Thermal measuring and testing – Temperature measurement – Composite temperature-related paramenter
Patent
1995-02-21
1998-09-01
Gutierrez, Diego F.F.
Thermal measuring and testing
Temperature measurement
Composite temperature-related paramenter
374201, 2524081, 252962, 128736, G01K 304, G01K 522, G01K 510, G01K 512
Patent
active
058000607
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a clinical thermometer with a maximum function and a eutectic mixture suited to it.
2. Description of the Related Art
In order to achieve the maximum function, conventional thermometers of this kind are filled with mercury and show a constriction between the bulb exposed to the temperature to be measured and the reading or measuring tube, which has the effect that in the cooling down process the mercury thread that entered the measuring tube separates.
Mercury is extremely poisonous and for health and environmental reasons is therefore increasingly met with disapproval.
Furthermore, in making the thermometer, an additional production step is necessary in order to create the constriction which requires a certain amount of precision so that the necessary inner cross-section is achieved which has to be small to facilitate the separation of the mercury thread upon a drop in temperature after having reached the maximum temperature, but not so small as to interfere with the reuniting of the mercury upon shaking down.
In accordance with US-PS 3,872,729 it was suggested to do without the problematic constriction and to coat the inside of the measuring tube to assure the necessary adhesion forces. The production of such a measuring tube is, however, very expensive and usually not very practical. Furthermore, it is necessary also with this thermometer to rely on toxic mercury.
So far, all attempts to produce a mercury-free clinical thermometer failed first of all because of the necessary maximum function. Similarly unsuitable are also the thermometers according to DE-PS 453 184, DE-PS 454 213 and GB-PS 246 843, which provide for the use of gallium with and without indium. Such thermometers have the disadvantage that their measuring liquid solidifies at low temperatures which may under certain circumstances result in the thermometer shattering.
Similar problems also arise when using a measuring liquid according to SU-PS 279 108.
The object of the present invention is therefore to specify the details of a thermometer with a maximum function which is simple to use, easy to produce and is harmless from the health and environmental standpoint.
SUMMARY OF THE INVENTION
According to the invention the solution to the given problems is found by using a eutectic alloy containing gallium in a concentration of 65-95 wt.-%, indium in a concentration of 5-22 wt.-% and tin in a concentration of 0-11 wt.-%, if necessary.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates one embodiment of a clinical thermometer in accordance with the subject invention.
FIG. 2 illustrates a cross-sectional view of the embodiment of the clinical thermometer of FIG. 1 taken across the region 16 of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The use of a eutectic gallium alloy as measuring liquid is of special significance because of its non-toxic characteristic. Furthermore, this liquid has a low melting point and a high vaporization point so that the necessary requirements of a clinical thermometer are met.
In this range of composition the liquid state of aggregation of the liquid extends from approx. -15.degree. C. to more than +1800.degree. C. under normal conditions. Gallium, indium and, if necessary, tin are preferential alloy elements because they lead to a particularly low eutectic point. Furthermore, this alloy is capable of conducting electricity so that it is also suitable for an embodiment as contact thermometer.
In a further embodiment of the present invention according to claim 2 the eutectic alloy may contain up to 2 wt.-% bismuth and up to 2 wt.-% antimony. Antimony raises the oxidation resistance while bismuth positively affects the fluidity of the alloy. Furthermore, antimony and bismuth are, like tin, readily available and inexpensive substances, while gallium and indium are expensive. A content of more than 2 wt.-% pf one of the two additional elements Sb and Bi leads to a noticeable and undesirable increase in the melting point.
REFERENCES:
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patent: 4083250 (1978-04-01), Goff et al.
patent: 4627741 (1986-12-01), Faller
patent: 4647224 (1987-03-01), Holm et al.
patent: 4659384 (1987-04-01), Daigo et al.
patent: 5120498 (1992-06-01), Cocks
patent: 5198189 (1993-03-01), Booth et al.
Author: E. Greil Wertheim, Title: Glass Thermometers: vacuum or pressure filled?, Date: Sep. 1972, Pertinent pp.: 1033-1040, see p. 1035 par. 5-p. 1036, par. 1, Published in: Git-Fachzeitschrift Fur Das Laboratorium vol. 16 No. 9, Sep. 1972.
"Expanding Fluid Thermometer Having Thermally Sensitive Bulb," J.M. Brady, published O.G. Sep. 29, 1953 (No. 245622).
Alt Marion
Kamitz Siegbert
Schmitt Heribert
Speckbrock Gerd
Geraberger Thermometer Werk GmbH
Gutierrez Diego F.F.
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