Abstract: An ultrasonic measurement method in an ultrasonic measurement system having an ultrasonic transducer includes emitting an ultrasonic pulse from the ultrasonic transducer. An ultrasonic pulse is received in accordance with a pulse travel time wherein the amplitude of the received ultrasonic pulse varies according to the pulse travel time. A first electrical signal is provided representative of the received ultrasonic pulse wherein the amplitude of the first electrical signal varies in accordance with the pulse travel time. A second electrical signal is provided in accordance with the first electrical signal wherein the amplitude of the second electrical signal is substantially independent of the pulse travel time. In order to determine the second electrical signal variable amplification is applied to the first electrical signal in accordance with the travel time.

Abstract: For monitoring a predetermined level of a liquid in a container an ultrasonic transducer is fitted on the outer surface of the container wall at a measurement point situated at the height of the level to be monitored. The ultrasonic transducer when excited by an alternating voltage pulse having a given transmission frequency which equals the thickness resonant frequency of the container wall, transfers an ultrasonic transmission pulse to the container wall and converts ultrasonic vibrations, generated by reflected echo pulses, into electrical reception signals that are transferred to an evaluation circuit. In the evaluation circuit, on the one hand the presence or absence of echo signals is detected, and, on the other, the ultrasonic vibrations generated by the after-vibration of the container wall at the end of the transmission pulse are evaluated.

Abstract: The determining and/or monitoring of a predetermined level of material in a container is implemented with the help of a level sensor having a mechanical oscillatory structure, an electromechanical excitation transducer and an electromechanical reception transducer. The reception transducer is connected to the input of an amplifier circuit, to the output of which the excitation transducer is connected, so that the mechanical oscillatory structure is excited to oscillate at its self-resonant frequency. The mechanical oscillatory structure is mounted at the height of the predetermined level of material in such a way that it comes into contact with this material when said material reaches the predetermined level, which causes the self-resonant frequency to change. The change in the self-resonant frequency is detected by an evaluation circuit connected to the output of the amplifier circuit.

Abstract: A small, compact, easily mountable ultrasonic transducer for measuring the filling level in a container is provided, which transducer transmits virtually no oscillation energy to the container, having a can-shaped transducer housing (1), an electronics housing (2) connected to the transducer housing (1), a transducer element (4), arranged in the transducer housing (1), for the transmission and reception of ultrasonic pulses, a union ring (3) for the sound-decoupling securing of the ultrasonic transducer on the container, in which ring the transducer housing (1) is supported coaxially with respect to the union ring (3) and is fixed therein against displacement in the axial direction, and two resilient elements (7, 8) which are arranged between the transducer housing (1) and the union ring (3) and by means of which the transducer housing (1) and the union ring (3) are held spaced apart from each other in the radial direction in such a way that there is no direct mechanical coupling between them in the radial di

Abstract: A local buffer circuit for use with a magnetostrictive transducer is disclosed wherein the magnetostrictive transducer includes a pickup coil and the local buffer circuit includes two diodes in parallel with the pickup coil to clip or short the energy produced in the pickup coil generated by an interrogation pulse, and also includes a common emitter amplifier to reduce the electrical impedance of the pickup coil, also in parallel with the pickup coil.

Abstract: An ultrasonic sensor for detecting the presence of a liquid having an elongated body of plastic material with spaced arms at one end defining an air gap between the arms with each arm having a piezoelectric element at its inner face. The body houses a circuit board on which components of an ultrasonic sensing circuit that reacts to produce a signal when liquid is present in the air gap. The body is small in dimensions and is flat making it easy to install into restricted space applications.

Abstract: A method of detecting the displacement of a target in a given environment includes storing reference data having data representative of the environment; transmitting a transmit signal towards the target; sensing the return signals from the target and the environment; and detecting the displacement of the target by comparing the return signals and the stored reference data. A method of detecting the level of a sample in a container is also disclosed. Analogous apparatus features are also disclosed.

