Abstract: The invention provides for a dynamic dew point analysis method as well as an apparatus for carrying out the method wherein the method comprises: arranging a moisture containing gas in the immediate vicinity of at least two thermocouples, where one thermocouple is shielded from the gas; creating an analogous temperature change in both thermocouples and registering the temperature in both thermocouples during a cycle where the condensation point of the moisture containing gas is passed, using the different temperatures from the at least two thermocouples as input for determining the dew point according to basic thermodynamic principles.

Abstract: A sensor means is proposed to determine an interior humidity and/or an interior volume delimited by a wall, in particular, of a vehicle passenger compartment 3, and a fogging up tendency of an inner surface of the wall, in particular, of a window 5 of the vehicle passenger compartment 3, with a dew point sensor 10 having a humidity sensor element 1 and a temperature sensor 2, wherein the humidity sensor element 1 and the temperature sensor 2 a thermally coupled, and a surface temperature sensor 4, wherein the dew point sensor 10 is designed to measure the air humidity and the room temperature of the interior volume and the surface temperature sensor 4 is designed to measure the temperature of the inner surface.

Abstract: In a mirror surface state detection device, a light-emitting element obliquely irradiates the mirror surface of a mirror with light. A light-receiving element is arranged adjacent to the light-emitting element to have an optical axis almost parallel to that of the light-emitting element and a tilt angle almost equal to that of the light-emitting element and receives scattered light of the light emitted from the light-emitting element. A condensation detection unit detects the state on the mirror surface on the basis of the scattered light received by the light-receiving element. A moisture detection device is also disclosed.

Abstract: An environment sensor (11) for measuring the temperature and humidity can be miniaturized and can respond at high speed. The environment sensor (11) includes a temperature sensing portion (111) having a temperature-sensitive material (1) made of a metal oxide, and a humidity-sensing portion (112) which is formed on the same substrate as the temperature sensing portion (111) and measures the ambient humidity by using a change in electrical characteristics. At least one of a pair of electrodes (2, 3) of the temperature sensor (111) is integrated with an electrode of the humidity-sensing portion (112).

Abstract: The present invention provides a method and system to overcome and eliminate the effects of condensation contamination of optical surfaces that are induced by radiative cooling. The invention counteracts the effects of radiative cooling on optical surfaces and maintains an optical system within a very tight limit to the ambient temperature by utilizing a resistive heater element that is in contact with the optical components subject to condensation. In thermal contact with this optical component is a solid-state precision temperature sensor. In addition, there is a matching solid-state precision temperature in thermal contact with the ambient air but thermally isolated from the optical element. Signals from these two sensors are applied to a comparator that functions to generate a data signal when the optical surface temperature is less than the ambient or reference temperature. This data signal is used to activate a solid-state power switch that applies a voltage to a resistive heating element.

Abstract: A dew point hygrometer for determining the dew point of a gas in which a displaceable transparent film is in contact with the gas and forms a condensation surface. The film is placed on a temperature control device controlling its temperature and an optic fiber, emits light on the film and reflected light is detected in another optic fiber, the two optical fibers being positioned at an angle with respect to the film. Condensation formed on the film changes the light transmitted by the film which is periodically displaced so that a new uncontaminated regions are exposed to the light.

Abstract: A cloud point monitoring device which includes thermal conductive surface, cooler, temperature sensor, detection volume, detection wall unit, fiber optic cables for transmitting light, lighter emitter, light detector, and a data acquisition and control unit. The cloud point monitoring device provides an instrument to accurately measure the cloud point of diesel fuel indicate the approximate level of crystallization in diesel fuel that has been chilled beyond its cloud point and indicate the approximate energy content of diesel fuel. The cloud point monitoring device design allows it to be made small enough to be mounted in a fuel system of a vehicle.

Abstract: The invention concerns dew point hygrometers based on condensation of dew on ends of optical fibers, or on surfaces of an optical prism. The invention also concerns a dew sensor for determining the natural dew condensation by optical means and a dew sensor capable of detecting dew by detecting a change in capacitance.

Abstract: The present invention provides a method and system to overcome and eliminate the effects of condensation contamination of optical surfaces that are induced by radiative cooling. The invention counteracts the effects of radiative cooling on optical surfaces and maintains an optical system within a very tight limit to the ambient temperature by utilizing a resistive heater element that is in contact with the optical components subject to condensation. In thermal contact with this optical component is a solid-state precision temperature sensor. In addition, there is a matching solid-state precision temperature in thermal contact with the ambient air but thermally isolated from the optical element. Signals from these two sensors are applied to a comparator that functions to generate a data signal when the optical surface temperature is less than the ambient or reference temperature. This data signal is used to activate a solid-state power switch that applies a voltage to a resistive heating element.

