Abstract: A proximity switch which can detect any metal with equal changing rate of oscillating frequency, regardless of what kind of metal it may be (magnetic or nonmagnetic), is disclosed. The invention employs a series circuit consisting of a resistor and a first capacitor connected to the output side of a comparator. A detector coil and a second capacitor are connected in parallel to the first capacitor. By selecting appropriate capacitance and resistance values for these components, it can be insured that the change in oscillating frequency corresponding to the distance of an approaching object will be very nearly be identical regardless of the type of metal of which the object is constituted. An embodiment employing a frequency to voltage converter is also disclosed. The arrangement provides continuous detection also suitable for use in range indicator and self diagnosis applications.

Abstract: A reflective-type photoelectric switch projects emitted light from a light-emitting element toward a detection zone by a light-projecting optical system, and guides reflected light from an object to be detected in the detection zone to a light-receiving element by a light-receiving optical system. A special optical element is used in part of at least one of the two optical systems. The optical element functions to diverge light in a direction parallel to a plane containing the optic axes of the light-emitting and light-receiving elements, and condense light in a direction perpendicular to the same plane. As a result, it is possible to detect, with excellent sensitivity, both an object which is far from the switch and an object very near the switch.