Darkfield - for objects with low contrast with relatively transparent backgrounds. The CCD video camera functions as a scanning light detector. An electronic beam moves across the objects in a series of horizontally adjacent lines, generating a continuous video signal. The video signal is compared with a present sensitivity and size threshold established initially by the operator. These thresholds are controlled by the sensitivity and size adjustments.
Optimum sensitivity is determined by an operator assisted sensitivity indicator.
When the thresholds are exceeded, a pulse is generated by each object. Therefore, the smaller particles and debris which are below the threshold are not detected. After the entire scan is completed, the total thresholds are exceeded, a pulse is generated by each object. Therefore, the smaller particles and debris which are below the threshold are not detected. After the entire scan is completed, the total of signals exceeding the threshold is displayed as the count.