The invention relates to a flow-meter apparatus for measuring relative fluid velocity, and more particularly, to a marine speedometer instrument used in the measurement of a marine vessel's speed, and a dynamic fluid flow measuring instrument used in the measurement of confined fluid flow characteristics such as pressure, velocity and/or flow rate. BACKGROUND OF THE INVENTION

Typically, marine speedometer systems use either pitot tube or paddle wheel type devices to measure vessel speed. The pitot tube senses stagnation pressure as a function of speed, while the paddle wheel supplies output pulses that are counted to indicate speed. The devices are usually mounted on the stern or the bottom of the vessel. It is common in the art to provide redundant marine speedometer systems as a backup for accuracy or dependability. Unfortunately, there are times when both the primary and redundant marine speedometer systems are inoperative. Problems occur most frequently when using a pitot tube on weedy inland lakes. When the pitot tube is partially clogged or blocked by weeds or other debris, a lower than actual speed will be indicated by the marine speedometer system. The paddle wheel devices experience problems in the form of mechanical wear, corrosion and inaccuracy due to rotational resistance.

SUMMARY OF THE INVENTION To overcome all of the perceived disadvantages of the present systems discussed above, the present invention of a marine speedometer system uses a completely solid state pressure sensor. While the intended use of this system is to measure vessel speed

relative to the unconfined media, such a system could also be used to measure confined flow, such as media flowing through ducts, pipes, conduits or the like.

The sensor used in the present invention is normally used to measure hydrostatic pressure. In order to adapt the sensor for use in measuring dynamic fluid pressure relative to an unconfined media., the sensor is uniquely mounted into a specifically shaped holder referred to herein as a transducer assembly. The assembly is fastened to the boat stern such that the sensor is slightly below the boat bottom. The holder is designed to maximize dynamic pressure sensitivity by resolving the largest pressure component possible, while minimizing drag, fluid spray and any tendency to catch debris. While this particular design does not preclude other mounting techniques with similar advantages, it does allow for immediate original equipment manufacturer applications as well as after market applications with minimum vessel modifications.

As fluid pressure is applied to the sensor diaphragm, this action causes an internal pressure transfer to a piezoresistive element via a coupling fluid, with virtually no physical movement, thus removing any mechanical criticality. The assembly could be hinged at the attachment so as to be tripped up at a predetermined force to prevent transducer assembly or vessel damage upon contact with debris, or during shipping or trailering. The holder is designed to house the sensor such that the sensor leads or connections are isolated from the fluid. A spanner nut is used to compress an 0-ring between the sensor and the holder, thereby creating a water tight seal and precluding the use of screws or other protrusions that could catch weeds or other debris. Other mounting options include injection molding the

sensor with its wires and connectors in place, or molding the housing in two halves, pressing the two halves together and sonically sealing the sensor in between. In any case, the sensor wires can be brought out of the holder directly and passed through the transom or passed through a bulkhead connector integrated into the hinge attachment.

Electronic circuity supplies the proper signals and power to the sensor, and converts the sensor output to an electronic signal suitable for further processing. Central 0 processing means converts the electronic signal, as provided by the electronic circuitry, to a value of speed. In determining the value of speed, the central processing means interprets the dynamic pressure characteristics of the pressure sensor assembly as a function of vessel speed. 5 The central processing means may also use the following inputs as information to further enhance system accuracy and flexibility. The vessel inclination, i.e., vessel pitch or angle of attack, can be used as an additional input to further enhance system accuracy and flexibility. In this configuration, vessel inclination is provided to the central processing means by an inclination sensor that is used, along with other possible inputs, to give an accurate measure of vessel speed that is independent of vessel inclination. Vessel configuration or hull-shape compensation, particularly transom angle, can also be used as an 5 additional input to further enhance system accuracy and flexibility. Sensor pressure, and therefore speed values, may be

* influenced by the particular hull shape or vessel configuration on which it is installed. Combinations such as engine option, seating arrangement, transom angle or load bias characteristics 0 are some of the possible configurations. The system may be

mechanically or electronically pre-set at the factory or dealer to conform to the particular vessel hull shape configuration. Electronically variable speed adjustment may also be used as an additional input to further enhance system accuracy and flexibility. The vessel operator may have the option to adjust the displayed speed to compensate for water conditions that may affect sensor pressure at a given speed. This may also be done to set the vessel speed as a function of a ski course length for consistency among vessels during the same competition skiing event. Water density and/or temperature may also be used as an additional input to further enhance the system accuracy and flexibility. Tftfese inputs may be provided to the central processing units _^ by respective density and temperature sensors, combined with other appropriate inputs and used by the control program in the. central processing unit to determine a compensated vessel speed such that accurate vessel speed is independent of variations in fluid density or temperature.

