BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION:

It is well known that in a fluidic oscillator, the rate of oscillation is a function of the fluid flow rate through the oscillator and that by transducing pressure piezoelectrically or thermistor measured temperature changes in a feedback flow path in the oscillator, the rate of fluid flow can be converted to an electrical signal to perform a control or monitoring function. In one commercial fluid flow meter, a heated thermistor is located in a feedback passage. When feedback flow is a maximum or minimum, the heat carried away at a corresponding maximum or minimum and the rate of fluctuation is linear and directly proportional to flow rate. Danisch patent 5,321,257 discloses a fiber optic bending and positioning sensor in which a fiber optic or light wave guide is attached to a member to be bent or displaced and light is injected at one end and detected at the other end. Bending of the fiber results in loss of light through a surface strip or bend along one side of the fiber and this loss is detected to produce an indication of the bending or displacement.

The object of the present invention is to provide an improved fluid flow metering system and method. A further object of the invention is to provide a fluidic oscillator with a highly flexible fiber optic wave guide which is

adapted to flex with changes in fluid flow and lose light on flexing, and a detector senses the oscillatory loss of light as a measure of fluid flow through the oscillator and produce an electrical signal for control and/or monitoring functions.

The device measures flow rates of all fluids either by the degree to which a flexible fiber optic lead or light guide is bent or flexed by the frequency of its oscillation. The device includes a fiber optic or light guide loop treated in such a way as to lose light into a light absorbing covering in a repeatable and predictable manner when bent or flexed. When connected to the appropriate light source and electronic circuitry, the device will provide an electrical output having a frequency proportional to the rate of oscillation. In oscillating chambers such as a fluidic,the light guide which is located in the plane of the flow will maintain a position in the center of the jet or stream. In the preferred embodiment, the flexible fiber optic light guide will seek the maximum velocity point in the stream. As the jet switches from side to side, the light guide is compelled to switch also. Since the frequency of oscillation of the jet and therefore the fiber optic is directly proportional to the flow rate the output signal may be fed into a frequency counter or totalizer to give an output related to flow rate (Mode 1). In an alternate embodiment, the fiber optic is embedded in

a section of the fluidic where flow reverses direction at a rate proportional to flow rate. In this case, when the flow is in a direction towards the free end of the light guide, the light guide will maintain a position in the center of the jet and will cause a certain output level. When the flow is from the free end of the fiber the flow forces the fiber towards the wall of the section, inducing a bend or flexure and changing the output level (Mode 2). A further operational mode (Mode 3) places the fiber in various planes perpendicular to the flow. The fiber may be held at one clamping location with the free end in the fluid flow or be held both at the free end and second clamping location. In each of these locations the fiber is used to detect the flow rate through its frequency of oscillation. Modes 1-3 utilize the fluidic oscillation of the fluid to compel the fiber to mirror the movement and hence generate an output whose frequency is proportional to flow rate. A pair of loops with light loss regions maintained at a 90° relation to each other can measure flow in multiple planes or three-dimensional directions.

DESCRIPTION OF THE DRAWINGS:

The above and other objects, advantages and features of the invention will become more apparent when considered with the following specification and accompanying drawings wherein:

FIG. 1A is a top plan view of a fluidic oscillator with a section of the cover plate removed to expose the oscillator silhouette and the fiber optic sensor in one position and condition of operation, FIG. IB is a top plan view similar to Fig.lA but illustrating the oscillator and fiber optic sensor position and condition during a further portion of a cycle of oscillation,

FIGS. 2A and 2B are top plan views of a similar fluidic oscillator showing the fiber optic sensor mounted in one of the feedback passages thereof,

FIGS. 3A, 3B and 3C are top plan views of a similar fluidic oscillator showing the fiber optic sensor mounted in one of the feedback passages thereof, FIG. 4 is a top plan view of a fluidic oscillator showing the fiber optic sensor mounted in a further position in one of the feedback passages,

FIG. 5 is a sectional view taken on lines A-A of Fig.4, FIGS. 6A and 6B are top plan views of a fluidic oscillator illustrating a further modification of the invention,

FIGS. 7A, 7B and 7C illustrate the invention as applied to an island-type oscillator,

FIGS. 8A, 8B and 8C illustrate various features of prior art fiber optic sensors or detectors useful in the practice of the invention,

FIG. 9 illustrates the fiber optic loop coupled to an interface box containing a light source or photoemitter and photodetector,

FIG. 10 illustrates the fiber optic measuring loop and an associated reference fiber optic loop,

FIG. 11 is a sectional view crossing the outbound loop section with cladding removed to form a light loss region and the inbound loop section,

FIG. 12A illustrates an embodiment of the invention for measuring flow, movements in multiple planes, FIG. 12B is a sectional view on lines XX of Fig. 12A, and FIG. 12C illustrates the multiple sensing plane.

