CA2064590A1

CA2064590A1 - Solid-state transducer based dynamic fluid sensing system

Info

Publication number: CA2064590A1
Application number: CA002064590A
Authority: CA
Inventors: Robert G. Malcolm; Thomas W. Richardson
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-08-03
Filing date: 1990-08-01
Publication date: 1991-02-04
Also published as: US5007286A; AU6292990A; EP0572381A4; AU635965B2; EP0572381A1; WO1991002218A1; JPH04507462A

Abstract

A dynamic fluid flow sensing system measures relative fluid velocity with respect to a reference member. The system includes a sensor housing (10) supported from the reference member such that the sensor housing is exposed to fluid flowing past the reference member. A solid-state pressure sensing transducer (30) is supported by the sensor housing for generating an electronic output signal in proportion to a sensed dynamic pressure of fluid flowing past the reference member. A central processing unit (40) receives the electronic output signal from the transducer and generates a processed electronic output signal in accordance with a stored control program. A display (48) receives the processed electronic output signal and displays a visual readout of desired fluid flow characteristics based on the processed electronic output signal.
The dynamic fluid flow sensing system can be used on marine vessels to indicate vessel speed or in confined fluid flow passages to indicate flow characteristics such as pressure, velocity and/or flow rate.

Description

~ t) 91/02218 PC'r/US90/04319 2064~90 A SO~Ip-ST~TE TR~N~UCE~ BA
Field of the Invention The invention relates ~o a flow-meter apparatus for measuring relative fluid velocity, and mora pa~ticularly, to a marine speQdomete~ i~strument ~sed in ~he measurement of a ~arlne vQs~nl's ~peed, and a dynamic ~uid flow measU~ing ~nstrument used ln the me~surement of con~ined ~luid ~low ~aracteristics 5UC~ as pr~-ure, velocity and~or flow rat~.
~A~KÇRQUN~ ~
Typically, marine ~peedometer sy~tems use either pitot tube or paddle wheel type devices to measure vessel speed. The pi~ot tube senses stagnatlon p~essUre as a funct~on of speed,`
whilQ the paddle wheel suppliRs output p~lses that are coun~ed to indicate ~peQd~ ~he ~evices are usually mounted on the stern or thR bottom of the vessel~ It i~ ~ommon in the art to provide redundant marine speedomQter systems as ~ ~ackup for accuracy or dependability. Unfortunately, thsre ar~ times when ~ot~ the prima~y and redun~ant marine speedometer 6y tems are inoperative.

