Adaptive thresholding for metal detection

摘要

A two-channel metal detector system disposed adjacent the crop feed path of a harvester to detect ferrous metal objects in the crop material is provided with both positive and negative adaptive detection thresholds for each channel, the thresholds being independently varied according to the average positive and negative peaks of the noise component in the channel output signals. A channel output signal is sampled and digitized and the positive and negative peaks of the noise component occurring over fixed time intervals are filtered to provide average positive peak and average noise peak values that are stored in an E2PROM and updated according to long term variations in the noise component. The positive and negative adaptive detection thresholds are set according to the average positive and negative peak values and the adaptive detection thresholds are compared with the sample channel output signal to determine if a ferrous metal object has been detected. By storing the positive and negative average peak values of the noise component in an E2PROM memory, the adaptive detection thresholds and the filters may be initialized at system start-up to the values existing at the time of system shut-down.