems as a warning device detec-ting the presence oE
fog.
Prior-art visibility meters have proved to be subject to malfunction as a result o~ weather conditions and environ-mental disturbances. In prior-art devices, maintenance is required in order to clean the exterior surfaces of the optical systems in the light transmitter and the light receiver~ If, for example, dust particles land upon either the light transmitter or the light receiver, readings derived from the visibility meter will be inaccurate. I'his can lead to severe problems, especially in the event that -the visibility meter is installed at, e.g., an airport when accurate visibility measurements are essential.
Therefore, it would be advantageous to provide a visibility meter which would require only minimal maintenance and which would be less sensitive to the influences of weather conditions and environmental dis-turbances, such as the presence of insects and the like.
These objects, along with others which will become apparent hereinafter, are achieved in this invention primarily by a novel orientation of the light transmitter and the light receiver with respect to each other. While in prior-art devices the light transmitter and the light receiver lie along a hori-zontal line which is interrupted by a diaphragm or partition, this invention improves upon such an arrangement by orienting the light transmitter and the light receiver with respect to each other such that the axes of light transmission and light recep-tion include an oblique angle which is bisected by a partition.
In this fashion, it is more difficult for dust particles and
fog.
Prior-art visibility meters have proved to be subject to malfunction as a result o~ weather conditions and environ-mental disturbances. In prior-art devices, maintenance is required in order to clean the exterior surfaces of the optical systems in the light transmitter and the light receiver~ If, for example, dust particles land upon either the light transmitter or the light receiver, readings derived from the visibility meter will be inaccurate. I'his can lead to severe problems, especially in the event that -the visibility meter is installed at, e.g., an airport when accurate visibility measurements are essential.
Therefore, it would be advantageous to provide a visibility meter which would require only minimal maintenance and which would be less sensitive to the influences of weather conditions and environmental dis-turbances, such as the presence of insects and the like.
These objects, along with others which will become apparent hereinafter, are achieved in this invention primarily by a novel orientation of the light transmitter and the light receiver with respect to each other. While in prior-art devices the light transmitter and the light receiver lie along a hori-zontal line which is interrupted by a diaphragm or partition, this invention improves upon such an arrangement by orienting the light transmitter and the light receiver with respect to each other such that the axes of light transmission and light recep-tion include an oblique angle which is bisected by a partition.
In this fashion, it is more difficult for dust particles and
-2~
other undesirable substances to adhere -to either the light transmitter or the light receiver and -thereby impair measurement accuracy.
In one embodiment o~ the invention, the partition blocks all direct transmission of light from the light trans-mitter to the light receiver~ In this embodiment, light received by the light receiver must of necessity be reflected off moisture particles in the air. There~ore, an accurate visibility reading is taken.
In another embodiment of this invention, the partition is perforated by a perforation which precisely limits direct transmission of light from th~ light transmitter to a prede-ter-mined level. In this embodiment, it is necessary to recalibrate the light receiver in order to achieve the necessary measurement accuracy. However, as will be seen hereinafter, the effects of light transmission to the receiver are additive, so that after satisfactory recalibration the receiver will operate as accur-ately as in the ~irst embodiment described above.
Of particular interest in this invention are advan-tageous features which may be b~ilt into the partition itself.
Advantageously, the partition can be manufactured not as a simple planar sheet but rather as a relatively thick structure with a predetermined width. As will be seen hereinafter, this con-struction helps to insure measurement accuracy even in the event that raindrops adhere to the bottom edge of the partition. Also advantaegously, -the partition is divided at its bottom to form two like downwardly and outwardly extending wings which are symmetrical about their centerline. As a result of this con-struction, raindrops tend to drip of~ rain gutters which may advantageously be located along the bottom edge, in order to further increase measurement accuracy. Other advantageous features which may be incorporated into the partition are a heater which heats the partition sufficiently to prevent spiders from forming webs upon it and water-repellant and insect-killing coatings on the partition that prevent the accumulation of raindrops and insects upon it.
secause the atmospheric region in which measurement takes place is below the inVention, no heating Of thiS region takes place, and thermals therein, which reduce accuracy, are reduced. By choosing an appropriate oblique angle, the invention can be made vertically compact. It therefore need not be mounted on an overly long post ~bove the g~ound. Moreover, noise at the light receiver is reduced by its inclination from the prior-art horizontal orientation.
The novel features which are considered as character-istic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of oparation, together with addi-tional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawing.
FIG~ 1 is a schematic side view of the invention;
FIG. 2 is a front view of the partition utilized in this invention;
FIG. 3 is a cross-sectional view of the partition taken along its centerline; and FIG. 4 is a view of the partition taken along line IV-IV as is shown in FIG. 2.
Referring first to FIG. 1, it can be seen that an elongated support 1 has a center 1~, a first end 1~ ~nd a second end lC. A light transmitte~ ~enerally indicated by re~erence numeral 2 is located beneath support 1 at ~irst end lB, while a light receiver generally indicated by reference numeral 3 is located beneath support 1 at seconcl end lC.
Light transmitter 2 is contained within housing 5, and contains a power supply 6 which energizes and deenergizes a flash lamp 7, which may advantageously be a gas dischar~e flash lamp.
