SPEED Measurement

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Presented by:

MA. THERESA C. JUSTO

MARICAR T. SORIANO

MEASUREMENT



HISTORY

In the most ancient times, speed at sea was

measured by dropping a piece of driftwood or a

small log off of the stern of the moving ship. As

the ship moved away from the wood, an

approximate speed could be guessed. This was

remedied by attaching a length of light twine or

line to the log; the same log could then be

retrieved and used repeatedly. Marks were

added to the line to allow for a more accurate

speed reading.



SPEED MEASUREMENT

has always been of the utmost

importance to the navigator

the speed of any object must bemeasured relative to some other point

at sea, speed may be measured relative

to either the seabed (ground reference

speed) or to the water flowing past the

hull (water reference speed)



SPEED LOG

It is a marine electronic deviceused to measure the speed of a

moving vessel The speed of a ship is measured

in KNOTS.

1 knot = 1.51miles/hr



CHIP LOG

It is also called as COMMON LOG or SHIP LOG.

It is a navigation tool used by Mariners in the old times to estimate the speed of a

vessel through water.



METHODS OF SPEED

MEASUREMENT

1. Speed Measurement using WATER PRESSURE

- measures W/T speed only

2. Speed measurement using ELECTROMAGNETIC INDUCTION

- measures W/T speed only

3. Speed Measurement using ACOUSTIC CORRELATION

TECHNIQUES- measures both W/T and G/T speed

4. Speed Measurement using DOPPLER PRINCIPLE

- measures both W/T and G/T speed



WATER

PRESSURE LOG



SPEED MEASUREMENT USING

WATER PRESSURE Pitometer logs (also known as pit logs) are devices

used to measure a ship's speed relative to the water.

They are used on both surface ships andsubmarines.

Data from the pitometer log is usually fed directly

into the ship's navigation system.

The pitometer log was patented in 1899 by Edward

Smith Cole.




WATER PRESSURE

Speed Log operates on Pitotmeter Principle based on the

pressure developed when an open-ended tube is exposed to

water movement due to a vessels speed. The difference of

head pressure of a Static tube and a Pitot tube is comparedin a pressure box, being applied to opposite sides of a flexible

diaphragm.

A mechanical arrangement employing the servo principle

converts the movements of the diaphragm and a synchrotransmitter coupled to a drive motor shaft transmits the

vessels speed electrically to remote synchro receivers to

drive display units of speed and distance.




WATER PRESSURE




WATER PRESSURE

Bernoulli's Principle states that as the speed of a moving

fluid increases, the pressure within the fluid decreases.




WATER PRESSURE

An expression can be derived for the velocity of waterimpacting the ship as a function of the difference indynamic and static water pressure using Bernoulli's

principle. The total pressure of the water in the tubewith moving seawater can be described by the equation:

pTotal = pstatic+ pdynamic

where:

pTotal is the total fluid pressure.

pStatic is the static pressure, which strictly depends on depth.

pDynamic is the fluid pressure caused by fluid motion.




WATER PRESSURE

PITOTS LAW state that pressure is

proportional to the square of the ships

speed v multiplied by the coefficient K .

= K x v 2

where t he constant K is deri v ed from t he v essels

tonnage, shape of hull, speed of t he ship and t he

lengt h of t he protruding part of t he Pitot tube

(distance d).




WATER PRESSURE

Note:

To ensure that the dynamic pressure

reading, and thus speed, is accurate, the

effect of static pressure must be

eliminated.



ELECTROMAGNETIC

SPEED LOG




ELECTROMAGNETIC

INDUCTIONELECTROMAGNETIC SPEED LOG

- this type of log uses Michael Fardays

well-documented principle of measuring

the flow of a fluid past a sensor by means

of electromagnetic induction

- the operation relies upon the principlethat any conductor which is moved across a

magnetic field will have induced into it a

small electromotive force (e.m.f.).




ELECTROMAGNETIC

INDUCTIONTypical Electromagnetic System consists of a:

Sensor unit

Preamplifier

Digital Display Unit




ELECTROMAGNETIC

INDUCTION

- Alternatively, the e.m.f. will also be

induced if the conductor remains stationaryand the magnetic field is moved withrespect to it.

-

Assuming that the magnetic field remainsconstant, the amplitude of the inducede.m.f. will be directly proportional to thespeed of movement.




ELECTROMAGNETIC

INDUCTION

EM Speed Log Translating System




ELECTROMAGNETIC

INDUCTION

The flow sensor is projected out into the sea

water through the hull. The sea water acts

as the conductor and generates an emf

and hence a current flows in the coil which

is transmitted to the bridge panel via a

master unit which amplifies the signal.




