Patent Application
20050247106
Embodiments are generally related to sensor methods and systems. Embodiments are also related to humidity sensors and moisture sensing elements thereof, flow sensors, pressure sensors, thermal sensors and temperatures sensors. Embodiments are additionally related to sensors utilized in fuel cell systems, such as, for example, PEM fuel cell applications.
Humidity sensors, flow sensors, pressure sensors and temperatures sensors and the like can be utilized in a variety of sensing applications. With respect to humidity sensors, for example, providing suitable instruments for the measurement of relative humidity (RH) over wide RH ranges (e.g., 1%-100%) continues to be a challenge. Humidity sensors can be implemented in the context of semiconductor-based sensors utilized in many industrial applications. Solid-state semiconductor devices are found in most electronic components today. Semiconductor-based sensors, for example, are fabricated using semiconductor processes.
Many modern manufacturing processes, for example, generally require measurement of moisture contents corresponding to dew points between −40° C. and 180° C., or a relative humidity between 1% and 100%. There is also a need for a durable, compact, efficient moisture detector that can be used effectively in these processes to measure very small moisture content in gaseous atmospheres.
Humidity can be measured by a number of techniques. In a semiconductor-based system, humidity can be measured based upon the reversible water absorption characteristics of polymeric materials. The absorption of water into a sensor structure causes a number of physical changes in the active polymer. These physical changes can be transduced into electrical signals which are related to the water concentration in the polymer and which in turn are related to the relative humidity in the air surrounding the polymer.
Two of the most common physical changes are the change in resistance and the change in dielectric constant, which can be respectively translated into a resistance change and a capacitance change. It has been found, however, that elements utilized as resistive components suffer from the disadvantage that there is an inherent dissipation effect caused by the dissipation of heat due to the current flow in the elements necessary to make a resistance measurement. The result is erroneous readings, among other problems.
Elements constructed to approximate a pure capacitance avoid the disadvantages of the resistive elements. It is important in the construction of capacitive elements, however, to avoid the problems that can arise with certain constructions for such elements. In addition, there can also be inaccuracy incurred at high relative humidity values where high water content causes problems due to excessive stress and the resulting mechanical shifts in the components of the element. By making the component parts of the element thin, it has been found that the above-mentioned problems can be avoided and the capacitance type element can provide a fast, precise measurement of the relative humidity content over an extreme range of humidity as well as over an extreme range of temperature and pressure and other environmental variables.
Humidity sensing elements of the capacitance sensing type usually include a moisture-insensitive, non-conducting structure with appropriate electrode elements mounted or deposited on the structure along with a layer or coating of dielectric, highly moisture-sensitive material overlaying the electrodes and positioned so as to be capable of absorbing water from the surrounding atmosphere and reaching equilibrium in a short period of time. Capacitive humidity sensors are typically made by depositing several layers of material on a substrate material. An example of a humidity sensor is disclosed in U.S. Pat. No. 6,724,612, entitled “Relative Humidity Sensor with Integrated Signal Conditioning,” which issued to Davis et al on Apr. 20, 2004, and issued to Honeywell International, Inc. U.S. Pat. No. 6,724,612 is incorporated herein by reference.
A limitation of humidity sensor is the relative humidity (RH) can be measured up to 100% RH above which the sensor reaches saturation. At levels higher than 100% RH, minute water droplets are formed in suspension (fog, a.k.a. two-phase flow) and the sensor may fail to operate. The technique used in this invention enables measurement of greater than 100% RH with a sensor that is capable of only 0 to 100% RH sensitivity by making a controlled, heated environment in the vicinity of the sensing area which can evaporate small water droplets and reduce RH to a measurable level.
This technique depends on a controlled, uniform temperature at the sensing area of the RH sensor which is particularly is critical because relative humidity varies with temperature for the same mole fraction of water vapor in the air. With respect to sensor housing and sensor parts thereof, flow and diffusion of humid ambient air and differences between the coefficients of thermal conductivity of the components will affect the uniformity of the temperature at the sensing surface can cause a shift in output over temperature, flow, and humidity changes. Therefore, a variety of sensor configurations, systems, and methods are disclosed herein, which attempt to rectify such problems.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is, therefore, one aspect of the present invention to provide for improved sensor methods and systems.
