Abstract: Temperature compensation methods for physical property sensors are disclosed herein, based on a simple bridge circuit. An imbalance of the bridge circuit can be driven to a zero value, while a supply voltage thereof is simultaneously driven to a level required to bring the heating element to the temperature rise above ambient temperature that optimally compensates for a number of temperature-dependent effects. The heating element can be configured as a thin-film heating material. The resulting total temperature dependence of the measuring system, which includes the heating element, the bridge-circuit with amplifier and the fluid to be measured, can be reduced to a level at which the need for additional digital temperature compensation circuitry and its associated costs may be reduced.

Abstract: Temperature compensation methods for physical property sensors are disclosed herein, based on a simple bridge circuit. An imbalance of the bridge circuit can be driven to a zero value, while a supply voltage thereof is simultaneously driven to a level required to bring the heating element to the temperature rise above ambient temperature that optimally compensates for a number of temperature-dependent effects. The heating element can be configured as a thin-film heating material. The resulting total temperature dependence of the measuring system, which includes the heating element, the bridge-circuit with amplifier and the fluid to be measured, can be reduced to a level at which the need for additional digital temperature compensation circuitry and its associated costs may be reduced.

Abstract: An apparatus to normalize a flow rate of a fluid in a main flow channel is provided. The apparatus uses a movable member, such as a flexible membrane disposed for reciprocating displacement, to produce a constant dither flow of the fluid that is independent of fluid composition. This dither flow generates a signal output from a normalizing flow sensor that both represents a characteristic property of the fluid and a flow rate calibration factor. A similar apparatus to determine the characteristic property or flow rate calibration factor is also provided. The devices disclosed may be used in numerous industrial, process, and medical flow system applications for normalization of flow sensors and to derive other properties of a fluid.

Abstract: An apparatus to normalize a flow rate of a fluid in a main flow channel is provided. The apparatus uses a moveable member, such as a flexible membrane disposed for reciprocating displacement, to produce a constant dither flow of the fluid that is independent of fluid composition. This dither flow generates a signal output from a normalizing flow sensor that both represents a characteristic property of the fluid and a flow rate calibration factor. A similar apparatus to determine the characteristic property or flow rate calibration factor is also provided. The devices disclosed may be used in numerous industrial, process, and medical flow system applications for normalization of flow sensors and to derive other properties of a fluid.

Abstract: An apparatus to normalize a flow rate of a fluid in a main flow channel is provided. The apparatus uses a moveable member, such as a flexible membrane disposed for reciprocating displacement, to produce a constant dither flow of the fluid that is independent of fluid composition. This dither flow generates a signal output from a normalizing flow sensor that both represents a characteristic property of the fluid and a flow rate calibration factor. A similar apparatus to determine the characteristic property or flow rate calibration factor is also provided. The devices disclosed may be used in numerous industrial, process, and medical flow system applications for normalization of flow sensors and to derive other properties of a fluid.

Abstract: A rugged microsensor assembly is disclosed that measures both the velocity and angular direction of an incoming air stream. The microsensor assembly includes at least two flow sensors, each orientated to measure a different velocity component of the incoming air stream. The velocity components are related by the geometry between the sensors, and the angular direction and velocity of the incoming air stream are determined by examining the measured velocity components. The preferred sensor is a fully passivated thermal differential microanemometer with back contacts, designed to operate in harsh environments.

Abstract: Signal processing methods are disclosed for processing Laser Doppler Velocimeter (LDV) signals. A true Doppler frequency is extracted from the phase noise frequencies by maintaining a highest frequency value. The highest frequency value is replaced with any measured frequency values that are higher than the current highest frequency value. This is continued for a predetermined lifetime period, after which the highest frequency value is stored and then reinitialized. The highest detected frequency values over a window of lifetimes are then averaged to provide a moving or rolling average value which is indicative of the velocity of a medium.

Abstract: An apparatus to normalize a flow rate of a fluid in a main flow channel is provided. The apparatus uses a moveable member, such as a flexible membrane disposed for reciprocating displacement, to produce a constant dither flow of the fluid that is independent of fluid composition. This dither flow generates a signal output from a normalizing flow sensor that both represents a characteristic property of the fluid and a flow rate calibration factor. A similar apparatus to determine the characteristic property or flow rate calibration factor is also provided. The devices disclosed may be used in numerous industrial, process, and medical flow system applications for normalization of flow sensors and to derive other properties of a fluid.

Abstract: An apparatus to normalize a flow rate of a fluid in a main flow channel is provided. The apparatus uses a moveable member, such as a flexible membrane disposed for reciprocating displacement, to produce a constant dither flow of the fluid that is independent of fluid composition. This dither flow generates a signal output from a normalizing flow sensor that both represents a characteristic property of the fluid and a flow rate calibration factor. A similar apparatus to determine the characteristic property or flow rate calibration factor is also provided. The devices disclosed may be used in numerous industrial, process, and medical flow system applications for normalization of flow sensors and to derive other properties of a fluid.

