Measuring and testing – Dynamometers – Responsive to force
Patent
1982-09-17
1985-06-11
Gill, James J.
Measuring and testing
Dynamometers
Responsive to force
73726, 338 3, G01L 122, G01L 904, H01C 1712
Patent
active
045220670
DESCRIPTION:
BRIEF SUMMARY
The invention relates generally to a thin-film strain gauge and more particularly to a gauge having elongation-sensitive resistors arranged in a Wheatstone bridge.
BACKGROUND
Strain gauges of this type are known, both in conventional form having wire or foil resistance elements and in the field of thin-film technology. Elastically deformable spring elements are used in a known manner in combination with at least one resistor which is sensitive to elongation; the spring elements are deflectable either at one end or centrally, stretchable in the longitudinal direction, or otherwise capable of being deformed. Four elongation-sensitive resistors are frequently interconnected to make a Wheatstone bridge, in order to increase the accuracy of measurement.
It is furthermore known to fabricate the resistance elements from a material or combination of materials such that the electric resistor has a low temperature coefficient, so that errors in measurement caused by temperature fluctuations are prevented; temperature fluctuations are perceived in the same manner as deflections of the element. Strain gauges have already been used in conventional technology where both the resistance elements and some of the leads are fabricated of constantan; however, in that case, losses in the measurement signal occurred on the leads.
THE INVENTION
Briefly, the thin-film strain gauge of the present invention has vacuum-deposited resistors and leads with similar temperature coefficients of resistance and has many critical advantages over the prior art. In particular, the temperature errors resulting from differences in temperature coefficients of the electrical resistances of the leads and the resistance regions are quite substantially avoided. Virtually no increased track resistance has to be tolerated, and thus no reduction in the measurement sensitivity of the resistor or of the bridge. Since both the low-impedance connections between the various resistance regions and the associated connecting leads can be fabricated of identical material, both sources of possible error can be eliminated. By fabricating the various elements using thermal vapor depositing or cathode sputtering, a means is attained which is tailor-made for thin-film technology and can be integrated without difficulty with another thin-film circuit on the same substrate. The production process is particularly simple. The makeup of the connection tracks for the external electric connections can be of any arbitrary embodiment, retaining a variety of possible types of bonding of the thin-film strain gauge; connections can be effected by soldering, cool-soldering or welding, for instance, depending on the conditions under which the measurement bridge will be used.
The proposal according to the invention results in an apparatus comprising an adherent metallization system for thin-film strain gauges and thin-film circuits which can be tinned and/or leaded and/or reinforced by electroplating, the production process being particularly economical. Expensive pretreatments of the surfaces of the elastically deformable spring elements are not required, especially when thin, high-impedance glass insulation layers are pressed on in two separate operations. The double pressing process results in a poreless insulating layer, and the individual layers are advantageously fired separately. This firing process may also be utilized, at no additional expense, for hardening copper-beryllium spring element substrates in the same operation.
DRAWINGS
FIG. 1 shows the basic layout of a circuit in which elongation-sensitive strips are arranged in a Wheatstone bridge;
FIG. 2 shows a thin-film strain gauge bridge disposed such that it is deflectable at one end;
FIG. 3 shows a centrally deflectable disposition on a membrane-like Spring element;
FIG. 4 is a section taken along the line IV--IV of FIG. 2; and
FIG. 5 shows a disposition having a multiplicity of spring elements with thin-film strain gauges, before they are separated into individual elements.
DETAILED DESCRIPTION
FIG. 1 sho
REFERENCES:
patent: 3242006 (1966-03-01), Gerstenberg
patent: 3251222 (1966-05-01), Fenner
patent: 3303693 (1967-02-01), Stedman
patent: 3341794 (1967-09-01), Stedman
patent: 4325048 (1982-04-01), Zaghi et al.
patent: 4329878 (1982-05-01), Utner et al.
Burger Kurt
Gruner Heiko
Gill James J.
Robert & Bosch GmbH
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