Abstract: For monitoring a predetermined level of a liquid in a container an ultrasonic transducer is fitted on the outer surface of the container wall at a measurement point situated at the height of the level to be monitored. The ultrasonic transducer contains a piezoelectric element which generates, when excited by an alternating voltage pulse having a given transmission frequency, an ultrasonic transmission pulse which is transferred via a diaphragm to the container wall and which converts ultrasonic vibrations transferred from the container wall to the ultrasonic transducer into electrical reception signals. The diaphragm comprises on the side facing the container wall protuberances which adjoin the container wall. Between the diaphragm and the container wall a coupling layer is arranged, the thickness of which is determined by the height of the protuberances.

Abstract: An acoustic method is disclosed for measuring fluid level in producing wells and other inaccessible cavities. The method uses flow induced pressure phenomena to locate the fluid level. Simplified equipment is involved and acoustic velocities can be measured externally from the well. The method applies to known uses for fluid levels such as well productivity, lift equipment design, and reservoir studies.

Abstract: The device for determining and/or monitoring a predetermined level of contents in a container comprises a sensor, which is so mounted on the container at the level of contents to be monitored that it comes into contact with the contents of the container when the same reach the predetermined level. The sensor is excited to mechanical vibrations at its natural resonant frequency by an exciting arrangement. An evaluating circuit serves for causing indicating and/or switching operations in a manner dependent on whether the frequency of the mechanical vibrations of the sensor is higher or lower than a switching frequency. Associated with the sensor is an electrical circuit element which has a characteristic parameter, whose value bears an unambiguous relationship to the natural resonant frequency of the sensor. In the evaluating circuit the switching frequency is set in accordance with the value of the characteristic parameter of the electrical circuit element.

Abstract: An improved housing assembly is used for a microwave level sensing instrument for sensing level of a process fluid in a vessel. The process vessel includes a vessel flange defining an opening into a storage space in the vessel. The housing assembly includes a flange assembly including a housing flange having a distal gasket face sealingly mateable with the vessel flange in use. The housing flange is connected to a window housing for housing a window spaced from the gasket face and providing a process seal. An electronics housing is mounted to the window housing. The electronics housing supports a microwave antenna proximate the window for focusing energy through the window to the process fluid.

Abstract: The level of a liquid is detected by an ultrasonic arrangement comprising a transmitter and a receiver. The transmitter has a vertical array of transmitter segments which transmit sequentially, while the receiver is a single transducer. The transmitter and receiver are formed as a single assembly operating in pulse echo mode in conjunction with a passive reflector. The difference in transmission time in liquid and gas allows a digital, depth representative output to be generated. The transmitter is formed by securing a single sheet of piezo polymer film over a printed circuit board having a conductive pattern defining the segments.

Abstract: A level measuring system for leveling structures using the principal that water seeks its own level. A plurality of sensor vessels each of which includes ultrasonic transducers for measuring the level of a liquid in the vessel. A liquid source provides liquid to the sensors and a vacuum pump withdraws the liquid after measurements are complete. Each sensor vessel includes two ultrasonic transducers, one of which measures the sonic velocity and the other measures the level of the liquid. A calibration device is provided to verify calibration of the level measuring sensor. In one embodiment, the two ultrasonic sensors are arranged vertically in a transparent cylindrical housing. In a second embodiment, a first horizontal bore and a second intersecting vertical bore are provided in a solid material, with the sonic velocity measuring sensor at one end of the horizontal bore and the level measuring sensor in the vertical bore.

Abstract: A flexible bar connected to an actuator is suspended within an ink reservoir. The bar is preferably mounted in a cantilever or free-standing mode and vibrates in response to signals from the actuator. When the actuator signals are discontinued the bar continues to vibrate and causes the actuator to generate signals that are analyzed to determine the level of ink in the reservoir.

Abstract: A magnetostrictive waveguide type position measuring system wherein the wire waveguide is mounted within a small diameter brass tube which, in turn, is mounted by way of resilient suspension components within a rigid outer tube affixed to a position reference frame. The resilient components isolate the waveguide from relatively high frequency shock inputs characteristic of rough environment applications. The waveguide is made of rolled and drawn wire with a round section, but the terminal ends are gradually reconfigured from round to flat, rectangular sections and are sandwiched between acoustic dampening pads to reduce or eliminate sonic reflections.

