US2921497A

US2921497A - Optical instrument for smoke determination

Info

Publication number: US2921497A
Application number: US418542A
Authority: US
Inventors: William P Yant; Robert C Hollobaugh; John P Strange
Original assignee: Mine Safety Appliances Co
Current assignee: MSA Safety Inc
Priority date: 1954-03-25
Filing date: 1954-03-25
Publication date: 1960-01-19
Anticipated expiration: 1977-01-19
Also published as: GB766518A

Description

Jan. 19, 1960 W. 'P. YANT ET AL OPTICAL INSTRUMENT FOR SMOKE DETERMINATION Filed March 25, 1954 205527 C- you-05.406 BY JOHN R STEANGL.

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United States Patent OPTICAL INSTRUMENT FOR SMOKE DETERMINATION William P. Yant, Murrysville, Robert C. Hollohaugh,

Verona, and John P. Strange, Murrysville, Pa., assignon to Mine Safety Appliances Company, Pittsburgh, 8., a corporation of Pennsylvania Application March 25, 1954, Serial No. 418,542 7 Claims. (CI. 88-14) fe'reiit smoke density. This system of density determination gives only a rough estimate, because the results are subject to many influences affecting the reproducibility of the determinations. Variations in lighting and background, against which the smoke is viewed, must be taken into account. Different readings may be obtained on dull days and bright days and when the position of the observer is shifted. Readings also are influ'enced by variations in the illumination of the chart, which in all cases is illuminated by the ambient light that may be different from that at the stack. Also, the observer must refocus his eyes in shifting from the smoke to the chart. In an attempt to improve results, smoke has also been viewed through a section of clear glass between darkened sections which represent standard densities. This still does not eliminate errors due to variations in ambient light and to the requirement that the observer must refocus his eyes in looking from the smoke to the density reference.

It is among the objects of this invention to provide an instrument, through which smoke can be observed and compared with a reference standard that receives light from the same source as the smoke and that appears to be located at about the same distance from the observer as the smoke. V

In accordance with this invention the instrument is provided with a reflecting plate, through only the central area of which the distant smoke can be seen. Located in the instrument near the reflecting plate is a translucent reference disc that receives light rays from the vicinity of the smoke. Means are provided in the path of those rays after they leave the disc for directing them in substantially parallel relation against the reflecting plate around its clear central area. The result is that a reflection of the disc appears on the plate but it appears to be about the same distance from the observer as the smoke, so it is unnecessary to refocus the eye while malt-- ing a comparison. The image of the reference disc surrounds the smoke seen through the clear central area of the reflecting plate. The reference disc is divided into areas of different light densities for visual comparison with the smoke. This instrument limits the field of vision to the area of the stack and eliminates stray light and the effect of ambient light.

The invention is illustrated in the accompanying drawings, in which- Fig. l is a perspective view of our instrument aimed at smoke issuing from a stack;

2,921,497 Patented Jan. 19, 1960 Fig. 2 is an enlarged longitudinal section through the instrument;

Fig. 3 is a transverse section taken on the line III- III of Fig. 2; and

Figs. 4 and 5 are longitudinal sections, similar to Fig. 2, of two other embodiments of the invention.

Referring to the first three figures of the drawings, a pair of parallel cylindrical barrels 1 and 2 are spaced apart a short distance by means of a tube 3 connecting the barrels near their rear ends. The sides of the barrels at the opposite ends of the tube are provided with open ings, so that both barrels open into the connecting tube. When the instrument is used, it can be held with one of the barrels-in any position relative to the other, but for convenience of description herein one barrel is shown above the other.

The upper barrel shown in the drawing is the sighting barrel, through which smoke 4 issuing from a stack 5 is seen. The rear or ocular end of this barrel is provided with a sight opening 7, and the opposite end is provided with a restricted light opening 8. In the back part of the sighting barrel, there is a reflecting plate 9 that extends at approximately a 45 angle across the barrel. The plate, preferably glass, extends from the front edge of the side opening in the barrel upward and backward so that it overlies the upper end of tube 3. The plate is designed for reflecting an image of a reference disc to the observer. For this purpose it is necessary that little or no light pass backwardly through the plate except through its clear central area through which the smoke is observed. Light can be prevented from striking the plate around the clear central area by providing it with a silver backing, in which case the central area is left unsilvered or is provided with a hole. However, it is preferred to mount a diaphragm 11 in the barrel a short distance in front of the plate, to help keep stray light from reaching the glass. The diaphragm has a small opening 12 in its center, through which the smoke can be seen. With such a diaphragm the image plate can be clear glass, because the diaphragm will form a dark background that will cause the plate to act like a mirror.

