Abstract: A vibration wave detector, having a receiver for receiving vibration waves such as sound waves and so on to be propagated in a medium, a resonant unit having a plurality of cantilever resonators each having such a length as to resonate at an individual predetermined frequency, a retaining rod for retaining the resonant unit, a vibration intensity detector for detecting the vibration intensity, for each predetermined frequency, of each of the resonators, by the vibration waves received by the receiver and propagated to the resonant unit by way of the retaining rod.

Abstract: The present invention concerns mechanical signal processing comprising a mechanical adder as a basic building block. Such a mechanical adder (40), which is a basic element of the present invention, comprises a first micromechanical member (40.1) being sensitive to a first frequency (f.sub.1) and a second micromechanical member (40.2) being sensitive to a second frequency (f.sub.2). The two micromechanical members (40.1, 40.2) are coupled via a linear coupling (41) to provide a superposition (sum) of the two frequencies (f.sub.1 and f.sub.2). Based on the adder, AND-gates and OR-gates can be realized by adding further micromechanical members and appropriate linear and non-linear coupling elements.

Abstract: A motion detector for detecting movement of a rail based vehicle and the direction of that movement is provided. The motion detector can be integral with or attachable to an end-of-train unit and can include a single axis accelerometer mounted at an angle from the rails for detecting acceleration in both the lateral and vertical directions. A systems controller, which can include an analyzer, can be provided to receive and analyze output from the accelerometer to determine a motion state and a direction. A power controller can be provided for supplying power to the accelerometer on an intermittent basis to conserve power. A calibration unit can be provided to both initially calibrate and to subsequently recalibrate the accelerometer after a stopped motion state is detected. Additionally, an input/output port and an output driver for conditioning the signal for output to the end-of-train unit can be provided.

Abstract: A sensor assembly for monitoring shocks and vibrations on sensitive devices is provided. The sensor assembly comprises a detector beam supported between a pair of support members. A detector weight is secured to the detector beam between the support members. The detector beam is fracturable in response to the application of a predetermined level of force. An electrical circuit may be coupled to the detector beam for monitoring electrical continuity and structural integrity of the detector beam. The detector beam provides passive monitoring as the detector beam will fracture irrespectively of the power state of the electrical circuit. One or more detector beams may be used to monitor forces along a variety of different axes.

Abstract: A vibration wave detector, having a receiver for receiving vibration waves such as sound waves and so on to be propagated in a medium, a resonant unit having a plurality of cantilever resonators each having such a length as to resonate at an individual predetermined frequency, a retaining rod for retaining the resonant unit, a vibration intensity detector for detecting the vibration intensity, for each predetermined frequency, of each of the resonators, by the vibration waves received by the receiver and propagated to the resonant unit by way of the retaining rod.

Abstract: A motion detector for detecting movement of a rail based vehicle and the direction of that movement is provided. The motion detector can be integral with or attachable to an end-of-train unit and can include a single axis accelerometer mounted at an angle from the rails for detecting acceleration in both the lateral and vertical directions. A systems controller, which can include an analyzer, can be provided to receive and analyze output from the accelerometer to determine a motion state and a direction. A power controller can be provided for supplying power to the accelerometer on an intermittent basis to conserve power. A calibration unit can be provided to both initially calibrate and to subsequently recalibrate the accelerometer after a stopped motion state is detected. Additionally, an input/output port and an output driver for conditioning the signal for output to the end-of-train unit can be provided.

Abstract: In a vibration sensing device for sensing a knocking vibration of an engine, a piezoelectric element is connected to an output terminal through a resilient conductive member. The resilient conductive member has a fixed base part, a sliding part at a position opposite to the fixed base part, and an intermediate V-shaped part resiliently contacting the piezoelectric element. When the sliding part moves slidingly in response to vibration of the piezoelectric element, the sliding friction force which exerts on the sliding part increases the spring constant of the resilient conductive member to be larger than the stationary spring constant of the same by hysteresis characteristics, thereby reducing damage to the piezoelectric element and enhancing reliability of the electric connection.

Abstract: An optical vibration sensor includes a built-in blade provided with a system for reflecting light, a system for directing light onto the reflecting system, system for collecting the light reflected by the reflecting system and a system for analyzing the intensity and/or the frequency and/or the phase of the reflected light. The blade forms an integral part of an appropriately cut block.

