Abstract: The earth leakage breaker of the invention includes a first comparator; a second comparator connected to the first comparator; a third comparator having a threshold higher than the threshold of the first comparator for distinguishing a leakage current from the grounding current caused by a lightning surge or by the heavy ground fault; a monostable multivibrator triggered by the output of the third comparator for forming a time gate of a predetermined period; a counter for detecting a pulse outputted from the first comparator to distinguish whether the grounding current is caused by the lightning surge or by the heavy ground fault; and a trip signal generator circuit for outputting a trip signal in the case of leakage and heavy ground fault. The earth leakage breaker facilitates avoiding unnecessary breaking of the impulsive grounding current caused by the lightning surge.

Abstract: An optical switch having two spherical or elliptical corner-reflecting surfaces provided in a light-conducting member, a shutter to open and close a light path between the corner-reflecting surfaces, and focusing lenses to focus the incident beam from an emitting optical fiber and to focus the emitting beam from the light-conducting member to a primary receiving optical fiber. Because almost all the beam transmitted through the light-conducting member is focused at one point in an air gap in which the shutter moves, the optical switch can transmit the beam with high efficiency without leakage to the outside, and a small stroke of the shutter is sufficient to completely transmit or stop the beam.

Abstract: The present invention relates to a photoelectric switch which has a light projecting means that projects light pulses as a result of a pulse signal and a light receiving means that receives the light pulses and outputs a light receiving signal. In one arrangement an enhanced voltage of about two times the supply voltage is applied to a light projecting element, such as an LED, thereby making it possible to provide a photoelectric switch which operates at a reduced power supply voltage. By providing a composite LED drive voltage the drop in supply voltage, inherent in conventional photoelectric switches when the output circuit is activated (thereby reducing the voltage to the light emitting element) does not inhibit operation.

Abstract: A photoelectric switch with a pulse width discrimination circuit ensuring that an object may be surely detected even when there are a plurality of adjacent photoelectric switches, and with an amplifier having a saturation characteristic preventing function ensuring that the pulse width is not changed when the input to the amplifier is large.

Abstract: A contactless switch for controlling a thyristor switching element by means of a sensor circuit includes a bridge rectifier across whose input terminals are connected in series on AC power supply and a load and across whose output terminals are connected the thyristor. The switch includes a constant-voltage circuit which charges a capacitor whose charge controls the state of the thyristor. The constant-voltage circuit is controlled by a disabling circuit which is controlled by the output of the sensor circuit. There is included a timing circuit supplied by the output of a current detection circuit which measures the charging current and is able to suspend the functioning of the disabling circuit for a prescribed period of time.