Light from flash lamp 7 passes through an optical system which is schematically represented as lens 8, and thence passes through window 9 and out of light transmitter 2. Window 9 and housing 5 are both air-tight, and an adsorbent bag or capsule 29 which may contain, e.g., silica gel is placed within housing 5 so as to prevent moisture from condensing within housing 5 at low tem-perature, preventing growth of bacteria and fungus.
Light receiver 3 is contained within housing 10, and receives light through window 11 which is attached to housing 10.
Window 11 and housing 10 are air-tight, and light receiver 3 likewise contains an adsorbent bag or capsule 29. After passing through window 11, light received by light receiver 3 then passes through an optical system schematically represented by lens 12, which focuses the light onto a photosensitive element 13, which may advantageously be a photodiode. Photosensitive element 13 is connected to electronic circuitry schematically indicated by reference numeral 14. Circuitry 14 includes an electrical filter 15 which calibrates the response of light receiver 3 so that it corresponds with a frequency band in which light received by light receiver 3 carries a maximum energy. Circuitry 14 further includes an electrical switch 16, which may advantageously be an AND-gate~ Electr:ical switch 16 switches light receiver 3 off inbetween flashes of flash lamp 7 in a fashion such as that disclosed in Swiss Patent No. 566 013.
To fur-ther reduce grow-th of bacteria and/or funyus in light transmi-tter 2 or light receiver 3, windows 9 and 11 can be made of either barite or quartz.
Light projected by light transmi-t-ter 2 is projected through window 9 in a generally conical beam 18 along a first axis 17. In a similar fashion, light received by light receiver
other undesirable substances to adhere -to either the light transmitter or the light receiver and -thereby impair measurement accuracy.
In one embodiment o~ the invention, the partition blocks all direct transmission of light from the light trans-mitter to the light receiver~ In this embodiment, light received by the light receiver must of necessity be reflected off moisture particles in the air. There~ore, an accurate visibility reading is taken.
In another embodiment of this invention, the partition is perforated by a perforation which precisely limits direct transmission of light from th~ light transmitter to a prede-ter-mined level. In this embodiment, it is necessary to recalibrate the light receiver in order to achieve the necessary measurement accuracy. However, as will be seen hereinafter, the effects of light transmission to the receiver are additive, so that after satisfactory recalibration the receiver will operate as accur-ately as in the ~irst embodiment described above.
Of particular interest in this invention are advan-tageous features which may be b~ilt into the partition itself.
Advantageously, the partition can be manufactured not as a simple planar sheet but rather as a relatively thick structure with a predetermined width. As will be seen hereinafter, this con-struction helps to insure measurement accuracy even in the event that raindrops adhere to the bottom edge of the partition. Also advantaegously, -the partition is divided at its bottom to form two like downwardly and outwardly extending wings which are symmetrical about their centerline. As a result of this con-struction, raindrops tend to drip of~ rain gutters which may advantageously be located along the bottom edge, in order to further increase measurement accuracy. Other advantageous features which may be incorporated into the partition are a heater which heats the partition sufficiently to prevent spiders from forming webs upon it and water-repellant and insect-killing coatings on the partition that prevent the accumulation of raindrops and insects upon it.
secause the atmospheric region in which measurement takes place is below the inVention, no heating Of thiS region takes place, and thermals therein, which reduce accuracy, are reduced. By choosing an appropriate oblique angle, the invention can be made vertically compact. It therefore need not be mounted on an overly long post ~bove the g~ound. Moreover, noise at the light receiver is reduced by its inclination from the prior-art horizontal orientation.
The novel features which are considered as character-istic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of oparation, together with addi-tional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawing.
FIG~ 1 is a schematic side view of the invention;
FIG. 2 is a front view of the partition utilized in this invention;
FIG. 3 is a cross-sectional view of the partition taken along its centerline; and FIG. 4 is a view of the partition taken along line IV-IV as is shown in FIG. 2.
Referring first to FIG. 1, it can be seen that an elongated support 1 has a center 1~, a first end 1~ ~nd a second end lC. A light transmitte~ ~enerally indicated by re~erence numeral 2 is located beneath support 1 at ~irst end lB, while a light receiver generally indicated by reference numeral 3 is located beneath support 1 at seconcl end lC.
Light transmitter 2 is contained within housing 5, and contains a power supply 6 which energizes and deenergizes a flash lamp 7, which may advantageously be a gas dischar~e flash lamp.
Light from flash lamp 7 passes through an optical system which is schematically represented as lens 8, and thence passes through window 9 and out of light transmitter 2. Window 9 and housing 5 are both air-tight, and an adsorbent bag or capsule 29 which may contain, e.g., silica gel is placed within housing 5 so as to prevent moisture from condensing within housing 5 at low tem-perature, preventing growth of bacteria and fungus.
Light receiver 3 is contained within housing 10, and receives light through window 11 which is attached to housing 10.
Window 11 and housing 10 are air-tight, and light receiver 3 likewise contains an adsorbent bag or capsule 29. After passing through window 11, light received by light receiver 3 then passes through an optical system schematically represented by lens 12, which focuses the light onto a photosensitive element 13, which may advantageously be a photodiode. Photosensitive element 13 is connected to electronic circuitry schematically indicated by reference numeral 14. Circuitry 14 includes an electrical filter 15 which calibrates the response of light receiver 3 so that it corresponds with a frequency band in which light received by light receiver 3 carries a maximum energy. Circuitry 14 further includes an electrical switch 16, which may advantageously be an AND-gate~ Electr:ical switch 16 switches light receiver 3 off inbetween flashes of flash lamp 7 in a fashion such as that disclosed in Swiss Patent No. 566 013.
