Abstract: An optical sensor system utilizes time multiplexing of two optical signals developed from a common light source. Relative amplitudes of the two optical signals are varied as a function of a measured parameter, time multiplexed, and coupled to a common optical transmission path. At the receiving end of the optical transmission path the two optical signals are converted to electrical signals by the same detector, thus eliminating sensitivity to source gain, interconnect fiber loss, and detector gain as sources of calibration error.

Abstract: A quartz crystal vibrating diaphragm pressure sensor includes a primary quartz crystal body having a diaphragm formed therein and electrodes on each side of the diaphragm for piezoelectrically exciting thickness shear mode oscillations of said diaphragm, said oscillations varying in frequency in accordance with variations in fluid pressures applied to the surfaces of said diaphragm. A second identical or substantially identical diaphragm similarly excited but exposed to a constant pressure provides a reference frequency for providing precision difference frequency pressure measurement and for inherently compensating for ambient conditions affecting both diaphragms.