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Week 5Lecture 1: Displacement and position measurementsLecture 2: Introduction to GPS/GNSSActivity: Module 5Tutorial: Getting started with Simulink

Hung NguyenDepartment of Maritime Engineering

Lecture 1: Displacement

• Learning outcomes:– State displacement and units for displacement– List displacement measurement methods– Describe the dial test indicator– Describe the potentiometer displacement

devices– Describe the l.v.d.t displacement devices

Displacement

• Displacement is a vector quantity and may be defined as the difference between two positions occupied by a body at different moments in time.

• Length of displacement is a scalar quantity which gives the magnitude of the displacement.

• Linear motion – metres, rotational or angular motion – degrees or radians

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UnitsLinear displacement: metre (m)

• 1791: the metre was defined by the French Academy of Sciencesas 1/10,000,000 of the distance from the equator to the north pole through Paris.

• Historical International Prototype Metre bar, made of an alloy of platinum and iridium, that was the standard from 1889 to 1960.

Historical International Prototype Metre bar, made of an alloy of platinum and iridium, that was the standard from 1889 to 1960.

Units• (SI – standard metre bar kept at Sèvres in

France) defined as the length equal to 1650763.73 wavelengths in a vacuum of the radiation corresponding to the transition between the levels 2p10 and 5d5 of the krypton-86 atom.

• Now, the metre is defined by the International Bureau of Weights and Measures as the length of the path travelled by light in absolute vacuum during a time interval of 1/299 792 458 (c: speed of light) of a second.

Units: Angular displacement• Angular displacement: radian (rad), which is

defined as the angle subtended at the centre of a circle by an arc of length equal to the radius. 1 radian = 57.3o.

The term radian first appeared in print on June 5, 1873, in examination questions set by James Thomson at Queen's College, Belfast. James Thomson was a brother of Lord Kelvin. Source: Wikipedia

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Measurement Methods

• Mechanical devices: steel rules, slip gauges, micrometer screw gauges, vernier calipers, and dial-test indicators

• Electrical displacement devices: Potentiometer, L.V.D.T, Inductive, Capacitive, Synchros, etc.

• Ship Position: GPS/GNSS, Inertial Navigation, Ultrasonic (Depth and Pos), etc

Dial Test Indicator

Potentiometer Type

Principle: PotentiometerWiper

OutputVoltage

vo

a b xxi

ixabx = RT

R1

RL

V

Lever linkage for a potentiometer

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Potentiometer Valve Positioner

Principle:

Adv and Disadv• Advantages:

High level of output signal could avoid the use of electronic amplifiers

Better linearity than other displacement transducersDisadvantages:

Friction at the wiper contact will cause wear, although a life of 80.106 cycle is quoted for conductive-plastics potentiometer

Any dirt entering the wiper contact area will affect the output signal. This is particularly applicable to the open construction of some wire-wound potentiometers

L.V.D.T. Type

• Principle

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Adv and Disadv of l.v.d.t.

• Advantages:– There is no frictional contact between the core

and the coils and therefore inductive devices has longer life than potentiometer

• Disadvantages:– Displacement frequencies of only up to 0.1 of

the excitation frequency can be measured– Complex electronic circuitry is required,

including an oscillator for frequencies other than mains frequency.

SynchrosSynchros are the a.c. equivalent of potentiometers and are used in many a.c. electrical systems for data transmission and torque transmission for driving dials.

Example: Complete System• An A.C.-excited potentiometer system to

measure hydraulic jack

U.V.

recorderFilterMatching

network

AC Amplifier

demodulator

High

Low

Wiper

xi

Power

piston Oil

10R 10R

10R 10R

Excitation AC

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Displacement Devices in Market

Ref: www.fylde.com

Capacitance Type L.V.D.T Type

More: www.waycon.com

Potentiometer Type

Summary of Displacement Measurement

• Displacement and Units• Mechanical: Dial test indicator, callipers• Electrical: L.V.D.T., inductive, capacitive

Any Questions?

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Lecture 2Introduction to GPS/GNSS and Applications

Learning outcomes

• State five basic forms of navigation• Describe the organisation of GPS/GNSS• State principles of GPS positioning methods• Describe generic GPS receiver• State sources of errors• Describe principles of DGPS/RTK-GPS• State the Australian DGPS Service• List applications of GPS/GNSS

GPS: Position and NavigationHow to navigate a sea-going vessel, an

airplane, a spaceship or a train? Navigation relates to Position Measurement5 Basic Methods of Navigation:1. Pilotage: based on recognizing landmarks

to know where you are.2. Dead Reckoning: based on knowing

where you started from, plus some form of heading information and some estimate of speed.

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GPS: Position and Navigation• 3. Celestial Navigation, using time and the angles

between local vertical and known celestial objects (sun, moon, or stars)

• 4. Ratio navigation: based on radio-frequency sources with known locations (including Global Positioning System satellites)

• 5. Inertial navigation: based on knowing your inertial position, velocity, and attitude and thereafter measuring your attitude rates and acceleration. This is the only form of navigation that does not rely on external references.

GPS Position Measurement

GNSS: GPS, GLONASS and GALILEOGNSS = Global Navigation Satellite SystemGPS = Global Positioning System (USA)GLONASS = Global Orbital Navigation

Satellite System (Russia)GALILEO (GNSS-II): GNSS (EU) (by 2008)Principle and Information: Same principle and

information in position (x, y, z) and time.

