Abstract: A triple authentication waste level monitoring system for an aircraft includes a point level sensor for monitoring a wastewater level within a waste tank, a load cell for measuring a weight of the waste tank, and a flush counter for counting a number of toilet flushes since a previous service to the waste tank. A controller receives data from these three sensors and determines whether the waste tank is at capacity. The controller can determine waste tank capacity whether or not the point level sensor is faulty and compares the sensor data with various thresholds to ensure accuracy of the waste tank fluid level determination.

Abstract: A sensor arrangement for measuring liquid height in a tank can include a housing, a transducer, and a couplant. The housing can have an interior and an aperture, the aperture placing the interior of the housing in communication with the environment external to the housing. The transducer can be seated within the aperture. The couplant can be mechanically connected to the transducer and can have a compressible couplant body. The couplant body can extend between the transducer and the external environment for transmitting an acoustic pulse from the transducer to a tank bottom for measuring height of a liquid overlaying the transducer.

Abstract: The system comprises a rainfall monitoring module, a self-calibration and rainfall measurement module, a central processing module, a water level monitoring module, and a drainage module. The rainfall monitoring module is configured to monitor rainfall and send a rainfall signal to the central processing module. The self-calibration and rainfall measurement module is configured to transmit ultrasonic signals and receive calibration echo signals to compute the calibrated flight time, and transmit ultrasonic signals to the water surface in the bucket and receive the measured echo signal reflected by the water surface to obtain the measured flight time under the control of the central processing module. The central processing module is configured to receive the rainfall signal to start the water level monitoring module and the self-calibration and rainfall measurement module, which are used to calculate the rainfall value and output it in a fixed format.

Abstract: A system for recognition and/or determination of the volume of bodies or substances made of dielectric and/or conductive material within an interior of a measuring cell in the form of a container, with a conductive and/or non-conductive measuring cell wall that has a surface directed into the interior, includes an ultra broadband microwave unit, and at least one ultra-broadband antenna having at least one disk-shaped carrier substrate which has a first surface facing a first side and a second surface which is opposed to the first surface and forms an outer side of the antenna, wherein the carrier substrate is arranged and intended to replace part of the surface of the measuring cell wall directed into the interior during operation, after fastening the ultra-broadband antenna to the measuring cell, or to extend in the interior at a distance in front of the measuring cell wall, wherein the ultra-broadband antenna includes emitter elements arranged on or in the carrier substrate is set up as an electrically shor

Abstract: A system and method for dispensing a beverage includes the detection of a presence of a cup underneath a nozzle, and in response to the detected presence of the cup, a target fill height is calculated. The controller operates to begin a dispense of a beverage into the cup. A beverage fill height determined and compared to a target fill height. When the beverage fill height exceeds the target fill height, the controller operates to stop dispensing the beverage into the cup.

Abstract: A system and method for measuring a sludge moisture content by ultrasound are provided, which relate to the technical field of sludge detection. The system includes: a measuring container, configured to load sludge; a pulse signal generator, configured to generate a pulse signal; a self-transmitting self-receiving (STSR) transducer, disposed on an outer wall of the measuring container, and configured to transmit a first ultrasonic signal into the measuring container under an excitation of the pulse signal and receive a second ultrasonic signal reflected from an inner wall of the measuring container; and an upper computer, configured to build a first mathematical model among a reflection coefficient, sludge acoustic impedance, and wall acoustic impedance of the measuring container, and build a second mathematical model between the sludge acoustic impedance and the sludge moisture content.

Abstract: An ultrasonic sensor detects a level of a fluid. A first probe has a first transducer element to transmit an ultrasonic signal through the first probe. A second probe of a helix shape has a second transducer element coiled around the first probe to receive the ultrasonic signal transmitted by the first probe through the fluid. A stabilizing rod and a plurality of stabilizing collets are disposed between the rod and the second probe parallel to both the first probe and the second probe.

Abstract: An apparatus which includes a mounting, a plurality of detectors provided to detect a condition of at least on parameter indicative of presence of one or more materials in a gutter channel and data processing capabilities. A sequence of signals are transmitted and received when the apparatus is in a detection mode, and the data processing analyses the received signals to provide an indication if a material is detected as being present in the channel and, if detected, a type of the material. On the basis of this analysis and identification of material, decision can be made as to whether any remedial action is required to clear the material and/or decide upon an ongoing monitoring and maintenance.