Abstract: A hydrophilic polymer material such as polyvinyl alcohol is formed into a porous film (301). A film (holding film) (303) made from a hydrophobic polymer material such as polyvinyl acetate is formed on the inner walls of a large number of pores (302) formed in the porous film (301). Lithium chloride (304) is held in these pores (302).

Abstract: A dew formation occurrence detection apparatus for detecting the dew formation on a drum 4 of a tape transport system provided on the electronic equipment 1 as an object for measurement. The dew formation occurrence detection apparatus includes a drum temperature detection unit 8 for detecting the temperature of the drum 4, an environment air temperature acquisition unit 6 for acquiring the environment air temperature of the electrical equipment 1 and a dew point temperature calculating unit 6 for calculating, from this environment air temperature, the dew point temperature at the humidity which takes the operating environment of the electronic equipment 1 into account. When the temperature of the drum 4 is not higher than this dew point temperature, it is verified that dew formation has occurred.

Abstract: The apparatus for determining the dew-point and/or the content of vapor in the air, particularly for the use in radio sondes, comprises a dew-point mirror assembly, including a source of light, a reflector, a cooling element thermally coupled to the reflector, a temperature sensor for measuring the temperature of the reflector, and a detecting sensor for receiving the light emitted by the light source and reflected by the reflector. The detecting sensor is located in a temperature stabilized region of the apparatus and optically coupled to the reflector by means of a light wave conductor. The light source is an incandescent lamp. A sensor head is provided that receives the reflector, the cooling element, the light source, and the input end of the light wave conductor. The sensor head is heated by means of an active heating element.

Abstract: A dew point sensor includes a micro-cantilever beam formed on a substrate. A cooling device and a temperature sensor are in thermal contact with the micro-cantilever beam and a control circuit is coupled to the micro-cantilever beam, the cooling device and the temperature sensor. The control circuit controls and monitors a resonance of the micro-cantilever beam, controls a temperature of the cooling device and receives a temperature indication from the temperature sensor. Using the above information, the dew point temperature is determined by identifying the temperature of the micro-cantilever beam when its resonance changes due to a change in mass caused by the formation of dew on the micro-cantilever beam when the dew point is reached. A method of determining the dew point is also disclosed. The method includes exciting a micro-cantilever beam in a vibratory mode and decreasing a temperature of the micro-cantilever beam.

Abstract: A moisture sensitive element in which a functional film is formed in contact with opposing electrodes arranged on a substrate. The element includes a mechanism for measuring the temperature of the functional film. The functional film has a porous structure made from a polymer material with hydrophilic properties and includes fine pores. A holding film is formed on inner walls of the pores and made from another polymer material having hydrophobic properties. An electrolytic salt is held within the pores.

Abstract: A frost deposition detecting device is provided. This frost deposition detecting device comprises: a base member 1; a heat-conductive container 4 including a frosting portion provided to the base member 1; a thermally sensitive element 6' for detecting the temperature of the base member 1; a protection pipe 8 inserted into the base member 1 and disposed in the cavity formed inside the heat-conductive container; a heat insulator integrally formed with the protection pipe 8 to reduce heat conduction to the protection pipe 8; and another thermally sensitive element 6 secured in the protection pipe 8. With such frost deposition detecting device, highly accurate frost detecting performance and excellent durability in terms of water resistance and humidity resistance can be achieved.

Abstract: A thermistor including a pill assembly, a connector body, and an adhesive sealant. The pill assembly includes a thermistor pill and a conductive lead operably attached thereto. The conductive lead extends through the connector body. The adhesive sealant bonds with both the connector body and the conductive lead proximate to where the conductive lead extends through the connector body.

Abstract: The invention relates to a method and an apparatus for metering evaporation. According to the invention the temperatures (T.sub.k, T.sub.m, T) are defined for a comparing piece (6) in an essentially non-evaporating state, for a comparing piece (8) in an essentially evaporating state and for the metered object (1). Based on a mutual comparison of the obtained temperature values (T.sub.k, T.sub.m, T) the evaporation index (n) dependent on the amount of liquid evaporated will be defined.

