Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Patent
1992-05-27
1994-04-26
Picard, Leo P.
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
174255, 338 2, 338 3, H05K 100
Patent
active
053068734
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a load cell of a type used in a weighing apparatus such as, for example, an electronic scale, comprising a strain gauge formed by the use of a sputtering technique on a surface of a strain inducing element.
BACKGROUND ART
It is well known that a load cell comprising a strain gauge formed by the use of a vapor deposition technique or a sputtering technique is manufactured by applying a heat-resistant high molecular material such as, for example, polyimide, on a surface of a strain inducing element to form an electrically insulating film, subsequently forming a thin film of nickel-chromium alloy or tantalum nitrate on a surface of the electrically insulating film by the use of a vapor deposition technique or a sputtering technique and finally photo-etching the thin film to form a resistance pattern.
The load cell particularly used in a weighing apparatus such as a scale comprises four strain gauges which are electrically connected to form a bridge circuit. Therefore, where all of the strain inducing elements vary uniformly with a change in temperature, temperature dependent changes in outputs from the respective strain gauges can be counter-balanced with each other. However, where an article of a temperature considerably different from a room temperature such as, for example, a frozen food material, is placed on a load supporting plate connected with one end of the load cell, a temperature gradient occurs in strain inducing elements to such an extent as to result in varying resistances of the respective strain gauges according to a temperature dependent coefficient of resistance. Once this occurs, the variations in resistance among those strain gauges can no longer be counterbalanced with each other by the bridge circuit.
By way of example, in the case of the load cell comprising strain gauges prepared by forming an electrically insulating film of polyimide on a surface of a strain inducing element and then sputtering a thin film of tantalum nitrate on a surface of the electrically insulating film, one of the resultant strain gauges may have a temperature dependent coefficient of resistance which is about -40 PPM/deg(.degree.C.) and, consequently, when this load cell is applied in a weighing apparatus, a problem would occur in that an measurement error in the order of about 200% per degree at maximum tends to occur.
The present invention has been devised with the foregoing problem taken into consideration and has for its object to provide a load cell wherein strain gauges each having an extremely small temperature dependent coefficient of resistance are integrally formed.
DISCLOSURE OF THE INVENTION
In order to solve the foregoing problem, in the practice of the present invention, in a load cell fabricated by forming a strain gauge pattern from a film of a copper-nickel alloy formed on a metallic strain inducing element by the use of a sputtering technique and subsequently heat-treating the strain gauge pattern under an oxygen-free atmosphere, the weight ratio of copper and nickel is chosen to be of a value effective to permit the temperature dependent coefficient of resistance of the strain gauge pattern, which undergoes shrinkage and expansion together with the strain inducing element, to be substantially zero, that is, a value effective to counterbalance a change in resistance resulting from the shrinkage and expansion of the strain gauge due to the linear expansion of the strain inducing element and the temperature dependent coefficient of the copper-nickel alloy used to form the strain gauges with each other.
The strain inducing element referred to above may be made of aluminum alloy, stainless steel, brass, phosphoric bronze, low alloyed steel or carbon steel.
By way of example, where the strain inducing element referred to above is made of aluminum alloy, stainless steel or brass, and if the coefficient of linear expansion of this strain inducing element is expressed by .beta., the content (wt %) of nickel in the copper-nickel alloy used a
REFERENCES:
patent: 4432247 (1984-02-01), Takeno et al.
patent: 4511877 (1985-04-01), Nishikawa et al.
patent: 4633721 (1987-01-01), Nishiyama
patent: 4677413 (1987-06-01), Zandman et al.
patent: 4786887 (1988-11-01), Bringmann et al.
patent: 4958526 (1990-09-01), Haggstrom
International Search Report, Japanese Patent Office, completed Nov. 21, 1991.
Konishi Hiroyuki
Suzuki Takao
Utsunomiya Michito
Figlin Cheryl R.
Ishida Scales Mfg. Co. Ltd.
Picard Leo P.
LandOfFree
Load cell with strain gauges having low temperature dependent co does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Load cell with strain gauges having low temperature dependent co, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Load cell with strain gauges having low temperature dependent co will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1713096