Electricity: measuring and testing – Electrolyte properties – Using a conductivity determining device
Patent
1991-09-11
1995-01-17
Wieder, Kenneth A.
Electricity: measuring and testing
Electrolyte properties
Using a conductivity determining device
324450, 324722, 204400, 204430, 174 11R, 174 27, G01N 2707
Patent
active
053829085
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a conductivity or capacitivity cell and a method of manufacturing such a cell. The invention also relates to a sensor and a reference sensor for measuring the relative moisture content of a material, preferably concrete, by using such cells, and a method for measuring the relative moisture content using such a sensor and a reference sensor.
BACKGROUND OF THE INVENTION
When measuring the relative moisture content, cells of different types are used. For example, cells are used for measuring the relative moisture content in building construction, when it is necessary to determine when in situ concrete is sufficiently dry to be able to put a covering on the concrete, for example, without risk of moisture and/or mould damage. When using known cells for measuring the relative moisture content, problems have arisen with the accuracy of the cells. Known cells can undergo changes after calibration without this being noticed, or they can be inadvertently read before a vapour balance between the cell and the concrete has been reached. In some cases, the accuracy is so poor that use is limited to sensing free water in the vicinity of the cell. This is for example the case when using the device described in Swedish Application B-375395.
When measuring the relative moisture content of concrete, it is desirable that measuring error does not exceed one percentage unit within the measuring range 85-98% relative moisture. This cannot be achieved with previously known cells, because the accuracy of these cells is too low to achieve this. Furthermore, significant measuring errors can be caused by the fact that insertion of sensors with known cells in the concrete changes the temperature in the concrete.
The purpose of the present invention is to provide a conductivity or capacitivity cell of the type described by way of introduction which fulfills the accuracy requirement specified above, and a method of producing such a cell, which makes it possible to manufacture simply and inexpensively a large number of cells with very little variation as regards properties.
Another purpose of the invention is to provide a sensor for measuring the relative moisture content of a material, preferably concrete, said sensor using a cell according to the invention to achieve the desired accuracy, and a method for measuring the relative moisture content of a material to a desired accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in more detail below with reference to the accompanying drawings, of which
FIG. 1 is a perspective view of a conductivity or capacitivity cell according to the invention;
FIG. 2 shows a cross section through the cell according to claim 1;
FIG. 3 is a schematic view showing the manufacturing of a work piece for a plurality of cells according to the invention;
FIG. 4 is a schematic view, showing how the work piece is cut into blanks for cells;
FIG. 5 shows a blank for a cell according to the invention;
FIG. 6 shows the finished cell according to the invention after removing the end portions of the blank;
FIG. 7 shows an end surface of a cell according to the invention;
FIGS. 8a and 8b show a cell according to the invention provided with a drop detector;
FIG. 9 shows a section through a sensor with a cell according to the invention embedded in concrete; and
FIG. 10 shows a section through a reference sensor with a cell according to the invention embedded in concrete.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a conductivity or capacitivity cell according to the invention. It comprises a cylindrical, for example circular cylindrical, possible tubular core 11 of an electrically non-conducting and moisture insensitive material, e.g. polypropylene. The core 11 is surrounded by a sock 13, which is braided from threads of an electrically non-conducting, elastic, relatively form-stable and moisture insensitive material, e.g. polypropylene. Along two diametrically opposite generatrices of the core 11, there extend two electrodes 15 and 17 o
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Forsstrom Bo G.
Unruh Leif A.
Wikefeldt Per E.
Brown Glenn W.
Forsstrom Bo Gosta
Wieder Kenneth A.
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