Abstract: This application describes a method, system, and apparatus for measuring the depth of a body of water ahead of the user's location or position. The user can be a driver of a vehicle. The apparatus includes a fording depth sensor, a second fording depth sensor, a proximity sensor to determine road angle or position ahead of the vehicle, wherein the proximity sensor is designed to operate underneath the water surface and a control unit configured to use signals of the wading depth and sensors to compute a wading depth at a location ahead of the direction of vehicle movement and/or to compute a distance ahead of the direction of vehicle movement to maximum wading depth. A method of building the apparatus, system, and vehicle is also provided.

Abstract: A bottle filling station may include a liquid dispenser configured to dispense liquid. A pan may be configured to collect at least a portion of the dispensed liquid. A sensor may detect a presence of a liquid container. A controller may control the liquid dispenser to dispense liquid when the liquid container is approximately near the sensor.

Abstract: The invention is based on speed changes of sound/ultrasound pulses and a fixed detecting depth between a transducer and sampling points to collect information of the detecting depth and/or a velocity of motionless and/or moving objects from the sampling points to construct two-dimension or three-dimension images of the sampling points. By taking advantages of a pulse ultrasound and a continuous ultrasound, a method of coded sound pulses can simultaneously collect the information of the detecting depth and the velocity from the sampling points, which improves imaging quality. Calculating a speed of the moving objects by simultaneously detecting time-of-flight (TOF) and TOF shift at same site from two separated piezoelectric (PZT) elements improves testing results with accuracy, simplification and reproducibility. An aliasing can be rectified based on the TOF and the TOF shift.

Abstract: The present disclosure relates to a method for determining fill level of a substance in a container using a measuring device working according to the travel time principle. The measuring device transmits signals to the fill substance and, based on signal fractions reflected back in the container, ascertains an echo curve. The echo curve is transmitted to a superordinate control unit, and an envelope curve enveloping the echo curve is created and transmitted to the superordinate control unit. The echo curve and envelope curve are evaluated by the superordinate control unit. A wanted echo signal of the echo curve and envelope curve is identified. During the determining of the fill level the fill substance and the container are subjected to a current process. Based on information concerning the current process, plausibility of the wanted echo signal is checked and the evaluation is dynamically adapted to the current process.

Abstract: A system and method for dispensing a beverage includes the detection of a presence of a cup underneath a nozzle, and in response to the detected presence of the cup, a target fill height is calculated. The controller operates to begin a dispense of a beverage into the cup. A beverage fill height determined and compared to a target fill height. When the beverage fill height exceeds the target fill height, the controller operates to stop dispensing the beverage into the cup.

Abstract: A filling element includes a radar for measuring fill level in a container during filling thereof and an antenna connected to the radar. The antenna is disposed along a flow path formed in a gas pipe that forms a flow path for fluid while the container is being filled. The antenna provides the radar with a signal indicative of a measurement of a level of the filing material in the container.

Abstract: Disclosed is a fill-level measuring device for determining the fill level in a container. The device comprises: a radar module for determining a distance to the surface of the filling material; a 3D camera for capturing at least one region of the surface of the filling material; and an evaluation circuit that is designed to measure a maximum distance and a minimum distance from the captured distance values and to determine the fill level on the basis of the distance, providing that the distance is smaller than the maximum distance value and greater than the minimum distance value. As a result of the redundancy or the verification provided by the 3D camera of the distance calculated by the radar module, the fill-level measuring device according to the invention is therefore more reliable with regard to the miscalculation of an incorrect fill level.

Abstract: A method of wellbore analysis using TM01 and TE01 modes of radar waveforms can include transmitting, at a first time, a radar waveform from a wellhead into a tubing disposed in a wellbore positioned in a reservoir. The radar waveform is either a TM01 mode or a TE01 mode waveform. The tubing includes a fluid, and the surface of the wellbore includes the wellhead. At a second time, a reflected waveform generated by reflecting the transmitted radar waveform on a fluid surface of the fluid is received at the wellhead. A fluid level of the fluid is determined based on the time difference between the first time and the second time, and on a transmission speed of the radar waveform from the wellhead to the fluid surface. The fluid level is a distance between the wellhead and the fluid surface of the fluid.

Abstract: Various apparatuses and methods for tracking the administration of medication by medication injection devices are provided. A plunger head for a medication injection device may include a first component that houses electronic components and a second component that couples to the first component to form the plunger head. When the plunger head is installed within a barrel of the medication injection device the second component may separate the first component from medication contained within the barrel.

