Electrical resistors – Resistance value responsive to a condition – Gas – vapor – or moisture absorbing or collecting
Patent
1982-09-29
1987-06-16
Envall, Jr., Roy N.
Electrical resistors
Resistance value responsive to a condition
Gas, vapor, or moisture absorbing or collecting
733365, H01C 700, G01N 2712
Patent
active
046739106
DESCRIPTION:
BRIEF SUMMARY
FIELD OF TECHNOLOGY
The present invention relates to a moisture sensitive element that is designed to detect the humidity of atmosphere by using the change in electrical resistance of the moisture sensitive section of the element.
BACKGROUND OF TECHNOLOGY
Heretofore, the moisture sensitive section of the element that has the capability described above has been made of an electrolyte such as lithium chloride or calcium chloride, a vapor-deposited film of a semiconductor such as selenium or germanium, as well as a metal oxide or metal oxide ceramic using aluminum oxide, titanium oxide or iron oxide.
Among these materials, the electrolyte has so much hygroscopicity in the high-humidity region that is becomes fluid and has low strength, with the result that the measurable moisture range is from 0 to about 60% rh. The vapor-deposited semiconductor film needs vacuum deposition and is not easy to fabricate, and in addition, the humidity reading is affected by temperature. The metal oxide is stable both physically and chemically and provides a strong element, but it generally needs a firing temperature of 1000.degree. C. or more which often reduces the area of the moisture sensitive surface. Therefore, the conventional moisture sensitive sections prepared from either of the above mentioned materials have their own defect and are not satisfactory.
SUMMARY OF THE INVENTION
The present invention has been developed to eliminate the above defects of the conventional techniques and one of its objects is to provide a moisture sensitive element having a moisture sensitive section that has high sensitivity to detect humidity, is capable of measuring a wide range of humidity, can be made from a cheap and easily available material, can be fabricated easily and which yet provides a strong element.
In the conventional ceramic moisture sensitive element, the metal and oxygen atoms are ionized by being charged positively and negatively to some extent, so if a static electrical field is applied, as by d.c. current, to the element, the two ions are polarized in opposite directions to change (increase) the electrical resistance of the element. To prevent this, it has been necessary to use an a.c. current that unavoidably needs a more complex detection circuit than when a d.c. current is used. Therefore, another object of the present invention is to provide a moisture detecting element that is capable of detecting humidity on d.c. current.
Still another object of the present invention is to provide a moisture sensitive element operable with d.c. current that uses a moisture sensitive section that contains 10 to 95 wt.% of a polymerized organic silicon compound, 5 to 90 wt.% of an amorphous silica powder and 0 to 30 wt.% of another additive component and which is sintered at a temperature of 300.degree. C. or higher.
A further object of the present invention is to provide a moisture sensitive element operable with d.c. current that uses a moisture sensitive section made of a sintered product containing 20 to 85 wt.% of a polymerized organic silicon compound, 0.5 to 15 wt.% of a carbonaceous powder and 5 to 60 wt.% of a siliceous powder.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a moisture sensitive element according to a first example of the present invention;
FIG. 2 is a curve graph showing the firing temperature vs. electrical resistance characteristics of the moisture sensitive element of the present invention;
FIGS. 3, 4 and 5 are graphs showing the relative humidity vs. logarithmic electrical resistance characteristics of the first to third examples;
FIG. 6 is a perspective view of a moisture sensitive element according to a fourth example of the present invention;
FIG. 7 is a graph showing the relative humidity vs. logarithmic electrical resistance characteristics of the moisture sensitive element according to the fourth example;
FIG. 8 is a graph showing the time-dependent relative humidity vs. logarithmic electrical resistance characteristics of a conventional moisture sensitive element and t
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patent: 4378691 (1983-04-01), Terada et al.
patent: 4386336 (1983-05-01), Kinomoto et al.
Miyao Kunihiko
Momiyama Kimio
Shimamoto Kozo
Takeuchi Morihisa
Uchikawa Fusaoki
Envall Jr. Roy N.
Mitsubishi Denki & Kabushiki Kaisha
Sears C. N.
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