The present invention discloses an AC impedance measurement circuit with a calibration function, which is characterized in that only one calibration impedance is needed, associated with a switch circuit. Based on the measurement results of the two calibration modes, an equivalent impedance of the switch circuit, circuit gain and phase offset can be calculated. Based on the above results, the equivalent impedance of the internal circuit is deducted from the measurement result of the measurement mode to accurately calculate an AC conductance and a phase of the AC conductance for impedance to be measured. In addition, by adjusting a phase difference between an input sine wave signal and a sampling clock signal, impedance of the same phase and impedance of the quadrature phase can be obtained, respectively, and the AC impedance and phase angle of the impedance to be measured can be calculated.

The present invention discloses an AC impedance measurement circuit with a calibration function, which is characterized in that only one calibration impedance is needed, associated with a switch circuit. Based on the measurement results of the two calibration modes, an equivalent impedance of the switch circuit, circuit gain and phase offset can be calculated. Based on the above results, the equivalent impedance of the internal circuit is deducted from the measurement result of the measurement mode to accurately calculate an AC conductance and a phase of the AC conductance for impedance to be measured. In addition, by adjusting a phase difference between an input sine wave signal and a sampling clock signal, impedance of the same phase and impedance of the quadrature phase can be obtained, respectively, and the AC impedance and phase angle of the impedance to be measured can be calculated.

A first method (100) of providing a secondary reference for subsequent use in evaluating a power measuring accuracy of a wireless power measurement device (60) under test is presented. An inanimate calibration object (50) is subjected (110) to electromagnetic field variations (38) by controlling operating points of a reference wireless power transmitter device (30). Key power absorption parameters (58) of the calibration object (50) resulting from the electromagnetic field variations (38) are generated (120) and stored (130) together with data (57) that defines the operating points in a data storage (52) being associated (54) with the calibration object (50). A second method (200) of evaluating a power measuring accuracy of a wireless power measurement device (60, DUT) under test then involves providing (210) an inanimate calibration object, and retrieving (220), from a data storage (52) associated with the calibration object (50), stored key power absorption parameters (58) for the calibration object together with data (57) that defines operating points. The second method (200) further involves subjecting (230) the calibration object (50) to electromagnetic field variations (68) by causing the wireless power measurement device (60, DUT) to operate at the operating points defined by the retrieved data (57), obtaining (240) key power absorption parameters of the calibration object resulting from the electromagnetic field variations (68); and comparing the obtained key power absorption parameters and the retrieved key power absorption parameters (58) to obtain a measurement result being indicative of the power measuring accuracy of the wireless power measurement device (60, DUT).

Example circuitry includes a first circuit to provide a low signal; a second circuit to provide a high signal, where the high signal has a greater voltage magnitude than the low signal; and a differential amplifier configured to receive the low signal from the first circuit and the high signal from the second circuit. The differential amplifier is for producing an output voltage that is based on the high signal and the low signal. The example circuitry includes a first measurement circuit to measure the output voltage; a second measurement circuit to measure the low signal at the first circuit; and processing logic to determine a differential measurement based on the output voltage measured by the first measurement circuit, the low signal measured by the second measurement circuit, and calibration values obtained for the circuitry.

A magnetic field sensor comprises a first coil configured to generate a magnetic field having a first frequency and induce a reflected magnetic field from a target. A second coil configured to generate a diagnostic magnetic field having a second frequency is included. The diagnostic magnetic field is configured not to induce a reflected magnetic field from the target that is measurable by the magnetic field sensor. At least two magnetic field sensing elements detect the reflected magnetic field and the diagnostic magnetic field and generate a signal representing the reflected magnetic field and the diagnostic magnetic field. A processing circuit is coupled to the at least two magnetic field sensing elements and configured to receive the signal, extract a diagnostic magnetic field portion of the signal representing the diagnostic magnetic field, and generate an error signal if a fault is detected.

The disclosure describes techniques for detecting a crack or defect in a material.

A pulse width modulation (PWM) digital-to-analog conversion circuit includes switches 102, 104, 114, 116 controlled by a first PWM signal, and switches 106, 108, 110, 112 controlled by a second PWM signal. A first operational amplifier (op-amp) includes a first input coupled to an output of a filter, and a second input coupled to an output of the first op-amp. During a first time period, an output of a second op-amp is coupled to an input of the filter via switches 102 and 104, and an output of a third op-amp is coupled to the output of the first op-amp via switches 114 and 116. During a second time period, the output of the second op-amp is coupled to the output of the first op-amp via switches 106 and 108, and an output of the third op-amp is coupled to the input of the filter via switches 110 and 112.

A calibration system for a magnetometer having an unknown gain is disclosed. A calibration magnetic field is generated at a calibration frequency of a known amplitude at the magnetometer. A measurement of the calibrating magnetic field is reported by the magnetometer. A ratio of an amplitude of the calibration magnetic field measurement reported by the magnetometer and the known amplitude of the calibrating magnetic field at the magnetometer is computed. The unknown gain of the magnetometer is determined at least partially based on computed ratio.

Example circuitry includes a first circuit to provide a low signal; a second circuit to provide a high signal, where the high signal has a greater voltage magnitude than the low signal; and a differential amplifier configured to receive the low signal from the first circuit and the high signal from the second circuit. The differential amplifier is for producing an output voltage that is based on the high signal and the low signal. The example circuitry includes a first measurement circuit to measure the output voltage; a second measurement circuit to measure the low signal at the first circuit; and processing logic to determine a differential measurement based on the output voltage measured by the first measurement circuit, the low signal measured by the second measurement circuit, and calibration values obtained for the circuitry.

Self-testing proximity testing systems and corresponding methods are discussed herein and can include a proximity probe and controller in electrical communication via a cable. A self-testing subsystem can be in communication with the controller and configured to determine whether proximity probes and cables assembled with a controller are compatible or incompatible. The self-testing subsystem can place a known impedance in electrical communication with the controller, modifying a proximity signal output by the controller. When the modified proximity signal differs from a predicted proximity signal by greater than or equal to a threshold amount, the self-testing subsystem can output a first indication indicating that incompatible proximity probes and cables are assembled with a controller. When the modified proximity signal differs from a predicted proximity signal by less than the threshold amount, the self-testing subsystem can output a second indication indicating that compatible proximity probes and cables are assembled with a controller.