To fur-ther reduce grow-th of bacteria and/or funyus in light transmi-tter 2 or light receiver 3, windows 9 and 11 can be made of either barite or quartz.
Light projected by light transmi-t-ter 2 is projected through window 9 in a generally conical beam 18 along a first axis 17. In a similar fashion, light received by light receiver
3 is received from a generally conical beam 20 along second axis 19. Angle a included between first axis 17 and second axis 19 is oblique, since axis 17 extends downwardly and towards center lA
and second axis 19 exkends upwardly and away from center lA.
A partition generally indicated by reference number 4 is attached to center lA of support 1 and extends vertically downwardly therefrom intermediate li~ht transmitter 2 and light receiver 3.
Partition 4, as can be seen in more detail in FIG. 2, has a centerline 4A and is divided at its bottom to form two like wings 4B and 4C which extend outwardly from centerline 4A and are symmetrical about it. Thus, bottom edge 24 is peaked at center-line 4A and extends downwardly and outwardly therefrom in the shape of an inverted V.
Partition 4 is formed by two parallel outer walls 21 which are held apart from each other by a distance b. Each outer wall 21 supports a rain gutter 25 which extends along bottom edge 24 and which is either riveted or screwed to that one of the outer walls 21 to which it is attached. Rair. gutter 25 extends upwardly and outwardly from its corresponding outer wall 21, so that drops oE water on wall 21 will be prevented in the main from hanging on bottom edge 24 on either side of partition 4. Advan-ageously, each outer wall 21 may be coated with a water-repellant coa-ting such as that ha~ing a trade mark name Teflon and/or an insecticide.
In a first embodiment of the invention, outer walls 21 are unperforated and thereby completely b~ock all light incident upon them. Partition 4 is so shaped that all direct transmission of light from light transmitter 2 to light receiver 3 is blocked by partition 4. However, as can be seen from FIG. l, conical beam 18 and conical beam 20 intersect each other below partition
and second axis 19 exkends upwardly and away from center lA.
A partition generally indicated by reference number 4 is attached to center lA of support 1 and extends vertically downwardly therefrom intermediate li~ht transmitter 2 and light receiver 3.
Partition 4, as can be seen in more detail in FIG. 2, has a centerline 4A and is divided at its bottom to form two like wings 4B and 4C which extend outwardly from centerline 4A and are symmetrical about it. Thus, bottom edge 24 is peaked at center-line 4A and extends downwardly and outwardly therefrom in the shape of an inverted V.
Partition 4 is formed by two parallel outer walls 21 which are held apart from each other by a distance b. Each outer wall 21 supports a rain gutter 25 which extends along bottom edge 24 and which is either riveted or screwed to that one of the outer walls 21 to which it is attached. Rair. gutter 25 extends upwardly and outwardly from its corresponding outer wall 21, so that drops oE water on wall 21 will be prevented in the main from hanging on bottom edge 24 on either side of partition 4. Advan-ageously, each outer wall 21 may be coated with a water-repellant coa-ting such as that ha~ing a trade mark name Teflon and/or an insecticide.
In a first embodiment of the invention, outer walls 21 are unperforated and thereby completely b~ock all light incident upon them. Partition 4 is so shaped that all direct transmission of light from light transmitter 2 to light receiver 3 is blocked by partition 4. However, as can be seen from FIG. l, conical beam 18 and conical beam 20 intersect each other below partition
4, so that point 3~ is located below partition 4 along certerline 4A thereof, and is formed at the intersection of line 31 (which indicates the lowest line along beam 18 and line 32 (which indicates the lowest line on beam 20). ~Ience, in this first embodiment of the invention, light in beam 18 can only reach light receiver 3 by reflecting off moisture particles in the atmosphere which are located below and around the bottom of partition 4. Hence, the output from photosensitive element 13 accurately reflects visibility, because in this first embodiment of the invention the only way that any light will be received by light receiver 3 is if such light reflects of:f atmospheric moisture particles such as are caused by clouds or fog.
Thickness b of partition 4 serves to reduce sensitivity of light receiver 3 to the effects of water droplets. In the event that water droplets adhere to the right-hand rain gutter 25 as viewed in Fig. l, such water droplets will be in the shade of the left-hand rain gutt,er 25 and will therefore have no effect in reflecting light to light receiver 3. Moreover, water droplets hanging from the left-hand rain gutter 25 as viewed FIG. l will tend to have only a minimal effect on reflection of light into light recelver 3, since partition 4 is comparatively thick and the water droplets are relatively small. It will be appre-`,~
ciated by those skilled in the art that in the event water droplets were permit-ted to reflect light from light source 7 into light receiver 3, that light receiver 3 would have an outpu-t indicating a lesser visibility thaII that which actually e~isted, since light receiver 3 would interpre-t light incident upon it as being reflected by moisture particl.es in the atmosphere rather than by water droplets on partition 4. Advantageously, formation of such water droplets .is Eurther impeded by coating outer walls 21 with a water-repellant coating, such as has been described above. Insects may be prevented from perching on partition 4 by coating outer walls 21 with an insecticide.