ELECTROMAGNETIC

INDUCTIONTo reduce the effects of electrolysis and make

amplification of the induced e.m.f. simpler, a.c. is

used to generate the magnetic field. The magnetic

field strength H now becomes Hmsint and induced e.m.f. = Hmlvsint. If t he strengt h of t he magnetic

field and t he lengt h of t he conductor bot h remain

constant then,

e.m.f. = velocity where:

l = t he lengt h of t he conductor

v = t he v elocity of t he conductor.

Hmsint = magnetic field strength



ACOUSTICCORRELATION

TECHNIQUE




ACOUSTIC CORRELATION

TECHNIQUES

The Single- Axis Speed Log (SAL-ICCOR log)

measures the speed with respect to the

seabed or to a suspended water mass.

The log derives the vessels speed by the use

of signal acoustic correlation. Simply, this is a

way of combining the properties of sonicwaves in seawater with a correlation

technique.





TECHNIQUES

Speed measurement is achieved bybottom-tracking to a maximum depth

of 200 m. If the bottom echobecomes weak or the depth exceeds200 m, the system automaticallyswitches to water-mass tracking and

will record the vessels speed withrespect to a water massapproximately 12 m below the keel.





TECHNIQUES





TECHNIQUES The transducer transmits pulses of energy at a

frequency of 150 kHz from two active piezoceramic

elements that are arranged in the fore and aft line

of the vessel. Each element transmits in a wide lobe

perpendicular to the seabed. As with an echo

sounder, the transducer elements are switched to

the receive mode after transmission has taken

place.





TECHNIQUESThe reflected signals possess a time delay (T)

dependent upon the contour of the

seabed. Thus, the received echo is uniquely

a function of the instantaneous position of

each sensor element plus the ships speed.

T = 0 .5 x sv where:

T time delay in seconds

s distance bet w een t he recei v ing elements

v ships v elocity





TECHNIQUES





TECHNIQUESThese are the factors that will not affect

the calculation of the speed of the

vessel: Temperature

Salinity of the seawater

Variables of sound velocity inthe seawater





TECHNIQUESIt is also possible to use t he time delay (T)

bet w een t he transmission and reception tocalculate dept h.

where:

d dept h in meters

C v elocity of sonic energy in seaw ater (1500ms-1 )

T time delay in seconds



DOPPLER PRINCIPLE




DOPPLER PRINCIPLE

Doppler Principle/Doppler Effect- named after Christian Andreas Doppler, isthe apparent change in frequency andwavelength of a wave that is perceived byan observer moving relative to the sourceof the waves.

-states that Doppler shift f (Hz) is proportional to bot h t he flow v elocity,v

(cm/s) and t he transmission frequency of t he ultrasound f (MHz)




DOPPLER PRINCIPLE

A source of waves moving to the left. The frequency is

higher on the left, and lower on the right.




DOPPLER PRINCIPLE

Examples of Doppler Effect:

Doppler phenomenon with sound and relati v emov ement

The whistle from a moving train: as the trainapproaches a stationary listener, the pitch(frequency) of the whistle sounds higher thanwhen the train passes by (recedes), at whichtime the pitch sound the same as if the trainwere stationary. As the train recedes from thelistener, the pitch decreases.

The car horn (noise from a car) exhibits the samephenomenon




DOPPLER PRINCIPLE

Principles of Doppler Speed Radar/Log

Traffic Radar:

Radar (wave transmitter and receiver) is stationary,target car is moving

Radar (wave transmitter and receiver) is moving,target car is moving

Ships Doppler Speed Log:

Wave transmitter and receiver are installed onboard the ship whose velocities are measured.




DOPPLER PRINCIPLE

Illustration of Doppler Effect




DOPPLER PRINCIPLE

Doppler Effect Doppler Shift

Frequency of Transmit Signal: ft (Hz)

Velocity of Transmit Signal: c (m/s2)

Frequency of Reflection Signal fr (Hz)

Velocity of Target: v




DOPPLER PRINCIPLE

Approaching (moving towards) target:

fr = ft + fd

Receding (moving away) target:

fr = ft fd

where fd is Doppler shift t he difference bet w een t he frequency of transmit signal and reflection frequency of reflection signal (echo)




DOPPLER PRINCIPLE

Both the source and target are moving:

Source and Target moving in the OPPOSITEdirection

Source and Target moving in the SAME direction

where:

v is velocity of moving target,

vs is velocity of moving source

vr is the relative velocity between the source and the target

+ opposite direction

- same direction




DOPPLER PRINCIPLE

Applications of Doppler effect

Speed logging systems (ship, police radar)

