US3416355A - Dew point indicators - Google Patents

Description

1968 P. E. NOKES v DEW POINT INDICATORS Filed Oct. 22, 1965 TIM:

TEMPERAn/RE Inventor Philip E NokEs By his Attornqy United States Patent 3,416,355 DEW POINT INDICATORS Philip E. Nokes, Beverly, Mass., assignor to United Shoe Machinery Corporation, Boston, Mass., a corporation of New Jersey Filed Oct. 22, 1965, Ser. No. 501,781 1 Claim. (Cl. 7317) ABSTRACT OF THE DISCLOSURE Apparatus for determining the dew point of an atmosphere confined in an enclosed chamber comprising an elongated member having a light source, a molded plastic member having a reflective surface and a thermocouple embedded therein, and a light responsive member mounted on one end thereof.

This invention relates to apparatus for determining the dew point of an atmosphere, and, more particularly, to apparatus for precisely determining the dew point in a controlled, humidified atmosphere artificially created in an enclosed chamber.

The dew point or dew point temperature of an atmosphere is the temperature corresponding to saturation (100% relative humidity) for a given weight of vapor. Any lowering of temperature from the dew point produces a contraction of volume and partial condensation. That is, the dew point of an atmosphere is the temperature at which a given sample of moist air will become saturated and deposit dew.

The dew point indicator taught by the subject invention was specifically intended for use in determining the dew point in a chamber used to heat set shoe uppers. Although the apparatus of this invention is applicable to all situations wherein it is desired to determine the dew point of an atmosphere and particularly an enclosed atmosphere, a statement of the 'heat setting application exemplifies the need filled by the invention and the deficiencies of prior art apparatus.

A commonly employed method of heat setting shoe uppers comprises heating the upper in a high-temperature moist atmosphere and thereafter drying the upper in a dry atmosphere. These operations are performed subsequent to lasting to impart the shape of the last to the shoe upper. The purpose of the heating operation is to heat moisture and fat liquors in the upper to soften the fibers thereof whereby to remove residual stresses therein. The combination of moisture and heat are the primary constituents required to accomplish stress relief, The subsequent drying operation removes moisture from the upper and imposes stresses which thereafter produce a permanent reproduction of the shape of the last. In one application of the method, individual chambers are used to enclose the moist and dry atmospheres. The initial step in the method is a heating operation which must be accomplished without drying the leather. Accordingly, the humidity level of the moist atmosphere must be maintained at a magnitude sufiicient at least to insure moisture equilibrium between the atmosphere and the leather thereby to prevent drying of the leather. This is accomplished by maintaining the dew point of the moist atmosphere above the temperature of the upper. The result of this step is to precipitate a film of water on the upper. The heated atmosphere condenses the water film and the heat of condensation results in rapid heating of the upper. The ability to determine the dew point within the chamber is thus critical.

The two steps of the above-described application of the method may, in an alternative embodiment, be combined in a unitary step employing a single atmosphere to both heat and dry the lasted upper. This is accomplished by the use of a high temperature moist atmosphere the dew point and temperature of which are controlled such that, for a given exposure interval, the temperature of the upper is elevated from a level below the dew point to a level thereabove. That is, when an upper is introduced into the chamber, the dew point of the chamber is above the initial temperature of the upper. Thus, initially, the temperature of the upper is raised without withdrawing moisture therefrom. When the temperature of the upper is raised above the dew point of the atmosphere by heat transferred thereto from the atmosphere, moisture is thereafter removed from the upper. The dew point of the atmosphere within the chamber is thus of utmost criticality in this embodiment.