Outer walls ~1 are held apart from each other by distance b by a support plate 27, which takes the form of an inverted V, as does bottom edge 24. Support plate 27 supports a thermostatically controlled heater 28. It has been determined that spiders will not spin ~ebs which would adhere to partition 4 if the partition is maintained at a temperature of between 50C
and 60C. Heater 28 serves the function of maintaining partition 4 at this temperature, in order to keep spiders and their webs away from partition 4. This is of importance to the practice of this invention in that under proper climatic conditions, a spider web (when attached to partition 4) can cause the visibility as measured by light receiver 3 to be understated by approximately 1 kilometer. As in the case of water droplets, a spider web attached to partition 4 will increase the amount of light re-ceived by light receiver 3, and will therefore tend to cause visibility to be understa-ted. In winter, partition 4 need not be heated to such high temperatures, and it is therefore advan-tageous if heater 28 is made adjustable, so as to maintain partition 4 at a temperature which is only slightly above 0C in order to prevent any buildup of snow or ice on partitiorl ~. It will be appreciated by those skilled in the art that heater 28 will not tend to heat the air below partition 4, so that haater 28 does not cause false readings by ligh-t receiver 3 to occur by developing thermals below partition 4.
In use, suppor-t 1 is suspended sufficiently high so that the visibility meter will be located above any level to which snow may rise, in order to prevent snow from interfering with visibility measurement accuracy. Furthermore, the entire device may be surrounded by a wire screen having a mesh size of, e.g., one centimeter. This screen will preven-t spiders from being blown by the wind onto partition 4. Moreover, the screen prevents insects, and particularly butterflies, from landing on partition 4. However, flow of air is not adversely influenced so that visibility measurements can take place without reduction in accuracy. Of course, for visibility meters which are intended for use in nautical applications, and which are mounted on bouys, the screen will not be necessary.
In order to reduce the likelihood of vandalism, the visibility meter will preferably be painted a drab color in order to avoid attracting the attention of vandals. For visibility meters which are installed at fixed locations above the ground, the ground will advantageously be coated with a unitary covering such as concrete, asphalt, plastic, or metal plating in order to prevent plant growth from arising in crevices and thereby growing into the open bottom of the device. Advantageously, whatever covering is utilized on the ground will be colored white or at least will have a l~ght hue, in order to prevent the covering from heating up as a result oE incident sunshine and a cor-responding heating up of the atmosphere underneath partition 4, which is undesirable as was described above.
Inasmuch as human beings do not see radi.atïon whi.ch is located in the in~rared portion o~ the spectrum, it is ~i6-advantageous ~or ligh-t receiver 3 to respond to in~rared light.
In order to prevent such response, and in order -to prevent light from conventional light sources and electrical components from disturbing measurement accuracy by virtue of the infrared radi-ation which they generate, it is aclvantageous -to provide either light transmitter 2 or ligh-t receiver 3 or both with means for preventing response to infrared radiation. Preferably, this can be done by providing either window 9 or window 11 with an infra~
red filter, or by making either windows 9 and 11 or lenses 8 and 12 of infrared-absorbing material. Preferably, at least light receiver 3 will be protected in this fashion.
Inasmuch as visibility only changes slowly, it is unnecessary to continuously monitor visibility of the atmosphere.
Moreover, non-continuous measurement of visibility will reduce power consumption and will prolong the useful life of the device, and will particularly increase the lifespan of flash lamp 7.
Therefore, it is advantageous to provide the device with a control system (not shown) which repeatedly operates the visi-bility meter for short periods. Furthermore, the visibility meter can be provided with a memory (not shown) in which readings of visibility measurements may be stored. If visibility, as measured, changes during two successive short periods of oper-ation~an indicating system lno-t shown) may be activated in order to inform a user that visibility has changed. Momentary events such as the presence of foreign matter blown into the visibility meter by the wind or the presence of a butterfly can thus be neglected, since they are transitory and will not continuously affec-t visibility measuremen-t.
Alterna-tively, and in the event that the invention is utilized as a warning device to in~orm motorists of the presence of fog, the invention can be provicled with an indica-ting system (not shown) which informs a user when visibility is less -than a prede-termined value. Advantageous]y, this value can be varied between 140 meters during the daytime and gO meters at night.
This may be accomplished by, e.g., a clock (not shown) which varies the predetermined value in accordance with times o~ day and night, or by a light sensor such as a photocell which varies the predetermined value in accordance with ambient light in-tensity.
In order to -test the device, a light-transmissive plate may be introduced below partition 4, in order to insure that light will be received by light receiver 3. This not only serves to indicate that the device is operating, but also serves to calibrate the device in the event that the light-transmissive characteristics of the plate are accurately known in advance.
Thus, such a light-transmissive plate can be used to calibrate the visibility meter. If desired, a plate-moving mechanism, preferably actuated by a magnet, can be used to automatically move the plate (not shown) below partition 4 in order to verify proper operation and in order to allow calibration to take place, and the plate can then be moved away from partition 4 by the plate-moving mechanism when such calibration has been finished.
