Surface temperature measuring device with reversible thermochromic film

United States Patent [191

[11] 4,445,787 [45] May 1, 1984

Parker [54] SURFACE TEMPERATURE MEASURING DEVICE WITH REVERSIBLE . THERMOCHROMIC FILM [76] Inventor: Robert Parker, 411 Rolling Hills La., Alamo, Calif. 94507 [21] Appl. No.: 365,763 [22] Filed: Apr. 5, 1982 [51] Int. Cl.3 G01K 1/16; GOIK ll/l2 [52] U.S. Cl. ............................... .. 374/141; 30/ 346.52; 30/51; 374/162; 374/208 [58] Field of Search ..................... .. 374/141, 162, 208; 252/962; 30/140, 346.52 [56] References Cited U.S. PATENT DOCUMENTS 3,002,385 10/1961 Wahlget al. ................... .. 252/962 X 3,031,888 5/1962 Wilhelm 374/155 X 3,382,512 5/1968 Atchley .... .. . 374/141 X 3,704,625 12/1972 Seto et al. .. 374/162 3,779,079 12/1973 Snook ........ .. 374/144 3,955,420 5/1976 Parker 252/962 X 4,070,911 1/1978 Makin . . . . . . .. 374/208 4,075,458 2/1978 Moyer 30/140 X 4,095,467 6/1978 McG1ynn 374/183 X 4,137,769 2/1979 Parker ............................... .. 374/134

Primary Examiner—Danie1 M. Yasich Attorney, Agent, or Firm-—Paul Hentzel

[57] ABSTRACT An array of thermochromic cells is formed along the

ASE

PORTION

I20

OBJECT

end portion of a thin, highly conductive blade. Each cell is visually responsive to a critical temperature incrementally different from the critical temperatures of the other cells. The thermochromic array defines a set of temperature ranges, set off by the critical temperatures. The undersurface of the end portion is pressed down into contact with the hot surface of an object of unknown temperature. The contact pressure is established and maintained constant by bending the blade against the surface. The high elastic strength of the blade permits generous bends having high bending moments without creating a permanent set in the blade. Heat from the hot surface flows upward across the contact area and into the interior of the thin blade. The interior increase in temperature uniformly, with minimum pertubation; and the end portion rapidly obtains an equilibrium temperature substantially equal to the temperature of the object surface. Heat transients are minimal because the contact area is very large relative to the extreme thinness, and small thermal mass, of the blade. The array of thermochromic cells on the top surface of the end portion simultaneously receive heat from the interior. The cells having a lower critical temperature then the equilibrium temperature undergoes the visual change. The condition of the array reveals the equilibrium temperature to within one temperature increment.

18 Claims, 4 Drawing Figures

252

MOMENT

PORTION 256

ARRAY FACE 266L

CONTAC

FACE 250

1

SURFACE MEASURING DEVICE WITH REVERSIBLE TI-IERMOCHROMIC FILM

TECHNICAL FIELD

This invention relates to rapid thermochromic measurement of surface temperatures, and more particularly to thermochromic cells bonded to a very thin base which is urged into contact with the object surface.

BACKGROUND

Heretofore, electronic devices have been available for measuring surface temperature, i.e. thermocouples, infrared detectors, thermistors. These devices are costly to purchase and maintain, required batteries or an external power source, werebulky, and easily damaged.

Thermochromic devices such as shown in U.S. Pat. No. 3,002,385 to Wahl, U.S. Pat. No. 2,928,791 to Laconti, and U.S. Pat. No. 4,137,769 to Parker, avoid many of these problems. However, these devices are permanently bonded to the surface in order to provide the required for good thermal contact. The devices may not be removed, and remounted on another site.