2 Problems occur mos~ frequen~ly when using a pitot tube on weedy inlan~ l~kes. When the pitot tube is partially clogged or ~locked by woeds or o~her debr~s, a lower than actual speed will b8 indicated by the marine ~peedDmeter sy~tem. The paddle wheel dev~ces eXp~rience p~oblems in the f orm of mechanical wear, ~S corrosion and inaccuracy due to rotational resistance.
SUMMARY OF THE INVENTI~
To overco~e all of the perceived disadvantages of the present systems discussed above, the present invention of a marine speedometer sy~tem uses a completely solid state pressure sensor.
While the ~ntended use of this system is to ~ea~ure ve~sel speed WO 91/0221~
I~CT/~JS90/~4319 2 206~90 relative ~o the unconfined media, suc~ a system could ~lso ~e u~ed to measure conflned flow, such as media flowing through ducts, pipes, conduits or the li~e~
The sensor used in the present invention ie normally used to measure ~lydrostatic pressur~. In or~r to adapt t~e s~nsor ~or u~ in mea~urlng dynamir- fluid pressurR rela~ive to an uncon$in~d m~dia, ~e sensor i~ uniquely moun~ed into a 5p~ ically ~hapod hoid~r r~srrRd ~o harein as a transdu~er ~s~Qmb~y~ The assembly is fast~ned to the boat s~rn ~uc~ t~at t~o ~ensor is ~lig~ly below the boa~ bottom. q~he holder is designQd to maximi2~ dynamic pressure sansiti~ity by resolvin~ the l~rg~st pressure component possible, w~ile minimizing dra~, fluid spray and any tendency t~ catch debris~ While this particular dQsign does not preclude other mounting techniques with similar advantages, it does allow for.immediate original equipmant manu~acturer applica~ions as well as af~e~ market applications with minimum vessel modi~ation~. ~
As ~luid pres~ure is applied to ~he sensor diaphragm, this action ca~ses an ~nternal pressure transfer to a piezoresis~lve element via a coupling fluid, with virtually no physical mo~ement, tnu~ removing any mechanical criticality. The assembly could be h~nged at the attach~ent BO as to be tripped up at ~ p~ade~ermined fo~ce to prev~nt transdu~er assembly or ves~el damag~ upon contact with debris, or during shipping or trailering~
~ he hold~r is designed to house ~he 6e~sor ~uch that the sonsor leads or connections are ifiDlated from the f luid.
spanner nut is used to compress an Q-ring between the sensor and the holder, thereby creating a water tight seal and precludln~ the use of screws or other protrusions that could catch weeds or other debris. Other mounting op~ions lnclude injection molding the ~'091/02218 r~T/~J~9n/04~19 3 2069~90 sensor wlth its wires and connectors in place, or ~olding the hou~in~ in ~wo halves, pressing the two halVeS toç~ather and sonically sealing the sensor in between. In any case, the sensor wires can be brought out of the holder directl~ and passQd throug~
; the transom or passed throu~h a bul~head connector integrated into t~ hinge a~tachment.
E~ctronic circui~y supplie~ th~ proper signals and p~wer to the sensor, and converts the sensor output to an electronic signal suitable ~or further processing. c~ntral 0 processing means converts the electronic si~nal, as provided by th~ electronic circuitry, to a ~alu~ of ~peed. In determining the ~alue of speed, ~he central p~oce~sing means interprets the dynamic pressu~e charac~eristics Or the pressure sensor assembly as a ~unction of vessel speQ~
~ The central processing means may also use ~he following inputs as information to further enhance system accuracy and flexibility, T~Q vessel incllna~ion, i.e., vessel pitch or angle ot attack, can be u~e~ as an ad~itional input to further enhance sycte~ accuracy and flexibility. In this configuration, vessel inclination is provided to the central proce~ing means by an inclination sensor that is used, along with other possible inputs, to give an a~curate mea~ure of v~ssel ~pead that is lndependent of ves~el inclination. Ve~sel configuration or hull-shape compensation, partic~larly transom angle, can also be used as an add~tional input to fur~her an~ance system accuracy and flQXibili~y, Sensor pressure, and therefore speed values, may be influenced by the particular hull shape or vessel configura~ion on which it is installed. Combina~ion~ such as engine option, seating ~rran~ement, transom angle or load bias characteristics are some of thc possible configurations. The sys~em may be ~091/02218 ~CT/~S90/0431~

4 2064~90 mechanically or electronically pre-~et at t~ factory or dealer to conform to the particular ve~sel hull sh~pe conflguratlon.
Electronically variable speed adjustment may also be u~ed as an additional input to further enhancQ system accuracy and ~lexibility. ~he vessel operator may ~ave th~ option to ad~ust the displayed epeed to compensatQ for water conditions that may a~ct ~nsor pressur~ at a givan speQd. This may a~so be don~ to set t~ vQs~el sp~d as a ~unction of a sk~ cours~ l~ngth for~
consi$t~ncy among ~assels ~uring th~ sam~ competition ~iin~
Qvent. Water d~nslty and~or temp~rature may also b~ used as an additional input to further enhance t~a syst~m accuracy and flexibili~y. T~ese inputs may be p~ovided to t~e c~n~ral proces~ing units by respect~ve density and ~em~erature ~en~ors, combined with other appropriate inputs and used Py t~e control program ~n t~e cQn~ra~ processing un~t to deter~ine a comp~nsated ~eQsel speed such ~at accurate vesRsl speed ~s independent of variations in fluid density o~ temperature~
The central processing unit ~ill also control t~e display device ~lectronics w~th sof~ware designed t~ display t~e values of speed in a ~mooth, easily readable manner. T~e d~splay de~ice can indicate the speed value ~y maans of digits, bar graphs, needles or other means ~a~ed on various display tec~nologies such as lig~t emittlng diodes, vacuum fluorescent, li~uid crystal or t~e ~ike.
S The present invention provides a sys~em for the accurate moasurement and display of marine vessel speed. T~e system ~s designed to operate in all marine media or waterways without being affected ~y we~ds or debris com~on to waterway~. The system co~s1sts of a solid state pressure sensor to monltor t~e dynamic S0 pressure applied to t~e sensor due to vessel movement, elec~ronic ~0~/02218 2 0 6 ~ ~ 9 ~/~s90/04~l9 logic to convert the ~ensor output to ~n electronic si~nal, a microproc~s~or or other central proces~ing means to convert t~is electronic signal to a valu~ of speed, and ad~itional electronic circuitry and display devices to d~splay speed value to the vessel operator.
Other obj~cts ~nd ~eatures o~ the inv~n~ion will b~coms appar~nt by re~Qrenc~ to the following ~pèCi~iCatiOn and to th~
drawings.

