In-circuit Impedance Research Articles

A Novel Single-Probe Setup for Multifrequency Simultaneous Measurement of In-Circuit Impedance

The single-probe setup (SPS) based on the inductive coupling approach is a promising candidate for in-circuit impedance measurement of an energized electrical system due to its non-contact characteristics and simple configuration. However, the conventional SPS performs the measurement with a frequency-domain measuring instrument via stepped swept-sine excitation. It measures in-circuit impedance at only single frequency at a time while sweeping across frequencies of interest, which is not only inefficient but also not fast enough to capture in-circuit impedance with time-variant characteristics. To overcome these limitations, this paper proposes a novel SPS with a time-domain measuring instrument via multi-sine excitation. The proposed SPS can perform multi-frequency simultaneous measurement of in-circuit impedance without direct electrical contact. By combining it with a short-time Fourier transform (STFT) algorithm, in-circuit impedance with time-variant characteristics can be captured. Experimental case studies validate the capability and accuracy of the proposed SPS.

Single-Probe Inductively Coupled In-Circuit Impedance Measurement

Conventional in-circuit impedance measurement setup of the inductive coupling approach requires two inductive probes. This article proposes a single-probe setup for the in-circuit impedance measurement, which not only eliminates the probe-to-probe coupling issue but also simplifies the setup with less instrument overhead. The basic principle behind the proposed setup will be elaborated, followed by experimental validation. To ensure the proposed setup can extract the in-circuit impedance with good accuracy, the required signal-to-noise ratio (SNR) of the setup is carefully studied. In addition, to improve the SNR and the ruggedness of the setup, signal amplification and protection devices are incorporated in the measurement. Finally, the proposed setup is deployed to demonstrate its ability to extract the in-circuit impedance of an energized induction motor.

Improved calibration technique for two-probe setup to enhance its in-circuit impedance measurement accuracy

The in-circuit impedance is a key parameter to evaluate the health and operation of many electrical systems. The two-probe setup (TPS) based on the inductive coupling approach is preferred for in-circuit impedance measurement because it does not require physical electrical contact with the energized system under test. However, the existing calibration technique for the TPS degrades its measurement accuracy at relatively high test frequencies. To enhance the measurement accuracy of the TPS, this paper proposes an improved calibration technique. It considers the frequency-dependent effects of the selected calibration components so that the TPS can maintain good measurement accuracy even at relatively high test frequencies. Using an actual TPS as a test case, experimental results show that the TPS based on the proposed calibration technique maintains good measurement accuracy up to 10 MHz, whereas the same TPS based on the existing calibration technique exhibits significant measurement errors when approaching 10 MHz.

Eliminating the Effect of Probe-to-Probe Coupling in Inductive Coupling Method for In-Circuit Impedance Measurement

The in-circuit impedance serves as a key parameter for evaluating the operating status and health condition of many critical electrical assets. For its noncontact nature and simplicity in on-site implementation, the inductive coupling approach is an attractive method to extract the in-circuit impedance of an electrical system. In some practical situations where there are space constraints, the inductive probes used in this approach are very close to each other and the probe-to-probe coupling between inductive probes cannot be ignored. This article investigates possible errors due to such coupling and proposes an open-short-load calibration technique and a proper measurement process to minimize the error in the measured in-circuit impedance.

Systematic Common-Mode Filter Design for Inverter-Driven Motor System Based on In-Circuit Impedance Extraction

Inverter-driven induction machines often suffer from premature bearing failure due to high-frequency common-mode (CM) voltage and induced CM current. One effective remedy is adding a CM filter to suppress the CM current. Optimal CM filter design requires prior knowledge of both noise source and termination impedances. With an improved in-circuit impedance measurement setup, the CM noise source impedance of a high-power inverter-driven motor system with strong background noise can be extracted. The setup also protects the measurement instruments from surges and transients from the harsh operating environment. The extracted noise source impedance allows a CM filter to be designed systematically without overdesigning. In the evaluation of the first-order single-inductor and second-order LC filters, it is found that the second-order CM filter is prone to differential-mode to common-mode (DM-to-CM) conversion, especially at the resonant frequency caused by the leakage inductance of the CM choke and the equivalent DM capacitance of the line-to-ground capacitors. Therefore, an additional DM inductor is necessary to curb the mode conversion, which may not necessarily result in final size reduction as compared to that of first-order single-inductor filter.

