Examples provide for a self-test circuit. The self-test circuit comprises input circuitry; testing circuitry; and a circuit to be tested, coupled between the input and testing circuitry and comprising at least a piezoelectric crystal. The input circuitry is configured to generate and transfer a predefined electric signal comprising at least a sinusoidal signal through at least the piezoelectric crystal of the circuit to be tested to generate an output signal. The testing circuitry is configured to analyze the output signal.

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.

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.

A piezoelectric field disturbance sensing system includes a piezoelectric element for generating mechanical energy when electrically excited and for generating electrical energy when mechanically deformed. A mass is coupled to the piezoelectric element. A signal generator is coupled to the piezoelectric element for applying electrical energy thereto for a fixed period of time. As a result, the piezoelectric element undergoes mechanical deformation and the mass reverberates in response to such mechanical deformation. A charge monitor is coupled to the piezoelectric element for monitoring electrical energy generated thereby during a time period subsequent to the fixed period of time.

A piezoelectric field disturbance sensing system includes a piezoelectric element for generating mechanical energy when electrically excited and for generating electrical energy when mechanically deformed. A mass is coupled to the piezoelectric element. A signal generator is coupled to the piezoelectric element for applying electrical energy thereto for a fixed period of time. As a result, the piezoelectric element undergoes mechanical deformation and the mass reverberates in response to such mechanical deformation. A charge monitor is coupled to the piezoelectric element for monitoring electrical energy generated thereby during a time period subsequent to the fixed period of time.

A noncontact voltage measurement apparatus includes a sensing electrode to which a voltage corresponding to an alternating current voltage is applied, a feedback electrode, a conductive movable body that is supported so as to be displaceable in accordance with the Coulomb force generated between the movable body and the sensing electrode and the Coulomb force generated between the movable body and the feedback electrode, an elastic force for causing the movable body to return to a predetermined neutral position acting on the movable body, a displacement detection unit configured to detect a displacement of the movable body, a voltage applying unit configured to apply an alternating current voltage to the feedback electrode, and a control unit configured to control the voltage to be output from the voltage applying unit such that a detection result of the displacement from the displacement detection unit approaches a predetermined reference value.

A method for performing diagnostics on a target transformer includes applying a voltage output of a voltage generator to a winding or phase of the target transformer; controlling the voltage generator to output an AC voltage at a first frequency and then a second frequency and measuring first and second excitation currents flowing into the target transformer associated with the first frequency and second frequency, respectively. The method further includes determining an actual excitation current of the target transformer as a function of both the first and second excitation currents, and comparing the actual excitation current of the target transformer to excitation currents associated with one or more benchmark transformers having known electrical characteristics. And when the actual excitation current of the target transformer matches an excitation current of one of benchmark transformers, determining the electrical characteristics of the target transformer to match electrical characteristics of the one benchmark transformer.

The present invention relates to a method for determining at least one physical characteristic value of an electromechanical oscillatory system, which comprises a piezoelectric element and at least one additional element coupled, with respect to oscillation, to the piezoelectric element, the piezoelectric element having an electrode and a counter electrode. The method comprises the following steps: (a) applying an electrical alternating voltage between the electrode and the counter electrode for the duration of an excitation interval in order to induce mechanical oscillation of the oscillatory system or of a sub-system of the oscillatory system, so that after the excitation interval has expired, the oscillatory system or the sub-system performs a free oscillation without excitation, (b) after the end of the excitation and during the free oscillation of the oscillatory system or of the sub-system without excitation: (i) measuring a time curve of a voltage U between the electrode and the counter electrode, or (ii) short-circuiting the electrode and the counter electrode with a line and measuring a time curve of a current I through the line, and (c) determining the at least one physical characteristic value of the electromechanical oscillatory system from the time curve of the voltage U, which time curve was measured in step b) i), or the time curve of the current I, which time curve was measured in step b) ii).

The present invention provides a method of surely detecting a crack in piezoelectric elements regardless of size of the crack. The method includes applying voltage to a first piezoelectric element of a pair of piezoelectric elements to cause deformation in the first piezoelectric element, forcibly deforming a second piezoelectric element of the pair of the piezoelectric elements to generate voltage from the second piezoelectric element according to the deformation of the first piezoelectric element, finding a transfer function of the pair of the piezoelectric elements based on values of the applied voltage and the generated voltage, and detecting presence or absence of a crack in the pair of the piezoelectric elements based on an objective value obtained from the found transfer function.

Systems, methods and piezoelectric patches are provided for monitoring the structural health of connectors in overhead transmission lines. A plurality of piezoelectric patches is mounted to different locations on the connector. At least one of the patches is actuated using an AC voltage and certain electrical properties either from the same patch or of a different patch are evaluated over time to determine the structural health of the connectors.