O Fig. 1 ~s a ~ide elevational view of the s~nsor housing means in acco~dance wlth ~he present invention;
Fig. 2 is a top view of the sensor housing means taken as shown in Fig. 1;
Fig. 3 is an end elevatlonal view ~aken as shown in ~ig.
1;
Fig. 4 is an electrical schematic diagram ~or a marin~
speed~meter sys~em according to the present in~ention;
Fiq. 5 is a partial cutaway view of another embodiment of the present inventicn used to measure confined ~low, such as flu~d media f~owing through pipes;
Fig. 6 is a cross-sectional view taken as shown in ~ig.
~; and Fig. ~ is a cross-sectional view of the flui~ ~ensor mounted on a pipe elbow.
~ESCRIPTION Q.~ PREFERRED EMBODIMENT
The present invention iR a marine speedome~er system for measurin~ rela~ive ~luid velo~i~y in an unconfined media to indicate speed of a vessel. The marine speedometer system inc}UdeR sen~or ~ou~ing means, designated generally 10, suppor~ed from the vessel such that the sensor housing means is exposed to ~'() 9t/1)22~8 PC~JS9û/01~19 6 20~;~;)90 fluid flowing past the vessel. T~e 6ensor ~ousing ~eans 10 i~
best seen in Fi~6. 1-3. The 8ensor houslng means 10 preferably includes an enlarged base portion 12 for connection to t~e stern or transom or a vessel, preferably t~rough a hinged at~achment means (not ~hown) w~ich can be tripped up at a prede~ermined force to pr~vent sen~or assembly or vessel damaga on contact wlt~ dabrls or during ahipping or ~railering o~ the vessel~ The sen~or housing means 10 al50 include~ a tapared ~iddlQ p~r~ion 14 extending outw~rdly and angularly downward w~t~ respect to the st~rn or ~ransom of t~e vessel. An enlargod end portion 16 of the sen~or ~ousing mQans 10 includ~ a for~ard facing surface ~8 having an apert~re 20 formed therein. Prefer~bly, the sen~or housing means 10 has a generally triangular &ross section formed by t~e forward ~acing surface 18 and two ~u~faces, 22 and 24 respectivaly, tapering toward one another as best seen in Fig. 2.
The ~dges of the sensor ~ousing mean~ 10 are rounded and smooth providing an aerodynami~ houRing with a minimum amount of fluid drag resistanc~ A pa6s~ge 26 comm~nlcates between the aperture 20 in the cnd portion 1~ of the sen~or housing means 10 and an alectrical ~onnector 28 disposed in t~e ~nlargad ~ase portion 1 o~ ~e s~nsor housing mR~ns 10 allow~ng oonnee~on of wires between t~e Rlectrica~ conn~ctor 2~ and the dyna~ic pressure sensin~ transducer maans 30 dispo~ad in ~he apertur~ ~o.
Apertures 32 can be formed in the enl~rged base portion 12 of t~e sensor housing means 10 ~or passa~e of screws or bolts to connect the sonsor ho~sing means 10 to a hinged attachment as~embly connected to t~e stern of the vessel.
The solid-state pressure sensing transducer means.30 are commerc~ally ava~lable from ~C Sensor~ located in Milpitas, Califo~nia. The ModQl 84 sensor ls a media compatible, solid-~O 91/0221~ 2 0 ~ ~ ~ 9 0 I'Cr/lJS9U/04319 state pres~ure censor that is intended for use in original equipment ~anufacturers applications where long term stability is desired combined wlth low cost. The stainle~s steel housin~
structure uses silioone oil to co~ple a diffused, piezoresistive s~nsor to a convolu~ed, flus~ stainless steel diaphragm t~at can b~ inter~c~d wit~ most ~arsh medla. ~ Nodel R4 is designQd to be moun~ed usin~ an o-ring a~ a faca seal or a bor~ s~al to ma~nt~in pre~sure integ~ity~ Integral temp~rature compensation ~s provi~nd along wit~ calibration over o to 50~ w~th la~r trimme~
resistors. No external resis~ors are rQquirad. An addltional ~as~r trimm~ resistor is inclùded to nor~ali~e pre5sure sensitivity variations by programming the ga~n of an external amplifier, thus providing l~ interchangeabillty alon~ wi~h high level output.