The rear end of the lower barrel is closed, but its front end has a large opening in it. Inside this barrel a reference disc 13 is mounted between a pair of transparent glass discs 14. This disc is made of translucent material and is divided into shaded areas, a, b, c, and d (Fig. 3) of different light densities comparing with the shaded areas of a Ringelmann chart. In other words, each of the dif* ferent areas of the disc is a different shade of gray. Only three or four of such areas are necessary, and they meet at the center of the disc. The disc will receive its light from the same source as the smoke because the lower barrel is aimed at the background area adjacent to the stack while the smoke is being observed. The light rays passing through the reference disc then strike a mirror 15 in the rear end of the lower barrel beneath the connecting tube 3. This mirror is parallel to image plate 9 above it and therefore reflects the rays from the disc upward through the tube toward the plate.

A major feature of this invention is that a lens 17 with a flat bottom and a convex top is mounted in the connecting tube of the instrument for the purpose of bending the rays reflected from the mirror below it in order to cause them to travel in parallel paths above the lens. The rays come from the reference disc, which is located at the focal point of the lens. Since the rays from the reference disc therefore are parallel when they reach the eye of the observer, the reflection of the disc on the plate is an image that is projected to the stack being observed. The density of the reference standards is chosen to provide a reflection on the reflecting plate that is areas of a Ringelmann chart.

To prevent the central part of the reference disc from appearing on the reflecting plate and thereby being superimposed on the smoke seen through the plate, provision is made for blocking out the light rays from the central part of the disc when the reflecting plate does not have a hole through its center. This blocking or occluding can be done by a small circular disc 18 attached to the center of the lens or the center of the mirror 15 or even to the center of the reference disc itself. Consequently, no reflection of the disc will reach the clear center of the reflecting plate, with the result that the reference disc will appear to surround the smoke seen through the plate. Comparison of the smoke density with the reference then can be made easily without changing the focus of the eyes, because the reference will appear to surround the smoke.

Another important advantage of the lens 17 is that it increases the intensity of the light coming from the refer ence disc. When the light rays are reflected from the mirror, their intensity is reduced considerably, and although the disc receives more light through the lower barrel than the image plate receives through the upper barrel, the reflection of the disc on the plate might not be bright enough for effective use. However, due to the lens, the light from the reference disc which has been reduced by the mirror is increased again so that the reflection of the disc on the reflecting plate has the necessary brightness and clarity.

Since the reference disc is not illuminated by ambient light at the observer, but by the light from an area adjacent the smoke being observed, errors due to changes in ambient light are eliminated. Direct comparisons of smoke density and a reference standard can be made. The lens 17 projects a virtual image of the reference to the stack, therefore making it unnecessary to refocus the eye in looking from the smoke to the reference. Altogether, this instrument makes it possible to make more accurate and consistent smoke density observations than have been possible in the past. 1

In the modification shown in Fig. 4, the sighting barrel 21 and its contents are essentially the same as just described. On the other hand, the lower barrel 22 does not contain anything. It is connected to an opening in the front of a long vertical connecting tube 23. Behind the lower barrel the tube contains a mirror 24 for reflecting light rays up through the tube to the reflecting plate 25 in the upper barrel. The reference disc 26 is mounted in the connecting tube below the lens 27, so light rays do not pass through the disc until after they have been reflected by the mirror.

The instrument in Fig. has only one barrel 30 and that is vertical. The top is closed and the bottom open. Mounted at a 45 angle in the upper part of the barrel is a reflecting plate 31 that has a silvered back around a clear central area. An ocular opening 32 is formed in one side of the barrel facing the mirror, while an objective opening 33 is provided in the opposite side of the barrel. Directly below the reflecting plate there is a lens 35, and below that the reference disc 36 is mounted. The lower end of the barrel has a large opening 37 below objective opening 33, and behind the large opening, a mirror 38 is located for reflecting light rays up to the reflecting plate. If desired, a light diffusion screen 39 may be mounted in the barrel directly above the mirror.

According to the provisions of the patent statutes, we have explained the principle of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

1. An optical instrument for the observation of smoke from a stack, comprising a rearwardly reflecting equivalent to the shaded plate through only a central area of which the smoke can be seen by an observer behind the plate, a translucent reference disc near the plate, means for directing light rays from only the vicinity of said smoke through the disc while the smoke is being observed through said central area of the plate, and means in the path of said rays after they leave the disc for directing them in substantially parallel relation against the rear face of the reflecting plate around said central area, said disc being divided into areas of different light densities for visual comparison with the smoke.

