US 2005O247 106A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2005/0247106A1 Speldrich et al. (43) Pub. Date: Nov. 10, 2005 (54) RELATIVE HUMIDITY SENSORENCLOSED Publication Classification WITH CERAMIC HEATER (51) Int. Cl." ....................................................... G01N 7/00 (75) Inventors: Jamie W. Speldrich, Freeport, IL (US); (52) U.S. Cl. ............................................................ 73/29.01 Michael P. Farrey, Freeport, IL (US) Correspondence Address: (57) ABSTRACT Kris T. Fredrick Honeywell International, Inc. Sensor Systems and methods are disclosed herein. A relative Attorney, Intellectual Property humidity Sensor can be associated with one or more ceramic 101 Columbia Rd., P.O. Box 224.5 heating elements configured from a porous material. In Morristown, NJ 07962 (US) general, a perimeter of the relative humidity Sensor is (73) Assignee: Honeywell International, Inc. Surrounded with a relatively conductive material. A resistive material Surrounds one or more of the ceramic heating (21) Appl. No.: 10/858,983 elements, Such that air that is Saturated with water vapor passes through the porous material of the ceramic heating (22) Filed: Jun. 2, 2004 element(s). Water vapor can therefore be heated by the ceramic heating element(s) in order to evaporate water Related U.S. Application Data droplets associated with the water vapor and thereby reduce relative humidity to a measurable level. The porous material (60) Provisional application No. 60/568,591, filed on May of the ceramic heating element(s) can be provided via a 6, 2004. plurality of laser drilled holes to create Such porosity. 1. 500 502 {d a a a Patent Application Publication Nov. 10, 2005 Sheet 1 of 5 US 2005/0247106A1 106 to % SSNYS 1021 O S 1 104 30 128 11 2 O 108 S N S. O 114 O 1161 118 122 110 O O O O O O O O Fig. 1 202 Patent Application Publication Nov. 10, 2005 Sheet 2 of 5 US 2005/0247106A1 1. 300 Heater 304 RH Sensor 302 Air 308 31 2 t t t t T 1. Porous Heater Fig. 3 2 Porous Heater 2% Fig. 4 Patent Application Publication Nov. 10, 2005 Sheet 3 of 5 US 2005/0247106A1 - 500 ZZZ ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ ŠL)?I Patent Application Publication Nov. 10, 2005 Sheet 4 of 5 US 2005/0247106A1 1. 700 % 703 RHS 2 2% % 2% % % 2% 3.2 %2ZzZ 716 US 2005/0247106A1 Nov. 10, 2005 RELATIVE HUMIDITY SENSORENCLOSED the elements necessary to make a resistance measurement. WITH CERAMIC HEATER The result is erroneous readings, among other problems. REFERENCE TO RELATED APPLICATION 0008 Elements constructed to approximate a pure capacitance avoid the disadvantages of the resistive ele 0001. This patent application claims priority under 35 ments. It is important in the construction of capacitive U.S.C. S 119(e) to provisional patent application Ser. No. elements, however, to avoid the problems that can arise with 60/568,591 entitled “Sensor Methods and Systems,” which certain constructions for Such elements. In addition, there was filed on May 6, 2004, the disclosure of which is can also be inaccuracy incurred at high relative humidity incorporated herein by reference. values where high water content causes problems due to excessive StreSS and the resulting mechanical shifts in the GOVERNMENT INTERESTS components of the element. By making the component parts of the element thin, it has been found that the above 0002 The United States government may have rights in mentioned problems can be avoided and the capacitance the invention described herein made in the performance of type element can provide a fast, precise measurement of the work under Department of Energy (DOE) Cooperative relative humidity content over an extreme range of humidity Agreement DE-FC36-02AL67615. as well as over an extreme range of temperature and pressure and other environmental variables. TECHNICAL FIELD 0009 Humidity sensing elements of the capacitance 0.003 Embodiments are generally related to sensor meth Sensing type usually include a moisture-insensitive, non ods and Systems. Embodiments are also related to humidity conducting Structure with appropriate electrode elements Sensors and moisture Sensing elements thereof, flow Sensors, mounted or deposited on the Structure along with a layer or preSSure Sensors, thermal Sensors and temperatures Sensors. coating of dielectric, highly moisture-Sensitive material Embodiments are additionally related to Sensors utilized in overlaying the electrodes and positioned So as to be capable fuel cell systems, such as, for example, PEM fuel cell of absorbing water from the Surrounding atmosphere and applications. reaching equilibrium in a short period of time. Capacitive humidity Sensors are typically made by depositing Several BACKGROUND OF THE INVENTION layers of material on a Substrate material. An example of a humidity sensor is disclosed in U.S. Pat. No. 6,724,612, 0004 Humidity sensors, flow sensors, pressure sensors entitled “Relative Humidity Sensor with Integrated Signal and temperatures Sensors and the