Abstract: A method of processing electrical signals which span a large dynamic range in order to enable the signal to be processed in its entirety without the need for any alteration to the signal gain or signal attenuation, comprises splitting of the signal along two or more paths each having a different amount of amplification or attenuation, the passing of each of these two or more different signals into one of two or more smaller dynamic range circuits which produce a logarithmically scaled representation of the average magnitude of the signal level at its input and the summation of the logarithmic outputs of the two or more smaller dynamic range circuits to produce a resultant logarithmically scaled signal representative of the average magnitude of the input signal over a very large dynamic range. The invention also includes apparatus for carrying out the above defined method.

Abstract: An acoustic emission transducer consists of a resonant detection element (10) which is attached to the base-plate (16) by a small area in comparison to the overall surface area of the resonant detection element (10) where this area of attachment is positioned with respect to the wave motion during the resonance of the resonant detection element (10) so as not to have a significant effect on the resonant detection element (10) other than to physically couple the resonant detection element (10) to the baseplate (16) and introduce elastic waves from the baseplate (16) to the resonant detection element (10) at the desired frequency, while allowing damping materials (24) to be acoustically coupled to the larger part of the resonant detection element surface area to produce a resonant acoustic emission transducer having reproducible characteristics of resonant frequency and rate of damping.

Abstract: A collision detector for a vehicle, comprises a waveguide which is locatable on and acoustically isolated from the vehicle. The waveguide allows stress waves to propagate therethrough, and the waveguide is arranged to produce stress wave activity when the waveguide is deformed due to collision. A pair of transducers are acoustically coupled to the waveguide and the transducers convert any stress waves into electrical signals. A processor analyses the electrical signals and gives an output signal to indicate the occurrence of a collision. The transducers detect different frequency bands and the processor compares the electrical signals and indicates the occurrence of a crash if the ratio or difference is greater than a predetermined value. The waveguide is a metallic member which has a glass coating and a protective coating. Alternatively the waveguide may be a fibre reinforced plastic, tin, or a metallic member which has an interface with a semi-rigid plastic member.

Abstract: An apparatus for processing electrical signals corresponding to acoustic emissions produced in a machine or process comprises a transducer acoustically coupled to the machine or process, which detects the acoustic emissions and converts them into an output signal. The output signal is amplified by an amplifier, rectified and enveloped by an enveloper having a short time constant to produce an electrical signal. An enveloper having a long time constant, measures the mean level of the electrical signal. A DC component remover removes the DC component from the electrical signal and an enveloper, having a long time constant, measures the mean level of the rectified AC component of the electrical signal. A processor having a low sampling rate, measures a power of the ratio between the mean level of the rectified AC component of the electrical signal and the mean level of the electrical signal.

Abstract: An apparatus for controlling an internal combustion engine comprises a transducer which detects acoustic emissions generated by the operation of the engine, and produces an output signal. The output signal is amplified, rectified and enveloped to produce an electrical signal. The electrical signal has its direct current component removed to leave the alternating current component of the electrical signal. The AC component of the electrical signal is rectified by a rectifier and the mean level of the AC component of the electrical signal is measured by a measurer. An analyzer monitors the mean level of the AC component of the electrical signal and sends a feedback signal to an ignition timing device of the internal combustion engine. The analyzer sends feedback signals such that the mean value of the AC component of the electrical signal lies in the region of a positive peak prior to the occurrence of preignition.

Abstract: A stress wave load cell comprises a propagation member to which is acoustically coupled a transducer. Electrical pulses are supplied to the transducer from a pulse generator and the electrical pulses are converted into stress wave signals which propagate through the propagation member. The transducer also detects the stress waves after propagation through the propagation member and supplies an electrical signal to processor which gives a measure of the load applied to the load cell.Damping members which have profiled surfaces are caused to move into damping contact with the propagation members when a load is applied to the load cell. The damping members damp the propagation of the stress waves in the propagation member and the damping is proportional to the area of damping contact, the area of damping contact increases with the load applied. May be used to measure tensile load or compressive load and may be used as a touch sensitive panel.

