Abstract: A proximity switch for determining the approach of a metal object includes an oscillating circuit which has a coil and a capacitor, and which produces a high-frequency field at the poles of the coil. A sensing resistor is connected to the oscillating circuit and serves to determine and evaluate the damping of the oscillating circuit by the object. Also, the sensing resistor is controlled as a function of the current measured in the sensing resistor such that the total resistance of the evaluation circuit remains constant. The voltage drop across the sensing resistor is measured and the measured voltage drop may be used to signal the approach of the metal object.

Abstract: A cutting machine for mining minerals from a seam thereof, the machine executing reciprocal movements parallel to the face of the seam and being provided with switches for generating signals indicative of the direction of movement of the machine for controlling the removal of protective bumpers on support structures located forwardly of the machine and for moving support structures against the face of the seam and relocating bumpers rearwardly of the machine.

Abstract: An apparatus is disclosed for adjusting the height of a monitor with respect to the rail head of a rail having a first bracket adapted to be connected to the rail and a secured bracket adapted to be connected to the monitor, the brackets are releasably connected to each other by a vertically movable slide arrangement comprising mating surfaces one of them having an elongate recess and the other having a complementary protrusion to prevent relative tilting or canting of the brackets.

Abstract: An overpressure-control valve has a valve housing formed with a front output chamber, a back intake chamber adjacent and back of the output chamber, and a valve seat lying between the chambers. A valve body can move in the housing forward toward the valve seat into a closing position on the seat and blocking flow between the chambers and backward from the valve seat and into an open position permitting flow between the chambers. This body has at least one forwardly directed face and at least one backwardly directed face exposed in the chambers. The effective surface area of the forwardly directed face is greater than that of the backwardly directed face. A spring urges the valve forward into the open position with a predetermined generally constant biasing force so that the valve body moves back against the spring into the closed position when the backwardly effective pressure on the forward face overcomes both the force of the spring and the pressure on the back face.