光電界センサの感度特性解析と伝導妨害波測定用容量性電圧プローブに関する研究 Study on Sensitivity Analysis of Optical Electric-Field Sensor and Capacitive Voltage Probe for Measuring Conducted
Study on Sensitivity Analysis of Optical Electric-Field Sensor and Capacitive Voltage Probe for Measuring Conducted
Along with the advent of Internet technologies, a configuration of telecommunication networks are changing and services provided by them are shifting from Plain Old Telephony System to Digital or Internet-Protocol (IP) Systems.This paper describes a sensitivity analysis of the electric field sensor using optical modulator and methodologies for measuring conducted electromagnetic disturbances. The purpose of this paper is to provide precise measurement technologies for evaluating electromagnetic environment in vicinity of telecommunication equipment. For this purpose, sensitivity analyses of the electric field sensor, development of capacitive voltage probe for non-contact measurement and method for determining a transmission direction were carried out.In sensitivity analysis of the electric field sensor, first, the sensitivity calculation method by using equivalent circuit was evaluated. The parameters of the circuit were obtained theoretically and experimentally. The electric field sensor with designed parameter was made and its experimental characteristics were compared with theoretical one, in order to clarify main factor of sensitivity deviation. The results show that the difference between measured and calculated results depended on the value of capacitance and insertion loss of the sensor. However, the calculated result using measured parameters agreed with measured one. This means that the sensitivity of the sensor can be calculated by using its equivalent circuit.Secondly, method for controlling the optical bias angle was carried out. An optical bias angle is an important parameter that determines a driving point of the electric field sensor. The adjustment method by applying a stress to the end of the optical modulator’s substrate was examined theoretically and experimentally. As a result, it is shown that the optical bias angle can be adjusted with the refractive index change by a photo-elastic effect and the elongation of a waveguide by a stress.Moreover, narrow band resonance of the electric field sensor in frequency range from 1 to 100 MHz was examined by taking the piezoelectric effect into consideration, theoretically. The result clarified that the narrow-band resonance depends on the width of the substrate. Therefore, it is shown that the resonance disappeared by changing the width of the substrate along the longitudinal direction.For conducted disturbance measurements, voltage probe by measuring common-mode disturbances without touching conductor and determination method for transmission direction of conducted disturbances were developed and evaluated theoretically and experimentally.A capacitive voltage probe was developed for measuring common-mode voltage on a cable without contacting its conductor. The characteristics of the probe and measurement error of the probe were evaluated. The results show that the probe has flat sensitivity in a frequency range from 10 kHz to 30 MHz. Also, dependence of the cable configuration (e.g. radius, position in an electrode) was evaluated by using equivalent circuit. The results show that this probe can measure the conducted common-mode disturbances, and its characteristics can be calibrated by theoretical analysis or experimental calibration data. Therefore, characteristics of this probe are enough to measure the conducted disturbances.Finally, determination method for transmission direction of the conducted disturbances on the cable was developed and evaluated its validity in the field. A transmission direction of the conducted disturbance can be obtained by focusing on an active power calculated by measuring voltage and current, simultaneously. Measurement system was developed and evaluated validity of this method. The experimental results show that transmission directions of both sinusoidal and non-sinusoidal waves can be obtained by measuring its active power. Moreover, this method was applied to EMC trouble in the field. The result shows that the source of the trouble can be determined by detecting transmission direction of the disturbance. This means that effective countermeasures against the trouble in the field can be carried out. Therefore, it is confirmed that proposed method is useful for searching disturbance sources in the field.