Abstract: A vibration sensing element includes a hermetically sealed case, a fixed electrode member made of a nonmagnetic electrically conductive material and fixed to the case with its tip portion projecting into the case, a movable electrode member made of an electrically conductive magnetic metal material exhibiting elasticity and fixed to the case with its tip portion projecting into the case and making pressure contact with the fixed electrode member, and a magnetic member disposed to face the movable electrode member. A glass breakage sensor includes a casing for attachment to the glass, the vibration sensing element, and a resin molding encasing the vibration sensing element. The contact pressure between the fixed and movable electrode members can be noninvasively checked by applying a magnetic field thereto.

Abstract: A vibration detecting sensor includes a pair of piezo-electric elements electrically connected together using a plate member, which eliminates the influences of temperature change to the surroundings by using a temperature compensating piezo-electric element, and prevents external noises from entering the device. Therefore, vibrations are detected efficiently.

Abstract: A combination of an implement employed in a sports game to impact with a body, and a device coupled to the implement which measures the natural frequency and the relative amplitude of vibration of the implement resulting from the impact. The implement can be a game racket, bat, club or the like and the body impacted can be a ball. The lower the value of the natural frequency of vibration of the implement the more flexible the implement is when it impacts the ball, the greater is the amplitude of the vibration of the implement and the rebound of the ball has a lower velocity. One of the embodiments, called a FLEX METER is a frequency measuring device which employs a series of reeds mounted on a base member each reed being adjusted to vibrate at a maximum amplitude when a vibration having a designated frequency is applied to the base member. Each reed is identified with a designated frequency.

Abstract: A method is provided for inhibiting stiction of suspended microstructures during post-release-etch rinsing and drying. The microstructures are shaped to include additional convex corners at regions of the released portion of the microstructure that can undergo substantial displacement toward the substrate. A stiction-inhibition method also includes incorporating clefts between the microstructure and adjacent field regions at regions of the microstructure which cannot undergo substantial displacement toward the substrate. Methods for inhibiting stiction are also provided wherein high-temperature rinse liquid is used and wherein a high-temperature anneal follows a rinsing step.

Abstract: A semiconductor type acceleration sensor comprises a flexible printed circuit board on which a semiconductor type detector chip section is mounted. The detector chip is formed with openings therethrough overlapping an opening formed in a rear-side base plate of the flexible printed circuit board such that the detector chip section is supported only by a bridge portion. In case of excess input in an acceleration direction, elastic deformation of the bridge portion and a bending portion of the flexible printed circuit board provide absorption of the excess input for protecting the detector chip section.

Abstract: A sensor arrangement principally for ice bank control using a single probe (9) allowed to resonate at its natural resonant frequency. That resonant frequency is different when ice has adhered to the probe and this is detected to indicate ice growth in the ice bank. A resonator/detector (11) oscillates the probe for short periods of time at regular intervals, which allows ice to form about the probe when not in oscillation.

Abstract: A digital accelerometer manufactured from arrays 11a-11e of micro-mechanical sensing elements 12. The sensing elements 12 of different arrays 11a-11e are designed for detecting acceleration in a particular rotational or translational direction, such that their response to acceleration in other directions is minimized. Further, the sensing elements 12 have size and proof mass parameters that may be adjusted to vary their frequency response and sensitivity to amplitude of acceleration. Arrays 11a-11e of sensing elements 12 provide detection of a range of frequency levels and amplitudes at each frequency. At an appropriate frequency and amplitude of an applied acceleration, a sensing element 12 moves to contact an electrode 126, producing an electrical signal, which may be stored as a data bit.

Abstract: A shock sensor includes an inductance coil, a magnet, a magnetically soft material, and a support bracket for the magnetically soft material. The inductance coil and the magnet are fixed relative to each other. The magnetically soft material has one side thereof fixed on the support bracket and lies relative to the coil and the magnet so that the magnetically soft material can move up and down as well as leftwardly and rightwardly and inwardly and outwardly when the shock device vibrates and thereby alter a magnetic flux from the magnet to the inductance coil so as to generate signals responsive to the fluctuations of a magnetic flux.

Abstract: An improved vibration warning device is disclosed for monitoring rotating machinery, and signaling the occurrence of an unsafe condition. The apparatus includes a one or more mercury wetted resonating reed gauge switches tuned to a critical frequency that lies within a predetermined range of the critical frequency of the rotor. An imbalance force imposed by the rotor is transmitted to the device and if the imbalance force exceeds a predetermined threshold, the mercury wetted reed gauge switch/switches will conduct an appropriate electrical warning signal.

