Abstract: A laser Doppler velocimeter which has an optical system using a semiconductor laser as a light source for receiving a scattered light by reflection from natural particulate in fluid to be measured passing interference fringes formed in a region to be measured by a semiconductor optical detector, and a signal processor having a converter for converting a Doppler signal from the semiconductor optical detector to a predetermined waveform (e.g., a square wave) according to at least two different threshold values, and an arithmetic unit for comparing the processed signals from each other to judge that the scattered signal is from one natural particulate or not (i.e., the propriety of its measuring accuracy) and to calculate the velocity of the fluid to be measured according to the judged result and the process result of the converter from the period of the square wave when judging "a normal measurement".

Abstract: A fiber optical displacement sensor having a wider range of measurable distances and displacements. The fiber optical displacement sensor includes a light source means for continuously providing a projection beam of a certain wavelength and a reference beam having another different wavelength. The projection beam and the reference beam are combined by a first photo coupler and transmitted through a projecting optical fiber. Only the projection beam is separated out by a first filter and transmitted to a vicinity of the surface to be measured. On the other hand, the reflection beam and the reference beam separated by the first filter are combined by a second photo coupler, transmitted through a receiving optical fiber, and separated out by a second filter before being processed.

Abstract: A fiber optical displacement sensor having a wider range of measurable distances and displacements. The fiber optical displacement sensor includes collimation device, attached to ends of projecting and receiving optical fibers, for collimating a projection beam to be emitted from an end of the projecting optical fiber facing toward a surface to be measured and a reflected beam to be received by an end of the receiving optical fiber facing toward the surface to be measured.

Abstract: A pressure measuring system wherein light is transmitted from a light source via a first optical fiber to a pressure-receiving diaphragm having a reflecting surface which undergoes a deflection in relation to the pressure being measured. The diaphragm reflects light transmitted thereto to a second optical fiber which transmits the reflected light to a first photosensitive element. A reference optical fiber is arranged approximately coextensive to the first and second optical fibers and transmits light from the light source in round trip fashion along substantially the same path as light transmitted by the first and second optical fibers to a second photosensitive element. The photosensitive elements produce respective electrical signals which are applied to an operational circuit which eliminates variations in the amount of light due to external disturbances by dividing one electrical signal by the other.