Voltage-Dependent Capacitance Extraction of SiC Power mosfets Using Inductively Coupled In-Circuit Impedance Measurement Technique

The voltage-dependent capacitances of silicon carbide power metal–oxide–semiconductor field-effect transistors ( mosfets ) affect the switching characteristics and have a direct impact on the electromagnetic compatibility (EMC) performance of the power conversion circuit. To predict and mitigate the potential impact on EMC in the early design phase, the capacitances have to be obtained accurately. In this paper, a novel method is proposed based on an inductively coupled in-circuit impedance measurement technique. The proposed method extracts the voltage-dependent capacitances of a mosfet under its actual biased voltage without making any direct electrical contact, and hence eliminates potential safety hazards. Once the inductive probes are characterized, there is no need to re-calibrate the setup prior to each measurement, and therefore, it simplifies the whole measurement process. The accuracy of the extracted voltage-dependent capacitances for the SiC power mosfet has been validated experimentally.

Time-Variant In-Circuit Impedance Monitoring Based on the Inductive Coupling Method

In-circuit impedance extraction of a time-variant electrical system is essential for real-time condition monitoring purpose. This paper looks into the design consideration of real-time in-circuit monitoring for a time-variant system based on inductive coupling approach and discrete Fourier transform in a moving window. By using two clamped-on-type inductive probes, the proposed setup eliminates the need of voltage sensors to measure the terminal voltages of system-under-monitoring (SUM) and, hence, eliminates direct electrical contact with the SUM. Therefore, it facilitates ease of mounting and disassembly. Experimental results show that with careful design consideration, the proposed method has the ability to measure the in-circuit impedance of a time-variant system in real time, which facilitates useful inputs for early detection of abnormality of the monitored electrical system that is time variant in nature.

Inductive Coupled In-Circuit Impedance Monitoring of Electrical System Using Two-Port <italic>ABCD</italic> Network Approach

By treating the inductive coupling probes and the electrical system to be monitored as three cascaded two-port ABCD networks, the in-circuit impedance of the electrical system can be extracted with ease. The proposed method simplifies the setup calibration and allows real-time impedance monitoring of critical electrical system to be implemented without interrupting its normal operating conditions. In this paper, the theory behind the proposed ABCD networks approach is described. The proposed approach has overcome the poor measurement accuracy of the conventional inductive coupling calibration method above 30 MHz and has achieved good accuracy up to 100 MHz with a maximum measurement deviation of 3.6%. Finally, using a dc-powered motor as a practical example, the ability to detect the change of in-circuit impedance of the motor under different operating conditions is demonstrated.

Development of Active Bridge Technique for Measuring Low Capacitance Over Wide Frequency Range

A new technique, employing active devices, is developed for the accurate measurement of a small capacitance. It is an extension of the method developed for the measurement of in-circuit impedance by TRA (Transformer Ratio Arm) bridge technique and an active bridge technique for measuring in-circuit resistance. It employs one inverter, one quadrature amplifier and a standard capacitance. The circuit developed minimizes the effect of earth capacitances and is useful for measuring capacitance over a wide frequency range (typically, up to 2 MHz). SPICE simulation and experimental results support the theory developed. The active bridge circuit has been utilized to obtain the sensitivity of a porous silicon capacitive relative humidity sensor.

A TRA Bridge Technique for In-Circuit Impedance Measurement

A bridge technique is given for the measurement of impedances of two-terminal passive components in an arbitrary network without opening the circuit connections. It is ideally suited to the in-circuit measurements of passive elements in hybrid integrated circuits (HIC's) and printed circuit boards (PCB's). The method employs a new type of bridge, basically improvised from a transformer ratio-arm (TRA), a quadrature amplifier (QA), and two standard capacitors. All the measurements are in terms of the capacitors and the turns ratios of the TRA, and provide results with good accuracy. The range of measurement, together with the sources of error and their minimization, are discussed. Experimental results are found to be in good agreement with the theory.