2. An optical instrument for the observation of smoke issuing from a stack, comprising a sighting barrel having an opening for light at its front end and an ocular opening at its rear end to permit said smoke to be seen through the barrel, a rearwardly reflecting plate mounted in the barrel at approximately 45 to its axis, means forming a dark background for all of the reflecting plate except a small central area through whichthe smoke can be seen, the side of the barrel opposite to the rear face of said plate being provided with an opening, a second barrel substantially parallel to the sighting barrel and having an opening in its front end, a mirror behind said last-mentioned opening and parallel to the reflecting plate for reflecting laterally light rays entering the second barrel through its front opening, a tube rigidly connected at one end to the sighting barrel around its side opening, 'the tube being positioned to receive rays reflected from the mirror, a leans in said tube in the path of said rays for directing them in substantially parallel relation against the rear face of the reflecting plate, a translucent reference disc mounted in the instrument between the lens and said front end opening in the second barrel at about the focal point of the lens, whereby the reflection of said disc on the reflecting plate will appear to be in space at a distance from the observer and to surround the smoke seen through the reflecting plate, said disc being divided into areas of different light densities for visual comparison with the smoke, and means for keeping the central area of the disc from being seen on the reflecting plate.

3. An optical instrument as defined in claim 2, in which said reference disc is mounted in said second barrel in front of the mirror.

4. An optical instrument as defined in claim 2, in which said background-forming means is a diaphragm in the sighting barrel in front of the reflecting plate.

5. An optical instrument for the observation of smoke issuing from a stack, comprising a sighting barrel having an opening for light at its front end and an ocular open ing at its rear end to permit said smoke to be seen through the barrel, a rearwardly reflecting plate mounted in the barrel at approximately 45 to its axis, means forming a dark background for all of the reflecting plate except a small central area through which the smoke can be seen, the side of the barrel opposite to the rear face of said plate being provided with an opening, a second barrel substantially parallel to the sighting barrel and provided in its side with an opening opposite to the side opening in the sighting barrel, a short tube rigidly con- 50 necting said side openings, a mirror in the second barrel at the end of said tube and parallel to the reflecting plate, the front end of the second barrel being provided with an opening, a lens in said tube in the path of light rays reflected from the mirror for directing them in substantially parallel relation against the rear face of the reflecting plate, a translucent reference disc mounted in the instrument between the lens and said front end opening in the second barrel at about the focal point of the lens, whereby the reflection of said disc on the reflecting plate will appear to surround the smoke seen through the reflecting plate, said disc being divided into areas of different light densities for visual comparison with the smoke, and means for keeping the central area of the disc from being seen on the reflecting plate.

' ,6. An optical instrument for the observation of smoke issuing from a stack, comprising a sighting barrel having an opening for light at its front end and an ocular opening at its rear end to permit said smoke to be seen through the barrel, a rearwardly reflecting plate through only a central area of which the smoke can be seen by an observer at said ocular opening, said plate being mounted in the barrel at approximately 45 to its axis, the side of the barrel opposite to the rear face of said plate being provided with an opening, a second barrel substantially parallel to the sighting barrel and provided in its side with an opening opposite to the side opening in the sighting barrel, a short tube rigidly connecting said side openings, a reflecting member in the second barrel at the end of said tube and having a reflecting surface parallel to the reflecting plate, the front end of the second barrel being provided with an opening for light, a lens in said tube in the path of light rays reflected from said reflecting member for directing them in substantially parallel relation against the rear face of the reflecting plate, and a translucent reference disc mounted in the instrument between the lens and said front end opening in the second barrel at about the focal point of the lens, said disc on the reflecting plate around said central area will appear to surround the smoke seen through the reflecting plate, said disc being divided into areas of different light 2 plate being mounted in the barrel at approximately 45 to the line of sight between said openings, a reflecting member positioned to reflect against the rear face of said plate light rays from only the vicinity of said smoke while it is being observed through the barrel by said observer, a lens mounted between said reflecting member and plate in a position to direct said rays in substantially parallel relation against the plate, and a translucent reference disc mounted in the instrument at about the focal point of the lens, said disc on the reflecting plate around said central area will appear to surround the smoke seen through the reflecting plate, said disc being divided into areas of different light densities for visual comparison with the smoke.

References Cited in the file of this patent UNITED STATES PATENTS 683,203 Grubb Sept. 24, 1901 1,385,940 Ellicott July 26, 1921 2,154,374 Byram Apr. 11, 1939 2,243,383 Leber May 27, 1941 2,336,239 French Dec. 7, 1943 FOREIGN PATENTS 21,086 Great Britain of 1911 225,690 Great Britain Dec. 11, 1924 350,236 Germany Mar. 16, 1922 OTHER REFERENCES Illumination Engineering Society Transcripts (London), vol. 3, 1938, Visual Telephotometry by Collier, pages 141-154.