like can be utilized in a Conditioning,” which issued to Davis et all on Apr. 20, 2004, variety of Sensing applications. With respect to humidity and issued to Honeywell International, Inc. U.S. Pat. No. Sensors, for example, providing Suitable instruments for the 6,724,612 is incorporated herein by reference. measurement of relative humidity (RH) over wide RH ranges (e.g., 1%-100%) continues to be a challenge. Humid 0010) A limitation of humidity sensor is the relative ity Sensors can be implemented in the context of Semicon humidity (RH) can be measured up to 100% RH above ductor-based Sensors utilized in many industrial applica which the Sensor reaches Saturation. At levels higher than tions. Solid-State Semiconductor devices are found in most 100% RH., minute water droplets are formed in Suspension electronic components today. Semiconductor-based Sensors, (fog, a.k.a. two-phase flow) and the Sensor may fail to for example, are fabricated using Semiconductor processes. operate. The technique used in this invention enables mea 0005. Many modern manufacturing processes, for surement of greater than 100% RH with a sensor that is example, generally require measurement of moisture con capable of only 0 to 100% RH sensitivity by making a tents corresponding to dew points between -40° C. and 180 controlled, heated environment in the vicinity of the Sensing C., or a relative humidity between 1% and 100%. There is area which can evaporate Small water droplets and reduce also a need for a durable, compact, efficient moisture detec RH to a measurable level. tor that can be used effectively in these processes to measure 0011. This technique depends on a controlled, uniform very Small moisture content in gaseous atmospheres. temperature at the Sensing area of the RH Sensor which is 0006 Humidity can be measured by a number of tech particularly is critical because relative humidity varies with niques. In a Semiconductor-based System, humidity can be temperature for the same mole fraction of water vapor in the measured based upon the reversible water absorption char air. With respect to Sensor housing and Sensor parts thereof, acteristics of polymeric materials. The absorption of water flow and diffusion of humid ambient air and differences into a Sensor Structure causes a number of physical changes between the coefficients of thermal conductivity of the in the active polymer. These physical changes can be trans components will affect the uniformity of the temperature at duced into electrical signals which are related to the water the Sensing Surface can cause a shift in output over tem concentration in the polymer and which in turn are related to perature, flow, and humidity changes. Therefore, a variety of the relative humidity in the air Surrounding the polymer. Sensor configurations, Systems, and methods are disclosed herein, which attempt to rectify Such problems. 0007 Two of the most common physical changes are the change in resistance and the change in dielectric constant, BRIEF SUMMARY OF THE INVENTION which can be respectively translated into a resistance change and a capacitance change. It has been found, however, that 0012. The following summary of the invention is pro elements utilized as resistive components Suffer from the Vided to facilitate an understanding of Some of the innova disadvantage that there is an inherent dissipation effect tive features unique to the present invention and is not caused by the dissipation of heat due to the current flow in intended to be a full description. A full appreciation of the US 2005/0247106A1 Nov. 10, 2005 various aspects of the invention can be gained by taking the offset from a Surface of the RH sensor, wherein air that is entire Specification, claims, drawings, and abstract as a Saturated with water vapor passes through and is heated by whole. the porous heating element in order to evaporate water droplets thereof to thereby reduce relative humidity to a 0013. It is, therefore, one aspect of the present invention measurable level. Additionally, a flat heating element can be to provide for improved Sensor methods and Systems. bonded to the base of the RH sensor to conduct heat and 0.014. It is another aspect of the present invention to insure uniform heating about the RH sensor. The porous provide for improved relative humidity sensor methods and resistive material can be formed from material Such as Systems. tantalum or nichrome. A filter material can also be located 0.015. It is a further aspect of the present invention to slightly offset from the RH sensor to create a thin space of provide for improved temperature, pressure and flow Sens Stagnant air adjacent to the RHSensor ing methods and Systems. 0020. In accordance with a fourth embodiment, an RH 0016. The aforementioned aspects of the invention and Sensor can be associated with one or more heating elements, other objectives and advantages can now be achieved as wherein a perimeter of the RH sensor is surrounded with a described herein.