Measurements of Electric and Magnetic Fields Using Optoelectronic Telemetry

Abstract

In the vicinity of the electric power network and near to the power electrical equipments the electromagnetic environment includes electric and magnetic fields, mainly at the spectral area of Extreme Low Frequencies (ELF). In some cases, very close to the working or areas of habitants, it is important to observe the values of the electric and magnetic fields and to compare those values with the appropriate biological limits and/or to the Electro-Magnetic Compatibility (EMC) limits. In these special cases the fields must be measured successfully and carefully. Therefore, the measurement equipment must have high accuracy and be as small as possible, in order to avoid any impact to the measured field values from the physical presence of the unit or of the observer. For application in these cases we develop an optoelectronic telemetry system, for measurements, of the ELF electric and magnetic fields, with small sensors in the measurement point and all the rest equipment in small distance. The system includes two electro-magnetic optoelectronic sensors, an optical transceiver and all the measurement electronic circuits. By that method we applied the two appropriate optoelectronic sensors at the measured point and in some distance (up to 100m) an optical (laser) transceiver followed by the measurement circuits. If the outcome laser beam from the transceiver strikes the optoelectronic part of these sensors. Then, that part is triggered to modulate the reflected and returned laser beam. The modulation value depends on the field value. At the receiver part of the optical transceiver, a special optical demodulator extracts the modulation signal from the incoming laser beam and the following measurement electronic circuits extracts the information with the measurement values of the electric and magnetic fields. We must point out that the few mW red beam from a diode laser, has very low power to be an injury problem to the observer or to any other person, except the case when someone stares at the laser beam (intrabeam view). In our paper we give details of the optoelectronic measurement unit, followed by the calibrating and testing results in two applications in Athens.