REFLECTION SENSOR

PURPOSE:To enable setting of a detecting level (threshold value) automatieally and at the optimum level corresponding to the coefficient of reflection of a specimen, by installing 2 light-receiving sensors in symmetrical positions viewed from a light- emitting element. CONSTITUTION:Light-receiving sensors 2, 2' are installed in positions symmetrically viewed from a light-in radiating element 1. A beam of light strikes at a specimen 4 from the light-emitting, element 1 and a portion of it is reflected by the sensors 2, 2'. At this moment, light quantities being reflected are of approximately the same and consequently, outputs from the sensors 2, 2' of the same character is turn out approximately the same. Further, an output of the sensor 2 is delayed by constant time by a delay circuit 8 and then admitted into a comparator 7 and an output of the sensor 2' is admitted into the comparator 7 after damping it to a certain fraction of the original magnitude by a voltage divider 6. When this certain fraction of the output is assumed as the reference voltage of a threshold value, as the reference voltage changes according to the coefficient of reflection of the specimen 4, detection error and deviation of detection position can be prevented. In this case, the output of the sensor 2 is delayed intentionally for prevention of erroneous operation, deterioration in reproducibility by giving the definition of the reference voltage first and then performing the comparison.