Abstract: In a device for measuring a fill level of a liquid in a container with an ultrasonic sensor which is arranged on a floor element, wherein a damping cup with a measuring tube is assigned to the ultrasonic sensor, the damping cup has an external housing and an internal housing. The internal housing contains the measuring tube, and either the internal housing has outwardly protruding contact elements that lie against the inside of the external housing or the external housing has outwardly protruding contact elements that lie against the outside of the internal housing. The external housing is also provided and designed for pluggable mounting of of the internal housing, and a channel is formed between the internal housing and the external housing.

Abstract: A closed tank system includes: a fuel tank; a canister adapted to adsorb evaporative fuel generated in the fuel tank; a fill-up limiting valve provided inside the fuel tank so as to be communicated with the evaporative fuel discharge passage and adapted to operate to close the evaporative fuel discharge passage when a fuel level reaches a predetermined full tank liquid level; a shut-off valve adapted to operate to open or close the evaporative fuel discharge passage; a fuel remaining amount sensor adapted to detect a remaining amount of fuel; and a hardware processor that causes a control section to carry out control for allowing the shut-off valve to be opened or closed. The hardware processor causes the control section to inhibit the control for allowing the shut-off valve to be opened when an engine is in operation and the detected remaining amount of fuel exceeds a predetermined threshold.

Abstract: During transmission, a speed of sound pulses gradually reduces due to acoustic impedance. Regulating a length or a density or a sound speed of the sound pulses affects their average speed in the transmitting medium, sound intensity and detecting depth. Time of flight (TOF) and TOF shift can be used to calculate the depth and moving speed of detecting objects. Calculating a speed of moving objects by simultaneously detecting TOF shift at same site from two separated piezoelectric (PZT) elements improves the testing results with accuracy, simplification and reproducibility. Coding sound pulses to obtained the TOF and the TOF shift will simultaneously calculate the depth and the moving speed of sampling points, which can be used to construct 2D and 3D images for these motionless and/or moving sampling points. Coded sound pulses also improves the quality of the imaging.

Abstract: An apparatus and method for frequency tuning/tracking between an electrical subsystem and a mechanical transducer subsystem is presented. An electromechanical transducer generates acoustic pulses as it is driven by a transmit signal from an electrical subsystem. As the transmit signal goes inactive, the settling behavior of the transducer is registered from which the difference in frequency between the resonance of the electromechanical transducer and the transmit signal frequency is determined and utilized for locking the electrical subsystem to the mechanical transducer subsystem by either tuning operating frequency of the electrical subsystem, or the mechanical transducer, to keep them matched (locked).

Abstract: An apparatus for measuring the inner volume of a cavity. According to one embodiment the apparatus comprises a hollow body coupleable to the cavity, such that the inner volume of the cavity and the inner volume of the hollow body are communicated. A solid body is housed in the hollow body. A detector monitors the position of the solid body. A processor determines the inner volume of the cavity which is calculated from the oscillation of the solid body according to the volume of gas inside the cavity.

Abstract: An ultrasonic transducer apparatus is provided. In one embodiment, the apparatus includes an outer housing, an inner housing disposed within the outer housing, and an ultrasonic transducer disposed within the inner housing. The outer housing has an aperture that enables pressurized fluid to enter the outer housing while allowing the outer housing to acoustically isolate the inner housing and the ultrasonic transducer from an additional component when the outer housing is connected to the additional component. Additional systems, devices, and methods are also disclosed.

Abstract: A kit for detection of an analyte of interest in a liquid sample, and methods of using, are provided. The kit may include a pipette and a disposable pipette tip configured to engage the pipette. The pipette tip may define an acoustic channel configured for allowing flow-through of a liquid. The kit may also include a vibratory device in communication with the acoustic channel and configured for imparting a vibratory force thereto. The impartation of the vibratory force may create standing acoustic waves, thereby separating any negative acoustic contrast particles (NACPs) from the remaining contents of the liquid sample. The NACPs may capable of biospecific recognition of the analyte of interest, thereby separating the analytes of interest, which can then be collected or analyzed accordingly.

