Abstract: A device for detecting a primary fault current at a three phase current system and converting the detected fault current into mechanical action for breaking the circuit includes circuitry for breaking the circuit in response to a selected secondary current substantially instantaneously rising to a predetermined level and a device for adjusting the predetermined level.

Abstract: Apparatus for detecting a primary fault current in a three-phase current system and converting the detected fault current in the mechanical action for breaking a circuit in which the primary fault current occurred includes a combination of transformers and diodes for receiving the three phases of current, providing corresponding phases of secondary current within a predetermined desired amperage metering range, choosing the largest magnitude secondary current and providing the largest magnitude secondary current as output, a resistor for providing voltage proportional to the largest magnitude secondary current, a capacitor for storing a peak value of the voltage which is proportional to the largest magnitude secondary current and a latching circuit for moving a trip member and providing mechanical action in response to the largest magnitude secondary current exceeding a predetermined level.

Abstract: An apparatus is disclosed for measuring the thickness of the cornea and for regulating the depth of a surgical blade in relation to the local corneal thickness. Corneal thickness is measured by first directing ultrasonic pulses towards the cornea and timing the interval between reflected pulses. The apparatus also includes a pulse stretcher for enlarging the width of the pulse representing the interval between pulses reflected from the inner and the outer surfaces of the cornea, so that the time between pulses can be accurately measured by a conventional, low-frequency electronic clock. The invention further comprises electronic gating means for rejecting spurious pulses.