PROXIMITY SWITCH

PURPOSE:To diagnose abnormality of the whole of a proximity switch regardless of existence of any object, and without affecting a normal operation condition. CONSTITUTION:An object is detected by an oscillation circuit 1 and a signal process circuit 2, and the output is given to a detection output holding circuit 3. When there is a self-diagnosis input signal, the output is held once, and oscillation condition is reversed after a delay time passes in a delay circuit 7. When the output of the signal process circuit 2 is reversed simultaneously, an AND circuit 11 or 13 reaches an H-level, enabling the judgment of a normal condition. Since such a change does not occur in an abnormal condition, abnormal condition can thus be judged.