A ~chematic diagrHm of the ele~trical circuitry of the present inVQntion i8 best seen in Fig. 4. T~e dynamic pr~ssure sensing transducer mean~ 30 is connected to a preo~sion constant c~rrent cource 34 for sensor excitation and to an instrumentation di~ferential amplifier 36 with the gain proqrammed by sensor 2 feedback resis~or R9. I~ ~hould be recognized that ~ircuit modlfica~ions coul~ b~ made to o~taln outpu~s othex than 0 to 5 volts as used in the present invention. The current source 3~ i~
controlled by t~e ~ and-~ap reference diode VR. Selectin~
a~pli~iQr Al wi~ an offse~ voltage below lmV and a ~ 1% toleranoe of resistor R2 delivers current with typical accuracy of + l.08%.
The first differential stage of ~he instrumentation amplifier 36, i~e., A2 and A~, has a zeroing pot~ntiometer P. For OP227 amplifiers A2 and A3, the zero range is typi~ally ~ 4mV in reference to the input with a differential of~se~ below 0.5mV.
~hi~ leaves approximately + 3.5mV zeroing range for the W091J02~18 2 0 ~ ~ ~ 9 o PCT/US90/0~l9 compensation of the sen~or offse~ which typically is below ~ lmV.
The second stage of t~e amplifier 38, i~e., A4 provides add~tion~l amplification through ~8/R5 and ~ranslatRs the diferential floating voltag~ rom the firs~ st~ge into a single en~ed output voltage.
T~e overall accuracy of t~e sp2n ~oltag~ is affect~d by thQ accuracy o~ f~d~a~ resi~ors R3 ~hrough R8. Using ~
re~tors, au~ as MQpco/Eleotra 50632, a ~ypical gain e~ror will bQ about ~ ~24~, The accuracy error may be ~ecreased ~hen matched ~in ~ilm resisto~s ar~ used, suCh ~s B~c~man ~94-3-A~ The co~bined Bpan error of ~e entire signal conditioning circuit at a re~erence ~empera~ure will then be ~ypically about l.1% ~ithout any adjustment or pre~sure testing. This will be superimposed on the sensor's accuracy of ~ 1%. If additional cal~brat~on and normali2ation is desired, rssistor R2 can be replaced with a ~erics combination of a potQntiometer and a r~si~tor. ~he po~entiom~ter can be adjusted to set the ~r~dge exci~ation current to achieve the exact ~pan voltage with full scale pressure applied to the sen~or.
The output from the single ende~ amplifier A~ i~ fed to a c~ntral processing unit, for example a microcontroller 40, s~ch as a Moto~ola MC68HC805~6. ~ low voltage regulator 42 malntains volta~e to the microcontroller 40 at preferably 5 volts. A low voltage detection circuit 44 monitors the voltage and if ~he voltage is low auto~atically resets the microcontroller 40 until t~e voltage comes bu¢~ up to an acceptable level. A crystal oscillator cl~ck q~ provides base timin~ for the microcontroller 40 and aSsociated circui~ry. A scale conversion input switch Sl allows the microcontroller 40 to convert betwe~n desired scales, such as miles per hour to ~nots. Swi~h Sl supplies voltage to ~o 9~/022l8 2 0 6 ~ ~ 9 r~:T/tJ~9~/04~l9 the microcontroller 40 for one scale and connects to ground for a different scale. A preci~ion voltage reference means formed by R13 and VR2 provides a 5.o volt ~e~erence to the analog to digital converter in ~he microcontroller.
The display means 48 can be a liquid crystal display, ~uch a~ a Hitachi Model ~D. HI333C-C for recQivin~ ~e process~d e~ctronic ~utput signal from the c~ntrAl proccssing m~ans 40 and ~or displaying a visual readout o~ ve~s~l SpQQd based on the procQ~J~d Qle~tronic output signal. In tha altern~tiv~, the O ~i~play means 4s ~an include a quartz ~Aircor~) speedohead di~play dri~en by a f~equency input from thQ oentral processing means 40, or a light emitting diode display driven as a function of a 0-~
vol~ input directly ~rom the prsssurc sensing transducer amplifier.
