The disclosure relates to a method for determining and/or monitoring the breakdown voltage of a transformer oil, comprising the steps of a) performing an acoustic impedance measurement of the transformer oil, the impedance of a medium partially or entirely disposed in the transformer oil and capable of naturally vibrating and/or transmitting vibrations to the transformer oil is determined in at least one frequency band of defined frequency width; and b) calculating a resonator quality factor for the frequency band based on the determination performed in step a); and c) calculating an acoustic disbalance of the transformer oil based on the calculation performed in step b); and d) ascertaining the breakdown voltage of the transformer oil based on the calculation performed in step c).

Furthermore, the disclosure relates to a device (100, 200) for determining and/or monitoring the breakdown voltage of a transformer oil.

A transfer impedance calibration device for transducers based on spatial frequency domain smoothing technology is provided. The calibration device comprises a signal transmitter, a power amplifier, a transducer pair, a measurement amplifier, a signal collector, a measurement processor and a current sampler. The device extracts acoustic channel information through the sound filed spatial information or measurement method to design a spatial domain smoothing filter, and then comprehensively processes the transmitted current signal and the received signal through the spatial frequency domain smoothing technology to obtain the transfer impedance of the transducer pair.

A transfer impedance calibration device for transducers based on spatial frequency domain smoothing technology is provided. The calibration device comprises a signal transmitter, a power amplifier, a transducer pair, a measurement amplifier, a signal collector, a measurement processor and a current sampler. The device extracts acoustic channel information through the sound filed spatial information or measurement method to design a spatial domain smoothing filter, and then comprehensively processes the transmitted current signal and the received signal through the spatial frequency domain smoothing technology to obtain the transfer impedance of the transducer pair.

An impedance tube and sample tube holder that includes a hollow tube, a first tube, a second tube, and a spool. The hollow tube has two halves which are detachable and can hold spacers and a sample. The first tube includes a first tube speaker end and a first tube spool end. The first tube has a speaker disposed at the first tube speaker end and microphones. The second tube includes an anechoic terminator tube end and a second tube spool tube. The second tube has microphones and an anechoic terminator at the anechoic terminator tube end. The spool holds the hollow tube with the spacers and the sample. The spool is attachable to the first tube spool end and the second tube spool end such that the sample is perpendicularly orientated to an incoming sound wave produced by the speaker.

An impedance tube and sample tube holder that includes a hollow tube, a first tube, a second tube, and a spool. The hollow tube has two halves which are detachable and can hold spacers and a sample. The first tube includes a first tube speaker end and a first tube spool end. The first tube has a speaker disposed at the first tube speaker end and microphones. The second tube includes an anechoic terminator tube end and a second tube spool tube. The second tube has microphones and an anechoic terminator at the anechoic terminator tube end. The spool holds the hollow tube with the spacers and the sample. The spool is attachable to the first tube spool end and the second tube spool end such that the sample is perpendicularly orientated to an incoming sound wave produced by the speaker.

The disclosure relates to a method for determining and/or monitoring the state of a transformer oil, comprising the steps of a) performing an acoustic spectroscopy of the transformer oil, multiple ultrasonic emission signals of different frequencies and/or amplitudes being emitted into the transformer oil and corresponding reflected and/or transmitted ultrasonic reception signals of different frequencies and/or amplitudes being received after having passed through the transformer oil; and b) comparing the ultrasonic emission signals with the corresponding ultrasonic reception signals, an n-dimensional function characteristic of the transformer oil being ascertained; and c) matching the ascertained characteristic n-dimensional function from step b) with a reference function of corresponding dimension known for transformer oils, a reference transformer oil being determined; and d) registering a first value of at least one characteristic physical property of the transformer oil; and e) comparing the first value with a corresponding value of the reference transformer oil; and f) ascertaining the state of the transformer oil based on the comparison performed in step e).

Furthermore, the disclosure relates to a device (100, 200) for determining and/or monitoring the state of a transformer oil.

An abnormality detecting device includes a processor coupled to a memory and configured to: detect an envelope of a sound signal representing a periodic sound emitted from the rotor including a predetermined number of blades and a periodic sound emitted from another object; perform a time frequency transform of the envelope for each of frames having a predetermined time length and calculate a frequency spectrum of the sound signal; detect a candidate of a frequency equivalent to a period of the sound emitted from the rotor; and obtain a duration in which a fluctuation in power with respect to power of a component of the frequency spectrum in the candidate detected with regard to the frame becomes lower than or equal to a certain level and identify the candidate in which the duration becomes longest as the frequency equivalent to the period of the sound emitted from the rotor.

An abnormality detecting device includes a processor coupled to a memory and configured to: detect an envelope of a sound signal representing a periodic sound emitted from the rotor including a predetermined number of blades and a periodic sound emitted from another object; perform a time frequency transform of the envelope for each of frames having a predetermined time length and calculate a frequency spectrum of the sound signal; detect a candidate of a frequency equivalent to a period of the sound emitted from the rotor; and obtain a duration in which a fluctuation in power with respect to power of a component of the frequency spectrum in the candidate detected with regard to the frame becomes lower than or equal to a certain level and identify the candidate in which the duration becomes longest as the frequency equivalent to the period of the sound emitted from the rotor.

The methods disclosed herein enable calculating otoacoustic emission (OAE) pressure independent of the acoustic load imposed by the ear canal and the OAE probe measurement system, e.g., for hearing tests. The OAE pressure is calculated in a form of either the first outgoing wave at the eardrum, referred as emitted pressure level (P.sub.EPL), or as a Thvenin-equivalent OAE source pressure level (P.sub.TPL) at the eardrum, as derived from a simple tube model of an ear canal. In both methods the OAE sound pressure level (P.sub.SPL), ear canal reflectance (R.sub.EC), OAE probe source reflectance (R.sub.S), and one-way ear canal delay () are measured at the entrance of the ear canal with the OAE probe. In contrast to P.sub.SPL, both methods result in an emission pressure that is not confounded by the effects of the residual ear canal space or the impedance of the OAE measurement system.

A method for inspecting a crystal unit, the method includes: generating a sub-vibration in a crystal blank of the crystal unit by applying an input signal to a plurality of electrodes formed on the crystal blank; obtaining frequency characteristics of impedance between the plurality of electrodes from an output signal of the plurality of electrodes; and comparing the frequency characteristics obtained with reference frequency characteristics indicating quality of the crystal unit.