Abstract: A method for measuring the dew point temperature of a moist gas in which a flow of moist gas (A) is passed over a surface (2); a moisture sensor (5) is positioned in the flow of gas downstream of the surface (2); cooling is applied to the surface; the moisture content (M) of the gas downstream of the surface (2) is monitored; and the temperature of the surface (2) is measured, the temperature which is measured being controlled by the detection of a decrease in moisture content due to moisture condensation from the moist gas at the dew point temperature (T.sub.D). An apparatus for carrying out the method is also described. The surface (2) may be a layer of heat-conducting material in contact with a heat pump (3) or the surface may be part of the wall of a coiled tube (40).

Abstract: A dew point temperature measuring apparatus and method, which may be used to determine water activity, includes a chamber in which a sample of air is measured, an air circulation device positioned within the chamber, a sensor to measure the sample temperature, a relative humidity sensor, and a diverter for causing air circulating within the chamber to directly impinge the relative humidity sensor. Another embodiment involves mounting an air circulation device within the chamber such that it forces air inside the chamber to impinge directly upon the relative humidity sensor to reduce boundary layer resistance. Still another embodiment of the invention involves utilizing a temperature control device to control the temperature of interior surfaces within the chamber at a temperature higher than the sample of air within the chamber.

Abstract: A method of predicting the formation of water condensation on a surface in contact with humid air includes the steps of placing on the surface an element that adopts initially a temperature approximately equal to a temperature of the surface. The element is thermally cycled. Each cycle includes a cooling phase and a heating phase. The cooling phase includes first and second steps. Electric current is supplied to a cooling mechanism in the first step of the cooling phase to decrease the temperature of the element to below the temperature of the surface. An electric current is supplied to the cooling mechanism in the second step of the cooling phase to further decrease the temperature of the element. The current of the first step is greater than the current of the second step, such that the temperature of the element decreases more rapidly in the first step than in the second step. The formation of water condensation on the surface is predicted based upon the formation of water condensation on the element.

Abstract: A dewpoint/frostpoint hygrometer that uses a surface moisture-sensitive sensor as part of an RF oscillator circuit with feedback control of the sensor temperature to maintain equilibrium at the sensor surface between ambient water vapor and condensed water/ice. The invention is preferably implemented using a surface acoustic wave (SAW) device in an RF oscillator circuit configured to generate a condensation-dependent output signal, a temperature sensor to measure the temperature of the SAW device and to distinguish between condensation-dependent and temperature-dependent signals, a temperature regulating device to control the temperature of the SAW device, and a feedback control system configured to keep the condensation-dependent signal nearly constant over time in the presence of time-varying humidity, corrected for temperature.

Abstract: A space heating system with a controllable air humidification capability calculates a theoretical value for the temperature of the interior surface of the space's windows. The system controls humidity in the space to a level just below that at which water will condense on the window surfaces.

Abstract: A process is disclosed to detect a water condensation risk on a surface in contact with a wet air volume, which uses the steps of (a) placing a sensitive element on the surface, which initially takes a temperature corresponding to that of the surface, (b) by means of a heating device on this sensitive element, initiating a first heating phase until a temperature higher than the surface temperature is reached, (c) by means of a cooling device having the same thermal power as the heating device, initiating a cooling phase until a temperature lower than the surface temperature is provoked on the sensitive element, and (d) a comparison is made between the ratio of the first heating phase time to the temperature rise during heating and the ratio of cooling phase time to the temperature decrease during the cooling, a noticeable difference between these two ratios indicating a significant risk of condensation on the surface.

Abstract: A microsensor system for determining water vapor content of the ambient atmosphere that uses a thin film suspended ceramic diaphragm structure featuring an embedded, patterned thin film heater, temperature sensor and an external film of an hygroscopic salt stabilized in a water-insoluble, crosslinked polymer matrix and contacting a pair of patterned electrodes which are proximate to the heater. The heater controls a selected electrical parameter of the salt to a fixed, predetermined value, as determined by its electrical characteristics. The dew point of the atmosphere is determined based on the dynamic relation with the salt dehydration temperature.

Abstract: A method of determining the dew point of a gas containing a very small amount of water using (1) a reflector mirror the temperature of which can be varied from room temperature down to at least -80.degree. C.; (2) a source of condensed rays of light for irradiating the reflector mirror; and (3) a light recovering device that detects changes in scattered light due to condensation on the reflector mirror by exposing the mirror to the gas. The method comprises cooling the mirror and detecting the temperature at which the scattered light has a maximum intensity; slowly raising the temperature and detecting the temperature at which the scattered light has a minimum intensity and repeating the cycle until the temperature at which the intensity is a maximum and the temperature at which the intensity is a minimum are almost the same.