Referring now to Figs. 5-7, the system can also be used to measure confined flow, ~uch as medla flowing through ducts, pipes, conduits or the like. The ~enqor hou~in~ means 10 can be adapted fo~ use in a stralght pipe section 50 a~ shown in F~gs. 5 and ~. An aperture 52 i formed in a side wall of the pi pe 50 allowin~ ~nsertion of ~he senRor housing 10 within the in~erior of the pipe 50. The enlarged bàse po~tion 12a ln ~his em~odiment ta~s the form of an arcuatQ cover plate matingly engagea~le with the exterior surface ~ the p~pe S~. A ~eal ring 54 ia dispo~ed ~etween the arcuate plate 12a and the exterior surfa~e of the plate 50 to seal the opening against any leakage from the interior o~ ~he pipe 50 to the exterior. Fastenin~ means 5~ secures the arcuate plate 12a to the pipe SO and compresses the 0-ring seal 54 . The sensor housing means lo al~o includes a tapered middle portion 14 extending inwardly and angularly with respect to the pipe 50. ~he sensor housing means lo is preferably () 91/02218 ~'CT/ JS9~/0~3 1 9 20~90 di~pos~d at an ob~use angle wlth respect to the direction of fluid flow F as best seen in Fig. 5. An enlar~ed end portion 16 of the sensor housing means 10 includes a ~orward facin~ surfaee 18 havin~ an ap~rture ~0 formed therein. In lts prererred ~orm, the ~ensor housing means 10 has a generally ~riangul~r cross-section ~ormQd by the ~orward ~acing surface ~8 an~ tw~ othQr surfaces tap~ring ~owArd on~ another in th~ downstre3~ dirac~ion. The e~g~s ~ tha aensor housing means ~0 in thts embo~iment ar~
ro~nded and smcot~ providing an aerodynamic ~ousing with a minimum amoun~ o~ ~luld dra~ r~sistancQ. A pa~saqe 2~ communicates b~tw~n the aperture 20 in the ~nd portion 16 of the s~n~or housin~ mQans 10 and t~rou~h the en~arg~d basa por~ion 12a allowing conn~ction of wires between the dynamic pressure senslng transducer means 30 dispofied in the ape~ture 20 and the associated electrioal cir¢uit~y desi~nated ~enerally as S8 in Fig. 5. The electrical circuitry 58 can best bQ ~een in ~lg. 4. The dynamic pr~ssure s~nsin~ tran~ducer means 30 in this embodiment is similar to that previously desc~ibed for use on ~arinQ vossels.
~ 5 best s~en in Fig. 7, in applications where it is desirable to el~minate any internal pip~ obstructions, the dynamic pres ure sensing tr~nsduc~ m~anQ 30 can be d~sposed in the outer r~dial side wall o~ a pipe elbow 6Q. An aperture 62 i~ formed in the oute~ radial side wall of the pipe elbow 60 allowin~ the ins~r~ion of the dynamic pressu~e ~ensing transducer means 30 to a position relatively ~lus~ with respe~t to th~ interior ~urface of the pip~ elbow 60. A short pipe se~tion 64 is flxedly secured to t~e 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 ~ember 66 to be threadingly engaged within the pipe section 64. The locking \~'091l0~2l8 PCT/~S90/04319 11 2~6~90 member ~6 engages an external surface of the dynamic pressure sensing transduc~r means 30 to compress an o-rinq seal 68 between the dynamic pre~sure sen~ing transducer means 30 and the exterior surface of the plpQ elbow 60.
~h~n u~ing the present invention to measur~ con~lned ~low, such ~s that s~own in ~igs. 5-~, t~e cen~ral proces~ing unit c~n bQ used to p~ovide an appropriate p~ocessed elec~ronic output si~nal to di~play values such ~ pre~sur~, velocity, or flow within the pipe line. Addltional input or cali~ration~ would be ~0 providQd to indica~ the size and type o~ pipe or cond~it, as well as information regarding the ~luid ~low charac~cri~tics of the media being transported throug~ the pipe or conduit.
Wh1lQ one embodiment of the ~nvention has been described in detail, it will ~e apparent to tho~e s~illed in the art the disclo~ed embodiment may be modified. Therefore, the foregoing description i8 to ~e considered exemplary rather than limiting, and the tr~e s~ope of the invention is that defined in the followinq cla1ms.

