Noise reduction in optical measurement systems

The cost of conventional current and voltage measurement equipment has led to an increasing interest in systems using a minimum of expensive insulation. At CERL, several optical systems for the measurement of current and voltage have been produced. These devices are found to suffer from noise due to intensity fluctuations of the light source and the wandering of the light beam across the photodetector surface caused by vibration and atmospheric turbulence. In the paper several possible techniques to reduce this noise are outlined, and a novel modulation scheme which has produced an improvement in the signal/noise ratio of over 20 dB is described. A device for the simultaneous measurement of voltage and current, making use of this system, is soon to go on trial at a generating station.