Abstract: An apparatus for determining the surface roughness of a material comprised of an acoustic element which is pivotally mounted to a support structure containing a polished end which is maneuvered into contact with the surface of a material to be tested by a spring element. The material is caused to move relative to the acoustic element by a driven roller. A transducer is acoustically coupled to the acoustic element and detects stress waves propagating in the acoustic element as a result of frictional and impact force generated by the rubbing of the acoustic element with the material. The relative stress wave activity is dependent upon the surface roughness of the material. A processor analyzes an electrical signal produced by the transducer to determine the surface roughness of the material which may analyze the electrical signal produced by the transducer to determine the presence of impurities on the surface of the material.

Abstract: A fluid level monitor for monitoring the fluid level in a tank comprises a first pair of transducers arranged in a vertically upper horizontal plane and a second pair of transducers arranged in a vertically lower horizontal plane. Pulse generators send electrical pulses to the transmitter transducers which transmit stress waves into the wall of the tank. The stress waves propagating peripherally are detected by the receiver transducers and processors analyze the amplitude of the detected stress waves to determine if the fluid is present or absent at the upper and lower horizontal planes. The pulse generators are arranged to send pulses out of phase so that stress waves propagating axially can be detected to determine alterations of the fluid level between the upper and lower horizontal planes. The processors may be arranged to operate alarms or to operate valves to control the fluid level in the tank.

Abstract: An apparatus for processing acoustic emissions or stress waves in order to recognize features indicative of variations in the process producing the acoustic emissions. The apparatus comprises a transducer acoustically coupled to a machine or industrial process and arranged to detect the acoustic emissions and produce an electrical signal. The electrical signal is amplified by an amplifier and the mean level of the electrical signal is measured by a mean level detector and the minimum level of the electrical signal is measured by a minimum level detector. A ratio measurer measures the ratio of the mean level of the electrical signal to the minimum level of the electrical signal. This method is self compensating for variations in the operating conditions of the machine or industrial process, is not significantly affected by electromagnetic switching transients, and can cope with very high numbers of transient excursions.

Abstract: The invention relates to a method and apparatus for testing the response of a stress wave sensor to confirm that the transducer and amplifier are functioning satisfactorily.A pulser is connected to the stress wave sensor at a point between the transducer and the amplifier. The pulser supplies a first and a second electrical pulse in series to the stress wave sensor. The first electrical pulse has a large amplitude such that it causes an operative transducer to oscillate and produce an additional electrical pulse. The first electrical pulse and the additional electrical pulse are supplied to the amplifier. An operative amplifier amplifies the first electrical pulse and any additional pulse to give an output signal, the output signal indicates if either the transducer or amplifier are not operating satisfactorily, the lack of an output signal indicates the amplifier is inoperative.

Abstract: An anti lock braking system for a vehicle includes transducers acoustically coupled to a non-rotating member of the wheel assembly and adapted to provide an electrical output signal dependent upon the degree of acoustic emission activity in the non-rotating member. A detector is adpated to analyze when the electrical output signal which corresponds to the= acoustic emission activity in the non-rotating member falls to zero when brake pads are in frictional contact with the confronting surface of the wheel. The detector is adpted to send a feedback signal to a control device which controls the pressure applied to the wheel by the brake pads. Preferably the detector measures the instantaneous change of electrical output signal as a funtcion of the pressure applied by the brake pad.

Abstract: The spectral content of a transient stress wave event occuring on a plate-like structure is determined by locating a transducer on the surface of the structure at a position remote from the location of the transient stress wave event. Lamb waves resulting from and characteristic of the transient stress wave event propogate through the plate-like structure in a dispersive manner to be intercepted by the transducer. Analysis of the transducer output enables the spectral content of the transient stress wave event to be realized.

Abstract: A method of inspecting a component in which the surface of the component is scanned with a loud speaker, the sonic output of which is arranged to be at such a frequency or frequencies as to cause any cracks, fractures or unbonded regions within the component to generate transient stress wave emissions. An acoustic emission transducer is attached to the component surface so as to detect any such transient stress wave emissions and thereby provide evidence of the existence of any such cracks, fractures or unbonded regions.