Abstract: Motion and direction sensors for end of train (EOT) telemetry equipment employ a piezoelectric film as the sensing element. The motion sensor has a mechanical design which is optimized for detecting vibration on a railroad car. The electrical circuitry of the motion sensor generates output pulses to the EOT microprocessor which are processed according to an algorithm to make a determination of train motion based on detected vibration levels and rates of occurrence. Also, the EOT microprocessor dynamically adjusts the sensitivity of the motion sensor as a function of detected motion. The direction sensor uses a pendulum aligned with the axis of train motion to stress the piezoelectric film and, like the motion sensor, generates output pulses to the EOT microprocessor. These pulses are processed by a direction sensing algorithm implemented on the EOT microprocessor to determine the direction of train motion.

Abstract: Shock or impact sensor which can be fixed to a structure (14) comprising, along a longitudinal axis (AL) perpendicular to the structure (14), a rod (12) which can be joined to the structure (14) by a first end (16), a weight or counterweight (24) joined to a second end of the rod (12) and acceleration detection fixed to weight or counterweight (24) to detect acceleration along an axis perpendicular to the longitudinal axis of the sensor.

Abstract: A micromechanical sensor comprises a support, a micromechanical element that is movable relative to the support under the application of a stimulus, and a transducer. The transducer comprises a first component carried by the micromechanical element and movable therewith, and a second component stationary relative to the support. One of the first and second transducer components is a member for establishing a magnetic field and the other of the first and second transducer components is a SQUID positioned in the magnetic field for detecting variation in the magnetic field due to relative movement of the micromechanical element and the support.

Abstract: An accelerometer apparatus capable of sensing accelerations ranging from steady state to at least 500 Hertz is described. The apparatus uses a piezo resistive pickoff for low frequency sensing and applies a potential to the accelerometer's pendulum to excite a secondary pickoff for frequencies above 100 Hertz.

Abstract: The sensor comprises a vibrating sheet (1), mechanically connected to the body (5A) to be analyzed, and an optical triangulation recording system for recording the displacements of the movable part of the sheet, in particular the free end (1B) opposite to that which is restrained. The recording system comprises two optical fibers (7, 9) ending in microlenses (10, 12) having optical axes mutually inclined and converging in the movable part (1B) of the sheet.

Abstract: A device to measure the tension of the stringing of rackets used for playing tennis, squash, etc. which entails an end area to strike the said stringing and another adjacent area which includes a multiple diapason or tuning device. On striking the stringing, and depending on the tension of the strings, one tooth of the multiple diapason vibrates, thus providing a signal which can later be measured or digitalized to provide a measurement of the tension of the stringing.

Abstract: Disclosed is a three dimensional coordinate measuring machine which is used to measure a workpiece. The machine has a probe containing a piezoelectric crystal which is capable of detecting the shockwave generated when the probe stylus contacts the surface of the workpiece, in order to provide a trigger signal. In order to reduce the risk of the piezoelectric crystal not triggering satisfactorily upon receipt of this shockwave, the workpiece is vibrated so that immediately upon contact the vibrations travel up the probe stylus to trigger the piezoelectric crystal. The vibrations are introduced by a vibration transducer which is bolted to the bed of the coordinate measuring machine.

Abstract: A system (11) for monitoring and controlling the movement of a mass (12) along a predetermined path (14) by a motor-driven flexible member (20) is provided to modulate the motor drive output so that the actual velocity of the mass corresponds more closely to the desired target velocity profile. The system preferably employs a dual loop servo system wherein an outer servo loop uses conventional linear encoding techniques and is supplemented by an inner servo loop utilizing a sensor (27) that detects a physical characteristic of the flexible member representative of the relative velocity of the mass. Relative velocity transducers utilizing magnetic circuits and operating according to variable reluctance principles for generating relative mass velocity signals directly are disclosed.

Abstract: An apparatus which measures the deflection of a single or double reed of a woodwind musical instrument. A strain measuring transducer affixed to the reed measures the amount of pressure applied by the players lip or lips to said reed. In the preferred embodiment, the signal indicative of the deflection is delivered to the bridge completion circuit. This circuit is amplified by the high gain amplifier to a level that can be read by the adjustable peak level indicator or viewed on a readout meter. A method whereby musicians are provided with an indication of lip pressure for comparison and analysis. The signal can also be viewed on a time based voltage recorder or spectrum analyzer for quantitative lip pressure effects as well as timbre characteristics of different mouthpieces, reeds, ligatures and instruments.

