Publications
1. Tetsuya Kajita, Un-Ku Moon and Gabor C. Temes, “A noise-shaping accelerometer interface circuit for two-chip implementation,” Proc. of IEEE International Symposium of Circuits and Systems, vol. IV, pp. 337-340, May 2000.2. Tetsuya Kajita, Un-Ku Moon and Gabor C. Temes, “A noise-shaping accelerometer interface circuit for two-chip implementation,” IEEE IMTC (Instrumentation and Measurement Technology Conference), May 2001.3. Tetsuya Kajita, Un-Ku Moon and Gabor C. Temes, “A noise-shaping accelerometer interface circuit for two-chip implementation,” VLSI Design, to appear in 2001.4. Tetsuya Kajita, Gabor Temes and Un-Ku Moon, “Correlated double sampling integrator insensitive to parasitic capacitance,” Electronics Letters, to appear.5. Kolodziej, W.J., and Khapalov A.Y.,
“Controllability and placement of FACTS devices,” Proc. of Stockholm Power Tech International Symposium on Electric Power Engineering, Stockholm, Sweden, June 1997.
“Controllability and placement of FACTS devices,” Proc. of Stockholm Power Tech International Symposium on Electric Power Engineering, Stockholm, Sweden, June 1997.
Report
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A detection technique was developed to identify the optimal sensor locations and to provide vibration signature patterns. The primary criterion was to maximize the measurement sensitivity with respect to vibrations corresponding to natural shaft frequencies, while controlling the influence of the electromagnetic noise. The best location for 16-sensors mounted on a coupled, two segments drive shaft was found numerically. Two models of the actual electromechanical machines were studied: a 300hp drive and a generator at John Day power plant (part of the North Western American Power System).A new architecture for a sensor interface circuit using a delta-sigma modulator was developed, specifically for the monitoring of sub-synchronous resonances (SSRs). A surface MEMS accelerometer sensor detects any unexpected vibration indicative of SSR.The interface circuit is implemented on a separate chip, to allow the use of commercial sensors, and the multiplexing of many sensor chips placed at strategically chosen points on the turbine-generator shaft. The major challenge is measuring extremely small capacitance variations, of the order of attofarads, occuring in the sensors in the presence of large parasitic capacitances as large as 20 picofarads.A novel high-order delta-sigma structure was used to improve the SNR. The newly proposed structure consists of a simple, trimm-free digital compensator and a novel multi-level force feedback branch using mismatch shaping. A new time-averaged force-feedback scheme is used to linearize the multi-level force feedback. This provides proper operation in the presence of process variations in the MEMS, e.g., imperfections in the mask alignment, as well as clock jitter and inaccuracies of the force-feedback period.Also, a new correlated-double sampling (CDS) integrator was developed, which reduces signal errors due to the op-amp’s finite gain and offset voltage and to charge injection and clock feedthrough noise from the switches. The cross-coupled CDS integrator structure reduces errors caused by the large parasitic capacitors, and enhances the small sensor signal superimposed on the large common-mode signal. An efficient dithering circuit was also developed.
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