As was stated above, the first embodiment of the invention blocks all direct transmission of light from the light transmitter to the light receiver. However, it is possible to build the invention in such a fashion that it monitors its own operation and thereby provides an indication when a ~ailure or a miscalibration takes place. It is known that the e~fects oE
light received by light receiver 3 have a cumulative, additive effect. Therefore, in a second embodiment o~ the invention partition 4 is perforated by a perforation shown by reference numeral 40 in the drawing. This perforation permits direct transmission of light from the light transmi-tter to the light receiver, but limits such transmission to a predetermined level.
This in turn, causes ligh-t receiver 3 to continuously indicate a lower visibility than actually exists. However, since such direct transmission of light is held to this predetermined level, it is possible to recalibrate light receiver 3 in order to correct for the direct transmission. For example, let it be assumed that a visibility of 120 meters produces a 0.5 mA current through photosensitive element 13. Furthermore, let i-t be assumed that by choosing perforation 40 to be of a suitably small size, a visibility of 800 meters can be simulated by direct transmission of light through perforation 40, creating a 0.1 mA
current through photosensitive element 13D Under these con-ditions, a current of 0.6 mA will be present through photo-sensitive element 13 when actual visibility is 120 meters.
It can be seen that a current of 0.6 mA would be ordinarily interpreted to correspond with a visibility of less than 120 meters, but that by a suitable recalibration of light receiver 3 accurate measurements can be obtained by virtue of the additive effects of light incident upon photosensitive element 13 upon current -flowing through it. Additionally, since perforation 40 will always permit enough light -to be transmitted directly from light transmitter 2 to light receiver 3 to cause a current of l mA to flow through photosensitive element 13, an automatic check on the operability of the invention is provided. If current through photosensitive element 13 ever decreases below 0.1 mA, a user will immediately realize that a malfunction has taken place.
As alternative constructions, it is possible to fill perforation 40 with a plug ~1 of a suitably light-transmissive material, or with a suitable light diffuser (not shown). Either of these alternative constructions may be utilized to reduce direct light transmission through partition ~. A suitable material for plug 41 is Teflon. This material is advantageous not only because of its light-transmissive properties, but also because it is a water-repellant substance. Furthermore, a ring 41' may be mounted on each of outer walls 21. This will inhibit formation of water droplets which can vary the predetermined level of light which is transmitted directly through partition 4.
When this second embodiment is utilized, the prede-termined level of light which is directly transmitted through partition ~ is empirically set at such a value that the arti-ficially derived visibility resulting therefrom will be higher than any visibility of which accurate measuremenk is deemed to be of consequence. Thus, for example, in the event that user re~uirements dictate that it is only necessary to detect whether or not visibility is below e.g. 120 meters, the predetermined level of direct light transmission through partition 4 may be set at, e.g., 800 meters.
It will be understood that each of the elements de-scribed above, or two or more together, may also Eind a useful application in other types of meters differing from the types described above.
While the invention has been described and illustrated as embodied in a forward-scatter visibility meter, it is not intended to be limited to -the details shown, since vario-us modifications and structural changes may be made without departing in any way Erom the spirit of the present invention.
Thickness b of partition 4 serves to reduce sensitivity of light receiver 3 to the effects of water droplets. In the event that water droplets adhere to the right-hand rain gutter 25 as viewed in Fig. l, such water droplets will be in the shade of the left-hand rain gutt,er 25 and will therefore have no effect in reflecting light to light receiver 3. Moreover, water droplets hanging from the left-hand rain gutter 25 as viewed FIG. l will tend to have only a minimal effect on reflection of light into light recelver 3, since partition 4 is comparatively thick and the water droplets are relatively small. It will be appre-`,~
ciated by those skilled in the art that in the event water droplets were permit-ted to reflect light from light source 7 into light receiver 3, that light receiver 3 would have an outpu-t indicating a lesser visibility thaII that which actually e~isted, since light receiver 3 would interpre-t light incident upon it as being reflected by moisture particl.es in the atmosphere rather than by water droplets on partition 4. Advantageously, formation of such water droplets .is Eurther impeded by coating outer walls 21 with a water-repellant coating, such as has been described above. Insects may be prevented from perching on partition 4 by coating outer walls 21 with an insecticide.
Outer walls ~1 are held apart from each other by distance b by a support plate 27, which takes the form of an inverted V, as does bottom edge 24. Support plate 27 supports a thermostatically controlled heater 28. It has been determined that spiders will not spin ~ebs which would adhere to partition 4 if the partition is maintained at a temperature of between 50C
and 60C. Heater 28 serves the function of maintaining partition 4 at this temperature, in order to keep spiders and their webs away from partition 4. This is of importance to the practice of this invention in that under proper climatic conditions, a spider web (when attached to partition 4) can cause the visibility as measured by light receiver 3 to be understated by approximately 1 kilometer. As in the case of water droplets, a spider web attached to partition 4 will increase the amount of light re-ceived by light receiver 3, and will therefore tend to cause visibility to be understa-ted. In winter, partition 4 need not be heated to such high temperatures, and it is therefore advan-tageous if heater 28 is made adjustable, so as to maintain partition 4 at a temperature which is only slightly above 0C in order to prevent any buildup of snow or ice on partitiorl ~. It will be appreciated by those skilled in the art that heater 28 will not tend to heat the air below partition 4, so that haater 28 does not cause false readings by ligh-t receiver 3 to occur by developing thermals below partition 4.