Abstract: During transmission, a speed of ultrasound pulses gradually reduces due to their energy loss from acoustic impedance. A thickness and a density of piezoelectric (PZT) elements and a sound speed in the PZT elements decides energy of the ultrasound pulses and their detecting depth. A speed of moving objects and an angle of the moving objects with the ultrasound pulses may change a speed of reflected ultrasound pulses and affect their time of flight (TOF) and TOF shift. A method of Coding ultrasound pulses combines advantages of a continuous wave ultrasound and a pulsed wave ultrasound. So, it can be used to obtained the TOF and the TOF shift and calculate the depth and the moving speed of the detecting objects, which also avoids a problem of an aliasing for highly moving speed of the objects.

Abstract: A system for detecting an interface between a polymer-rich phase and a solvent-rich phase comprising a liquid-liquid separator configured to receive a polymer solution as an inlet stream comprising solvent, polymer and unreacted monomer produced in a solvent-based polymerization reactor through an inlet feed, wherein a tank is configured to provide a residence time of at least 20 minutes and to permit the stream to separate into the polymer rich phase and the solvent rich phase; a first sonic transponder for sending a first sonic signal from either a top or bottom of the liquid-liquid separator and for receiving a first reflected portion of the sonic signal, the reflected portion of the sonic signal created by the passage of the sonic signal through a liquid-liquid interface between the solvent rich phase and the polymer rich phase, wherein the first sonic transponder is positioned such that it transmits the signal which travels perpendicularly to the liquid-liquid interface is provided.

Abstract: Embodiments of a system and method for providing a float-based sensor are disclosed. Embodiments of the system and method provide a sealed pipe or tube, also referred to as a barrier chamber, that is located inside a tank (or body of water) to measure a fluid level in the tank, such as a fuel tank, an oil tank, a chemical tank, a water tank, and the like. No fluid is able to penetrate the interior of the sealed pipe to avoid any electrical, mechanical, or chemical problems, or degradation. Embodiments of the system and method use a float having a magnet that magnetically couples to a target located within the barrier chamber's interior. The movement of the target is constrained to one dimension, allowing it to move up and down as the fluid level in the tank (or body of water) moves the magnetically coupled float up and down.

Abstract: An apparatus for metering the delivery of a fluid. The apparatus has a variable acoustic source and a microphone, both acoustically coupled to a volume having a fluid region and an air region. The apparatus may also include a processor to determine a volume of the air region based on signals received from the microphone and the variable acoustic source. A fluid valve is coupled to the processor, and is configured to allow an amount of fluid to exit the fluid region associated with the volume of the air region.

Abstract: A method, non-transitory computer readable medium and a system that includes a confidence level module arranged to calculate, in response to detection signals, estimated upper surface points and to associate a non-binary confidence level with each estimated upper surface point; wherein the detection signals are generated by a receiver in response to an irradiation of at least a portion of the upper surface of the content with radiation pulses transmitted by a transmitter; and an estimator that is arranged to calculate an estimate of the upper surface based upon the estimated upper surface points and the non-binary confidence level associated with each estimated upper surface point.

Abstract: Provided is a liquid level measuring technique capable of measuring a liquid level with high accuracy even if a liquid stored in a container is boiling.

Abstract: A method for metering the delivery of a fluid. The apparatus has a variable acoustic source and a microphone, both acoustically coupled to a volume having a fluid region and an air region. The apparatus may also include a processor to determine a volume of the air region based on signals received from the microphone and the variable acoustic source. A fluid valve is coupled to the processor, and is configured to allow an amount of fluid to exit the fluid region associated with the volume of the air region.

Abstract: A method to deliver medication. The apparatus has an acoustic volume sensor that acoustically excites a reference volume and variable-volume chamber with an acoustic source and measures the acoustic response with microphones acoustically coupled to the reference and the variable-volume chamber. A disposable drug cassette is coupled to the acoustic volume sensor and includes a drug reservoir and valve. The method includes receiving a volume signal and inputs from a user input or a second sensor and controlling the valve based on these inputs.

Abstract: An apparatus for metering the delivery of an aerosol. The apparatus has a variable acoustic source and a microphone, both acoustically coupled to a volume having a fluid region and an air region. The apparatus may also include a processor to determine a volume of the air region based on signals received from the microphone and the variable acoustic source. A fluid valve is coupled to the processor, and is configured to allow an amount of fluid to exit the fluid region associated with the volume of the air region. An atomizer, coupled to the fluid region, is configured to aerosolize at least a portion of the fluid.

Abstract: A predictive method of detecting the depth of water ahead of a wading vehicle comprises providing a wading sensor and an attitude sensor on the vehicle, and using this information to estimate the depth of water at a location ahead of the direction of vehicle movement. Corresponding apparatus is disclosed.

