An apparatus for measuring air flow in a duct includes a sensor fittable into connection with the duct. The sensor includes an ultrasound transmitter, at least two ultrasound receivers, and a control unit to which the ultrasound transmitter and ultrasound receivers are connectable. The apparatus further includes means for measuring temperature. In a method, with the apparatus, the temperature of the air and/or of a sensor in a duct is measured with means for measuring temperature. A sensor calibration measurement at the temperature in question is performed with the apparatus if a calibration of the sensor at the measured temperature and/or within a certain predefined temperature range has not been performed earlier from the environs of the measured temperature, and temperature compensation data for the measurement result of air flow, the data being formed on the basis of calibration measurement, is determined and/or recorded in memory with the apparatus.

A method of ultrasonic clamp-on flow measurement according to the transit time difference method and apparatus for the implementation of the method, wherein the electromechanical transducer element of at least one of the two acoustic transducers is comprised of at least two array elements and a correction factor is determined by comparing the transit times between the acoustic transducers while using different array elements.

There are provided piezoelectric element, case having conductivity, first acoustic matching layer bonded on case, and second acoustic matching layer stacked on and bonded to first acoustic matching layer. A joining part between first acoustic matching layer and second acoustic matching layer is located inside an outer periphery of a joining surface of first acoustic matching layer that is joined to second acoustic matching layer. This configuration can prevent indirect wave generated in first acoustic matching layer from propagating to second acoustic matching layer, and can therefore reduce reverberation of an ultrasonic wave.

A method for calibrating a temperature measuring unit based on ultrasound measurement includes: establishing an empirical functional relationship between the medium temperature of a medium to be measured and the velocity of sound of a measurement signal passing through the medium to be measured; capturing at least the velocity of sound of the measurement signal, the temperature measured by means of a temperature sensor, and the time variation of the sensor temperature at at least two measuring points, wherein the at least two measuring points have a different medium temperature; determining the medium temperature from the measured temperature, taking into account the time variation of the sensor temperature, so that at least two pairs of values and exist; running a compensating curve through the pairs of values which corresponds to the empirical functional relationship; and storing the functional relationship.

A method for measuring a speed of a fluid includes transmitting an ultrasonic measurement signal; acquiring and digitizing a measurement portion of an ultrasonic measurement signal received after traveling a defined length to obtain measurement samples; estimate, from the samples, an amplitude of the measurement portion; access reference samples forming a reference curve which is an interpolation of the measurement samples; produce adjusted measurement samples by multiplying the samples by ratio between an amplitude of the reference curve and the amplitude of the measurement portion; determine a unit time delay between the adjusted measurement sample and the reference curve; estimate a zero-crossing time of the measurement portion from the unit time delay and from the reference samples, estimate, from an average of the zero-crossing times, the time it takes the ultrasonic measurement signal to travel the defined length; estimate the speed of the fluid from the travel time measurement.

A method and system for measuring a time of flight can involve correlating a signal comprising a reflected signal from a first transducer to a second transducer, or a subsequent reflected signal at the first transducer or the second transducer, with a previously received signal to produce a correlation for a measurement of a time of flight. The signal(s) can include one or more of a pulse train, acoustic sound; ultrasonic sound; or light, and the previously received signal can be a signal that has been reflected one or more times.

Methods and systems for flow measurement can involve calculating an absolute-time-of-flight with respect to a flow of a fluid in a flow channel by reflected signals, reflected and unreflected signals, or a pulse train, determining a delta-time-of-flight with a cross correlation of two signals with respect to the flow of the fluid in the flow channel, and calculating the flow rate of the flow of the fluid in the flow channel based on the absolute-time-of-flight and the cross correlation of the delta-time-of-flight.

A method for detecting fluid consumption that includes: detecting, by a fluid meter mounted on an exterior of a pipe containing fluid, a first time of flight between a first ultrasonic transducer and a second ultrasonic transducer; detecting, by the fluid meter, a second time of flight between the second ultrasonic transducer and the first ultrasonic transducer; determining a time of flight difference between the first time of flight and the second time of flight; determining a volumetric flow rate based on an environmental correction parameter and the time of flight difference; and generating a fluid volume consumption total for fluid flowing through the pipe based on the volumetric flow rate.

A fluid measuring device for determining at least one characteristic property of a fluid includes a measuring tube having a fluid duct and a measuring section in which an area of a measuring tube wall is configured as a waveguide for surface acoustic waves which forms an interface to the fluid. At least two piezoelectric transducers are arranged in direct contact with an outer surface of the waveguide and one of which serves as a transmitter for exciting acoustic waves and at least one as a receiver for receiving acoustic waves. Acoustic waves excited by the transmitter can propagate as a volume wave through the fluid, and the piezoelectric transducers are configured to be elastically flexible while retaining their function in that the piezoelectric transducers have strip-shaped piezoelectric elements arranged parallel to each other, are rigid per se and between which a respective layer of an elastic material is arranged.

A fluid measuring device for determining at least one characteristic property of a fluid includes a measuring tube having a fluid duct and a measuring section in which the measuring tube is cylindrical on the inside and an area of a measuring tube wall is configured as a waveguide, and a transmitter for exciting acoustic waves in the waveguide and a receiver for receiving acoustic waves which are in direct contact with an outer surface of the waveguide, wherein acoustic waves excited by the transmitter are adapted to propagate as a volume wave through the fluid. The waveguide has an elongated waveguide path which extends at an acute angle to a longitudinal extension direction of the measuring tube and with a component in the circumferential direction, wherein in the area of the waveguide path, the measuring tube wall has a smaller wall thickness than in areas adjoining the waveguide path.