It is another aspect of the present invention to provide for improved relative humidity sensor methods and systems.
It is a further aspect of the present invention to provide for improved temperature, pressure and flow sensing methods and systems.
The aforementioned aspects of the invention and other objectives and advantages can now be achieved as described herein. Sensor systems and methods are disclosed herein. In accordance with a first embodiment, an RH sensor can be associated with one or more heating elements, wherein a perimeter of the RH sensor is surrounded with a relatively conductive material. A thin substrate material can surround and laminate the heating element, such that the heating element is perforated to permit humid air to pass through the heating element and wherein the heating element is assembled slightly offset from a surface of the RH sensor.
Air that is saturated with two phase flow of water vapor and minute droplets can then pass through and be heated by the heating element in order to evaporate water droplets associated with the water vapor to thereby reduce relative humidity to a measurable level. An additional heating element can be bonded to a base of the RH sensor. The thin substrate material can be configured from a polymide polymer, such as Kapton® material. Additionally, a filter material can be located slightly offset from the RH sensor to create a thin space of stagnant air adjacent to the RH sensor. The filter material may be a hydrophobic material such as Goretex® which can limit the size of water droplets, which pass through and therefore reduce the volume of water needing to be evaporated.
In accordance with a second embodiment, a RH sensor can be associated with one or more ceramic heating element, wherein a perimeter of the RH sensor is surrounded with a relatively conductive material. A resistive material can surround and laminate the ceramic heating element. The ceramic heating element can be configured from a porous material, wherein air that is saturated with water vapor passes through and is heated by the ceramic heating element in order to evaporate water droplets associated with the water vapor to thereby reduce relative humidity to a measurable level. One or more other heating elements can be bonded to the base of the RH sensor. The porous material forming the ceramic heating element can be formed by providing a plurality of laser drilled holes to create porosity thereof. Additionally, a filter material can be located slightly offset from the RH sensor to create a thin space of stagnant air adjacent to the RH sensor.
In accordance with a third embodiment, a RH sensor can be associated with one or more heating elements, wherein the RH sensor is surrounded by a sheet of porous resistive material in a woven or perforated pattern or state. The porous heating element can be configured to permit humid air to pass through the porous heating element. The porous heating element can be further assembled slightly offset from a surface of the RH sensor, wherein air that is saturated with water vapor passes through and is heated by the porous heating element in order to evaporate water droplets thereof to thereby reduce relative humidity to a measurable level. Additionally, a flat heating element can be bonded to the base of the RH sensor to conduct heat and insure uniform heating about the RH sensor. The porous resistive material can be formed from material such as tantalum or nichrome. A filter material can also be located slightly offset from the RH sensor to create a thin space of stagnant air adjacent to the RH sensor
In accordance with a fourth embodiment, an RH sensor can be associated with one or more heating elements, wherein a perimeter of the RH sensor is surrounded with a relatively conductive material. A thin substrate material can surround and laminate the heating element, such that the heating element is perforated to permit humid air to pass through the heating element and wherein the heating element is assembled slightly offset from a surface of the RH sensor.
An additional heating element can be bonded to a base of the RH sensor. The thin substrate material can be configured from a polymide polymer, such as Kapton® material. Additionally, a filter material can be located at vent openings in the RH sensor housing to create a relatively large space of stagnant air adjacent to the RH sensor. The filter material may be a hydrophobic material such as Goretex® which can limit the size of water droplets which pass through and therefore reduce the volume of water entering the sensor housing and needing to be evaporated.
The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the present invention and, together with the detailed description of the invention, serve to explain the principles of the present invention.
The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment of the present invention and are not intended to limit the scope of the invention.
