Process for operating a measurement instrument, and measurement

Details Process for operating a measurement instrument, and measurement Process for operating a measurement instrument, and measurement

1993-05-10

1995-10-31

Miller, Jr., George H.

Weighing scales

Computer

Electrical

177165, 364567, G01G 1940, G01G 1314

Patent

active

054631920

DESCRIPTION:

BRIEF SUMMARY
The present invention concerns a procedure for operation of a measuring apparatus for force and mass with a numerical evaluation device which has several measuring ranges and an automatic zero point correction and a measuring apparatus operating according to this procedure.
Such measuring apparatuses are known; thus, e.g., from the Swiss Patent 550,999 with respect to the automatic zero point correction and from the West German Patent Application (Offenlegungsschrift) 2,743,326 with respect to the several measuring ranges.
In such known measuring apparatuses, the transfer from one measuring range to the next is performed as a function of force and is controlled by force. If a mass measuring apparatus is being considered, the force effected by the heavy mass of the working load is compared to that produced by a comparative mass in which the local acceleration of gravity and if necessary the inclined position of the mass measuring apparatus are taken into consideration.
In measuring apparatuses of this type, particularly in their design as commercial balances, the size of the display increment for the displayed results is selected automatically depending on the measuring range, however the computing increment used internally in the evaluation device remains constant, as is shown in the following tables by means of an example:


TABLE I ______________________________________ Load Range Internal Computing Display Increment L.sub.j (kg) Increment m(g) d.sub.j (g) ______________________________________ 0:10 0.1 10 10:20 0.1 20 20:50 0.1 50 50:100 0.1 100 ______________________________________
In other words: The result is always determined with the same absolute computing increments (for example 0.1 g) and then, corresponding to the load range, is displayed in larger display increments.
Certain parts (springs, beams, torsion elements or pneumatic elements) of the measuring apparatus are deformed when such a measuring apparatus must determine the weight of a mass falling within one of the upper load ranges. As a rule, elastic deformation results simultaneously with the stress. If the small part of the total spring deflection not present at the beginning is called .DELTA.S, the final position is striving toward the form
In this case, the time constant .tau. is dependent on the type of deformation, the material and the temperature. This phenomenon is known and is called creep. In addition, allowance must be made for plastic deformations of very small degree.
These facts are taken into account both in construction and by the Office of Weights and Measures by placing the size of the respective display increment in a specified relationship to the maximum load of the concerned load range. Now if the load is removed from the above-mentioned measuring apparatus, the principal portion of the elastic deformation is simultaneously recovered. Creep portions and in certain cases small to very small plastic deformations remain behind.
Now if the series of display increments would be further refined, which would be possible based on the internal computing increments m, on the one hand this would have the consequence that with partial load removal from the measuring apparatus the new load would be depicted in smaller display increments, however the displayed result due to creep phenomena would reach its final value possibly only after an appreciable time, i.e. after the creep subsides. On the other hand, the measuring apparatus with complete load removal could not display "zero". I.e., the residual load remaining because of creep would certainly fall in the smallest display range, however not directly to zero because of the residual deformation. A result with numbers becoming increasingly smaller would be displayed which would always approach zero, however at best would not reach it.
The goal of the present invention is the creation of a procedure and a measuring apparatus with several display increments which will not exhibit the mentioned disadvantages and will permit the range of the display increments

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