Kaihao Tang

PT-symmetric exceptional points (EPs) are singular points where both eigenvalues and eigenvectors become degenerate, and whose bifurcation characteristics have been utilized to design high-sensitivity sensing systems. In this Letter, an amplitude-readout EP-locked displacement sensing system with sensitivity beyond conventional frequency-based methods is proposed. We observed that when a PT-symmetric coupled-resonator reader operates at the EP, the amplitude variation in the gain resonator shows significantly higher sensitivity to LC sensor displacement than the frequency shifts. The amplitude change exhibits a linear dependence on κs, significantly simplifying system calibration and enabling more accurate displacement measurements compared to the nonlinear dependence. A printed circuit board-based circuit prototype is built to validate our findings. This work enriches the sensing methodologies based on PT-symmetric EPs, showing potential applications in implanted medical devices, industrial nondestructive testing, etc.

It is of great significance for power systems to realize an accuracy and reliable monitoring of the weak shaft current since it is usually associated with early failures of generators. To achieve an effective measurement for weak shaft current, this paper proposes a non-contact shaft current measurement method for mA-level alternating current used in power systems. Firstly, principles and challenges of CT’s being applied to mA-level alternative current sensing are discussed. A split CT with magnetic shielding is proposed for mA-level current detection, along with a specially designed signal conditioning circuit. Correspondingly, the calculation method of the CT’s signal amplitude based on the quad-phase phase-sensitive detection algorithm is proposed, with a preprocessing algorithm used to eliminate modulation signal interference. Then, a multi-branch shaft voltage sampling circuit in cooperation with the least square optimization used for current demodulation is introduced, considering the actual CT output model. Further, the designed current measurement system which consists of the split CT, the CT’s conditioning circuit, and the multi-branch shaft voltage sampling circuit is analyzed. Finally, an experimental platform is designed and built for verification. The experimental results show that the non-contact measurement method for shaft current proposed in this paper is feasible, and the designed current measurement system can achieve an accuracy rate of over 90% for current detection within 10–50 mA. It provides a new solution for the detection of weak shaft current in power systems.

This study investigates the security control problem of interconnected nonlinear power systems (INPSs) involving the wind farm subjected to actuator deception attacks. A dynamic event-observer-based sliding mode controller is presented to guarantee the stability of the INPSs. First, a novel memory-based integral composite observer is presented to estimate the unknown variables, including lumped disturbances, deception attack functions and partial states of the power system. In this estimation scheme, a dynamic event condition is designed to achieve the transmission efficiency. Then, based on the estimation outputs, an observer aided sliding mode manifold is designed, and the stability of the overall INPSs is analyzed after the trajectory of the power system reach onto the manifold. Moreover, a security controller is designed to ensure the reaching ability and to recover the system performance with the help of the estimation values. Finally, the compensation ability of the presented method is verified by a class of two area power systems.

An electrical capacitance tomography (ECT) sensor is an array capacitive sensor that is sensitive to the medium of the measured object and can be widely used in oil, natural gas, machinery and other industrial fields to solve the problem of multiphase fluid object parameter detection in industrial processes. However, ECT sensor uniformity defects need to be addressed. Aiming at the problem that the non-uniform electrode spacing angle affects the characteristics of the measured value of the actual ECT sensor, a method for compensating the measured value of the ECT sensor based on the assumption that the geometric factor is invariant is proposed. The simulated measurement value in the case of the tube and the measurement value of the actual sensor in the case of an empty tube and a full tube are to compensate the measurement value of the actual ECT. Experiments show that, without compensation, non-ideal sensor monitoring has large error, and, after compensation, it has a good effect and can be expected to perform satisfactorily in practical use.

By applying an electrical capacitance sensor to sectional water fraction measurement for gas–water (salinity) two-phase flow, this paper investigates the effect of a medium’s conductivity on the measurement of capacitance sensors and its elimination. Firstly, the mechanism of how a medium’s conductivity influences the capacitance measurement of a capacitance sensor is analyzed by combining a physical model of the sensor with its conditioning circuit. The theoretical analysis indicates that the applied exciting frequency is a key factor influencing the conductivity effect; the effect can be restrained by increasing the excitation frequency. Then, an exciting frequency optimization rule is proposed accordingly. In addition, sensor configuration and geometry optimization (based on finite element method simulations) are discussed to achieve better performance. Dynamic and static calibration experiments are carried out for stratified gas–liquid (salinity) two-phase flow for the purpose of validating the proposed method. The experimental results confirm the effectiveness of the proposed method. This work is constructive to the design of capacitive sensing technologies applied to conductive objects, and offers insights into the structural design and optimization of capacitance sensors.

This paper presents a sectional water fraction measurement method using electrical capacitance tomography (ECT) image. To achieve a desired measurement accuracy, an optimal threshold-search method based on fast simulated annealing (FSA) algorithm is applied for image binarization; and to guarantee the imaging time consumption, fast fixed point continuation (FFPC) iterative algorithm cooperating with the compressed sensing (CS) theory was applied to the image reconstruction. In this study, the imaging time consumption and the measurement accuracy of water fraction are used to compare the proposed method and other methods. A numerical model is established with COMSOL Multiphysics to conduct the simulative validation of the proposed method firstly and physical experiments are conducted then. The experiment results show the average relative error of water fraction is lower than 15%, where the even as low as 3.68%.

In industrial production processes, rotational speed is a key parameter for equipment condition monitoring and fault diagnosis. To achieve rotational speed measurement of rotational equipment under a condition of high temperature and heavy dust, this article proposes a digital approach using an electrostatic sensor. The proposed method utilizes a strip of a predetermined material stuck on the rotational shaft which will accumulate a charge because of the relative motion with the air. Then an electrostatic sensor mounted near the strip is employed to obtain the fluctuating signal related to the rotation of the charged strip. Via a signal conversion circuit, a square wave, the frequency of which equals that of the rotation shaft can be obtained. Having the square wave, the M/T method and T method are adopted to work out the rotational speed. Experiments were conducted on a laboratory-scale test rig to compare the proposed method with the auto-correlation method. The largest relative errors of the auto-correlation method with the sampling rate of 2 ksps, 5 ksps are 3.2% and 1.3%, respectively. The relative errors using digital approaches are both within ±4‰. The linearity of the digital approach combined with the M/T method or T method is also superior to that of the auto-correlation method. The performance of the standard deviations and response speed was also compared and analyzed to show the priority of the digital approach.

To realize non-contact measurement of rotational shaft centerline orbit, a shaft centerline orbit reconstruction method using a specifically designed electrostatic sensor in conjunction with neural network approximator is proposed in this paper. The sensing principle of the designed electrostatic sensor is based on partial capacitance theory. The proposed sensor consists of one electrostatic field excitation electrode, two sensing electrodes, and a cylindrical metal shield covering the three electrodes. It directly establishes the map from sensor output (voltages between sensing electrodes and shield) to shaft center position through neural network approximator, so that the shaft centerline orbit can be reconstructed. The CAE software COMSOL Multiphysics is used for sensor modeling and simulation analysis. The simulation reconstruction experiment is carried out to test the performance of the proposed sensor and to obtain training data for the neural network. The experiment result shows that the RMS error of the proposed sensor is within 0.4 μm, which has proved the feasibility of the novel sensor combined with neural network fitting algorithm for industrial applications.