A gap 128 can be formed between RH sensor 130 and porous heater 110. A heater or conductive material 112 can be located between heater 106 and porous heater 110. In
System 100 can be implemented to control temperature and reduce the relative humidity associated with RH sensor 130. In general, when humidity is greater than 100%, the atmosphere becomes two-phase, meaning that a mixture of water vapor and minute water droplets (e.g., fog) is present. Conventional RH sensing systems are limited to a relative humidity sensing range of 0% to 100%, which includes only water vapor without droplets. To overcome such conventional limitations, system 100 in essence implements a “mini-oven” approach, wherein water droplets are heated as they pass through porous heater 110. Such a technique creates a small environment that maintains a humidity level within a required sensing range. The actual humidity level at the ambient temperature can then be calculated. Such a calculation can be accomplished by measuring the temperature at the surface of the humidity sensor and also at the ambient temperature. The humidity level at the ambient temperature can then be inferred.
A ceramic substrate 212 can be located adjacent conductive spacer 211. Ceramic substrate 212 can function as a substrate of a resistive heater 210. Depending upon a desired implementation, resistive heater 210 can function as a porous heater. In such a configuration, the ceramic substrate 212 functions as a porous ceramic heating element assembled with a relatively thermally conductive material (e.g., conductive spacer 211) about the perimeter of the RH sensor 204. Another heating element (e.g., heater 206) can be assembled to the base of RH sensor 204 to ensure uniform heating at the sensing surface thereof. Air that is supersaturated with water vapor and/or fog can therefore pass through the porous ceramic material of ceramic substrate 212, so that water droplets thereof are heated from the fog and/or water vapor and evaporated to reduce RH to a measurable level.
An electrical connection 214 may extend from ambient temperature sensor 202 to a printed circuit board (PCB) 216, which can function as a PCB for all or most electrical components of system 200. An air gap 218 can be formed between PCB 216 and insulating spacer 2081 to create an insulator, which helps to control power dissipation and temperature uniformity. An external housing portion 220 can surround components such as PCB 218, electrical connection 214, air gap 218 and so forth. Ambient temperature sensor 202 can protrude, however, through housing portion 220. A plurality of holes 222, 224, 226, 228, 230 can be implemented as laser drilled holes in the ceramic substrate 212 to effectively make the ceramic substrate porous. The porosity may be also accomplished with a ceramic or other material that is powderized, pressed, and sintered to a low density.
In general, RH sensor 202 of
Another heating element, such as a heater 404 can be bonded to a base of RH sensor 402 to insure uniform temperature at the sensing surface thereof. Air that is supersaturated with water vapor and fog, for example, can then pass through the filter material of porous heater 414 and heating elements thereof, so that water droplets are heated and evaporated to reduce relative humidity to a measurable level. Polyimide polymer 414 can be, for example, a Kapton® material. Note that Kapton® is a trademark of the DuPont™ Corporation. A Kapton® material, in film form, can provide an enhanced dielectric strength in very thin cross sections and very good bonding and heat transfer capabilities. Heater 410 can therefore be implemented as a Kapton® type heater. Note that resistive heater 210 of
An air gap 518 can be formed between PCB 516 and insulating spacer 511 to create an insulator, which helps to control power dissipation and temperature uniformity. An external housing portion 520 can surround components such as PCB 516, electrical connection 514, air gap 518, porous heater 510, RH sensor 506 and so forth. Ambient temperature sensor 502 can protrude, however, through housing portion 520.
The hydrophobic filter 607, for example, can be located proximate or adjacent to housing portion 621. A printed circuit board (PCB) 622 can be located adjacent to insulating spacer 608. An air gap 624 can be located between PCB 622 and insulating spacer 608. Air gap 624 helps to control power dissipation and temperature uniformity. Air gap 624 is similar, for example, to air gap 218 of
The filter material for hydrophobic filter 607 can be configured as a material, such as a Goretex® material, which can limit the size of water droplets that pass through and therefore reduce the volume of water entering the sensor housing and needing to be evaporated. Finally, an ambient temperature sensor 602 can be implemented in association with heater 606, porous heater 610 and RH sensor 602. Filter material or filters 607, 609, 611, 613 can be located slightly offset to create a thin space of stagnant air.
Note that heater 610 can also be formed from a ceramic type heating element made porous, for example, via a plurality of laser drilled holes 612 formed in order to insure that such a ceramic type heating functions as a porous heating element. Air that is supersaturated with water vapor and fog can pass through the porous heater 610, heat the water droplets from the fog and/or water vapor and thereafter evaporate such water droplets to reduce RH to a measurable level.