Abstract: An externally mounted transducer assembly for an ultrasonic liquid level measuring device that utilizes a piezoelectric crystal for generating ultrasonic pulses to be transmitted through a tank or the line containing a volume of liquid. Electrical conductors are formed integrally with the fuel tank for connecting the transducer to other components of the system. The wall of the tank is provided with an arrangement for removably attaching the transducer housing thereto. The tank is provided with electrical contacts that connect to the conductors that are integral with the tank. Also, electrical contacts in the transducer housing are connected to the transducer for providing current thereto. When the transducer housing is attached to the tank, the transducer is thereby connected to the measuring system circuit.

Abstract: An ultrasonic fuel gauging system has several ultrasonic transducers mounted on the bottom of a tank, the transducers being unconstrained by any tube or still well so that they each propagate diverging energy upwardly to the fuel surface. Each transducer receives a reflection of its own propagated energy from a region of the fuel surface directly above and also receives energy from others of the transducers reflected from regions of the fuel surface between those directly above the transducers. Using three transducers, the heights of six different regions of the fuel surface can be computed.

Abstract: This ultrasonic transducer has a high chemical resistance and a small diameter and can be used over a very wide temperature range. It has a single-piece, can-shaped housing (1) sealed off by a diaphragm (12), a sensor element (2), arranged in the housing (1), for transmitting and receiving ultrasound, a matching layer (3) arranged between the diaphragm (12) and the sensor element (2), a stress equalizing layer (5) which completely encloses the sensor element (2) apart from a front area adjoining the matching layer (3) and is made of a thermosetting plastic, especially of an epoxy resin, a clamping ring (4) coaxially enclosing the matching layer (3), and a damping layer (6) that fills a cavity that remains in the housing (1) and is bounded by the clamping ring (4), the stress equalizing layer (5) and the housing (1).

Abstract: The liquid level sensor comprises a graduated tape or cable whose free end is fixed to a plunger core that includes a housing and a probe for detecting the presence of a liquid. The probe comprises a metal waveguide having a cylindrical solid top portion, a portion of smaller section constituting a mechanical amplifier, a frustoconical portion, and a cylindrical bottom end portion constituting the sensitive portion of the probe. The metal waveguide is connected to the housing of the plunger core in sealed manner via a support flange which is fixed to the conical portion of the metal waveguide in such a manner that only the portion of the waveguide situated beneath the fixing zone emerges from the housing and can come into contact with a liquid. A transducer electrically powered by electronic processing circuits is disposed at the free end of the top portion and is excited at a predetermined frequency f.sub.i to create incident elastic waves in the waveguide.

Abstract: A method and apparatus (10) for sensing a surface level (24) of fluid (12) in a tank (14) having an electrically conducting pickup tube (20) extending through a wall (16) of the tank (14) and into the fluid (12) includes a time domain reflectometry circuit (40) connected to the tube (20) for generating an incident pulse (68) that travels down the tube (20) and a portion of which is reflected at the surface (24) as a reflected pulse (70,72) which travels back along the tube (20) and is sensed by the circuit (40). The circuit (40) includes a microprocessor (92) which utilizes the elapsed time between the generation of the incident pulse (68) and the receipt of the reflected pulse to determine the position of the surface (24) relative to a reference point and the amount of the fluid (12) in the tank (14) and indicate the amount of fluid at a display (106). The tube (20) forms a transmission line with one of a plate (48), an outer tube (110) and a return tube (130).

Abstract: Apparatus for indicating material level that includes a pair of ultrasonic transducers on opposed sides of a space for receiving the material at the level to be detected. A swept frequency oscillator is coupled to one of the transducers so that the transducer radiates into the material space ultrasonic energy that continuously sweeps back and forth between a low frequency range at which such energy is transmitted to the other transducer by resonance of the entire apparatus and independent of presence of material in the material space, and a higher frequency range at which such energy is transmitted to the other transducer only when material is present in the space between the transducers. Detection circuitry indicates presence of material between the transducers upon receipt of the higher frequency energy, and failure of the apparatus upon failure to receive the lower frequency energy.