Abstract: The shock resistance of an accelerometer for the measurement of an axial acceleration, having a sensing part consisting of an electromechanical beam, a spacer and a beam carrier can significantly be improved by making the two sections of the oscillating beam of unequal lengths and by providing the beam with a length between 8 mm and 11 mm and a width between 2.5 mm and 6.5 mm at a thickness of 0.6 mm. That way an optimum relationship between measuring sensitivity and shock resistance of the accelerometer will be reached.

Abstract: A vibration/acceleration sensor is provided which includes a basic sensor unit fixed to a casing adapted to be mounted on a body the vibrations of which are to be detected. The sensor unit is surrounded by a resinous material having a low heat transfer coefficient. The sensor unit includes a vibration detecting unit including a piezoelectric bending vibrator, thin plates each formed of, for example, a resinous material having a low heat transfer coefficient, provided respectively on the upper and lower surfaces of the vibration detecting unit, and a signal processing circuit formed on the upper thin plate.

Abstract: The bearing failure sensor includes a micromachined mechanical resonator h a conductive cantilevered beam mounted on a conventional insulating substrate to form a microchip. A conductive contact is mounted in close proximity to the free end of the conductive beam to form a gap. An integrated circuit is connected between the fixed end of the beam and the conductive contact. The microchip is mounted on a vibrating machine to be monitored. When vibrations having a given frequency and magnitude occur, the free end will vibrate and move sufficiently to close the gap completing a circuit and causing currents to flow that are detectable by the integrated circuit. Multiple resonators, having different gap sizes and natural resonant frequencies, may also be mounted on a single substrate to monitor vibrations at a plurality of different frequency and amplitude thresholds.

Abstract: A transducer element for measuring angular and linear accelerations including a pair of electromechanically reacting oscillating beams held symmetrical to a main axis y on a base plate by fixing elements. The electrical output signals proportional to the flexure of the beams under rotation about the y axis are provided to a signal processing circuit, which is designed so that with similar or dissimilar polarity of the oscillating beams a summing amplifier determines the linear acceleration along the z axis and a differential amplifier the angular acceleration about the y axis. The oscillating beams may be piezoelectric bending elements, or bending elements coated with piezoresistive semiconductors, or else provided with strain gauges.

Abstract: A high temperature sensor for use with an induced vibration dynamic touch sensor system comprising a pad element adapted for sliding contact with an object so as to induce vibrations in the pad, a mechanical coupling means comprising a stiff, substantially straight member for coupling the pad to a transducer assembly, the transducer assembly for converting the vibrations into electrical signals. The electrical signals are processed to produce a normalized spectral signature characteristic of the size and shape of the object, and the sizes and shapes and nature of its surface features. A pattern vector is extracted from the spectral signature and subjected to discriminant analysis to classify and recognize the object.

Abstract: First to third frames are formed by etching to penetrate a silicon substrate on the substrate. A plurality of thin cantilevered beams are formed in different lengths by cutting by etching the substrate in the frames; the beams formed in the first frame are formed perpendicular to the surface of the substrate to bend only in the X-axis direction, parallel to the surface of the substrate; the beams formed in the second frame are formed perpendicular to the surface of the substrate to bend only in the Y-axis direction, parallel to the surface of the substrate; and the beams formed in the third frame are formed to bend only in the Z-axis direction, perpendicular to the surface of the substrate. Masses are formed at the free ends of the beams, and piezo resistance layers are formed at the fixed ends.

Abstract: A semiconductor accelerometer includes a package containing damping liquid. A base is fixedly disposed within the package. A semiconductor plate is disposed within the package and is supported on the base. The semiconductor plate has a movable free end and a deformable diaphragm. A semiconductor strain gauge is associated with the diaphragm and deforms in accordance with deformation of the diaphragm. The base has a first surface opposing the semiconductor plate free end. The first surface of the base has a recess for limiting movement of the semiconductor plate free end. The recess extends to and opens at a second surface of the base which differs from the first surface.

Abstract: The movement of a body (1) is determined by mounting on or in the body one or more sources (3,4) and one or more detectors (12,14) such that each source propagates polychromatic light along a path to a detector. Radiation modulation means (19;25) is supported by the body such that a change in the movement of the body causes a displacement of the radiation modulation means in at least one light path to vary the distributed spectral content of the light reaching the detector. The or each detector is adapted to detect the intensity of incident radiation at a plurality of different wavelengths, and analysis means (18) interprets the output of each detector in terms of the movement of the body.