Abstract: A method for determining the relative humidity of the air entering the cooling heat exchanger of an air conditioning system as well as an apparatus for implementing the method. The cooling capacity of the system is varied and, if occurring, the transition between a condition where moisture is condensing in the heat exchanger and a condition where moisture is not condensing in the heat exchanger. At this transition, the temperatures of the exiting air and the entering air are measured. From the measured exiting air temperature, state point of the saturated exiting air can be determined. From the exiting air state point and the entering air state point, the entering air relative humidity can be determined. If no condensation occurs even at maximum cooling capacity, the maximum that the relative humidity of the entering air can be determined. If condensation continues even at minimum cooling capacity, the minimum that the relative humidity of the entering air can be determined.

Abstract: The present invention is a humidity sensor which can be used in a radiosonde. The humidity sensor includes a heat sink attached to the radiosonde, a Peltier cooler attached to the heat sink, a carbon element with a thermistor attached therein or thereon, and a control means. The resistance of the carbon element is adjusted to a predetermined level to maintain a relative humidity of about 33, in particular. The control means monitors this resistance and adjusts the Peltier cooler accordingly. The thermistor responding to the temperature of the carbon element outputs a resistance indicative of the temperature on the sensor surface.

Abstract: An uncoated interdigitated transducer is cooled from a temperature above the dew point to a temperature below the dew point, while a parameter of a signal of the transducer is measured. The reduction in temperature causes a monotonic change in transducer signal because that signal is sensitive primarily to the water loading of the transducer surface as water forms on that surface due to the reduction in temperature. As the dew point is approached with temperature reduction, the slope of the curve of transducer signal with respect to temperature, remains relatively constant. However, as the dew point is reached the slope of that curve increases and because of changes in the structure of the water layer on the surface of the transducer, at the dew point the transducer responds with a clear shift in the rate at which the transducer signal changes. The temperature at which the second derivative of signal vs. temperature peaks can be readily used to identify with extreme accuracy, the precise dew point.

Abstract: Apparatus and method for determining and tracking dew point temperatures. The dew point is measured by lowering the temperature of a condensing surface that is associated with a heat flow sensor. After condensation occurs the heat flux across the condensing surface is maintained at a preselected value by adjusting the temperature of the condensing surface. As long as a positive heat flow is maintained into the condensing surface, the temperature of the condensing surface is maintained at a slightly lower temperature than the saturation temperature which is by definition the dew point. The dew point temperature calculation is based on the relationship that when condensate forms on the condensing surface, the temperature of the condensing surface approaches the dew point temperature as the heat flow rate across the condensing surface approaches zero, i.e., at adiabatic conditions.

Abstract: A new method for determination of the dew-point of a humid gas by means of a light beam reflected by a dew-point mirror. During measurements of dew-points, particularly in the range between -50.degree. C. to -95.degree. C., excess moisture is added to the humid gas under measurement in the manifold. Thus the dew-point mirror is for a short period of time, impacted with a humid gas of higher water content. This results in a fast build-up of a layer of dew on the mirror. In the subsequent process of dew-point determination, this reduces the time of measurement significantly. For carrying out the method, a dew-point measuring device is described, which comprises a manifold with a by-pass circuit having a gas valve, an injector unit and a humidification unit. Particularly useful in the device is a humidification unit made of hygroscopic polyamide tube which ensures maintenance-free humidification of the gas by the water molecules diffusing into this tube from the ambient atmosphere.

Abstract: A dew point temperature measuring apparatus is positioned in a sample flow channel that withdraws a sample of a gaseous atmosphere within an enclosure for measuring the dew point temperature of the gaseous atmosphere from which its humidity may be determined. The dimensions of the sample flow channel and the velocity of the gas flow past the dew point temperature measuring apparatus is controlled to assure that the flow is laminar in order to avoid unwanted heat transfer between the sample gas and the dew point temperature measuring apparatus. The dew point temperature measuring apparatus includes a pair of sensors positioned side-by-side in a top wall of the sample flow channel.