In the commercial use of the heat setting method and apparatus described above, means must be provided which permit frequent checking of the dew points within the enclosed chambers. One possible laboratory technique for determining the dew point is by the use of a thermocouple pyrometer. A thermocouple pyrometer consists essentially of a thermocouple of two different metals or alloys the wires of which are fused together at one end to form the measuring (hot) junction which is exposed to the temperature to be measured. The other ends of the wires are connected to an indicating instrument such as a multivoltmeter or potentiometer. The electromotive force induced by the difference in temperature between the different metals or alloys is proportional to'the temperature difference. Temperature-EMF data for thermocouples is readily available to make the necessary conversion of data. Thus, the temperature within an enclosed chamber can be determined by this device. The dew point temperature may be determined by plotting the temperatures obtained against time, see FIG. 4 of the drawings. The dew point temperature is that point on the graph of FIG. 4 at which the temperature remains constant for a relatively extended period. After the dew point is past, the temperature will again being to rise. The reason for a sustained constant temperature at the dew point is that heat is being absorbed in the evaporation of condensation and is not available to elevate the temperature of the enclosed atmosphere.

The thermocouple pyrometer technique is an accurate laboratory technique. However, it requires the services of a skilled artisan capable of operating and interpreting a multivoltmeter or potentiometer to determine the plateau in temperature rise which denotes the dew point. Such a skilled artisan is not normally available in a shoe factory where the above described heat setting method would be practiced.

The commonly employed technique for determining dew point is by cooling a flat polished metal surface until it becomes clouded with a film of water; the dew point being the temperature at which the film appears. However, this technique is not adaptable for use within an enclosed chamber where visual access is not available.

The teachings of the prior art do not, in fact, provide apparatus by which the dew point of an enclosed atmosphere can be readily determined by an unskilled artisan. A number of alternate techniques to the thermocouple pyrometer discussed above are taught by the prior art for determining temperature. However, each of these techniques requires a skilled artisan to determine the dew point by the use thereof.

Accordingly, it is an object of the present invention to provide apparatus for precisely and easily determining the dew point of an atmosphere.

To this end and in accordance with a feature of this invention there is provided apparatus for determining the dew point of an atmosphere comprising a conducting member having a reflective surface and a means mounted therein for determining the temperature thereof, a light source directed at said reflective surface, a light responsive member positioned in the path of light reflected by the reflective surface when said surface is free of moisture, and means responsive to the activation of said light responsive member to record the same.

The above and other features of the invention including various and novel details of construction and combinations of parts will now be more particularly described with reference to the accompanying drawings and pointed out in the claim. The principles and features of this invention maybe employed in various and numerous embodiments without departing from the scope of the invention.

In the drawings:

FIG. 1 is a side elevation, partly in section, of apparatus embodying features of the present invention;

FIG. 2 is a plan view of the light source, reflector means, and light responsive means employed in the embodiment of this invention generally illustrated in FIG. 1;

FIG. 3 is an electrical wiring diagram of the apparatus illustrated in FIG. 1; and

FIG. 4 is a graph illustrating the dew point plateau in a temperature-time plot.

The apparatus of this invention comprises a light source 10, a reflective surface 12 formed on a mounting unit 14 and a light responsive member 16 all of which are utilized in combination with a thermocouple pyrometer 2 whereby to facilitate the determination of the dew point of an atmosphere without the need to interpret the readings on a multivoltmeter or potentiometer. The light source and light responsive member 16 are both mounted in a unitary mounting block 20. The mounting block 20 and mounting unit 14 are mounted at spaced positions on the end portion of an elongated hollow member 24. The elongated member 24 may be used as a handle to insert the mounting block 20 and mounting unit 14 into a chamber 22 housing an atmosphere the dew point of which is to be determined.

The mounting block 20 and mounting unit 14 are positioned on the member 24 such that light emanating from the light source 10 will be directed at the reflective surface 12 on the mounting unit 14. The reflective surface 12 is concave and is so positioned on the member 24 as to reflect a beam of light from the light source 10' in the direction of the light responsive member 16 whereby to activate said light responsive member 16.