Filters 607, 609, 611, 613, which are located at the perimeter of the housing formed by housing portions 615, 617, 621 and 621 are important feature that can be utilized in the even more control on the water allowed inside the housing is required. Filters 607, 609, 611, 613 can be implemented to partially block water droplets. Most Gore type filters totally block liquid. A requirement exists, however, to sense above 100% RH, which is referred to as “two-phase” or “in-trained” water. The design depicted in
A filter, such as, for example, filter 607, 609, 611, 613 depicted in
The sensors disclosed herein can be applied to a number of important industrial and commercial devices and systems. One significant application of the sensors disclosed herein involves fuel cell applications. There are several kinds of fuel cells, but Polymer Electrolyte Membrane (PEM) fuel cells-also called Proton Exchange Membrane fuel cells-are the type typically used in automobiles. A PEM fuel cell uses hydrogen fuel and oxygen from the air to produce electricity. In general, most fuel cells designed for use in vehicles produce less than 1.16 volts of electricity, which is usually not sufficient to power a vehicle. Therefore, multiple cells must be assembled into a fuel cell stack. The potential power generated by a fuel cell stack depends on the number and size of the individual fuel cells that comprise the stack and the surface area of the PEM.
One example of a fuel cell application in which one or more of the methods and systems disclosed herein can be implemented is disclosed in U.S. Pat. No. 6,607,854, “Three-Wheel Air Turbocompressor for PEM fuel Cell Systems,” and issued to Rehg et al. on Aug. 19, 2003. U.S. Pat. No. 6,607,854 discloses a fuel cell system comprising a compressor and a fuel processor downstream of the compressor. In U.S. Pat. No. 6,607,854, a fuel cell stack is configured in communication with the fuel processor and compressor. A combustor is downstream of the fuel cell stack. First and second turbines are downstream of the fuel processor and in parallel flow communication with one another. A distribution valve is in communication with the first and second turbines. The first and second turbines are mechanically engaged to the compressor. A bypass valve is intermediate the compressor and the second turbine, with the bypass valve enabling a compressed gas from the compressor to bypass the fuel processor. U.S. Pat. No. 6,607,854 is assigned to Honeywell International, Inc., and is incorporated herein by reference.
Another example of a fuel cell application in which one or more of the methods and systems disclosed herein can be implemented is disclosed in U.S. Patent Publication No. 2003/0129468A1, “Gas Block Mechanism for Water Removal in Fuel Cells” to Issacci et al., which was published on Jul. 10, 2003 and is assigned to Honeywell International, Inc. U.S. Patent Publication No. 2003/0129468A1 is incorporated herein by reference. A further example of a fuel cell application in which one or more of the methods and systems disclosed herein can be implemented is disclosed in U.S. Patent Publication No. 2003/0124401A1, “Integrated Recuperation Loop in Fuel Cell Stack” to Issacci et al., which was published on Jul. 3, 2003 and is assigned to Honeywell International, Inc. U.S. Patent Publication No. 2003/0124401A1 is also incorporated herein by reference.
A heated humidity sensor 806 can be located on PCB/connector assembly 812 and may be received by probe 816. PCB/connector assembly 812 is analogous, for example, to PCB 216 of
Probe 816 may possess a length X and the entire length of fuel cell humidity sensor 800 may possess a length Y. A non-limiting measurement for length X can be, for example, 32 mm or 1.25 inches. A non-limiting measurement for length Y can be, for example, 84 mm or 3.30 in. It can be appreciated of course, that such measurements for X and Y are merely suggestions and that varying measurements can be implemented depending upon design considerations.
Based on the foregoing, it can be appreciated that varying sensor systems and methods are disclosed herein. In accordance with a first embodiment, an RH sensor can be associated with one or more heating elements, wherein a perimeter of the RH sensor is surrounded with a relatively conductive material. A thin substrate material can surround and laminate the heating element, such that the heating element is perforated to permit humid air to pass through the heating element and wherein the heating element is assembled slightly offset from a surface of the RH sensor.