Abstract: The determination and/or monitoring of a predetermined material level in a container is effected with the help of a material level sensor which contains a mechanical oscillatory structure, an electromechanical excitation transducer and two electromechanical reception transducers. The mechanical oscillatory structure is secured at the height of the predetermined material level in such a way that it comes into contact with the material when said material reaches the predetermined material level. Each reception transducer is connected to the input of an assigned circuit channel, which contains an amplifier circuit, the output of which is connected to the excitation transducer and which is so constructed that the mechanical oscillatory structure is excited to produce oscillations with its natural resonance frequency. The two circuit channels are activated alternately by means of a control circuit.

Abstract: In devices for determining and/or monitoring a predetermined level with a sensor that is excited to perform mechanical oscillations at its self-resonant frequency by means of an electronic excitation circuit which is excited via a piezoelectric excitation and a reception transducer and an evaluation circuit for triggering display and/or switching processes, there exists the difficulty that the natural frequencies of the sensors are different due to the manufacturing conditions, and that the operating frequency must be adjusted individually for each sensor. This disadvantage makes repair and maintenance procedures quite difficult.

Abstract: A liquid level monitoring system for underground storage tanks includes a submersible monitoring pipe system having telescoping sections that are biased to an extended position enabling the pipe to be self-retained within the tank between its upper and lower walls adjacent to and offset axially from a selected access opening in the tank, such as the discharge opening which normally accommodates the pump for the tank. The pipe system houses an electronic level sensor which is coupled to an above ground control system via conductor wires. An elongate accessing member having an openable and closable clamp jaw assembly for gripping the pipe system and disposing it in a compressed condition within the tank offset from the riser opening is provided as a part of the system.

Abstract: A device for gauging the level of a fluid in a container includes a floating roof, a transmitter for feeding a first microwave signal downwards in the direction of a fluid surface of the fluid, and a receiver for receiving a reflected microwave signal. The device includes a collector located above and in the vicinity of the floating roof, collecting the first microwave signal producing a collected microwave signal. The device also includes a vertical wave guide passing through the floating roof. The vertical wave guide guides the collected microwave signal to the fluid surface, and receives a reflected microwave signal reflected from the fluid surface. The vertical wave guide then guides the reflected microwave signal back to the collector and further to the receiver. It is a special feature to permit accurate measurement of the level of the fluid surface without having direct access to the surface.

Abstract: A microwave point level instrument is adapted to detect level or change of products in a storage vessel. The instrument includes a microwave transducer periodically developing a pulse of microwave energy. A microwave bridge is driven by the transducer for receiving pulses of microwave energy. The bridge includes a reference arm receiving a portion of each pulse of microwave energy to be altered by a variable impedance tuning circuit. A measurement arm receives another portion of each pulse of microwave energy to be altered by dielectric properties of a product at a process seal installed in a storage vessel, in use. A detector arm develops a microwave signal responsive to imbalance in the bridge between the microwave energy altered by the tuning circuit and the microwave energy altered by the dielectric properties of the product. A sensing circuit is coupled to the bridge detector arm for developing an electrical signal responsive to the microwave signal representing the imbalance.

Abstract: The present electronic multi-purpose material level sensor is based on time domain reflectometry (TDR) of very short electrical pulses. Pulses are propagated along a transmission line that is partially immersed in a liquid, powder, or other substance such as grain in a silo. The time difference of the reflections at the start of the transmission line and the air/liquid interface are used to determine levels to better than 0.01 inch. The sensor is essentially independent of circuit element and temperature variations, and can be mass produced at an extremely low price. The transmission line may be a Goubau line, microstrip, coaxial cable, twin lead, CPS or CPW, and may typically be a strip placed along the inside wall of a tank. The reflected pulses also contain information about strata within the liquid such as sludge-build-up at the bottom of an oil tank.

