Stock material or miscellaneous articles – Composite – Of polycarbonate
Reexamination Certificate
2001-08-30
2003-10-14
Hampton-Hightower, P. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polycarbonate
C428S411100, C428S413000, C428S416000, C324S534000, C324S600000, C324S601000, C324S632000, C324S642000, C324S643000
Reexamination Certificate
active
06632534
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to a probe adapted to measure the dielectric properties of soil and other materials. More specifically, this invention relates to a probe for measuring the moisture content of soil or other medium.
2. Background Art
In the past, there have been a number of instruments used to measure the moisture content in soil so that farmers, ranchers, conservationists and the like could determine when to irrigate crops, plants, trees, etc. Early devices included taking bore samples of soil and placing the samples in devices that would measure the amount of moisture content in the soil. These devices generally required time-consuming oven-drying processes to determine the moisture content. The time delays, sometimes taking several days to characterize the moisture content of the soil, resulted in crops being either over- or under-irrigated for periods of time. As a result, crop damage or quality loss was a common occurrence.
Other soil moisture measuring devices, such as neutron source back scatter devices have also been used to measure soil moisture. These devices are bulky to transport to the field where soil measurements are typically taken and they rely on radioactive elements. These radioactive devices often are costly, require specialized personnel to operate, and have to be calibrated in the field prior to use at each measurement site.
In contrast to the prior art described above, more recent moisture measuring devices have been devised which operate on the principles of Time Domain Reflectrometry (TDR). Geologists and others have long recognized a relationship between the dielectric properties of soil, rock and other materials, and their moisture content. However, they initially lacked the instrumentation necessary to make full use of this knowledge. Time Domain Reflectometry, largely developed as the result of World War II radar research, offered a method to define these dielectric relationships. With the advent of commercial TDR research oscilloscopes in the early 1960s, it became feasible to test this new technology. Today, TDR technology is the “cutting edge” methodology for many diverse applications including the determination of basic soil water and material/water relationships.
TDR systems utilize the principle of TDR in order to convert the travel time of a broadband, electromagnetic pulse into volumetric water content. In practice these TDR systems generate a fast-rise pulse and send it at the speed of light down a transmission line consisting of at least two parallel wave guides or a coaxial arrangement of probes that are inserted or buried in the soil or other material to be measured. The velocity of propagation of the broadband pulse (often that incorporates frequencies that exceed 3 GHz) in soil is determined primarily by its water content. The pulse is reflected from the open ends of the wave guides/probes and returns along the original path. By microprocessor or other computing device, the travel time of the pulse is used to calculate the apparent dielectric constant of the soil. The actual digitized TDR wave form created as the pulse progresses down the wave guides can be displayed on a high resolution graphic LCD display for storage and interpretation. The actual time delay and correlated volumetric water content may also be digitally displayed on the screen.
TDR systems eliminate the need for using nuclear based instrumentation and the associated radiation, health and safety hazards. These systems eliminate site-specific calibration and the requirement for costly, specialized licensed personnel associated with neutron probes. They also provide auto logging capabilities that are not practical with nuclear techniques.
In the past, probes used with TDR systems have been manufactured having an inner conductive core that is surrounded by a dielectric material. This thin dielectric layer between the transmission element and the material being measured retains and reflects some of the energy along the transmission element as the pulse progresses from start to endpoint within the probe. This dielectric layer is key as it provides for a high coefficient of reflection that is necessary for the determination of the probe's end points in highly conductive materials such as saline water, or conductive particle mixtures. This determination of these endpoints is used in the calculations to determine the apparent dielectric constant of the material being measured. For some measurements in high conductivity materials, end point reflections are attenuated to an insignificant level, undetectable by waveform analysis. In such cases, the high coefficient of reflection provided by the dielectric layer surrounding the inner conductive core is absolutely necessary to obtain accurate TDR measurements.
Although the dielectric layer provides for a high coefficient of refection, one problem with having the outer layer being made of soft or brittle dielectric materials is that it wears, scratches or breaks during multiple insertions into the ground or other material where the moisture is to be measured. This is particularly true when the probe is used to measure the moisture content of hard or abrasive soils, since the probes are typically repeatedly inserted in the soil to obtain the desired measurements. Additionally, the outer dielectric material is often difficult to manufacture such that an even layer is achieved. When the outer layer of dielectric is worn uneven, scratched or is unevenly manufactured the dielectric properties, and therefore the accuracy of the probe, is degraded.
Therefore, what is needed is a TDR probe that is immune to wear and scratching of the dielectric material coating the inner conductive element and that is easily manufactured to achieve reliable and consistent dielectric measurement results.
SUMMARY
The system and process of the present invention satisfies all of the foregoing needs. The system and process provides a wave guide-like structure or probe (usually used in pairs or sets) that can be used for measuring the moisture content of soil or other materials. Probes according to the present invention, using the techniques described herein, can also be used in the following measurement areas:
(1) determination of concentrations of particles suspended in water and other liquids;
(2) determination of the amount of air entrapped in liquids, slurries and gels;
(3) determination of the liquid levels of immiscible fluids having differing dielectric character;
(4) determination of the proportional content in differing dielectrics soluble in water; and
(5) determination of the bulk content of the material being measured.
In the probe according to the present invention, the inner core of the probe is composed of an inner metallic element. This metallic element is a conductor that is used to transmit a broadband pulse. A dielectric liquid, solid or gel surrounds this inner conductive core, and assists in retaining broadband signal strength. The outer dielectric material is then encased in an outer shell that serves as a protective housing for the probe. This outer shell is preferably made of stainless steel, but can be made of other conductive materials as they serve to protect the inner dielectric material and metallic core. This combination of features allows a pulse transmitted through the probe to penetrate into the material being measured, while protecting the dielectric-coated transmission elements. Only the inner conductive elements (conductor and dielectric layer) are active and electrically connected to the components of the TDR system. Since the outer shell is not electrically connected in any manner to the transmission elements it simply acts as a tough and effective housing that protects a “dielectrically-coated” transmission element. This invention combines the need for a dielectric coating on the transmission element and strong outer covering into a single assembled unit that provides both protection for multiple insertions into abrasive or in highly corrosive materials wh
Rudolics Laszlo
Skaling Whitney
Hampton-Hightower P.
Lyon Katrina A.
Lyon Richard T.
Lyon & Harr LLP
Soilmoisture Equipment Corp.
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