Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specified electrical sensor or system
Reexamination Certificate
2000-09-20
2001-12-11
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specified electrical sensor or system
Reexamination Certificate
active
06327913
ABSTRACT:
The present invention relates to a force measuring cell with an oscillating string measuring transducer. It especially relates to force measuring cells, in which the measuring transformer is set into a circular hole in a plate or a web of a carrier, whereby the axis of the hole is arranged perpendicular to the load direction and parallel to the neutral surface of the plate or the carrier.
Many such force measuring cells are known, thus for instance from GB-A 1,518,359 (D
1
), EP-A1 0 675 032 (D
2
), U.S. Pat. No. 3,132,319 (D
3
), U.S. Pat. No. 4,530,245 (D
4
), EP-A1 0 129 331 (D
5
), U.S. Pat. No. 3,906,788 (D
6
). A common feature of all the quoted publications is the use of strain gauge strips (DMS) as analog measuring transformers, which are connected into bridge circuits in a known manner. In D
1
the measuring transformer is glued into the hole, in D
3
, D
4
, DS it is pressed in, in the axial direction, only in D
2
and D
6
are defined contact points or lines provided.
Whilst D
2
works with the effect of the compression cone and is therefore consequently applied only as a railway axle counter, in D
3
, D
5
, D
6
the tensile force applied to a rod or plate formed element is measured as a function of the changing of the shape of the hole parallel or perpendicular to the effective force. Due to the method of fitting, the DMS transducer into the hole, only relatively modest accuracies, made up of resolution and reproducibility, are to be expected in so far as the known devices are to be used for force measurement—with the exception of D
2
and D
6
. The replacement of a defective pressed in or glued in measuring transformer is difficult and expensive and brings with it the reworking of the hole in any case. This, in combination with the known limitations of DMS such as temperature dependence, sensitivity to humidity and variable quality of glue positions with sudden, age dependent failures especially under rough operation.
In the application of such measuring cells as railway weighing scales, in which the carriers, whose deformation is to be measured, are indeed the railway tracks, in the use of DMS a problem can arise which should not be underestimated: if the DMS is attached directly to a part of such a rail, then it is almost impossible to provide the conditions of humidity, cleanliness and temperature reproduceably on an already laid rail, which are required for the gluing on of the DMS. As an alternative, there remains the removal and welding in again of a piece of rail, which makes the production of such a weighing device enormously expensive. Additionally, in the event of a failure of the DMS the whole process must be repeated. The aim of the present invention is the production of a measuring cell for force, which can be produced easily and cost effectively, facilitates a high accuracy of the measured values, has high durability even in rough operation and can be installed and if necessary replaced with only a small outlay.
The addressing of the stated aim is given in the appended claims, with respect to the essential features and further advantageous developments.
REFERENCES:
patent: 3862569 (1975-01-01), Lucas et al.
patent: 4420755 (1983-12-01), Primbs, Jr.
patent: 5095764 (1992-03-01), Saner
patent: 5478975 (1995-12-01), Ford
patent: 5710426 (1998-01-01), Reed et al.
Lustenberger Martin
Wirth Johannes
Digi Sens AG
Jenkens & Gilchrist P.C.
Noori Max
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