Abstract: The High Accuracy Electronic Material Level Sensor (electronic dipstick) is a sensor based on time domain reflectometry (TDR) of very short electrical pulses. Pulses are propagated along a transmission line or guide wire that is partially immersed in the material being measured; a launcher plate is positioned at the beginning of the guide wire. Reflected pulses are produced at the material interface due to the change in dielectric constant. The time difference of the reflections at the launcher plate and at the material interface are used to determine the material level.

Abstract: An ultrasonic inspection technique using a specially designed electromagnetic acoustic transducer (EMAT) launches and receives longitudinal ultrasonic waves into a thin metal wall or thin metal foil seal of a container, causing it to vibrate and launch ultrasonic compressional waves into liquid contained therein. The contents of plastic containers having a metal foil seal forming one wall are easily inspected. The EMAT establishes a magnetic field in the surface of the metal parallel to the surface. Radio frequency (RF) eddy currents are also induced by the EMAT in the surface of the metal. A Lorentz force is generated in the metal surface according the vector product of J, the current density, and H, the magnetic field, and the force generated by the interaction of the perpendicular components of the magnetic field H and the eddy currents J is directed normally to the surface of the metal.

Abstract: A carrier frequency based system employs a capacitive probe which is located at a predetermined desired fluid detection level in a fluid containing vessel. The probe forms one plate of a capacitor where the other plate is formed by the fluid in which the probe is immersed. A carrier frequency is injected into the fluid by means of a suitable oscillator and at a frequency which is close to the system resonant frequency. When the probe is immersed in fluid, the probe will receive a predetermined carrier frequency of an amplitude determined by the system. The output of the probe is coupled to suitable sensing circuits which monitor the amplitude of the signal frequency coupled to the probe. When the fluid level recedes and therefore a portion of the probe or the total probe is out of fluid, the capacitance of the system changes.

Abstract: A liquid level monitoring system for underground storage tanks includes a submersible monitoring pipe having telescoping sections that are spring biased to an extended position enabling the pipe to be self-mounted within the tank between its upper and lower walls adjacent to and offset axially from a selected axis opening in the tank, such as the discharge opening which normally accommodates the pump for the tank. The pipe houses an electronic level sensor which is coupled to an above ground control system via conductor wires. A tank adapter is secured to the tank opening and provided with a passage through which the conductor wires extend for routing out of the tank without interfering with the clearance normally provided for insertion and removal of the pump.

Abstract: A circuit for use with an ultrasonic transducer utilized to measure depths of liquids in tanks is described.

Abstract: A container having affixed thereto an ultrasonic transducer, including a connection for electrically linking the transducer to electronic circuitry located outside the container. Flexible and semi-rigid containers having rigid structures surrounding the signal path of an ultrasonic transducer are also provided. In addition, adaptors are disclosed for use in connecting an ultrasonic transducer to a container. Such adaptors can include a rigid tubular member, a tubular outlet connected to the tubular member for draining liquid from a container, and a seat for engaging an ultrasonic transducer.

Abstract: A piezoelectric liquid level switch is provided which can be made immune to standing wave effects and provides an unequivocal response to liquid contact.

Abstract: An ultrasonic probe utilized in an ultrasonic ranging system for determining fluid volume and/or fluid leakage in an underground storage tank, as well as monitoring fluid inventory, is provided which is characterized by (i) having its calibration reflectors positioned whereby each of the secondary echo packets formed by the calibration reflectors of the ultrasonic probe becomes imbedded into the trailing edge of a primary echo packet of another calibration reflector or to cause its secondary echo packet to be detected by the transducer after the transducer has detected a primary echo packet associated with the fluid surface, (ii) each of the calibration reflectors being positioned perpendicular to and offset from the longitudinal axis of the probe body, (iii) an ultrasonic sound wave dampening member fixedly positioned in the probe body between the transducer assembly and the tank bottom, the wave dampening member having a surface facing toward the transducer assembly wherein the surface is configured to damp

Abstract: A magnetostrictive liquid level probe in a double-walled liquid container develops liquid level data and external sensors in the space between the walls respond to the presence of liquid leaked into the space from inside or outside the container. Other sensors external of the liquid level probe may sense other conditions. The probe electronics determines binary states of the external sensors and digitally encodes the states for inclusion in data transmission of the liquid level information to a remote controller via a two-wire transmission line. One embodiment develops pulses spaced as a digital function of the sensor states and includes liquid level data between the pulses for transmission. The pulse space is measured at the remote controller and decoded to determine the external sensor states, while the liquid level data is analyzed to determine the contents of the container.