Depth logging systems

Astronomy

Medical imaging

Temperature measurement

Laser Doppler velocimeters

Acoustic Doppler velocimeters




DOPPLER PRINCIPLE

Principles of Speed Measurement

using the Doppler Effect

The phenomenon of Doppler frequency shift is often used to

measure the speed of a moving object carrying a transmitter.Modern speed logs use this principle to measure the vesselsspeed, with respect to the seabed, with an accuracyapproaching 0.1%. If a sonar beam is transmitted ahead of avessel, the reflected energy wave will have suffered afrequency shift, the amount of which depends upon:

- t he transmitted frequency

- t he v elocity of t he sonar energy w av e

- t he v elocity of t he transmitter (t he ship)




DOPPLER PRINCIPLE

Speed: Doppler Speed Log

Illustration of the change of wavelength that occurs when an acoustic wave crosses a

water mass




DOPPLER PRINCIPLE

It follows that if the angle changes, the speed

calculated will be in error because the angle of

propagation has been applied to the speed

calculation formula in this way.

If the vessel is not in correct trim (or pitching in

heavy weather) the longitudinal parameters will

change and the speed indicated will be in error.

To counteract this effect to some extent, twoacoustic beams are transmitted, one ahead and

one astern.

JANUS configuration it is the transducer

assembly used for this type of transmission




DOPPLER PRINCIPLE

(a) Derivation of longitudinal speed using trigonometry. (b) The effect of pitching on a

Janus transducer configuration.




DOPPLER PRINCIPLE

The figure shows the

advantage of having a

Janus configuration over

a single transducer

arrangement. It can be

seen that a 3° change of

trim on a vessel in a

forward pointing Doppler

system will produce a 5%

velocity error. With aJanus configuration

transducer system, the

error is reduced to 0.2%

but is not fully

eliminated. Graphs of Speed Error caused by Variations of the Vessels Trim




DOPPLER PRINCIPLE

Speed V ectors during aSt arboard T urn

-A dual axis Doppler speed log

measures longitudinal andtransverse speed, at the location of the transducers. If transducers aremounted in the bow and stern of avessel, the rate of turn can becomputed and displayed. Thisfacility is obviously invaluable to the

navigator during difficultmanoeuvres.

- Starboard - Starboard, or the right side of a boat, comes from the word steorbord,an old English term meaning side on whicha boat is steered.




DOPPLER PRINCIPLE

CHOICE OF TRANSMISSION

MODE:

Continuous Wav e Mode (CW)

Transmission

Pulse Mode Operation




DOPPLER PRINCIPLE

C ontinuous W ave Mode ( C W) T r ansmission

-Two transducers are used in each of the Janus positions. A continuous

wave of acoustic energy is transmitted by one element and

received by the second element.

-Received energy will have been reflected either from the seabed, or, if the depth exceeds a predetermined figure (20 m is typical), from a

water mass below the keel.

-Problems can arise with CW operation particularly in deep water when

the transmitted beam is caused to scatter by an increasing number

of particles in the water. Energy due to scattering will be returned

to the transducer in addition to the energy returned from thewater mass.

-The receiver is likely to become confused as the returned energy from

the water mass becomes weaker due to the increasing effects of

scattering. The speed indication is now very erratic and may fall to

zero. CW systems are rarely used for this reason.




DOPPLER PRINCIPLE

P ulse Mode O per ation

-To overcome the problems of the CW system, a pulse mode

operation is used.

-This is virtually identical to that described previously for depth

sounding where a high energy pulse is transmitted with the

receiver off.

-The returned acoustic energy is received by the same

transducer element that has been switched to the receive

mode.

- In addition to overcoming the signal loss problem, caused by

scattering in the CW system, the pulse mode system has the

big advantage that only half the number of transducers is

required.




DOPPLER PRINCIPLE

C om parison of the P ulse and the C W systems

Pulse systems are able to operate in the ground reference mode at depths

up to 300 m (depending upon the carrier frequency used) and in the water

track mode in any depth of water, whereas the CW systems are limited todepths of less than 60 m. However, CW systems are superior in very

shallow water, where the pulse system is limited by the pulse repetition

frequency (PRF) of the operating cycle.

The pulse system requires only one transducer (two for the Janus

configuration) whereas separate elements are needed for CW operation.

CW systems are limited by noise due to air bubbles from the vessels ownpropeller, particularly when going astern.

Pulse system accuracy, although slightly inferior to the CW system, is

constant for all operating depths of water, whereas the accuracy of the

CW system is better in shallow water but rapidly reduces as depth

increases.




DOPPLER PRINCIPLE

Environmental Factors Affecting the Accuracy of Speed Logs

Unfortunately environmental factors can introduce errors and/or produce sporadic

indications in any system that relies for its operation on the transmission and

reception of acoustic waves in salt water.

W ater cl arity. In exceptional cases t he purity of t he seaw ater may lead to

insufficient scattering of the acoustic energy and prevent an adequate signal

return. It is not likely to be a significant factor because most seawater holds

the suspended particles and micro-organisms that adequately scatter an

acoustic beam.

