US 3482944 A
Description (OCR text may contain errors)
Dec. 9,` 1969 C. A. PLANTZ GAS DOSIMETER USING COLORIMETRIC STRIP ALSO 'SENSITIVE TO LIGHT Filed May 2. 196'? United States Patent O 3,482,944 GAS DOSIMETER USING COLORlMETRIC STRIP ALSO SENSITIVE T LIGHT Charles A. Plantz and Cecelia C. Jenca, Pittsburgh, and Paul W. McConnaughey, Wilkinsburg, Pa., assignors to Mine Safety Appliances Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed May 2, 1967, Ser. No. 635,499 Int. Cl. G01n `i1/08; G01j 3/48 U.S. Cl. 23-254 7 Claims ABSTRACT 0F THE DISCLOSURE It is among the objects of this invention to provide a dosimeter which can detect a given gas by the use of colorimetric material that is sensitive to light, and which is simple in construction and extremely easy to use.
The preferred embodiment of the invention is illustrated in the accompanying drawings, in which:
FIG. 1 is a front view of our dosimeter;
FIG. 2 is a view similar to FIG. 1, but showing the dosimeter open;
FIG. 3 is a central vertical section taken on the line III- III of FIG. 1; and
FIG. 4 is a horizontal cross section taken on the line IV-IV of FIG. l.
Referring to the drawings, a rectangular open front receptacle 1 is formed from any suitable material such as a molded plastic. The receptacle has a back wall and forwardly projecting side walls around its four sides. The receptacle is intended to be worn on a persons clothing, such as by suspending it from a spring clip 2 by means of a strap 3 that may be looped through a slot 4 in the top side wall of the receptacle.
As shown in FIG. 3, the central portion of the back Wall is outset rearwardly or outwardly to form a long narrow recess 6, the lower end of which is provided with a transverse slit 7. Sealed into the front of this recess is a partition 8 provided near its upper end with an opening 9. Most of the partition is opaque, but preferably a short length of it directly below the opening is transparent and colorless to form a clear window 10. A convenient way of making the partition is to make it of glass or clear plastic that is covered with an opaque paint except for the window area and opening 9. The recess between the offset portion of the back of the receptacle and the partition forms a thin pocket intended for receiving a strip 12 of colorimetric material which can be inserted through the slit 7 at the bottom of the pocket. To hold the strip in the pocket and also for another purpose to be described later, springs are mounted in the pocket behind the strip and press it forward against the partition. A convenient form for the springs to take is a pair of parallel spring wires 13 having bent ends anchored in holes in the rear wall of the pocket, with the intermediate portions of the springs bowed forward to press against the strip.
When a gas-sensitive colorimetric strip is exposed to the gas to be detected, the color of the strip changes and the degree of color change indicates the product of the concentration of the gas in the atmosphere multiplied by the exposure time, as is well known. This change in color 3,482,944 Patented Dec. 9, 1969 ICC can be viewed through the opening 9 in the front of the pocket. The color of the strip then is compared with color standards 14 located near the exposed portion of the strip. These color standards are colored plaques, insensitive to light, that may be glued to the back wall of the receptacle around opening 9. Colors are selected that will indicate certain concentrations of the gas in question.
The colorimetric strips intended for use with this dosimeter are a type that not only are sensitive to a gas, but also are sensitive to actinic light. Such strips are used for detecting hydrazine, substitute hydrazines, and certain other volatile gases in air. For detecting hydrazine, for example, the colorimetric material may be formed by impregnation of bindone in some porous substance, such as paper or thin layer chromatography material or the like. If this colorimetric material is exposed to direct light for very long, the light will cause a chemical reaction that will reduce the sensitivity of the strip and therefore the strip will give a false reading of the gas being detected. It is therefore a feature of this invention that the colorimetric strip in the back of the receptacle is protected from direct light. This is accomplished by means of a shield 16 mounted in the receptacle in front of pocket 6. The shield is spaced from the back wall of the receptacle and from some or all of its side walls so as not to prevent the colorimetric strip from being exposed to the atmosphere surrounding the dosimeter. The shield and receptacle preferably are black or some other color that absorbs actinic light in order to reduce reflection of that light onto the sensitive strip.