Abstract: A volumetric measurement apparatus is provided which measures the volume of a liquid material stored within a container. The volumetric measurement apparatus includes a reference enclosure having disposed therein a single pressure sensor. The pressure sensor has a pressure sensitive element exposed to both internal spaces of the reference enclosure and the container to detect a pressure difference between the container and the reference enclosure. A sensor shielding member is arranged in the reference enclosure to selectively shield the pressure sensitive element from the internal space of the reference enclosure to detect only a pressure within the container. The volumetric measurement is made based on the pressure difference between the container and the reference enclosure and the pressure in the container.

Abstract: A fill level indicating device of the rod-in-tube type has a pair of propping struts gusseting the vibratory tube to the membrane and to the membrane support. One strut is arranged above the vibratory tube and the other below, with both struts aligned in a common plane which is vertical when the device is installed in a container. The vibration excitation and detection systems are arranged on the membrane at 90.degree. to the plane of the struts, so that with the device installed in a container the direction of vibration is horizontal. The membrane is made with thickened portions extending through its middle in the direction of vibration. Material may be removed from the thickened portions by grinding or filing to tune the device to the desired resonant frequency.

Abstract: A non-intrusive mounting system and method for coupling microwave instruments to a container flange having an opening into a container. The mounting system includes a microwave transparent window and a mounting flange having a window recess for accommodating the microwave transparent window. The microwave transparent window is compressively fastened over the container opening between the mounting flange and the container flange. Microwave instruments such as radar level sensing apparatus can be mounted on and removed from the mounting flange without breaking the seal to the container.

Abstract: The ultrasonic transmitter (E) is subjected to two different excitation modes, and is mounted on the support (2) which at the same constitutes a waveguide.Excitation of the transmitter at its axial-resonance frequency transmits ultrasonic waves through the liquid to provide a detection signal. Its excitation at its radial-resonance frequency creates ultrasonic waves propagated along the support (2) to provide an operation-control signal.The invention is applicable to the detection of various liquids in a broad range of conditions and is suitable for industrial applications, notably in safety and control systems.

Abstract: An acoustic liquid level detector system includes, a) a first acoustic wave guide; b) an acoustic wave transmitter and an acoustic wave receiver operably associated with the first acoustic wave guide to transfer acoustic waves between, i) the acoustic transmitter and receiver; and ii) the first acoustic wave guide; c) a second acoustic wave guide; d) an angled juncture interconnecting the first acoustic wave guide to the second acoustic wave guide; e) a primary acoustic reflector provided in the angled juncture to angularly reflect acoustic waves between the first and second acoustic wave guides; and f) a secondary acoustic reflector positioned to directly reflect an acoustic wave emanating from the acoustic wave transmitter to the acoustic wave receiver. The second acoustic wave guide is provided with a plurality of longitudinally spaced orifices to facilitate ingress of liquid and flow of a cleaning purge gas outwardly of the second acoustic wave guide.

Abstract: A method and apparatus for detecting fluid level in a tank in the vicinity of a transmission line (1), the fluid level being such as to cause reflection of a signal transmitted along the transmission line. The method includes the steps of:a) transmitting a signal along the transmission line;b) monitoring the transmission line for any reflections of the signal;c) generating an analysis window of time (t.sub.1, t.sub.2, t.sub.3) if the magnitude of a given characteristic of the reflected signal is greater than a predetermined threshold value; andd) analyzing the reflected signal received during the period of an analysis window to provide the required information on the fluid level.