The central processing unit will also control the display device electronics with software designed to display the values of speed in a smooth, easily readable manner. The display device can indicate the speed value by means of digits, bar graphs, needles or other means based on various display technologies such as light emitting diodes, vacuum fluorescent, liquid crystal or the like. The present invention provides a system for the accurate measurement and display of marine vessel speed. The system is designed to operate in all marine media or waterways without being affected by weeds or debris common to waterways. The system consists of a solid state pressure sensor to monitor the dynamic pressure applied to tϊje sensor due to vessel movement, electronic

logic to convert the sensor output to an electronic signal, a microprocessor or other central processing means to convert this electronic signal to a value of speed, and additional electronic circuitry and display devices to display speed value to the vessel

5 operator.

Other objects and features of the invention will become apparent by reference to the following specification and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

10 Fig. 1 is a side elevational view of the sensor housing means in accordance with the present invention;

Fig. 2 is a top view of the sensor housing means taken as shown in Fig. 1;

Fig. 3 is an end elevational view taken as shown in Fig.

15 1;

Fig. 4 is an electrical schematic diagram for a marine speedometer system according to the present invention;

Fig. 5 is a partial cutaway view of another embodiment of the present invention used to measure confined flow, such as

__• fluid media flowing through pipes;

Fig. 6 is a cross-sectional view taken as shown in Fig.

5; and

Fig. 7 is a cross-sectional view of the fluid sensor mounted on a pipe elbow.

2 _* 5 DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is a marine speedometer system for * measuring relative fluid velocity in an unconfined media to indicate speed of a vessel. The marine speedometer system includes sensor housing means, designated generally 10, supported 30 from the vessel such that the sensor housing means is exposed to

fluid flowing past the-,vessel. The sensor housing means 10 is best seen in Figs _* 1-3. The sensor housing means 10 preferably includes an enlarged base portion 12 for connection to the stern or transom of a vessel, preferably through a hinged attachment means (not shown) which can be tripped up at a predetermined force to prevent sensor assembly or vessel damage on contact with debris or during shipping or trailering of the vessel. The sensor housing means 10 also includes a tapered middle portion 14 extending outwardly and angularly downward with respect to the stern or transom of the vessel. An enlarged end portion 16 of the sensor housing means 10 includes a forward facing surface 18 having an aperture 20 formed therein. Preferably, the sensor housing means 10 has a generally triangular cross section formed by the forward facing surface 18 and two surfaces, 22 and 24 respectively, tapering toward one another as best seen in Fig. 2. The edges of the sensor housing means 10 are rounded and smooth providing an aerodynamic housing with a minimum amount of fluid drag resistance. A passage 26 communicates between the aperture 20 in the end portion 16 of the sensor housing means 10 and an electrical connector 28 disposed in the enlarged base portion 12 of the sensor housing eaps 10 allowing connection of wires between the electrical connector 28 and the dynamic pressure sensing transducer means 30 disposed in the aperture 20. Apertures 32 can be formed in the enlarged base portion 12 of the sensor housing means 10 for passage of screws or bolts to connect the sensor housing means 10 to a hinged attachment assembly connected to the stern of the vessel.

The solid-state pressure sensing transducer means .30 are commercially available from IC Sensors located in Milpitas, California. The Model 84 sensor is a media compatible, solid-

state pressure sensor that is intended for use in original equipment manufacturers applications where long term stability is desired combined with low cost. The stainless steel housing structure uses silicone oil to couple a diffused, piezoresistive sensor to a convoluted, flush stainless steel diaphragm that can be interfaced with most harsh media. The Model 84 is designed to be mounted using an O-ring as a face seal or a bore seal to maintain pressure integrity. Integral temperature compensation is provided along with calibration over 0 to 50C with laser trimmed resistors. No external resistors are required. An additional laser trimmed resistor is included to normalize pressure sensitivity variations by programming the gain of an external amplifier, thus providing ± 1% interchangeability along with high level output. A schematic diagram of the electrical circuitry of the present invention is best seen in Fig. 4. The dynamic pressure sensing transducer means 30 is connected to a precision constant current source 34 for sensor excitation and to an instrumentation differential amplifier 36 with the gain programmed by sensor feedback resistor R9. It should be recognized that circuit modifications could be made to obtain outputs other than 0 to 5 volts as used in the present invention. The current source 34 is controlled by the ± 1% band-gap reference diode VR. Selecting amplifier Al with an offset voltage below ImV and a ± 1% tolerance of resistor R2 delivers current with typical accuracy of ± 1.08%. The first differential stage of the instrumentation amplifier 36, i.e., A2 and A3, has a zeroing potentiometer P. For OP227 amplifiers A2 and A3, the zero range is typically ± 4mV in reference to the input with a differential offset below 0.5mV. This leaves approximately ± 3.5mV zeroing range for the

compensation of the sensor offset which typically is below ± ImV.

The second stage of the amplifier 38, i.e., A4 provides additional amplification through R8/R5 and translates the differential floating voltage from the first stage into a single ended output voltage.

