Weighing scales – Processes
Reexamination Certificate
1999-09-17
2001-07-31
Gibson, Randy W. (Department: 2859)
Weighing scales
Processes
C177S025130, C177S245000, C073S076000, C374S014000
Reexamination Certificate
active
06268570
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to methods of measuring the weight of sample materials before, during, and after heating. In particular, the invention is directed toward improving the accuracy of weight measurements by adjusting apparent weight to true weight by considering weight bias caused by air density gradients.
BACKGROUND OF THE INVENTION
The determination of sample solids fraction or sample moisture content is a routine laboratory determination. Many agricultural products, food products, and manufactured products (e.g., textiles, films, coatings, paper, and paints) are sold based on solids content or moisture content. Consequently, solids and moisture analyses are frequently run. Unfortunately, monitoring moisture and solids content using conventional techniques is exceedingly time consuming. For example, drying a sample in a convection oven to achieve solids content takes upwards of four hours and typically requires desiccation of the dried sample.
There are, however, high-speed analytical procedures for volatilizing moisture or solvents to facilitate quantitative analysis of various substances (e.g., agricultural commodities, foodstuffs, dairy products, chemicals, paper products, and tobacco). These procedures often employ microwave energy to heat a material sample to remove various volatiles. Thereafter, moisture, solids, or other residuals and losses can be determined. To achieve these weight measurements rapidly and accurately, the sample is not removed from the balance, but rather weighed in place after each succeeding step. Such automation reduces the possibility of human error.
The weight of the substance is often sensed or measured repeatedly during the microwave heating while volatiles are being removed from the heated sample. Consequently, such methods not only require sensitive analytical balances, but the capability to measure weight while the sample is hot. These methods, however, fail to correct weight measurements for the buoyancy effects that are caused by temperature and pressure variances within the microwave cavity. This failure can introduce significant errors to determinations of solids or moisture content.
U.S. Pat. No.4,753,889 (hereinafter the Collins '889 patent), which is commonly assigned with this application, is directed to rapid quantitative analyses of materials having high moisture content. The Collins '889 patent discloses the evaporation of moisture to determine the solids and other materials present without removing or destroying the other materials when removing moisture. In particular, rapid analysis is facilitated by microwave heating to drive off moisture, followed by solvent extraction, and content determinations. U.S. Pat. No. 4,753,889 is hereby entirely incorporated by reference.
Similarly, U.S. Pat. No. 4,291,775 (hereinafter the Collins '775 patent), which is commonly assigned with this application, addresses the problem of disruptive convection currents. More specifically, the Collins '775 patent describes a method and apparatus for improving the weighing accuracy of sensitive automatic balances when weighing heated substances by introducing an air barrier shield to cover the balance plate without contacting or touching the automatic balance. This tends to reduce the convection currents that can interfere with the sensitive balance and, consequently, hinder the achievement of accurate sample weight measurements. In other words, the eliminating convection air currents reduces movement of the balance and thereby fluctuations in the measurement of sample weight being sensed. U.S. Pat. No. 4,291,775 is hereby entirely incorporated by reference.
Finally, U.S. patent application Ser. No. 09/397,825 (Microwave Apparatus and Method for Achieving Accurate Weight Measurements), which is commonly assigned with this application, improves upon the teachings of the Collins '775 patent by including an air shield that is removably secured to the inside of the heating cavity such that the air shield does not contact an analytical balance when the air shield is fastened to the heating cavity. By securing the air shield to the interior of the microwave cavity, a laboratory technician or instrument operator need not manipulate a movable barrier that must rest on the cavity floor, yet be placed so that the barrier substantially surrounds both the analytical balance and the sample to be heated. U.S. patent application Ser. No. 09/397,825 (Microwave Apparatus and Method for Achieving Accurate Weight Measurements) is likewise entirely incorporated by reference.
While these methods overcome specific problems associated with microwave heating and drying, none discloses nor teaches a method for correcting apparent sample weight to account for buoyancy effects caused by different air densities surrounding a sample. Therefore, there is a need for a method to correct weight measurements for the buoyancy effects that are caused by temperature and pressure variances within a heating environment.
OBJECT AND SUMMARY OF THE INVENTION
Therefore, it is an object of this invention to provide a method for adjusting measured, apparent sample weight to account for buoyancy effects that occur during microwave heating in order to achieve more accurate sample weight measurements.
It is a further object of the invention to provide a method for accurately determining solid fraction of a sample by correcting weight measurements to account for lift effects that occur during heating.
The invention achieves this, in part, by measuring the surface temperature of a sample pad and the ambient air temperature surrounding the sample pad, and thereafter calculating the buoyancy of the sample pad caused by this temperature variance.
The foregoing, as well as other objectives and advantages of the invention and the manner in which the same are accomplished, is further specified within the following detailed description and its accompanying drawings.
REFERENCES:
patent: 3973636 (1976-08-01), Uchida
patent: 4106329 (1978-08-01), Takahashi et al.
patent: 4291775 (1981-09-01), Collins
patent: 4438500 (1984-03-01), Collins et al.
patent: 4457632 (1984-07-01), Collins et al.
patent: 4554132 (1985-11-01), Collins
patent: 4566312 (1986-01-01), Collins et al.
patent: 4651285 (1987-03-01), Collins et al.
patent: 4681996 (1987-07-01), Collins et al.
patent: 4750143 (1988-06-01), Heitz et al.
patent: 4753889 (1988-06-01), Collins
patent: 4838705 (1989-06-01), Byers, Jr. et al.
patent: 5055262 (1991-10-01), Czarnecki
patent: 5318049 (1994-06-01), Henderson et al.
patent: 5625170 (1997-04-01), Poris
patent: 5801337 (1998-09-01), Peake
patent: WO 97/10482 (1997-03-01), None
King Edward Earl
McLendon Byron E.
CEM Corporation
Gibson Randy W.
Philip Summa, P.A.
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