Abstract: A baffle assembly for use in an ultrasonic system for measuring the level of a contained volume of liquid by calculating the density of the liquid by determining the dielectric constant thereof. The baffle assembly is located at the lower end of a stillwell located within the volume of liquid, The assembly includes a pair of concentric sleeves formed of electrically conductive material located to surround the lower end portion of the stillwell. The sleeves are uniformly radially spaced from one another so as to function as a capacitor so that the electrical capacitance between the respective opposed surfaces of the sleeves may be determined.

Abstract: A sensing system detects elastic waves propagated along a sensing path in a sheet to detect a characteristic of material contacting the other side of the sheet. An acoustic load applied between transducers discriminates characteristics in diverse environments. Different systems detect density, stiffness, presence, degree of coupling, thickness, or fill height of the material, with applications to areas as diverse as aircraft wing ice measurement, storage tank fill height detection, and mass flow detection. In one preferred embodiment a protective housing covers and protects the first side of the sheet over a region of the sheet encompassing the sensing path, and may secure transducers in defined positions. The housing preferably defines a closed reservoir that is temporarily filled to determine a normative measurement such as transit time or change in phase velocity.

Abstract: An ultrasonic level instrument detects the presence of a fluid at a defined location and provides a self-diagnostic integrity check. An excitation circuit simultaneously induces vibrations at a first and second frequency in a transmitting piezoelectric crystal, and the vibrations are detected by a receiving crystal. A first and second filter circuit generate first and second filter outputs, respectively, by selectively passing the receiving crystal output at the first and second frequencies, respectively. The first filter output is indicative of the presence of fluid and the second filter output is indicative of the sensor integrity.

Abstract: A noninvasive ultrasonic liquid level indicator for indicating the level of a liquid in a reservoir is disclosed which comprises an ultrasonic transducer assembly, structures for holding the transducer assembly in a dry coupled attachment with the reservoir at selectable locations against an exterior surface of the reservoir, and a monitor for revealing a change in liquid height. The transducer assembly conveys signals regarding changes in liquid height to a monitor which warns the user in time to add more liquid or replace the reservoir before the liquid supply "runs dry." The manners for holding the assembly in place include, but are not limited to, a strap, a clamp, or adhesive material, such as tape. These allow the user to selectively place the transducer assembly along the reservoir at the desired triggering point.

Abstract: A process for measuring the level of a liquid in a tank according to the radar principle, in which microwave energy is transmitted in the direction of the liquid level and the bottom of the tank from an antenna located above the liquid level, a measuring signal reflected from the liquid level is received by an antenna, and the liquid level may be determined from the transit time of the measuring signal, other signals than the measuring signals, i.e.

Abstract: An ultrasonic transducer for measuring a property of a material within a defined space has a function of a velocity at which ultrasonic signals travel through the defined space includes a controller. The controller is adapted for coupling to a plurality of ultrasonic transducers. The controller include a multiplexer for selecting one of the plurality of ultrasonic transducers, signal processing means for processing an output of the selected ultrasonic transducer and controller means for providing parameters to the signal processing means based upon the selected ultrasonic transducer. The controller couples to a two wire 4-20 mA communication loop. The controller periodically excites the ultrasonic transducer to obtain a measurement. The controller stores power received from the two wire communication loop and excites the transducer using stored power. The controller is capable of providing power which exceeds that available directly from the two wire communication loop for a brief period of time.

Abstract: An ultrasonic liquid level sensor includes an ultrasonic coupling element for use in self testing. The sensor includes a gap and a pair of transducers spaced apart by the gap. The sensor senses presence of liquid in the gap. The ultrasonic coupling element extends between the transducers and acoustically couples them together. The coupling element is used to test ultrasonic sensor integrity.

Abstract: The disclosure is directed to a Lever oscillator for use in high resistance resonator applications, especially for use with quartz resonator sensors. The oscillator is designed to operate over a wide dynamic range of resonator resistance due to damping of the resonator in mediums such as liquids. An oscillator design is presented that allows both frequency and loss (R.sub.m) of the resonator to be determined over a wide dynamic range of resonator loss. The Lever oscillator uses negative feedback in a differential amplifier configuration to actively and variably divide (or leverage) the resonator impedance such that the oscillator can maintain the phase and gain of the loop over a wide range of resonator resistance.