Electrical resistors – Resistance value responsive to a condition – Ambient temperature
Reexamination Certificate
2002-06-03
2003-10-28
Easthom, Karl D. (Department: 2832)
Electrical resistors
Resistance value responsive to a condition
Ambient temperature
C073S204250, C073S204120
Reexamination Certificate
active
06639506
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a sensor, associated circuitry, and method of operation for sensing, measuring and displaying one or more physical properties of a substance or medium such as a gas or liquid. Typically, one of the properties to be sensed and measured is temperature, although the applications of the invention are not limited to those in which temperature is one of the properties to be sensed and measured. Other properties and quantities to the sensing and measurement of which this invention is well suited are rate of flow, direction of flow, wind-chill factor, and position of a physical element or component.
The invention is especially well suited to applications in which the sensor comprises, at least in part, a positive-temperature-coefficient device (a “PTC device”) formed from positive-temperature-coefficient (“PTC”) material together with interfaces, resistors, and terminals of ohmic material. In most applications of the invention, the PTC material of the sensor device is “sectored” or divided into a plurality of zones which are electrically interconnected but which may be exposed to a medium whose temperature, rate of flow, or other property varies from place to place therewithin. Different zones of the PTC material are exposed to different respective values of such properties of the medium. But all zones are operated within the self-stabilizing mode of the PTC material, which tends to hold its temperature just above the “transition temperature” or “Curie point”.
A remarkable feature of the invention is that it makes possible the sensing and measurement of more than one property or quantity of a substance or medium without using more than one sensing device. The method in accordance with the invention is directed to this remarkable feature. In order to facilitate the full comprehension of this method, it will be illustrated graphically as well as in the text of the following disclosure.
2. Description of the Prior Art
The prior art includes various devices for measuring the speed of the wind and of other gas flows. Sometimes, as in the so-called “hot-wire anemometer,” the speed of the wind, gas or other medium is evaluated by the rate at which it abstracts heat energy from an electrical resistance wire to which electrical energy is being supplied at a measurable rate. The heat power dissipated to the wind, gas or other medium is substantially equal to the electric power supplied to the resistance wire in maintaining it at a constant temperature.
The hot-wire anemometer may measure the rate of speed of the wind or other gas flow, but it is not well adapted to measurement of the direction, and hence the velocity, of the wind or other gas flow. Moreover, it is thermally inefficient and has no inherent “multiplier” to impart “leverage” to the measurement of gas flow. Furthermore, it does not lend itself readily to combination with other elements to measure quantities such as “wind-chill factor.”
For a few applications, the measurement of rate of flow alone is sufficient. But for many more applications, it is necessary to ascertain both the velocity of flow and the temperature of the medium undergoing measurement. Although those quantities are combined in the wind-chill factor, the usual situation requires that they be separately determined and displayed. In the patented art, we find the following references:
U.S. Pat. No. 4,890,494—Osbond et al, issued on Jan. 2, 1990, discloses a probe comprising multiple toroidal PTC disks having ohmic facings and connected together in parallel. Each of the disks is not divided into zones or sectors which are differently exposed to plural aspects of the atmosphere or other gas in which the probe is immersed. Since there is no such differential treatment of various portions of the probe, there can be no source of plural signals that would permit the evaluation of two or more distinct properties of the atmosphere, such as temperature and humidity, or temperature and velocity of flow.
U.S. Pat. No. 3,604,261—Olin discloses a multidirectional thermal-anemometer sensor. As illustrated in FIGS. 10 through 14 of the drawings of the Olin patent, one of his sensing elements is spherical, and is divided in three dimensions like the sections of an orange in order to give a three-dimensional velocity-vector indication. But the sensing element is covered with a thin film of a metal such as segmented platinum, rather than PTC material. And the film is said to be maintained at a constant elevated temperature by control systems 29 to 32, of which no further description is given. Clearly, the temperature is maintained constant by the self-stabilizing mode of PTC material, which is not present in the anemometer sensor of Olin.
U.S. Pat. No. 4,615,214—Burns shows segmented sensors disposed around the periphery of a continuous electrode in order to determine direction of the wind around the zimuth. But the sensors are piezoelectric, rather than PTC, in their operative properties.
SUMMARY OF THE INVENTION
In view of the aforementioned inadequacies of the prior art, I have provided a sensor which is new in its concept and surprising in its capabilities. In its preferred embodiment, the sensor in accordance with my invention is built around a single tablet of positive-temperature-coefficient (“PTC”) material to which are bonded, preferably on two sides, layers of ohmic resistive (or conductive) material. At least one of those layers of ohmic material is divided into sectors or zones. If the tablet of material is circular, the sectors may be divided along radial lines. On the other hand, if the tablet is essentially rectangular, the dividing lines may be transverse so as to produce, typically, three zones as defined by the divided layer of ohmic material.
Although the PTC material itself may be selectively reduced in cross section, it is not generally separated into disjointed pieces. And the layer of ohmic material bonded to one side of the PTC material is maintained continuous. In operation, this continuous layer, which may in turn be bonded to some other structure, is connected to a source of electric potential, preferably at a constant level.
It will be understood that the layers of ohmic material serve primarily to make electrical contact with the PTC material. In operation, the ohmic layer which is maintained continuous imparts to the “base” side of the PTC material an electric potential allowing current to flow through the PTC material. The divided ohmic layer, on the other hand, is in thermal communication with the substance or medium whose properties are to be sensed. That layer need be only substantial and conductive enough to couple the respective sectors or zones of the PTC material to respective different portions of the substance or medium, even though those portions may be spatially very close to one another.
The respective parts of the divided ohmic layer are electrically connected through resistive elements to a different electric potential. Although the resistive elements may be made variable for the purpose of adjustability, their primary purpose is to provide “tapping points” for reading out voltages determined by the currents through the respective resistive elements.
On the other hand, the respective parts of the ohmic layer, or the portions of the PTC material beneath them, are coupled thermally, through contact, to respective portions of the substance or medium whose properties are to be sensed and measured. Typically, the “substance or medium” is a fluid which either flows freely over its interface with the PTC material (e.g. the wind) or flows past it in a tube, pipe, or other channel which, with its contents, is thermally closely coupled to the PTC material.
Because of the energization of the “base” at a controlled level of potential, electrical currents flow from it through the respective sectors or zones of the PTC material and through their respective resistive elements to a different potential. The respective magnitudes of those currents are determined more by the “appa
Crooks Robert G.
Easthom Karl D.
Lansense, LLC
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