Air that is saturated with two phase flow of water vapor and minute droplets can then pass through and be heated by the heating element in order to evaporate water droplets associated with the water vapor to thereby reduce relative humidity to a measurable level. An additional heating element can be bonded to a base of the RH sensor. The thin substrate material can be configured from a polymide polymer, such as Kapton® material. Additionally, a filter material can be located slightly offset from the RH sensor to create a thin space of stagnant air adjacent to the RH sensor. The filter material may be a hydrophobic material such as Goretex® which can limit the size of water droplets, which pass through and therefore reduce the volume of water needing to be evaporated.
In accordance with a second embodiment, an RH sensor can be associated with one or more ceramic heating element, wherein a perimeter of the RH sensor is surrounded with a relatively conductive material. A resistive material can surround and laminate the ceramic heating element. The ceramic heating element can be configured from a porous material, wherein air that is saturated with water vapor passes through and is heated by the ceramic heating element in order to evaporate water droplets associated with the water vapor to thereby reduce relative humidity to a measurable level. One or more other heating elements can be bonded to the base of the RH sensor. The porous material forming the ceramic heating element can be formed by providing a plurality of laser drilled holes to create porosity thereof. Additionally, a filter material can be located slightly offset from the RH sensor to create a thin space of stagnant air adjacent to the RH sensor.
In accordance with a third embodiment, an RH sensor can be associated with one or more heating elements, wherein the RH sensor is surrounded by a sheet of porous resistive material in a woven or perforated pattern or state. The porous heating element can be configured to permit humid air to pass through the porous heating element. The porous heating element can be further assembled slightly offset from a surface of the RH sensor, wherein air that is saturated with water vapor passes through and is heated by the porous heating element in order to evaporate water droplets thereof to thereby reduce relative humidity to a measurable level. Additionally, a flat heating element can be bonded to the base of the RH sensor to conduct heat and insure uniform heating about the RH sensor. The porous resistive material can be formed from material such as tantalum or nichrome. A filter material can also be located slightly offset from the RH sensor to create a thin space of stagnant air adjacent to the RH sensor
In accordance with a fourth embodiment, an RH sensor can be associated with one or more heating elements, wherein a perimeter of the RH sensor is surrounded with a relatively conductive material. A thin substrate material can surround and laminate the heating element, such that the heating element is perforated to permit humid air to pass through the heating element and wherein the heating element is assembled slightly offset from a surface of the RH sensor.
An additional heating element can be bonded to a base of the RH sensor. The thin substrate material can be configured from a polymide polymer, such as Kapton® material. Additionally, a filter material can be located at vent openings in the RH sensor housing to create a relatively large space of stagnant air adjacent to the RH sensor. The filter material may be a hydrophobic material such as Goretex® which can limit the size of water droplets which pass through and therefore reduce the volume of water entering the sensor housing and needing to be evaporated.
The embodiments and examples set forth herein are presented to best explain the present invention and its practical application and to thereby enable those skilled in the art to make and utilize the invention. Those skilled in the art, however, will recognize that the foregoing description and examples have been presented for the purpose of illustration and example only. Other variations and modifications of the present invention will be apparent to those of skill in the art, and it is the intent of the appended claims that such variations and modifications be covered.
The description as set forth is not intended to be exhaustive or to limit the scope of the invention. Many modifications and variations are possible in light of the above teaching without departing from the scope of the following claims. It is contemplated that the use of the present invention can involve components having different characteristics. It is intended that the scope of the present invention be defined by the claims appended hereto, giving full cognizance to equivalents in all respects.
This patent application claims priority under 35 U.S.C. § 119(e) to provisional patent application Ser. No. 60/568,591 entitled “Sensor Methods and Systems,” which was filed on May 6, 2004, the disclosure of which is incorporated herein by reference.
The United States government may have rights in the invention described herein made in the performance of work under Department of Energy (DOE) Cooperative Agreement DE-FC36-02AL67615.
| Number | Date | Country | |
|---|---|---|---|
| 60568591 | May 2004 | US |