In the use of the apparatus of this invention to determine the dew point of an enclosed atmosphere, the elongated member 24 is inserted into the chamber 22 whereby to position the mounting block 20 and mounting unit 14 in exposed relation to the atmosphere. The temperature of the enclosed atmosphere is initially higher than the temperature of the mounting unit 14 and, therefore, also for the reflective surface 12 thereon. Likewise, the temperature of the unit 14 and surface 12 is below the dew point of the enclosed atmosphere. In the heat setting application discussed above, the temperature within the chamber 22 is in the 220 F. to 375 F. range while the mounting unit is at room temperature when it is inserted. Accordingly, moisture initially will be collected on the unit 14 and the surface 12 as a result of this temperature differential. The film of water thus formed on the reflective surface 12 results in the diffusion of light directed thereat from the light source 10. That is, although the water vapor is transparent when suspended in the atmosphere, it results in diffusion of the light beam cast upon the reflective surface 12 rather than in the reflection thereof. Accordingly, light will not be reflected in the direction of the light responsive member 16 with suflicient candle power to activate the member 16. It should be noted that although in the embodiment illustrated in FIG. 1 both the mounting unit 14 and the mounting block 20 are inserted into the enclosed chamber, only the mounting unit 14 need be exposed to the atmosphere.

Further exposure of the mounting unit 14 to the enclosed atmosphere will result in the transfer of heat to the reflective surface 12 from the atmosphere and, accordingly, in an increase in the temperature thereof. When the temperature of the reflective surface 12 is elevated to the dew point of the atmosphere, the water film on the reflective surface 12 will evaporate. Thus, when the temperature of the reflective surface 12 corresponds to the dew point temperature of the atmosphere, light will be reflected by the surface 12 in the direction of the light responsive member 16 whereby to activate the same. The activation of the light responsive member is recorded on an indicating instrument 40 which may be of any convenient design. The electrical connection between the member 16 and instrument 40 is accomplished by wires in the hollow member 24. The point at which the reflective surface reaches the dew point is thus recorded without the necessity of reference to a temperature graph or potentiometer interpretation.

The exact temperature of the reflective surface 12 corresponding to the dew point of the atmosphere is recorded by means of a thermocouple 50, 50 housed in the mounting unit 14 adjacent the surface 12 and an associated potentiometer 54. That is, by a thermocouple pyrometer which functions in the manner described above. In the preferred embodiment, the mounting unit comprises a solid molded plastic member in which the thermocouple is mounted such that the juncture thereof is adjacent the reflective surface 12. The reflective surface comprises a silver coating. The plastic member insulates the thermocouple from the temperature of the atmosphere. Accordingly, the thermocouple is essentially influenced only by heat transferred thereto from the reflective surface 12. The temperature of the surface 12 at the dew point is thus recorded. The lead wires for the thermocouple are also housed in the hollow member 24.

In the use of the apparatus, an operator need only record the temperature level on the potentiometer at the time the activation of the light responsive number 16 is registered on the instrument 40. There is no need to apply the skill required to interpret the potentiometer reading to recognize the temperature plateau which denotes the dew point as shown in FIG. 4.

The circuitry delineated in FIG. 3 illustrates the cooperation between the light source 10, reflective surface 12 and light responsive member 16. The electrical connection between the light responsive member 16 and the indicating instrument 40 is also shown. The thermocouple 50, 50 must be located in close proximity to the reflective surface 12 in order to ensure comparative temperature levels. This is shown in FIG. 3 as well as FIG. 2. The remainder of the circuitry shown in FIG. 3 denotes a potentiometer comprising storage cells 60, 62, a rheostat 64, a series of resistance members 66, a microammeter 68 and a key 70.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for determining the dew point of an atmosphere confined to an enclosed chamber comprising a light source, a mounting unit comprising a solid molded plastic member having a reflective silver coated surface and a thermocouple mounted in said plastic member with the juncture thereof adjacent the reflective surface, a light responsive member, said light source, mounting unit and light responsive member being mounted on one end of an elongated member such that light emitted from said light source will be directed at said mounting unit and light 5 reflected by said mounting unit will be directed at said light responsive member when the said end of the elongated member is inserted into an enclosed chamber and the 'light source activated, means responsive to the actuation of said light responsive member to indicate the same, and means for recording the temperature measured by the thermocouple when the light responsive member is actuated.

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