Abstract: An electronics unit and a method for a filling-level measuring device for determining a filling level. The unit including an arithmetic unit determining a functional relationship between a distance between a filling material surface and the filling-level measuring device and an amplitude of a signal component reflected by the filling material surface and received by the filling-level measuring device; an amplitude profiler creating a profile of amplitude values of filling level echoes which have been measured so far; and an amplitude evaluator determining an expected amplitude of the filling level echo at a particular location with help of the profile of amplitude values.

Abstract: In a pulse-echo measuring system, echo signals are compared by a difference calculator with the output of a model simulating the system. The detected differences are used to re-calculate parameters in the model. Other parameters are directly measured and applied to the model. A primary measurement, such as level, is detected more accurately and other parameters such as froth height and turbulence are estimated accurately.

Abstract: A method for determining an ultrasonic detecting cycle is provided. Firstly, an initial detecting cycle T is set. Then, a first sensing wave is generated. Then, a first time-of-flight value is calculated corresponding to the first sensing wave. After the first sensing wave has been generated for the initial detecting cycle T, a second sensing wave is generated. Then, a second time-of-flight value is calculated corresponding to the second sensing wave. Afterwards, the second time-of-flight value is compared with the first time-of-flight value. If a difference between the second time-of-flight value and the first time-of-flight value is smaller than a threshold value, the initial detecting cycle T is determined as the ultrasonic detecting cycle.

Abstract: A level measurement system suitable for use in a high temperature and pressure environment to measure the level of coolant fluid within the environment, the system including a volume of coolant fluid located in a coolant region of the high temperature and pressure environment and having a level therein; an ultrasonic waveguide blade that is positioned within the desired coolant region of the high temperature and pressure environment; a magnetostrictive electrical assembly located within the high temperature and pressure environment and configured to operate in the environment and cooperate with the waveguide blade to launch and receive ultrasonic waves; and an external signal processing system located outside of the high temperature and pressure environment and configured for communicating with the electrical assembly located within the high temperature and pressure environment.

Abstract: A process measurement instrument with target rejection comprises a sensor circuit. The sensor circuit comprises a drive circuit for transmitting a pulse signal at a target of interest and a receive circuit receiving reflected echoes of the pulse signal and developing an analog receive signal representative of the reflected echoes. An analog processing circuit receives the analog receive signal and comprises a summer subtracting an analog target rejection signal from the analog receive signal to develop a corrected receive signal. A programmed digital processing circuit is operatively coupled to the analog processing circuit and comprises a memory storing target rejection signal value data representing false target reflections and developing the analog target rejection signal for transfer to the analog processing circuit.

Abstract: A fish locating system combines the functionality of a remote controlled miniature electric boat with an underwater sonar system. The watercraft is provided with a sonar transponder attached to an exterior deck. The sonar transponder wirelessly transmits sonar readings including bottom depth and terrain, schools of fish, underwater obstructions, water temperature, and the like, to the watercraft's wireless remote controller's display screen. The remote controller comprises a display screen that visually depicts the sonar scan in real-time. In use, a person can be on shore or on an anchored boat while performing underwater reconnaissance.

Abstract: A method of determining the volume or height of fluid in a reservoir is provided. A first burst of focused acoustic energy is used to raise temporarily a protuberance on a free surface of the fluid. A second burst of acoustic energy is directed to the free surface of the fluid. Echoes from the second burst of acoustic energy are detected. The detected echoes are employed to compute the height of the fluid.

Abstract: A method of operating an acoustic pulse echo ranging system is provided. A series of acoustic energy pulses of successively increasing or decreasing burst frequencies are transmitted through a transducer assembly. For each transmitted energy pulse associated echoes are received and converted into an echo function over time. The obtained echo function is stored in a two-dimensional pattern whose first dimension is the burst frequency and whose second dimension is the time. Based upon the two-dimensional pattern a frequency response function is evaluated as a function of echo function values over burst frequency at a selected point of time.

Abstract: A device for controlling the filling of a receptacle with liquid by a drink vending machine. The device includes visual marking device for marking the liquid fill level in the receptacle, a device for emitting a signal towards the receptacle, a device for receiving an incident signal and which receives the incident signal returning from the receptacle and a controlling device configured for commanding the stoppage of filling on the basis of a variation of the incident signal. The receiving device includes a series of photoelectric receivers and at least one variable which is a displacement of a light incident signal measured by the receivers. The visual marking, emitter and receiver are displaceable en masse so as to make it possible to modify the marking of the level of fill in the receptacle.

