Field distortion effects by an electro-optical field sensor and the resulting influence on the sensor output

The use of electro-optical sensors to measure the electrical field in or around technical devices is becoming more common. The paper deals with the following problems: how and how much does the sensor deform the field by its presence in the field region? does the field deformation around the sensor have an influence on the validity of the calibration? and which differences according to the field deformation during calibration and measurement have to be expected between the “real” field vectors of the undistorted field distribution and the vectors derived from the measured signals? The investigations are performed using a common type of field-sensor. At first some possible sources of error due to the change of field vectors inside the given inner structure of the sensor are mentioned. Then the usual calibration procedure of the sensor inside a plane-plane capacitor in air is discussed on the basis of field simulation results. Particular emphasis is on proximity effects near the electrodes. A field simulation of a complete measuring session is discussed. This simulated session includes on the one hand the above mentioned calibration procedure. On the other hand the measurement at several field positions around a cable termination was simulated. Besides the “measured” field vectors at these positions, the undistorted field vectors at the same positions were determined. In order to evaluate the field distortion effect by the sensor and the resulting inaccuracy, each couple of vectors were compared by absolute value and angle