Abstract: The integrity of mine roofs and rock bolts is tested by determining the natural frequencies of the roof and bolt. The roof is struck at a plurality of locations and the resulting vibrations sensed with accelerometers. The output of each accelerometer is separated into a plurality of signals of different frequencies by a comb filter having selected band passes. The amplitude of the outputs of each of the band passes of the filter are used to determine the condition of the roof and bolt adjacent each accelerometer. The high amplitude signal resulting from the initial impact of the striking implement is electrically gated from the accelerometer output.

Abstract: An electrode assembly formed by three pairs of electrodes creates a three axis electrical field which surrounds a charged particle confined in a sealed space consisting either of a vacuum or one filled with a selected gas. The field is energizable whereby to support the particle centerably in a state of stable equilibrium. A detector mounted exteriorly with respect to the electrode assembly is responsive to displacement of the particle from the central position, as the result, for example, of acceleration due to gravity or other motion, and a restoring force in operable association with the detectors and the electrical field is triggered by the displacement to return the particle to the central position.

Abstract: An apparatus for maintaining sliver thickness uniform whereby the web from a carding machine is gathered by a trumpet and passed between a grooved driven roller and a sensor roller riding in the groove so that the movements of the sensor roller vary as a function of sliver density. The sensor roller is mechanically connected to a magnetic core so that movement of the sensor roller varies the coupling between a primary transformer winding and a pair of secondary windings. The voltages induced in the secondary windings are applied, after a delay, to a first differential amplifier whose output in turn is connected to a second differential amplifier which is periodically rendered operative by a pulse generator and to which is also connected a potentiometer for adjusting desired density. The output of the second amplifier is connected to a pair of relay coils, one responsive to positive excursions and the other to negative.

Abstract: The disclosed triangular folding reflective marker comprises a reflective base member and a pair of reflective side members which are pivotally connected to opposite ends of the base member and are swingable between folded positions, adjacent the base member, and inclined erected positions, in which the side members and the base member form an upright triangular reflective warning device, for use in warning motorists of the presence of a disabled automobile or other vehicle. Latching elements are provided to fasten the upper ends of the side members together in their erected positions. Such latching elements may comprise latching pins projecting laterally from flanges on the side members, such flanges being adapted to overlap. Portions of the flanges may be formed with latching slots adapted to receive the latching pin elements with a detent action. The side members may be formed with end elements which are adapted to project beyond the edges of the opposite side members when they are erected.