DETAILED DESCRIPTION OF THE INVENTION:

Fiber optic sensors useful in the practice of the invention are disclosed in Danisch patents 5,321,257 and 4,880,971, incorporated herein by reference. Figs. 8A, 8B and 8C disclose fiber optic light guides 10 having a light emission surface 11 extending along one side of the fiber. Light emission from surface 11, which can be treated as at 12, increase when the fiber is bent or flexed in one direction and decrease when the fiber is bent or flexed in the opposite direction. The fiber optic light guide can be

in the form of a simple strand or plural fiber strands. One end 14 of the fiber optic light guide can be coupled to a light source or photoemitter LS and the opposite end coupled to photodetector PD which are part of an electronic circuit 16 which measures the difference in intensity between light emitted by source 15 and detector PD. Optionally, a second fiber optic light guide loop 20 made of the same length and material, but without the light emission surface, may be provided as a reference or standard. Reference fiber optic light guide loop 20 is coupled to a second source LS ₂ , and detector PD ₂ .

Figs. 8A, 8B and 8C illustrate serrated SE corrugated CU and notched NO regions of surface treatments to show various ways in which light loss in a selected surface area can be achieved. In Fig. 9, the loop has a light input end LIE coupled to a light source LS. Light loss region or surface area RC is positioned where flex or bend of the fiber optic light guide occur due to changes in flow direction. In the embodiment illustrated in Fig. 9, the outbound leg OL of the fiber optic loop is selected as having the light loss region RC (see Fig. 11). The inbound or return leg has its end RIE coupled to a photodetector PD and a signal processing circuit SPC is coupled to the photodetector. As shown in Fig. 11, the fiber optic light guide is comprised of a fiber optic core FOC, fiber optic cladding

FC, a portion of the cladding being removed as at RC to form a light loss or treated region. A light absorbing sheath LAS may be provided to reduce stray light effects. As shown in Figs. 8A, 8B and 8C, various methods of causing light loss upon flexure or bending of the sensor include serration, corrugation and notching, or other roughening treatments.

A pair of fiber optic waveguide loops 30, 31 in which the outbound and inbound portions are maintained in a fixed relation to each other is shown in Figs. 12A and 12B. Loop 30 has a light loss region or treated section 32 (facing in a given direction (right in Fig. 12B) and the fiber optic loop 31 has a treated light loss or treated region 33 facing in a direction 90° relative to the facing direction of treated section 32 (e.g., down in Fig. 12B). Thus, since the loops are maintained in fixed relation, any direction and degree of flex or bend of the combined loops can be detected and measured.

The invention can be applied to measure flow rates wherever there is an oscillatory movement of fluid flow that is proportional to flow rate. While several forms of fluidic oscillators are disclosed herein, the invention is believed to be applicable to all forms of fluidic oscillators or systems where there is oscillatory fluid flow.

Referring now to Figs. 1A to 7C, the device measures flow rates of all fluids by the frequency of oscillation of the fiber optic lead or light guide. The device includes a fiber optic or light guide loop treated in such a way as to lose light into a light absorbing covering in a repeatable and predictable manner when bent. When connected to the appropriate electronic circuitry and light source, the device will provide an output proportional to the degree of bending. In oscillating chambers such as a fluidic (Figs. 1A and IB), the light guide which is located in the plane of the flow will maintain a position in the center of the jet or stream. As the jet switches from side to side, the light guide is compelled to switch also. Since the frequency of oscillation of the jet and therefore the fiber optic is directly proportional to the flow rate the output signal may be fed into a frequency counter or totalizer to give an output related to flow rate (Mode 1). In an alternate embodiment, the fiber optic is embedded in a section of the fluidic where flow reverses direction at a rate proportional to flow rate (Figs. 2A and 2B). In this case, when the flow is in a direction towards the free end of the light guide (Fig. 2A), the light guide will maintain a position in the center of the jet and will cause a certain output level. When the flow is from the free end of the fiber (Fig. 2B) the flow forces the fiber towards the wall of the section, inducing a bend or flexure and

changing the output level (Mode 2). A further operational mode (Mode 3) places the fiber in various planes perpendicular to the flow (Figs. 3-6). The fiber may be held at one clamping location with the free end in the fluid flow (Figs. 3-5) or be held in two clamping location (Fig. 6). In each of these locations the fiber is used to detect the flow rate through its frequency of oscillation. Modes 1-3 utilize the fluidic oscillation of the fluid to compel the fiber to mirror the movement and hence generate an output whose frequency is proportional to flow rate. An island oscillator 40 of the type shown in Stouffer patents 4,151,955 and 5,099,753 is shown in Figs. 7A-7C. In this case, the fiber optic loop 43 is mounted at the apex 41 of island 42. While there has been shown and described various preferred embodiments of the invention, it will be appreciated that various other embodiments, modifications and adaptations of the invention will become readily apparent to those skilled in the art. It is intended that such other obvious adaptations and modifications be incorporated within the true spirit and scope of the claims appended hereto.