Abstract: In a frost and dew sensor composed of two thermosensitive resistors, a power source and an arithmetic circuit, frost or dew is detected from the change of a differential temperature between the two thermosensitive resistors as two different currents from the power source are supplied to the respective thermosensitive resistors. In an alternative form, the sensor has a single thermosensitive resistor, which is energized as two different currents are alternately supplied from the power source so that frost or dew is detected by comparison of the time-lags between the two outputs from the thermosensitive resistor.

Abstract: In a frost and dew sensor composed of two thermosensitive resistors, a power source and an arithmetic circuit, frost or dew is detected from the change of a differential temperature between the two thermosensitive resistors as two different currents from the power source are supplied to the respective thermosensitive resistors. In an alternative form, the sensor has a single thermosensitive resistor, which is energized as two different currents are alternately supplied from the power source so that frost or dew is detected by comparison of the time-lags between the two outputs from the thermosensitive resistor.

Abstract: A dew-point sensor for a dew-point measuring device for measuring the water vapor dew point in gases comprises a sensor surface which is exposed to the gas to be measured and on which on cooling to the dew-point temperature water vapor condenses. Mounted on the sensor surface are two electrode structures which comprise electrode portions which are arranged a uniform interval parallel to each other and which are covered with a moisture-insensitive insulating layer. The reaching of the dew-point temperature is determined by measuring the impedance or capacitance between the two electrode structures. The distance between the electrode portions, arranged parallel to each other, of the two electrode structures is of the order of magnitude of the diameter of the largest condensation droplet forming on reaching the dew-point temperature, or smaller than said diameter, and the thickness of the insulating layer is small compared with the distance between the electrode portions.

Abstract: The dew points of condensible hydrocarbon and water in a gas stream are determined independently in a single run by observing changes in intensity of light scattered from a mirror surface which is cooled to below both of the dew points. A decrease in intensity denotes the hydrocarbon dew point while an increase in intensity denotes the water dew point. The apparatus is simple and operates automatically. The mirror surface has a first polished and highly reflective portion and a second, roughened, less reflective portion. The intensity of scattered light is preferably monitored separately for each mirror portion.

Abstract: A heat conducting support having electrodes is located in a chiller block. The electrodes form a temperature sensor, a heater electrode and electrodes for the measuring of the conductivity. The electrodes are covered by an electrically insulating layer, which layer limits or defines, respectively, over a length L a bedewable surface. The chiller block is encased in a heat insulation and its temperature is measured by a second temperature sensor. The cross-sectional area of the heat transfer between chiller block and bedewable surface is substantially smaller than the bedewable surface itself. This makes it now possible that the temperature at the bedewable surface during the forming of the condensate is determined substantially by the temperature of the condensate at the bedewable surface such that increasing formation of condensate a plateau is determinable at the dew point temperature.

Abstract: For measuring the water vapor dew point in gases, a moisture-dependent electrical quantity of a sensor surface suitable for indicating formation of dew droplets is held by temperature control at a desired value corresponding to a stable dew mass. The temperature of the sensor surface corresponding to the desired value of the moisture-dependent electrical quantity is measured as dew point temperature. For compensating the influence of soiling, from time to time the desired value of the moisture-dependent electrical quantity is set in that the temperature of the sensor surface is lowered from a value lying above the dew point temperature and a periodic time temperature variation superimposed on the lowering. If the sensor surface is soiled, periodic time variations of the moisture-dependent electrical quantity occur at the same time but they become a monotonic variation when the dew point temperature is reached.

Abstract: A method for measuring the dew point according to patent application P 36 33 015 is expanded so that an automatic zero point correction can be carried out. For this purpose, the heating power on the heating device is raised to a point, at which the dew evaporates and the sensor-specific property, for example the capacity, is measured and supplied to the evaluating unit as a calibration signal.

Abstract: The temperature of liquid in a tank and of the environment adjacent the tank are measured and a heater in the tank is controlled to heat the liquid if its temperature is sufficiently below that of the environment to cause water vapor in the atmosphere to condense on the outer surface of the tank.

Abstract: A system is provided for determining the concentration of a condensable vapor in the presence of at least one other condensable vapor, such as hydrogen peroxide and water vapors. The system includes generally a dew point sensor, a device for measuring at least one additional property of at least the other vapor such as relative humidity, and a microprocessor for fitting the dew point and additional property measurements into a modeled construct representative of the relationship between the vapors at a plurality of concentrations for each such vapor and at a plurality of corresponding dew point measurements. When used to determine the concentration of sterilant vapor in a sterilization system, the system also includes a sterilization chamber and an injector for injecting a measured quantity of the multicomponent condensable vapor into the chamber.