Abstract: A method for measuring a fill level of a fill substance in a container and for monitoring at least one predetermined fill level (LMIN, LMAX), using a fill level measuring device working according to the travel-time principle, as well as a corresponding fill level measuring device, wherein the monitoring satisfies high safety standards, wherein, in each measuring cycle, transmission signals (S) are sent toward the fill substance and their echo signals (E) are received, the fill level is determined, based on the echo signals (E), in a first evaluation method, and it is determined, based on the echo signals (E), in a second evaluation method independent of the first evaluation method, whether the fill level exceeds or falls beneath the predetermined fill levels (LMIN, LMAX).

Abstract: A device for controlling the filling of a receptacle with liquid by a drink vending machine. The device includes visual marking device for marking the liquid fill level in the receptacle, a device for emitting a signal towards the receptacle, a device for receiving an incident signal and which receives the incident signal returning from the receptacle and a controlling device configured for commanding the stoppage of filling on the basis of a variation of the incident signal. The receiving device includes a series of photoelectric receivers and at least one variable which is a displacement of a light incident signal measured by the receivers.

Abstract: A circuit with two terminals that receive an input current. The circuit includes a sensor, and a controller to generate a modulated signal. The circuit also includes a flyback circuit that receives the modulated signal. The flyback circuit generates a first output voltage based on the modulated signal, shunts or redistributes at least a portion of the input current, and enables the controller to regulate the input current in proportion to the modulated signal.

Abstract: In a method for processing an echo profile generated by a pulse-echo ranging system, the echo profile is compared with a time-varying threshold function to identify valid echoes in those portions of the echo profile which exceed the TVT function. Based on the amplitude and/or area above the TVT function, each echo is rated and attributed a level of confidence. The echo with the highest level of confidence is selected as the echo of interest, and the level of confidence is reported. To provide an improved echo processing with increased accuracy in determining the confidence level of the selected echo of interest, it is furthermore determined whether the portion of the threshold function which timely corresponds to the selected echo of interest is part of a hump-shaped section of the threshold function. If so, said section is reshaped to reduced hump amplitude, and the confidence level of the echo of interest is redetermined based on the amplitude and/or area above the reshaped TVT function.

Abstract: A system for measuring distance in a gas or liquid operating medium has an even number of ultrasonic signal transmitters (12, 14), and a single ultrasonic signal receiver (16). The ultrasonic signal transmitters are adapted to transmit ultrasonic signals to a target (18) in the operating medium. Each of the transmitters and receiver are so spaced apart in a geometrically symmetrical planar array within an acoustically attenuating substrate medium, and each of the transmitted ultrasonic signals are so pulse driven in an acoustically symmetrical relationship, that opposing ultrasonic signals transmitted through the substrate medium by symmetrically opposed transmitters are cancelled at the receiver and a signal for measuring distance to the target is formed at the receiver by combination of the transmitted signals through the operating medium.

Abstract: A fluid detector for determining a presence of a fluid within a container includes a piezoelectric element that outputs a first ultrasonic signal in response to an input electrical signal and a lens with an upper portion and a lower portion. The piezoelectric element is coupled to the upper portion of the lens so that, when the lens is disposed adjacent the outer surface of the wall such that the lens is intermediate the piezoelectric element and the wall, the lens focuses the first ultrasonic signal toward the wall so that the first ultrasonic signal enters the wall.

Abstract: Apparatus for indicating the oil level in a central heating oil tank comprises a battery powered monitoring unit (1) for mounting on the oil tank which determines the oil level by an ultrasonic signal transmitter/receiver (18). A first microprocessor (14) in the monitoring unit (1) determines the oil level from the ultrasonic transmitter/receiver (18) and operates a primary transmitter (12) for transmitting a radio signal which includes data indicative of the oil level. A remotely mounted mains electricity powered receiving unit (3) comprises a primary radio receiver (15) for receiving the transmitted signal, and a second microprocessor (16) in the receiving unit (3) controls the operation of a visual display unit (10) for graphically displaying the oil level. The monitoring unit (1) and the receiving unit (3) are operable in a teaching mode initially on power-up of the receiving unit (3) during which the monitoring unit (1) teaches the receiving unit (3) its address.