Abstract: An accelerometer (50, 80, 90) provided with a plurality of mounting means for selectively mounting the accelerometer on a test structure. The mounting means include a magnet (64 or 96) carried by the accelerometer (58, 60), a threaded aperture (62) in the housing capable of receiving a mounting stud, and a planar external surface (66, 68; 82; or 94) on the housing, which surface is capable of being secured to the test structure by an adhesive or wax.

Abstract: A mechanical vibrator for resonance operation, and particularly well suited for use with a beam chopper, comprises a mechanically stiff vibrator arm representing a fixed mass. A spring with a fixed spring constant is attached to and acts upon the vibrator arm. The vibrator arm and the spring comprise a mass/spring system. A drive means is connected to the vibrator arm and has a positive feedback circuit for self-excitation at the resonance frequency of the mass/spring system. At least one first magnetic system is arranged on the vibrator arm and at least one second magnetic system is located off the vibrator arm in operational connection with the first magnetic system for measuring and/or influencing the time ratio of the two half waves (t.sub.o, t.sub.g) of the vibration amplitude waveform of the vibration arm.

Abstract: A housing (A) which is connected with an internal combustion engine to be vibrated therewith. A diaphragm (B) is mounted in an interior chamber of the housing to undergo vibration therewith. The diaphragm is constructed to have a natural resonant frequency which substantially matches the knock frequency of the engine model for which the knock sensor is designed. The diaphragm is mounted to the housing by a central portion (20) such that an edge portion (24) undergoes maximum resonant displacement. To facilitate the passage of air from one side of the diaphragm to the other during near resonant displacement, a plurality of apertures (26) are provided through the diaphragm edge portion. In this manner, viscous drag is reduced which increases the magnitude of the resonant displacement and decreases the bandwidth or range of frequencies over which the diaphragm undergoes significant displacement.

Abstract: A sensing apparatus has a probe displacement with respect to a support arm and to a reference position. The probe has a flat disc mounting three transducers which are spaced apart from one another at regular intervals. Each transducer has an elastomeric dielectric and is capable of producing an electrical output signal in response to displacement of the probe from the reference position. An electrical circuit compares output signals produced by the transducers and evaluates the direction and/or extent of probe displacement. Such evaluation may be used in the manipulator control system of an article-handling equipment.

Abstract: A method and apparatus for non-destructively measuring twist in a translating yarn (2) by means of a blade (1) which is in rubbing contact with the translating yarn (2) so that vibrations are imparted to the blade (1). The frequency of vibration of the blade (1) provides a measure of the twist imparted to the yarn (2) so that the signal frequency can be used as a measurement of the twist in a yarn (2) under test or as a feedback signal controlling the rate of twist imparted by a twist insertion station(8) during the formation of a yarn.

Abstract: A system for scanning vibrations of a mass and for converting the mechanical vibrations into corresponding electrical signals is disclosed. The system includes a source of a scanning radiation beam, preferably of a light beam, which has a larger transverse cross section than the vibrating mass. The umbra behind the mass and the surrounding illuminated area are collected by a focussing lens and projected onto an optoelectric converter. The collecting surface and/or the active light receiving surface of the converter have an outline which is variable in the direction of displacement of the vibrating mass so that the illuminated area varies in size during the vibration of the mass.

Abstract: An improved method and apparatus are provided for making vibration sensors, particularly of the type used in automotive applications wherein a piezoelectric element is affixed to a flexing plate which is mounted on a support stem in "umbrella" fashion. A desired resonant vibrating frequency of the sensor is obtained by progressively working a neck portion of the support stem, as by peening, to effectively decrease the vibrating radius of the plate and thus increase its resonant frequency toward and to a desired resonant frequency. The plate's frequency is monitored and the working of the stem neck portion is terminated when a desired resonant frequency is attained. An inclined support shoulder on the stem below the neck portion facilitates the aforementioned manufacture. An undercut positioned in the stem neck portion near its transition into the support shoulder further facilitates the manufacture.