Aer ation. Aerated w ater bubbles beneat h t he transducer face may reflect

acoustic energy of sufficient strength to be interpreted erroneously as seabottom returns producing inaccurate depth indications and reduced speed

accuracy. Proper siting of the transducer, away from bow thrusters, for

instance, will reduce this error factor.

V essel trim and list. A change in t he v essels trim from t he calibrated normal

w ill affect fore/aft speed indication and an excessive list will affect athwartship

speed. A Janus configuration transducer reduces this error.




DOPPLER PRINCIPLE

Environmental factors affecting the accuracy of speed logs

Ocean current profile. T his effect is prev alent in areas w it h strong tides

or ocean currents. In t he water track mode, a speed log measures

velocity relative to multiple thermocline layers several feet down in the

water. If these layers are moving in opposite directions to the surfacewater, an error may be introduced.

Ocean eddy currents. W hilst most ocean currents produce eddies t heir

effect is minimal. T his problem is more likely to be found in restricted

waters with big tidal changes or in river mouths.

Sea st ate. Follow ing seas may result in a change in t he speed indication

in t he fore/aft and/or port/ starboard line depending upon the vectorsum of the approaching sea relative to the ships axis.

Temperature profile. T he temperature of t he seaw ater affects t he

v elocity of t he propagated acoustic. Temperature sensors are included in

the transducer to produce corrective data that is interfaced with the

electronics unit.




DOPPLER PRINCIPLE

Major Components:

Transducer The transducer assembly transmits

sonic energy into the water and receives back the

Doppler shifted echoes.

Electronics Unit The electronics unit houses the

majority portion of the electronics for the system

speed and distance processing.

Master Display Unit The master display unit

indicates vessel speed and distance traveled and

contains switching that controls all system power

and operations.




DOPPLER PRINCIPLE

Dist ance dis pl ay . This shows the distance run innautical miles or km.

-Depending upon the selected mode and depth, the

display indicates over-the-bottom distance or, whenthe unit is water tracking, the distance travelledthrough the water.

- If the ALT characters are showing, the system tracksboth bottom and water simultaneously and provides

both outputs to external devices.

-This display also provides a numerical indicationwhich, when used in conjunction with the systemmanual, provides clues to any system malfunction.




DOPPLER PRINCIPLE

Different DI SPLAY U nit

Speed dis pl ay. This shows the vessels fore/aft

speed in knots, m/s (metres per second) or ft/s

(feet per second).

P ort/st arboard dis pl ay. This indicates

athwartship speed in knots, m/s or ft/s.

De pth/time dis pl ay. This indicates water depth

to the seabed, in fathoms, metres or feet, when

in either water or bottom-tracking mode,

providing the depth is within 200 m. The depth

indication circuitry also includes a depth alarm.



DEFINITION OF TERMS

Aeration - The formation of bubbles on the transducer face causing

errors in the system.

Beamwidth - The width of the transmitted acoustic pulsed wave. The

beam spreads the further it travels away from a transducer.

CW Mode (Continuous Wave Transmission) - Both the transmitter and

receiver are active the whole time. Requires two transducers.

Distance integrator - The section of a speed log that produces an

indication of distance travelled from speed and time data.

Doppler principle - A well-documented natural phenomenon enabling

velocity to be calculated from a frequency shift detected between

transmission and reception of a radio signal.

E.M. log - An electronic logging system relying on the induction of

electromagnetic energy in seawater to produce an indication of velocity.



DEFINITION OF TERMS

G/T - Ground-tracking or ground referenced speed.

Pitot log - An electromechanical speed logging system using

changing water pressure to indicate velocity.

Pulse Mode - Acoustic energy is transmitted in the form of pulses similar to an echo sounding device or RADAR

Transducer - The transmitter/receiver part of a logging

system that is in contact with the water. Similar to an

antenna in a communications system. Translating system - The electronic section of a logging

system that produces the speed indication from a variety of

data.

W/T - Water-tracking or water referenced speed.



DEFINITION OF TERMS

Starboard - Starboard, or the right side of a boat, comesfrom the word steorbord, an old English term meaning sideon which a boat is steered.

Port - The nautical term "port" refers to the left side of aboat when facing the front, or bow. Another version of theterm "port" is larboard, which dates back to the 16th centuryand was used up until the 1800s to describe the left side of the boat. The port side of a boat is marked with a red light inthe front.

Bow (also known as fore) The "bow" is a term for the

front of a ship. Structurally, the bow curves to a point that iscentered on the ship itself.

Stern (also known as aft) The stern is a term for theback of a ship.



THE END

THANK YOU!! =p

SPEED Measurement

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