In use, suppor-t 1 is suspended sufficiently high so that the visibility meter will be located above any level to which snow may rise, in order to prevent snow from interfering with visibility measurement accuracy. Furthermore, the entire device may be surrounded by a wire screen having a mesh size of, e.g., one centimeter. This screen will preven-t spiders from being blown by the wind onto partition 4. Moreover, the screen prevents insects, and particularly butterflies, from landing on partition 4. However, flow of air is not adversely influenced so that visibility measurements can take place without reduction in accuracy. Of course, for visibility meters which are intended for use in nautical applications, and which are mounted on bouys, the screen will not be necessary.
In order to reduce the likelihood of vandalism, the visibility meter will preferably be painted a drab color in order to avoid attracting the attention of vandals. For visibility meters which are installed at fixed locations above the ground, the ground will advantageously be coated with a unitary covering such as concrete, asphalt, plastic, or metal plating in order to prevent plant growth from arising in crevices and thereby growing into the open bottom of the device. Advantageously, whatever covering is utilized on the ground will be colored white or at least will have a l~ght hue, in order to prevent the covering from heating up as a result oE incident sunshine and a cor-responding heating up of the atmosphere underneath partition 4, which is undesirable as was described above.
Inasmuch as human beings do not see radi.atïon whi.ch is located in the in~rared portion o~ the spectrum, it is ~i6-advantageous ~or ligh-t receiver 3 to respond to in~rared light.
In order to prevent such response, and in order -to prevent light from conventional light sources and electrical components from disturbing measurement accuracy by virtue of the infrared radi-ation which they generate, it is aclvantageous -to provide either light transmitter 2 or ligh-t receiver 3 or both with means for preventing response to infrared radiation. Preferably, this can be done by providing either window 9 or window 11 with an infra~
red filter, or by making either windows 9 and 11 or lenses 8 and 12 of infrared-absorbing material. Preferably, at least light receiver 3 will be protected in this fashion.
Inasmuch as visibility only changes slowly, it is unnecessary to continuously monitor visibility of the atmosphere.
Moreover, non-continuous measurement of visibility will reduce power consumption and will prolong the useful life of the device, and will particularly increase the lifespan of flash lamp 7.
Therefore, it is advantageous to provide the device with a control system (not shown) which repeatedly operates the visi-bility meter for short periods. Furthermore, the visibility meter can be provided with a memory (not shown) in which readings of visibility measurements may be stored. If visibility, as measured, changes during two successive short periods of oper-ation~an indicating system lno-t shown) may be activated in order to inform a user that visibility has changed. Momentary events such as the presence of foreign matter blown into the visibility meter by the wind or the presence of a butterfly can thus be neglected, since they are transitory and will not continuously affec-t visibility measuremen-t.
Alterna-tively, and in the event that the invention is utilized as a warning device to in~orm motorists of the presence of fog, the invention can be provicled with an indica-ting system (not shown) which informs a user when visibility is less -than a prede-termined value. Advantageous]y, this value can be varied between 140 meters during the daytime and gO meters at night.
This may be accomplished by, e.g., a clock (not shown) which varies the predetermined value in accordance with times o~ day and night, or by a light sensor such as a photocell which varies the predetermined value in accordance with ambient light in-tensity.
In order to -test the device, a light-transmissive plate may be introduced below partition 4, in order to insure that light will be received by light receiver 3. This not only serves to indicate that the device is operating, but also serves to calibrate the device in the event that the light-transmissive characteristics of the plate are accurately known in advance.
Thus, such a light-transmissive plate can be used to calibrate the visibility meter. If desired, a plate-moving mechanism, preferably actuated by a magnet, can be used to automatically move the plate (not shown) below partition 4 in order to verify proper operation and in order to allow calibration to take place, and the plate can then be moved away from partition 4 by the plate-moving mechanism when such calibration has been finished.
As was stated above, the first embodiment of the invention blocks all direct transmission of light from the light transmitter to the light receiver. However, it is possible to build the invention in such a fashion that it monitors its own operation and thereby provides an indication when a ~ailure or a miscalibration takes place. It is known that the e~fects oE
light received by light receiver 3 have a cumulative, additive effect. Therefore, in a second embodiment o~ the invention partition 4 is perforated by a perforation shown by reference numeral 40 in the drawing. This perforation permits direct transmission of light from the light transmi-tter to the light receiver, but limits such transmission to a predetermined level.
This in turn, causes ligh-t receiver 3 to continuously indicate a lower visibility than actually exists. However, since such direct transmission of light is held to this predetermined level, it is possible to recalibrate light receiver 3 in order to correct for the direct transmission. For example, let it be assumed that a visibility of 120 meters produces a 0.5 mA current through photosensitive element 13. Furthermore, let i-t be assumed that by choosing perforation 40 to be of a suitably small size, a visibility of 800 meters can be simulated by direct transmission of light through perforation 40, creating a 0.1 mA
current through photosensitive element 13D Under these con-ditions, a current of 0.6 mA will be present through photo-sensitive element 13 when actual visibility is 120 meters.