Claims

What is claimed is:

1. A system for measuring relative fluid velocity with respect to a marine vessel, the system comprising:
solid-state pressure sensing transducer means for generating an electronic output signal in proportion to a sensed dynamic pressure of flowing fluid with respect to said marine vessel; and sensor housing means connected to said marine vessel, said sensor housing means supporting said transducer means such that said solid-state pressure sensing transducer means is exposed to fluid flowing past said marine vessel.

2. The system of Claim 1, further comprising:
central processing means for receiving said electronic output signal from said transducer means and for generating a processed electronic output signal in accordance with a control program stored in memory; and display means for receiving said processed electronic output vessel signal and for displaying a visual readout of vessel speed based on said processed electronic output signal.

3. The system of Claim 1, wherein said sensor housing means comprises:
an elongated housing having an enlarged base portion connected to said marine vessel, a generally triangular shaped cross-sectional middle portion protruding outwardly and downwardly from the base portion with a first surface of said middle section facing forwardly toward a bow of said marine vessel, and an enlarged generally tear-drop shaped end portion having an aperture formed in a forwardly facing surface contiguous with said first surface for receiving said transducer means, said housing having trailing edges tapering off away from said forwardly facing surface.

4. The system of Claim 1, wherein said solid-state pressure sensing transducer means comprise:
a piezoresistive transducer sensor for sensing dynamic pressure;
constant current source means for exciting said piezoresistive transducer sensor;
differential amplifier means for amplifying a difference between two input signals from said piezoresistive transducer sensor into a differential floating output signal; and single ended amplifier means for translating said differential floating output signal into a single output signal with reference to a ground.

5. The system of Claim 2, wherein said sensor processing means comprising:
a central processing unit;
low voltage regulator means for supplying constant voltage to said central processing unit;
low voltage detection and reset means for protecting said central processing unit against low voltage by holding said central processing unit in a reset condition during low voltage detection;
crystal oscillator clock means for providing base timing for said central processing unit;

scale conversion means for changing said processed electronic output signal to reflect a differnet scale reading to be displayed; and precision voltage reference means to allow the central processing unit to accurately read said electronic output signal independent of any voltage regulator variation.

6. The system of Claim 2, wherein said display means is selected from a group consisting of a liquid crystal display, a light emitting diode display, a dial with an electronically driven vacuum fluorescent pointer display, and a quartz speedohead display driven by said processed electronic output signal from said central processing means.

