ANALYSIS OF ADAPTIVE DIGITAL AC BRIDGE EMPLOYING STOCHASTIC GRADIENT SEARCH ALGORITHM
Dr.S. EDWARD RAJAN Dr.K.MUNEESWARAN
Bridges are the measuring devices used for accurate measurement of impedance. This paper proposes an automatic digital AC Bridge model employing closed loop control system to measure impedance of passive networks for frequencies even up to 1 MHz. In this adaptive digital AC Bridge, balancing is achieved by means of Stochastic Gradient Search Algorithm. Among the various gradient search techniques, the Widrow-Hoff’s Least Mean Square (LMS) technique has been chosen, as it involves less computational burden. The digital AC Bridge is balanced by controlling the in-phase and quadrature component of the complex voltages. The stability of the bridge is controlled by the parameter (), which also determines the adaptation rate. The system is tested for measuring impedances of pure and impure inductors, capacitors, and a series combination of an inductor and a capacitor. The effects of various parameters like input voltage, reference resistance, learning rate, and sampling rate are simulated and studied using programs written in C++ and the results are reported. The proposed model is advantageous over the traditional heuristic method with higher accuracy, faster convergence, better reproducibility, and reliability.
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