It can be seen that a current of 0.6 mA would be ordinarily interpreted to correspond with a visibility of less than 120 meters, but that by a suitable recalibration of light receiver 3 accurate measurements can be obtained by virtue of the additive effects of light incident upon photosensitive element 13 upon current -flowing through it. Additionally, since perforation 40 will always permit enough light -to be transmitted directly from light transmitter 2 to light receiver 3 to cause a current of l mA to flow through photosensitive element 13, an automatic check on the operability of the invention is provided. If current through photosensitive element 13 ever decreases below 0.1 mA, a user will immediately realize that a malfunction has taken place.
As alternative constructions, it is possible to fill perforation 40 with a plug ~1 of a suitably light-transmissive material, or with a suitable light diffuser (not shown). Either of these alternative constructions may be utilized to reduce direct light transmission through partition ~. A suitable material for plug 41 is Teflon. This material is advantageous not only because of its light-transmissive properties, but also because it is a water-repellant substance. Furthermore, a ring 41' may be mounted on each of outer walls 21. This will inhibit formation of water droplets which can vary the predetermined level of light which is transmitted directly through partition 4.
When this second embodiment is utilized, the prede-termined level of light which is directly transmitted through partition ~ is empirically set at such a value that the arti-ficially derived visibility resulting therefrom will be higher than any visibility of which accurate measuremenk is deemed to be of consequence. Thus, for example, in the event that user re~uirements dictate that it is only necessary to detect whether or not visibility is below e.g. 120 meters, the predetermined level of direct light transmission through partition 4 may be set at, e.g., 800 meters.
It will be understood that each of the elements de-scribed above, or two or more together, may also Eind a useful application in other types of meters differing from the types described above.
While the invention has been described and illustrated as embodied in a forward-scatter visibility meter, it is not intended to be limited to -the details shown, since vario-us modifications and structural changes may be made without departing in any way Erom the spirit of the present invention.
Claims (32)
1. A forward-scatter visibility meter, comprising:
an elongated stationary support with a center and first and second ends;
a light transmitter located beneath the support at the first end and directing a generally conical beam of light along a first axis which extends downwardly and towards the center;
a light receiver located beneath the support at the second end and receiving a generally conical beam of light along a second axis which extends upwardly and away from the center in a manner that the first and second axes are symmetrical about the center of the support and include an obtuse angle; and a stationary partition attached to the center of the support and extending downwardly therefrom in a manner that at least a part of direct transmission of light from the light trans-mitter to the light receiver is blocked by the partition.
an elongated stationary support with a center and first and second ends;
a light transmitter located beneath the support at the first end and directing a generally conical beam of light along a first axis which extends downwardly and towards the center;
a light receiver located beneath the support at the second end and receiving a generally conical beam of light along a second axis which extends upwardly and away from the center in a manner that the first and second axes are symmetrical about the center of the support and include an obtuse angle; and a stationary partition attached to the center of the support and extending downwardly therefrom in a manner that at least a part of direct transmission of light from the light trans-mitter to the light receiver is blocked by the partition.
2. The visibility meter defined in claim 1, wherein the partition has a bottom and a vertical centerline, and wherein the partition is divided at its bottom to form two like downwardly and outwardly extending wings which are symmetrical about the centerline.
3. The visibility meter defined in claim 2, wherein each of the wings has a bottom edge and two outside faces, and wherein a rain gutter is located along the bottom edge along each outside face.
4. The visibility meter defined by claim 1, wherein the partition is coated with a water-repellant coating.
5. The visibility meter defined by claim 1, wherein the partition is coated with an insecticide.
6. The visibility meter defined by claim 1, wherein the partition includes a heater heating the partition to a temperature between approximately 50°C and 60°C.
7. The visibility meter defined by claim 6, wherein the heater is adjustable in a manner that the partition can be heated to a temperature above 0°C and below 50°C.
8. The visibility meter defined by claim 1, wherein the partition has two parallel outer walls separated from each other by a predetermined distance.
9. The visibility meter defined by claim 8, wherein the partition is hollow.
10. The visibility meter defined by claim 1, wherein the light transmitter and light receiver contain a moisture adsorbent and are airtight.
11. The visibility meter defined by claim 1, wherein the light transmitter transmits light through a first window, and wherein the light receiver receives light through a second window.
12. The visibility meter defined by claim 11, wherein the first and second windows are made of barite.
13. The visibility meter defined by claim 11, wherein the first and second windows are made of quartz.
14. The visibility meter defined by claim 1, wherein at least the receiver is provided with a means absorbing infrared light received by the receiver.
15. The visibility meter defined by claim 14, wherein the means is an infrared filter.
16. The visibility meter defined by claim 14, wherein the means is an infrared-absorbing lens.
17. The visibility meter defined by claim 1, wherein the light transmitter includes a flash lamp.
18. The visibility meter defined by claim 17, wherein the light receiver includes an electrical filter calibrating response of the light receiver to a frequency band in which light received by the light receiver carries a maximum energy.
19. The visibility meter defined by claim 17, wherein the light transmitter includes an electrical switch which auto-matically cuts the light receiver off in pauses inbetween flashes of light from the flash lamp.
20. The visibility meter defined by claim 1, further including a control system, a memory, and an indicating system, wherein the control system repeatedly operates the visibility meter for short periods, wherein the memory stores visibility measurements obtained during such repeated operations, and wherein the indicating system informs a user when a visibility measurement changes during at least two successive short periods.
21. The visibility meter defined by claim 1, further including an indicating system which informs a user when visi-bility is less than a predetermined value.