The shield can be removed temporarily so that the portion of the strip viewed through opening 9 can be cornpared in color with the surrounding color standards. A preferred way of mounting the shield in the receptacle and providing for its removal from in front of the strip is to hinge the lower end of the shield to the receptacle. This can be done by providing the lower ends of the opposite sides of the shield with rearward projecting parallel lugs 17, through which a hinge pin 18 extends, as shown in FIGS. 3 and 4. The ends of the pin are sprung into holes in the vertical side walls of the receptacle. A torsion spring 19 is mounted on the pin, with one end of the spring hooked under the lower end of the shield and the outer end pressing against the back of the receptacle. This spring normally holds the shield in a vertical position entirely within the receptacle. This is the closed position of the shield. The upper end of the shield is provided with a short leg 20 to space it from the back of the receptacle. In order to open the shield, its lower portion is provided with an outwardly projecting tab 21 that can be pressed down by the thumb or a finger to cause the upper end of the shield to swing forward out of the receptacle and down to a substantially horizontal portion, as shown in FIG. 2. This will expose opening 9 fully to view for checking the color of the strip with the color standards.
Although short exposures of the colorimetric strip to light will not affect its sensitivity, it is preferred that the dosimeter be constructed in such a way that it is not necessary to swing the shield out of the receptacle in order to see whether the colorimetric strip has changed color. Consequently, the shield is provided with a central opening 23, through which the strip can be seen. However, to prevent actinic light from reaching the strip through this opening and affecting its color by reducing its sensitivity, a light lter 24 is mounted in the opening to form a window. This lter is a plastic or glass of a color that will lter out the rays of light that would cause the strip to change its color sensitivity to the gas.
Since the color of the filter makes the strip seen through it appear colored, it is desirable to be able to compare the color of the portion of the strip viewed through pocket opening 9 with an adjoining portion of the strip that has not been exposed to the gas being detected. This can be done by comparing the portion of the strip'viewed through the pocket opening with the adjoining portion seen through the window 10. The portion of the strip behind Window is not exposed to the atmosphere because it is held tightly against the window by springs 13 behind it.
In the use of this dosimeter, it is attached to a persons clothing by means of clip 2, with the open side of the receptacle facing forward. Periodically, the wearer can lift up the dosimeter and look at the colorimetric strip through the iilter window of the shield. If he notices that the color of the strip seen through shield window 24 and pocket opening 9 is different from the color of the strip behind the pocket window, he knows that the strip has been affected by the gas that is being detected. He then presses down on tab 21 to swing the shield out so that he can compare the real color of the strip with the color standards located around the pocket opening. If he does not already know what exposure to gas is indicated by each color standard, he can get that information from a chart that he carries, which also will tell him whether or not the exposure is dangerous.
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 specically illustrated and described.
1. A dosimeter comprising a receptacle having back and side walls and an open front, means `for holding in the receptacle a colorimetric strip sensitive to light and a predetermined gas, a colorimetric strip sensitive to light and to a predetermined gas in said receptacle, a shield in the receptacle for normally covering the strip to protect it from direct light before and during exposure to said gas, the shield being spaced from the back wall of the receptacle and from at least some of its side walls t0 expose lthe area behind the shield to the surrounding atmosphere, means in said area for spacing the strip from the shield, color standards in the receptacle adjacent said holding means, and means for temporarily moving the shield out of the receptacle far enough to permit the color of said said standards'.
2. A dosimeter according to claim 1, including a hinge attaching said shield to theV receptacle, and said shield moving means being a rigid tab projecting from the shield a short distance from the hinge.
3. A dosimeter according to claim 1, in which said strip-holding means include a pocket formed in said back wall of the receptacle and provided with a front opening, one end of the pocket outside of the receptacle having a slot `for insertion of a colorimetric strip behind said open- 4. A dosimeter according to claim 3, including a clear transparent Window forming part of the front of said pocket and located next to said front opening for engagement by the strip'.
5. A dosimeter according to claim 4, including spring means in said pocket for pressing a colorimetric strip forward against said window.
6. A dosimeter according to claim 1, in which said shield is provided with an opening therethrough, and a light lter is mounted in said opening to form a window for viewing a colorimetric strip behind it.
7. A dosimeter according to claim 2, in which said shield is provided with an opening therethrough, a light filter is mounted in said opening to 'form a Window for viewing a colorimetric strip behind it, a clear transparent window is disposed behind the shield for covering part of the colorimetric strip, and spring means connected to the receptacle are adapted to press the strip forward against the transparent window.
References Cited UNITED STATES PATENTS 2,680,816 6/1954 Stern. 3,194,963 7/1965 McKee. 3,283,153` 11/1966 Geiger.
MORRIS 0. WOLK, Primary Examiner R. M. REESE, Assistant Examiner U.S. Cl. XR. 23-253