Abstract: Various forms of hydraulic cylinders having axial bores formed in their piston rods, and probes projecting axially from the closed end of the cylinder body with two spaced coils thereon are disclosed. The coils are connected into external circuitry which responds to change in inductance of either coil whereby to generate a reference signal upon the occurrence of preselected changing conditions of inductance of either coil caused by movement of that coil into or out of mutual induction with a shorted turn arrangement formed by or carried by the piston. The coils may be the drive coils of a displacement transducer arranged to indicate either end of the stroke of the piston. Alternatively either a supplementary shorted turn or an additional drive coil may be provided to generate an intermediate stroke reference signal. The reference signals may be used in operation of a system for effecting automatic continuous reciprocation of the piston.

Abstract: A stacking method is employed to assemble a structure which includes a plurality of substantially identical, uniformly spaced parallel glass plates. The method includes the use of a fixture having a slotted surface in which rigid cylindrical spacers can be slidably disposed. Each glass plate is placed with its edge surface on the slotted surface and spaced from the adjacent plates by at least two of the cylindrical spacers, each of the spacers being disposed in a separate slot. Reference planes which are perpendicular to the surface of the fixture are provided so as to maintain the plates in the desired spatial relation. Then, a glass base is bonded onto the opposing edge surface of each of the spaced glass plates. The glass plates and glass base are preferably chosen to be of the same material. The spacers are chosen to be of a material having an expansion coefficient slightly greater than that of the glass plates and glass base.