22. The visibility meter defined by claim 21, wherein the predetermined value is variable.
23. The visibility meter defined by claim 22, further including a clock which varies the predetermined value in ac-cordance with times of day and night.
24. The visibility meter defined by claim 22, further including a light sensor which varies the predetermined value in accordance with ambient light intensity.
25. The visibility meter defined by claim 1, further including a light-transmissive plate and a plate-moving mechan-ism, the plate-moving mechanism moving the plate below the partition in order to calibrate the visibility meter and with-drawing the plate away from the partition in order to allow the visibility meter to be utilized.
26. A forward-scatter visibility meter, comprising:
an elongated support with a center and first and second ends;
a light transmitter located beneath the support at the first end and directing a generally conical beam of light along a first axis which extends downwardly and towards the center;
a light receiver located beneath the support at the second end and receiving a generally conical beam of light along a second axis which extends upwardly and away from the center in a manner that the first and second axes are symmetrical about the center of the support and include an obtuse angle; and a partition attached to the center of the support and extending downwardly therefrom in a manner that direct trans-mission of light from the light transmitter to the light receiver is limited by the partition to a predetermined level.
an elongated support with a center and first and second ends;
a light transmitter located beneath the support at the first end and directing a generally conical beam of light along a first axis which extends downwardly and towards the center;
a light receiver located beneath the support at the second end and receiving a generally conical beam of light along a second axis which extends upwardly and away from the center in a manner that the first and second axes are symmetrical about the center of the support and include an obtuse angle; and a partition attached to the center of the support and extending downwardly therefrom in a manner that direct trans-mission of light from the light transmitter to the light receiver is limited by the partition to a predetermined level.
27. The visibility meter defined by claim 26, wherein the partition is perforated by a perforation along a line ex-tending between the light transmitter and the light receiver.
28. The visibility meter defined by claim 27, wherein the perforation is covered by a light diffuser.
29. The visibility meter defined by claim 27, wherein the perforation is filled by a light-transmissive plug.
30. The visibility meter defined by claim 29, wherein the plug is made of a water-repellant substance.
31. The visibility meter defined by claim 27, wherein the perforation is surrounded by a ring located on the partition.
32. The visibility meter defined by claim 31, wherein the ring is made of a water-repellant substance.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CH8849/79-2 | 1979-10-02 | ||
| CH884979A CH639769A5 (en) | 1979-10-02 | 1979-10-02 | Sichtweitenmessgeraet according to the principle of vorwaertsstreuung and use thereof. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1141191A true CA1141191A (en) | 1983-02-15 |
Family
ID=4345438
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000361226A Expired CA1141191A (en) | 1979-10-02 | 1980-09-29 | Forward-scatter visibility meter |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5651647A (en) |
| CA (1) | CA1141191A (en) |
| CH (1) | CH639769A5 (en) |
| DE (1) | DE3016610C2 (en) |
| GB (1) | GB2059576B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5956829U (en) * | 1982-09-30 | 1984-04-13 | ティーディーケイ株式会社 | noise filter |
| FI83822C (en) * | 1989-02-02 | 1991-08-26 | Valtion Teknillinen | Procedure and apparatus for observing traffic conditions |
| JPH079395B2 (en) * | 1990-06-12 | 1995-02-01 | 明星電気株式会社 | Visibility measurement method |
| DE4106289A1 (en) * | 1991-02-28 | 1992-09-03 | Bayerische Motoren Werke Ag | TEST METHOD FOR THE VISIBILITY ON ROADWAYS AND DEVICE FOR IMPLEMENTING THE METHOD |
| JPH0534280A (en) * | 1991-07-26 | 1993-02-09 | Kaijo Corp | Infrared absorption type humidity fluctuation meter |
| US5628609A (en) * | 1996-04-05 | 1997-05-13 | Chevron, Inc. | Wheel lift vehicle lifting and towing device |
| US5692871A (en) * | 1996-11-21 | 1997-12-02 | Chevron, Inc. | Wheel lift towing device |
| US5908280A (en) * | 1997-04-29 | 1999-06-01 | Allison; James | Wheel lift apparatus for vehicle towing and related methods |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1946864A1 (en) * | 1969-09-16 | 1971-04-01 | Siemens Ag | Laser rangefinder |
| DE2135611C2 (en) * | 1971-07-16 | 1975-02-06 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Mode coupler for direction finding systems |
| DE2208904C3 (en) * | 1972-02-25 | 1975-11-06 | Fruengel, Frank, Dr.-Ing., 2000 Hamburg | Device for measuring sight bets |
-
1979
- 1979-10-02 CH CH884979A patent/CH639769A5/en not_active IP Right Cessation
-
1980
- 1980-04-30 DE DE19803016610 patent/DE3016610C2/en not_active Expired
- 1980-06-26 JP JP8598580A patent/JPS5651647A/en active Pending
- 1980-07-17 GB GB8023361A patent/GB2059576B/en not_active Expired
- 1980-09-29 CA CA000361226A patent/CA1141191A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| CH639769A5 (en) | 1983-11-30 |
| DE3016610C2 (en) | 1984-04-26 |
| JPS5651647A (en) | 1981-05-09 |
| DE3016610A1 (en) | 1981-04-16 |
| GB2059576A (en) | 1981-04-23 |
| GB2059576B (en) | 1984-04-04 |
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