Abstract: An apparatus usable in process control applications for detecting the position of a movable element in a sensor wherein first and second beams of light, each having different wavelengths and each preferably being alternately generated with respect to one another by a light source, are transmitted to a filter by means of an optical fiber cable connected between the light source and filter. The filter and the movable element cooperate for modulating the intensity of the first beam in accordance with the position of the movable element and thereby transforming that first beam into a measurement beam which appears at an output stage of the filter. The filter also transmits the second beam therethrough unaffected by the movable element and produces a reference beam appearing at the output stage. A first optical detector coupled to the light source the respective intensities of the two light beams being transmitted towards the filter.

Abstract: An element interacting with a stream of a fluid moving through a pipe generates periodic sub-flows at a rate that varies in accordance with changes in the velocity of the moving fluid. The generation of sub-flows also modulates the electrical charges contained in and moving with the fluid thus permitting a detector which is responsive to the energy being radiated by the modulated charges to produce a sensor signal having a frequency corresponding to the generating rate of the periodically produced sub-flows. In one preferred embodiment, the element is a vortex-shedding body and the sub-flows are vortices being shed therefrom. Electrical circuitry which receives the sensor signal converts it into a flow signal representative of the velocity of the moving fluid.

Abstract: A vortex-shedding mass flowmeter which includes a shedding body mounted in a pipe containing a flowing fluid, a first detecting element that responds to the vortices generated when the fluid flows past a surface of the shedding body for producing a velocity signal proportional to the flow rate of the fluid, a second detecting element for sensing in a measuring plane that includes the surface of the shedding body where vortices are generated a moving fluid characteristic dependent on the product of fluid density and the square of the fluid flow rate, and electronic circuitry coupled to the outputs of the first and second detecting elements for producing therefrom a mass flow rate signal. In one preferred embodiment, the second detecting element is a pitot-type head device which senses a pressure differential between static and dynamic pressures existing at two locations on the measuring plane.