drift correction technique

sensitivity of an electromagnetic type metal detector is directly related to stability, the higher the required sensitivity, the more frequently the rebalancing controls will have to be adjusted. thus, for maximum sensitivity in the head ,the use of automatic drift compensation network is necessary in order to cancel out the signal resulting from a slow drift in the coil system due to the temperature changes. the imbalance signal, although small in the head itself, gives rise, after amplification, to a large unwanted signal. the purpose of this article is to indicate how drift correction technique can be applied to a 100 khz electromagnetic field type metal detector.