Abstract: An apparatus for recording information about the angular motion of a rotatable disk disposed in a first structure is provided. The disk has regions with differing properties with respect to electromagnetic energy. The apparatus includes first means for emitting a first sequence of electromagnetic energy pulses in a first direction toward the disk. The first emitting means are mounted on the first structure adjacent a first side of the disk. The apparatus also includes second means for emitting a second sequence of electromagnetic energy pulses in a second direction toward the disk, the second emitting means also being mounted on the first structure adjacent the first side of the disk. The first and second directions are such that the first and second sequences of electromagnetic energy pulses reflect from the first side of the disk in different areas, the areas being separated in the direction of rotation of the disk.

Abstract: A solid state pressure sensor utilizes a brittle diaphragm made of a material such as silicon, which is mounted between base plates of glass, and which deflects in response to pressure. The base plates of glass can have recesses formed therein to receive the diaphragm and provide a full support across the diaphragm under overpressure conditions to prevent overstressing the diaphragm, or the diaphragm can have such contoured surfaces for forming overpressure stop surfaces against the facing base plate. The diaphragm has grooves defining a central portion that deflects, and whereby the grooves will form webs joining the central portion to an outer rim so that the diaphragm acts similarly to a "free edge" diaphragm in its deflection characteristics. The grooves defining the webs can have various configurations for achieving the results desired.