Abstract: A method and apparatus for measuring the velocity of a fluid relatively independently of the physical properties of the fluid. This is preferably accomplished by spacing two sensor elements at different distances from a heater element. The present invention also contemplates minimizing the effects of the non-zero heater time lag and/or the non-zero sensor time lag for increased accuracy. This is preferably accomplished by either measuring the time lags and subtracting the values thereof from an uncorrected transit time measurement, forcing the sensor elements to track the thermal disturbance in the fluid thereby minimizing the effects of the sensor time lags, or measuring the transit time using sensors that have substantially zero thermal mass.

Abstract: A method and apparatus for determining selected fluid properties using a self-oscillating fluid sensor. In a preferred embodiment, a sensor is provided that oscillates at a frequency that is related to the transit time of a temperature disturbance through the fluid. Based on the transit time, selected fluid properties of the fluid can be determined.

Abstract: A viscometer having a fluid volume-displacer or driver, such as a speaker membrane, and a pressure sensor or detector, such as a microphone membrane, forming the inside surfaces of a cavity that is sealed from the ambient environment of the viscometer except for a controlled leak such as a capillary tube. An electrical signal from the sensor or detector is processed to indicate viscosity of the fluid in the cavity. Additionally determined from the viscosity are heating value, oxygen demand and other thermophysical properties of the fluid. Also, absolute pressure is derived after viscosity is determined.

Abstract: A method and apparatus for using a common frequency generator for measuring selected properties of a fluid of interest via one or more heater and/or sensor elements. The common frequency generator may sequentially and/or simultaneously provide input signals to selected heater and/or sensor elements. Application of more than one frequency component by the common frequency generator enables the determination of one or more time and/or phase lags more efficiently, especially when using an FFT analysis technique. From the time and/or phase lags, the selected fluid properties including fluid flow speed can be determined.

Abstract: A method and apparatus for determining selected fluid properties including thermal conductivity, pressure and/or temperature using a single heater element of the sensor, and in a relatively short period of time. This is accomplished by measuring a variable phase or time lag between an input signal provided to the heater element and a subsequent transient temperature response of the heater element.

Abstract: A method and apparatus for providing a more direct approach to determine the thermal conductivity, thermal diffusivity and specific heat of a fluid of interest, independently of the amplitude of the sensor output. This is preferably accomplished by measuring one or more variable phase or time lags between selected input and output AC signals, and directly deriving the thermal conductivity, thermal diffusivity and specific heat therefrom. Such derivation is therefore less dependent than amplitude-based sensors on occasional or unpredictable drift in sensor resistive elements.

Abstract: A low-cost portable handheld still-frame thermal camera for capture of calibrated digital thermographic infrared images having a lens assembly, a slideable linear array of uncooled 8-12 um thermal IR sensors, a slider actuation mechanism, and associated digital processing capability for calibrating, displaying, and storing images captured by the camera. The sensors are preferably thermoelectric sensors. The lens passes infrared radiation, the array is contained in an evacuated chamber, and operates at room temperature. The thermographic images may be displayed immediately or remotely or may be printed by conventional techniques.

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 plurality of fluid condition sensors are combined together to provide a sensor cluster that senses turbidity, temperature, conductivity and the movement of a ferromagnetic object. The plurality of sensors are attached to a substrate and encapsulated, by an overmolding process, with a light transmissive and fluid impermeable material. The sensor cluster can be disposed at numerous different locations within a body of fluid and does not require a conduit to direct the fluid to a particular location proximate the sensor. In a preferred embodiment of the present invention, a circuit is provided which monitors the signal strength of first and second light sensitive components to determine turbidity and, in addition, those signal strengths are also used to advantageously determine the most efficient magnitude of current necessary to drive a light source, such as a light emitting diode.

Abstract: A turbidity sensor is provided with a light source and a plurality of light sensitive components which are disposed proximate a conduit to measure the light intensity directly across the conduit from the light source and at an angle therefrom. The conduit is provided with a plurality of protrusions extending radially inward from the walls of the conduit to discourage the passage of air bubbles through the light beam of the sensor. The direct light beam and scattered light are compared to form a relationship that is indicative of the turbidity of the liquid passing through the conduit. The rate of change of turbidity is provided as a monitored variable.

Abstract: A method for correcting the flow measurement of a gaseous or liquid fluid of interest for changes in the composition and temperature of that fluid in a flowmeter of the hot element type is disclosed in which an uncorrected flow value signal for the fluid of interest in relation to a hot element sensor output is corrected by applying a first correction factor to the output based on certain unique physical parameters of the fluid of interest which nominally include thermal conductivity, k, specific heat, c.sub.p, and temperature, T, obtaining an uncorrected flow measurement value from the corrected output and obtaining the corrected flow measurement by applying a second correction factor to the uncorrected flow measurement value based on the certain unique physical parameters.