Measuring and testing – Moisture content or absorption characteristic of material – By desiccation or extraction
Reexamination Certificate
1998-09-17
2001-05-08
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Moisture content or absorption characteristic of material
By desiccation or extraction
C374S014000, C219S711000
Reexamination Certificate
active
06227041
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to methods and apparatuses for measuring volatile content of a sample using microwave radiation. More particularly, the invention pertains to a method and an apparatus that helps to control sample temperatures during volatile content analyses.
BACKGROUND OF THE INVENTION
Measuring the sample volatile content (which in many cases is the moisture content) is a frequent and repetitive chore in many analytical laboratories. In its simplest form, determining volatile or moisture content consists of weighing a representative sample of material, drying the material, then re-weighing the material to ascertain the losses on drying and, consequently, the initial volatile content of the sample. Convective, hot-air ovens, which are typically used for this task, can be relatively slow to bring the sample to “oven-dry” equilibrium. Such devices can also be expensive to operate as they inefficiently consume energy. These problems lessen the utility of hot-air devices for volatile analysis.
Drying substances using microwave energy to determine volatile or moisture content is generally convenient and precise. More importantly, microwave drying to measure moisture content is usually faster than equivalent hot-air methods. As in hot-air techniques, however, certain substances tend to burn, rather than merely become dry, when microwave power is applied to them. Stated differently, the rapid manner in which microwaves tend to interact with certain materials-which is an obvious advantage in some circumstances-can cause secondary heating of other materials that is disadvantageous (at least for volatile or moisture measurement purposes). Certain food products such as cheese are exemplary (although certainly not limiting) of materials that tend to burn rather than dry.
Additionally, microwaves interact with materials in a fashion known as “coupling,” i.e., the response of the materials (“the load”) to the microwave radiation. Some materials do not couple well with microwave energy, making drying or other volatile removal techniques difficult or imprecise. Other materials couple well when their moisture content or content of other microwave-responsive materials (e.g., alcohols and other polar solvents) is high. As they dry under the influence of microwaves, however, they couple less and less effectively; i.e., the load changes. As a result, the effect of the microwaves on the sample becomes less satisfactory and more difficult to control. In turn, the sample can tend to burn rather than dry, or degrade in some other undesired fashion. Both circumstances, of course, tend to produce unsatisfactory results.
As another factor, volatiles such as “loose” water (i.e., not bound to any compound or crystal) respond quickly to microwave radiation, but “bound” water (e.g., sodium carbonate monohydrate, Na
2
CO
3
.H
2
O) is typically unresponsive to microwave radiation. Instead, such bound water must be driven off thermally; i.e., by heat conducted from the surroundings. The nature of microwave radiation is such, however, that not all such surroundings may be heated when exposed to microwaves. Thus, the simple application of microwaves is typically less satisfactory for determining bound water than are more conventional heating methods.
Maintaining the sample's temperature below that which will cause pyrolysis helps prevent burning. To the extent moisture analysis is based upon weight measurements, however, measuring the sample's temperature cannot be permitted to hinder measuring the sample's weight. Thus, conventional direct probe temperature measurement is often unsatisfactory for this purpose. The temperature sensor's contact with the sample can lead to erroneous weight measurements when using sensitive weighing devices. Furthermore, in a microwave environment, the type, location, and function of a temperature probe must be compatible with the proper propagation of energy to, and absorption of energy by, the sample.
Some indirect methods have been developed to measure temperature in a way that avoids contacting the sample in an effort to avoid interfering with measuring sample weight. Many such indirect techniques, however, determine the temperature of something besides the sample itself. Thus, such techniques can lack accuracy, and can give a relatively slow response, particularly when heat conduction from the sample to the sensor is required.
Therefore, a need exists for taking advantage of the rapid response characteristics of microwave heating, while avoiding burning the sample, and while measuring the sample weight on a continuous basis that provides quick results.
OBJECT AND SUMMARY OF THE INVENTION
It is an object of the invention to quickly measure the volatile content of a sample in a way that will neither burn the sample nor interfere with the measurement of sample weight. Accordingly, the invention is an apparatus and method for quickly determining sample volatile content, and usually moisture content, through losses on drying while controlling the sample's temperature. In particular, this invention provides quick and accurate moisture analysis while helping to prevent sample burning.
The method includes initially measuring sample weight and sample temperature. Then, microwave radiation is introduced to the sample to drive off moisture or other volatiles. Meanwhile, the changes to the sample weight and sample temperature are monitored. The introduction of microwave radiation is varied to maintain sample temperature at a set point or within a set range chosen to prevent sample pyrolysis. Once the incremental change to the weight of the sample reaches or approaches equilibrium, the introduction of microwave radiation is stopped. Thereafter, the moisture content of the sample is calculated.
The apparatus includes a structure forming an enclosed cavity to hold a sample and to contain microwave radiation, a microwave power source, a means to measure sample weight, a means to measure sample temperature, and a controller that moderates the introduction of microwave radiation to the sample based upon the sample temperature. The controller is programmed to moderate the applied microwave power (the manipulated variable) to maintain the sample's temperature at a set point or within a set range.
The foregoing and other objects and advantages of the invention and the manner in which the same are accomplished will become clearer based on the following detailed description taken in conjunction with the accompanying drawings in which:
REFERENCES:
patent: 3292417 (1966-12-01), Hayden et al.
patent: 3534260 (1970-10-01), Walker
patent: 3693079 (1972-09-01), Walker
patent: 3813918 (1974-06-01), Moe
patent: 3902354 (1975-09-01), Harlan et al.
patent: 3909598 (1975-09-01), Collins et al.
patent: 4291775 (1981-09-01), Collins
patent: 4304289 (1981-12-01), McMullen
patent: 4447693 (1984-05-01), Buck
patent: 4484133 (1984-11-01), Riggin
patent: 4485284 (1984-11-01), Pakulis
patent: 4554132 (1985-11-01), Collins
patent: 4566804 (1986-01-01), Collins et al.
patent: 4578998 (1986-04-01), Gard
patent: 4600879 (1986-07-01), Scully et al.
patent: 4606650 (1986-08-01), Harris
patent: 4674325 (1987-06-01), Kiyobe et al.
patent: 4709579 (1987-12-01), Parker et al.
patent: 4716360 (1987-12-01), Pakulis
patent: 4750143 (1988-06-01), Heintz et al.
patent: 4767982 (1988-08-01), Florig et al.
patent: 4771631 (1988-09-01), Lehtikoski et al.
patent: 4787052 (1988-11-01), Yamaguchi
patent: 4798252 (1989-01-01), Knothe et al.
patent: 4835354 (1989-05-01), Collins et al.
patent: 4970374 (1990-11-01), Ueda et al.
patent: 4977377 (1990-12-01), Durrett et al.
patent: 5001434 (1991-03-01), Marrelli et al.
patent: 5014010 (1991-05-01), Helms et al.
patent: 5046356 (1991-09-01), Osaki et al.
patent: 5086279 (1992-02-01), Wochnowski et al.
patent: 5237142 (1993-08-01), Cigarini et al.
patent: 5256978 (1993-10-01), Rose
patent: 5589094 (1996-12-01), Bu
patent: 5796080 (1998-08-01), Jennings et al.
patent: 5919389 (1999-07-01), Uehashi et al.
patent: 5983711 (1999-11-01), P
Collins Michael J.
Jennings William Edward
CEM Corporation
Larkin Daniel S.
Philip Summa, P.A.
LandOfFree
Method and apparatus for measuring volatile content does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for measuring volatile content, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for measuring volatile content will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2450200