Abstract: An engine vibration sensor for detecting the engine vibration as an electric signal including a vibrator set to resonate at a specific frequency of vibration of an engine to which it is attached, the vibrator being composed of at least one piezoelectric plate and having a root and a vibrator element; means for increasing the cross-sectional area of the vibrator element to make the second moment of area of the root of the vibrator relatively larger than that of the vibrator element; a base to be connected to an engine body; and a clamp for retaining the root firmly between the clamp and the base. The clamp may be provided with a projection having a flat surface for retaining the root of the vibrator. This construction prevents a change in the effective length of the vibrator element, thereby stabilizing the characteristics of the resonant frequency of the vibrator.

Abstract: A force sensor comprising a field effect transistor (FET) structure formed on a substrate, having an insulating layer overlying the substrate adjacent to the channel region of the transistor structure. A layer of piezoelectric material overlies the insulating layer, the layer of piezoelectric material having a portion which extends beyond the insulating layer to form a cantilever structure overhanging a portion of the channel region. A control electrode overlies the cantilever structure. Forces acting on the cantilever structure modify the charge distribution in the underlaying channel region, thereby to cause the drain current of the transistor to vary with any variation of force on the cantilever structure.

Abstract: This invention provides a vibration sensor for detecting vibrations having preselected frequencies. The sensor has a plurality of tuning mechanisms each being mechanically resonant with a different preselected vibrational frequency. The resonating vibrational movements of these tuning mechanisms apply varying stresses to a plurality of glassy magnetostrictive elements associated therewith. Each of the magnetostrictive elements is responsive to a different one of the tuning mechanisms. A magnetic biasing element imparts a magnetization to the magnetostrictive elements and a detecting mechanism associated with the magnetostrictive elements detects changes in the magnetization thereof caused by the varying stresses applied thereto.

Abstract: A process control instrument, in which the resonant frequency of a vibrating string varies in accordance with changes in a process parameter being monitored, employs a pneumatic drive system to induce the string into oscillation. Pressurized gas is discharged through a port, such as a jet nozzle, which is disposed to allow the gas to impinge on the outer surface of the string. Variations in the alignment between the gas discharge port and the string permits different modes of vibration, one of which is particularly suitable for process measurement purposes. In a particular embodiment of the apparatus, an optical sensor detects the frequency of vibrations, resulting in an intrinsically safe instrument for use in explosive environments.

Abstract: A knock detecting apparatus for an internal combustion engine includes a vibrating sheet branched into a plurality of vibrating reeds by forming a recess from one end of the vibrating sheet. The vibrating reeds have different lengths, shapes or thicknesses, and the other end of the vibrating sheet is fixed to a supporting member which is secured to the engine thereby to allow the vibrating reeds to vibrate with different resonance characteristics in response to the vibration of the engine caused by the knocking. The vibration of the vibrating sheet is detected, for example, as a change in reluctance by forming a magnetic path through the vibrating sheet and air gaps respectively located between the free ends of the vibrating reeds and a core.

Abstract: This invention comprises a vibration sensor for detecting engine knock. The sensor has a tuning mechanism which is mechanically resonant with a preselected vibrational frequency. The resonating movements of this tuning mechanism are adapted to apply varying stress to an associated magnetostrictive element. A magnetic biasing element imparts a magnetization to the magnetostrictive element and a detecting means is associated with the magnetostrictive element for detecting changes in the magnetization caused by the varying applied stress.

Abstract: This invention is an on-board electro-mechanical system designed to detect and indicate abnormal or defective conditions in any or all wheels of a car while it is in motion at highway speed.Each wheel of the car has a vibration sensor to detect abnormal vibration and send a signal to a defect indicator panel. The defect indicator panel of four lights visible to the driver is that unit of the system which warns the driver that a potentially hazardous condition exists, thus minimizing the liklihood of an accident resulting from the condition if the warning is heeded.

Abstract: An imbalance detector for a centrifuge includes a pendulum arm that is tuned to a critical frequency that lies within a predetermined range of the critical frequency of the rotor of the centrifuge. An imbalance force imposed by the rotor is transmitted to the detector and if the imbalance force exceeds a predetermined threshold the arm contacts an electrical contact to generate an appropriate electrical signal.

Abstract: An improvement in an engine vibration sensor of the type including a vibrator set to resonate at a specific frequency of vibration of the engine to which it is attached, for example the engine knocking vibration frequency, wherein the vibration of the vibrator is converted to an electric signal representing the specific engine vibration. The improvement consists of forming the vibrator from a magnetic material and providing a magnetic field generator for applying a magnetic field of controlled intensity to the vibrator, whereby the resonant frequency of the vibrator can be adjusted by varying the intensity of the magnetic field.