U.S. Pat. No. 3,955,420 and U.S. Pat. No. 3,827,301, both to Parker teach a rod thermochromic device with cooling fin heat exchange characteristics. The tip of the device is pressed against the surface to be measured. A temperature gradient is established along the device causing a progressive thermochromic change extending outward from the contact end. The surface temperature is indicated by the extend of the thermochromic change present at equilibrium. This rod device requires many seconds to reach the equilibrium required for accurate readings. The time element is especially burdensome when measuring high surface temperatures which have a correspondingly high transient time.

SUMMARY

It is therefore an object of this invention to provide a reversible thermochromic temperature indicating device which is very fast.

It is another object of this invention to provide such a device which has a uniformly short measurement period.

It is a further object of this invention to provide such a device which has minimum initial pertubation effects.

It is a further object of this invention to provide such a device which has minimum steady state pertubation effects.

It is a further object of this invention to provide such a device which is passive, and does not require an external source of power.

It is a further object of this invention to provide such a device which is inexpensive, reliable, rugged, and accurate. t

It is a further object of this invention to provide such a device which has a constant and reproducible contact pressure and heat exchange flow rate.

Briefly, these and other objects of the present invention are accomplished by providing a thermally conductive thin member having a contact side and a cell array side opposed thereto. The contact side is placed in heat transfer engagement with the surface to be measured defining an active heat transfer area on the contact side, and a corresponding active volume within the portion of the thin member adjacent thereto. Heat from the surface simultaneously flows across each region of the active area into the thin active volume. Each region of

2

the active volume simultaneously obtains an equilibrium temperature substantially equal to the "temperature of the object surface. An array of cells containing a reversible thermochromic material form a thin layer on the array side of the thin member. Each of the cells responds to the heat within the thin member at a different critical temperature determined by the composition of the thermochromic material therein.‘ A resilient structure connects to the thin member for urging the contact side into fum heat transfer engagement with the object surface.

BRIEF DESCRIPTION OF THE DRAWING

Further objects and advantages of the thin blade construction and the operation of the thermochromic cell array will become apparent from the following detailed description and drawing in which:

FIG. 1 is an isometric view, partially in section, showing a thin blade and the-interior of the housing;

FIG. 2 is a sectional side view of the device of FIG. 1 showing the blade in contact with the surface to be measured;

FIG. 3 is fragmentary sectional front view showing the blade in contact with the an irregular surface; and

FIG. 4 is an isometric view, partially in section, showing a flat blade within a single ended housing.

GENERAL DESCRIPTION FIG. 1

The temperature indicating device 100 has a thin blade 106 enclosed in an insulative handle or housing 110 as shown in the cut-away-view of FIG. 1. Thin blade 106 is highly conductive, and has an array of thermochromic films or coatings arranged in cells 112A at one end thereof and array 112B at the other end. The cell material is preferable bonded to blade 106 to enhance the heat exchange therebetween. Each cell visually responds at a different critical temperature defining a corresponding set of temperature increments which may be indicated by the arrays 112.

A displacement knob 116 projects upward from the center or base portion 120 of blade 106, and through a top slot opening 122 extending longitudinally along the top surface of housing 110. The user grips housing 110 in his hand, while sliding knob 116 along slot opening 122 with his thumb for displacing blade 106 along a longitudinal channel 126 within the housing 110. Base portion 120 is guided by the side walls of channel 126.

Blade 106 is normally in a retracted secure position within housing 110, and is displaced longitudinally (in the direction of arrow A) into the sensing position shown in FIG. 1. End portion 130A of blade 106 extends from housing 110 through a lateral aperture 132A. A detent 136A at the end of slot opening 122 catches knob 116 for retaining blade 106 in the extended measuring position.

If desired, blade 106 may have a slight bow along base portion 120 (showm more clearly in FIG. 2) for providing a resilient, light pressure against the ceiling and floor of longitudinal chamiel 126. The resulting static friction is easily overcome by the user, and eliminates free movement of blade 106 (i.e. vibrating, rattling around channel 120, slipping into the extended position while being transported in a tool box). In addition, the upwards bow pressure of blade 106 causes knob 116 to lock into detents 136. The user releases knob 116 from