Abstract: A humidity detector using a ceramic sensor and a heater to periodically clean the sensor. The output of the sensor is sampled and held while the heater is on. When the detector is turned on, the heater is not started until the sensor has been sampled and held. The timer controlling this operation can be externally reset. When the ceramic sensor is temperature corrected, the humidity output indicates a dew point at a fixed temperature. By adjusting this fixed temperature dew point output according to a sensed temperature, the dew point can be detected.

Abstract: An apparatus useful for determining the water dew point temperature of a water, hydrocarbon-containing gaseous material in which the water dew point is lower than the hydrocarbon dew point temperature comprises: an elongated column capable of being filled with liquid in substantial equilibrium with the water, hydrocarbon-containing gaseous material and placed in an environment having a temperature reduced relative to the water dew point of the material; a signal source acting to send signals through the column; a signal receiver acting to receive the signals sent through the column; a control system acting in response to the received signals to control the temperature of the liquid in the column at substantially the water dew point of the water, hydrocarbon-containing gaseous material; and a temperature indicator acting to determine the temperature of the liquid in the column. Improved methods for determining such water dew point temperature are also disclosed.

Abstract: A dew-point measuring instrument has a capacitive dew-point sensor 1 which is cooled by a cooling device 17 to the dew-point temperature measured by a temperature sensor 8. A phase measuring circuit 14 measures the phase angle of the impedance of the capacitive dew-point sensor 1. The measured phase angle is used as a gauge for the contamination of the dew-point sensor 1.

Abstract: Apparatus for determining the relative humidity of an atmosphere by measuring the dew point of the atmosphere. The dew point is measured by lowering the temperature of a condensing or sensing surface associated with a heat flow sensor. When condensation begins to occur this is detected by the heat flow sensor as a change in the rate of heat flow through the condensing surface. In one embodiment a pair of heat flow sensors are employed, one maintained at a slightly lower temperature than the other. The sensors are connected in series opposition so that output signals due to background or convective heat transfer are cancelled, any change in the combined output signal of the two sensors then indicating heat flow resulting from condensation. The temperature of the cooler face will be the dew point temperature. Two arrangements of sensors are disclosed.

Abstract: A computer cooling system has a mixing valve which supplies coolant to the computer and receives hot return coolant from the computer and also chilled return coolant from a chiller intermediate the computer and the mixing valve. The mixing valve mixes the hot return coolant with the chilled return coolant to adjust the cooling system temperature. Control circuitry senses, or estimates, the dew point temperature of the computer room environment, compares it with the cooling system temperature, and adjusts the mixing valve to maintain the cooling system temperature a few degrees above the dew point temperature. A condensation sensor comprised of a light emitting diode (LED), reflective tape applied about a cooling system supply conduit, and a phototransistor is disclosed. Light from the LED is fully reflected by the reflective tape to the phototransistor in dry conditions, but only partially reflected when condensation forms on the tape.

Abstract: A method and apparatus for determining the dew point or dew point depression which is arranged for unattended operation and is extremely accurate in the vicinity of very small dew point depressions. In addition to measuring present dew point depression, historical records are maintained and the device is arranged to perform a time trend analysis so as to provide for short term future prediction. Output is provided via a voice synthesizer and a radio. Dew point depression is computed by determining the adiabatic change in volume required to produce condensation. The change in volume is produced by rapidly expanding a test chamber. The measurement cycle concludes with a compression step to raise chamber temperature to at least freezing.

Abstract: A dewpoint sensor has an inlet connected to a gas flow switch that first its air at 100 percent saturation at ambient temperature for determining a reference dewpoint temperature. The switch then connects the sensor to ambient air for determining the ambient dewpoint temperature. Entry of this temperature data in standard tables establishes relative humidity with improved accuracy at high humidity due to the measurement of both temperatures on the same sensor instrument.

Abstract: A piezoelectric sensor consists of material for transmitting elastic waves and has a surface subjected to the condensation and presence of dew and liquid to be detected. A wave producing device includes a transmitter for producing an acoustic surface wave on the surface in conjunction with piezoelectric phenomena of the sensor. A detector includes a receiver for receiving the wave after transmission thereof across the surface. The wave is variably attenuated in transmission between the transmitter and receiver in accordance with dew or liquid on the surface. A measuring device measures the attenuation of the detected wave and thereby indicates the dew point or presence of liquid on the surface.