7. A system for measuring relative fluid velocity with respect to a fluid passage having an outer wall, the system comprising:
solid-state pressure sensing transducer means for generating an electronic output signal in proportion to a sensed dynamic pressure of flowing fluid with respect to said transducer means; and sensor housing means connected to said outer wall, said sensor housing means supporting said transducer means such that said solid-state pressure sensing transducer means is exposed to fluid flowing within said fluid passage.

8. The system of Claim 7 further comprising:
central processing means for receiving said electronic output signal from said transducer means and for generating a processed electronic output signal in accordance with a control program stored in memory; and display means for receiving said processed electronic output signal and for displaying a visual readout of a desired fluid flow characteristic based on said processed electronic output signal.

9. The system of Claim 7, wherein said sensor housing means comprises:
an elongated housing having an enlarged base portion connected end portion having an aperture formed in an upstream facing surface for receiving said transducer means.

10. The system of Claim 7, wherein said solid-state pressure sensing transducer means comprises:
a piezoresistive transducer sensor for sensing dynamic pressure;
constant current source means for exciting said transducer sensor;
differential amplifier means for amplifying a difference between two input signals from said transducer sensor into a differential floating output signal; and single ended amplifier means for translating said differential floating output signal into a single output signal with reference to a ground.

11. The system of Claim 8, wherein said central processing means comprises:

a central processing unit;
low voltage regulator means for supplying constant voltage to said central processing unit;
low voltage detection and reset means for protecting said central processing unit against low voltage by holding said central processing unit in a reset condition during low voltage detection;
crystal oscillator clock means for providing base timing for said central processing unit;
scale conversion means for changing said processed electronic output signal to reflect a different scale reading to be displayed; and precision voltage reference means to allow the central processing unit to accurately read said electronic output signal independent of any voltage regulator variation.

12. The system of Claim 7 further comprising display means for receiving said electronic output signal and for displaying a visual readout of a desired fluid flow characteristic based on said electronic output signal.

13. The system of Claim 8 wherein said display means is selected from a group consisting of a liquid crystal display, a light emitting diode display, a dial with an electronically driven vacuum fluorescent pointer display, and a quartz speedohead display driven by said processed output signal from said central processing means.

14. The system for measuring relative fluid velocity comprising the steps of:

sensing dynamic fluid pressure with a solid-state transducer connected to a relative reference member and exposed to fluid flowing past said relative reference member;
generating an electronic output signal from said transducer in proportion to the sensed dynamic pressure;
sending said electronic output signal to a central processing unit;
generating a processed electronic output signal in accordance with a control program stored in memory of said central processing unit; and displaying a visual readout of a desired fluid flow characteristic based on said processed electronic output signal.

15. The method of Claim 14, wherein said relative reference member comprises a marine vessel in an unconfined media.

16. The method of Claim 14, wherein said relative reference member comprises a fluid passage with fluid flowing confined within said fluid passage.

17. The system of Claim 15, further comprising the steps of:
sensing inclination of said marine vessel in said unconfined media with an inclinometer mounted on said marine vessel;
sending an electronic signal to said central processing unit from said inclinometer; and compensating for marine vessel inclination on said sensed dynamic pressure prior to displaying said visual readout.

18. A system for measuring relative fluid velocity with respect to a relative reference member comprising:
solid-state transducer means for sensing dynamic fluid pressure, said transducer means connected to said relative reference member and exposed to fluid flowing past said relative reference member, said transducer means generating an electronic output signal in proportion to sensed dynamic pressure;
central processing means for receiving said electronic output signal from said transducer means and for generating a processed electronic output signal in accordance with a control program stored in memory; and display means for receiving said processed electronic output signal and for displaying a visual readout of a desired fluid flow characteristic based on said processed electronic output signal.

19. The method of Claim 15, wherein said relative reference member comprises a marine vessel in an unconfined media.

20. The method of Claim 16, wherein relative reference member comprises a fluid passage with fluid flowing confined within said fluid passage.