The overall accuracy of the span voltage is affected by the accuracy of feedback resistors R3 through R8. Using ± .1% resistors, such as Mepco/Electra 5063Z, a typical gain error will be about ± .24%. The accuracy error may be decreased when matched thin film resistors are used, such as Beckman 694-3-A. The combined span error of the entire signal conditioning circuit at a reference temperature will then be typically about l.1% without any adjustment or pressure testing. This will be superimposed on the sensor's accuracy of ± 1%. If additional calibration and normalization is desired, resistor R2 can be replaced with a series combination of a potentiometer and a resistor. The potentiometer can be adjusted to set the bridge excitation current to achieve the exact span voltage with full scale pressure applied to the sensor. The output from the single ended amplifier A4 is fed to a central processing unit, for example a microcontroller 40, such as a Motorola MC68HC805B6. A low voltage regulator 42 maintains voltage to the microcontroller 40 at preferably 5 volts. A low voltage detection circuit 44 monitors the voltage and if the voltage is low automatically resets the microcontroller 40 until the voltage comes back up to an acceptable level. A crystal oscillator clock 46 provides, base timing for the microcontroller 40 and associated circuitry. A scale conversion input switch SI allows the microcontroller 40 to convert between desired scales, such as miles per hour to knots. Switch SI supplies voltage to

the microcontroller 40 for one scale and connects to ground for a different scale. A precision voltage reference means formed by

R13 and VR2 provides a 5.0 volt reference to the analog to digital converter in the microcontroller. The display means 48 can be a liquid crystal display, such as a Hitachi Model No. HI333C-C for receiving the processed electronic output signal from the central processing means 40 and for displaying a visual readout of vessel speed based on the processed electronic output signal. In the alternative, the display means 48 can include a quartz (Aircore) speedohead display driven by a frequency input from the central processing means 40, or a light emitting diode display driven as a function of a 0-5 volt input directly from the pressure sensing transducer amplifier. Referring now to Figs. 5-7, the system can also be used to measure confined flow, such as media flowing through ducts, pipes, conduits or the like. The sensor housing means 10 can be adapted for use in a straight pipe section 50 as shown in Figs. 5 and 6. An aperture 52 is formed in a side wall of the pipe 50 allowing insertion of the sensor housing 10 within the interior of the pipe 50. The enlarged base portion 12a in this embodiment takes the form of an arcuate cover plate matingly engageable with the exterior surface of the pipe 50. A seal ring 54 is disposed between the arcuate plate 12a and the exterior surface of the plate 50 to seal the opening against any leakage from the interior of the pipe 50 to the exterior. Fastening means 56 secures the arcuate plate 12a to the pipe 50 and compresses the

O-ring seal 54. The sensor housing means 10 also includes a tapered middle portion 14 extending inwardly and angularly with respect to the pipe 50. The sensor housing means 10 is preferably

disposed at an obtuse angle with respect to the direction of fluid flow F as best seen in Fig. 5. An enlarged end portion 16 of the sensor housing means 10 includes a forward facing surface 18 having an aperture 20 formed therein. In its preferred form, the

5 sensor housing means 10 has a generally triangular cross-section formed by the forward facing surface 18 and two other surfaces tapering toward one another in the downstream direction. The edges of the sensor housing means 10 in this embodiment are rounded and smooth providing an aerodynamic housing with a minimum

10 amount of fluid drag resistance. A passage 26 communicates between the aperture 20 in the end portion 16 of the sensor housing means 10 and through the enlarged base portion 12a allowing connection of wires between the dynamic pressure sensing transducer means 30 disposed in the aperture 20 and the associated

15 electrical circuitry designated generally as 58 in Fig. 5. The electrical circuitry 58 can best be seen in Fig. 4. The dynamic pressure sensing transducer means 30 in this embodiment is similar to that previously described for use on marine vessels.

As best seen in Fig. 7, in applications where it is

2. desirable to eliminate any internal pipe obstructions, the dynamic pressure sensing transducer means 30 can be disposed in the outer radial side wall of a pipe elbow 60. An aperture 62 is formed in the outer radial side wall of the pipe elbow 60 allowing the insertion of the dynamic pressure sensing transducer means 30 to a

25 position relatively flush with respect to the interior surface of the pipe elbow 60. A short pipe section 64 is fixedly secured to the outer side wall of the pipe elbow 60 by means such as welding or suitable adhesive or the like. The short pipe section 64 has an internal thread permitting a locking member 66 to be

30 threadingly engaged within the pipe section 64. The locking

member 66 engages an external surface of the dynamic pressure sensing transducer means 30 to compress an O-ring seal 68 between the dynamic pressure sensing transducer means 30 and the exterior surface of the pipe elbow 60. When using the present invention to measure confined flow, such as that shown in Figs. 5-7, the central processing unit can be used to provide an appropriate processed electronic output signal to display values such as pressure, velocity, or flow within the pipe line. Additional input or calibrations would be provided to indicate the size and type of pipe or conduit, as well as information regarding the fluid flow characteristics of the media being transported through the pipe or conduit.

While one embodiment of the invention has been described in detail, it will be apparent to those skilled in the art the disclosed embodiment may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting, and the true scope of the invention is that defined in the following claims.