What is GPS?

▲ GPS Satellites in Space

Global Positioning System

Satellite-based positioningsystem

Latitude/Longitude/Height/Time

Worldwide coverage

Continuous 24-hour coverage

Developed and managed by US Department of Defence since 1970s

Available for any users without any charge

GNSS: GPS, GLONASS, GALILEO

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3 SegmentsSpace

Segment

Control Segment

User SegmentMaster control station

Monitor stations Uplink ground

antenna

Band navigation signals

MCS: Colorado Springs (Colorado, USA)Monitor Stations (4)1. Ascension (Atlantic)2. Diego Garcia (Indian)3. Kawajalein (Pacific)4. Hawai (Pacific)

Space, Airplane

Survey Ship

Car, Train

L1 & L2 (Pseudo Range & Carrier Phase) including Navigation Message

- 24 Satellites or More- 6 Orbital Planes (550 Inclination)- Orbit Altitude: about 20,000km- Orbit Period: Approx. 12 Hours- Weight: 844kg- High-precision atomic clocks

- Civil and Mil- Navigation- Survey, etc.

Command signals

What is GPS?

Space Segment24 Artificial Satellites or More (28 in 3-02)

GPS satellites are powered by solar energy. They have backup batteries onboard to keep them running in the event of a solar eclipse, when there's no solar power. Small rocket boosters on each satellite keep them flying in the correct path.Here are some other interesting facts about the GPS satellites (also called NAVSTAR, the official U.S. Department of Defense name for GPS):

• The first GPS satellite was launched in 1978. • A full constellation of 24 satellites was achieved in 1994. • Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit. • A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended. • Transmitter power is only 50 watts or less.

Locations of Control Segment StationsControl Segment

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Antenna – Receiver - DisplayUser Segment

The current position of each satellite can be

calculated by the ephemeris on the broadcast signal.

The current position of each satellite can be

calculated by the ephemeris on the broadcast signal.

Range measurement to the satellite from the

receiver

Range measurement to the satellite from the

receiver

The receiver’s position is on

the surface of the sphere.

The receiver’s position is on

the surface of the sphere.

Observed Range

GPS Satellite

Ephemeris

Calculate Satellite Position

ReceiverAntenna

On the Surface of the Sphere

Receiver and satellite

GPS Positioning Principle

Receiver Clock

Arrival time

Satellite Clock

Departure time

Crystal (Low precision)Atomic Clock (High precision)Send Signal every 1/1000 second

precise

Range measurement between receiver and satellite

Receiver GPS Satellite

Observed = ( Arrival time － Departure time ) × Range Velocity of Light

True Range

Pseudo Range

Range error due to the receiver clock error

contains error

GPS Positioning Principle

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Correction of Observed Ranges and Solution of Position

With more than 4 Satellites

With 3 range measurements the receiver position cannot be solved due to the range

errors.

The forth range measurement allows us to solve the receiver position and clock

bias.

With 3 Satellites

GPS Positioning Principle

Field Navigation Survey Timing Receiver Code Receiver (1) Carrier Phase Receiver (2) Carrier Phase Receiver (1)

Accuracy 10m DGPS 2-3m 1mm ～ 2-3cm 100ns

Use Navigation (Vehicle, Ship, Airplane)

･Geodetic Survey ･Crystal Movement ･Construction Survey ･Marine Survey ･Machine Control

Mobile Communication (CDMA)

System Composition

Single point positioning Relative positioning Synchronization

GPS Applications in Civil Use

SPS = Standard Positioning ServicePPS = Precise Positioning Service

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1. Carrier: L1 1575.42 MHz (λ=19cm）L2 1227.6MHz (λ=24cm）

(Civilian use: L1 in in UHF Band)2. PRN (Pseudorandom Number) Code:

C/A 1.023Mbps only L1P 10.23Mbps L1 & L2W 0.5115Mbps L1 & L2

3. Message:Navigation message 50bps

GPS Signal Structure

GPS Satellite Signals

Information from GPS Signal• Satellite Almanac Data: Orbital data called the

Almanac to enable the user to calculate the approximate location of every satellite in the GPS constellation at any given time. Not accurate enough, but primarily used to determine which satellites are visible at a given location.

• Satellite Ephemeris Data: Ephemeris data is similar to almanac data but enables a much more accurate determination of satellite position needed to convert signal propagation delay into an estimate of user position. In contrast to almanac data, ephemeris data for a particular satellite is only broadcast by that satellite, and the data is valid for only several hours.

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Information from GPS Signal• Signal Timing Data: The 50-bps data stream

includes time tagging, which is used to establish the transmission time of specific points on the GPS signal. This information is needed to determine the satellite-to-user propagation delay used for ranging.

• Ionosopheric Delay Data: Ranging errors due to ionospheric effects can be partially cancelled by using estimates of ionospheric delay that are broadcast in the data stream.

• Satellite Health Message: The data stream also contains information regarding the current health of the satellite, so that the receiver can ignore that satellite if it is not operating properly.

GPS satellite

Receiver Controlstation

Carrieｒ wave

（L1, L2）

C/A codeNavigationmessage

Propagationtime

Pseudo range

ephemeris

Satellite position

Positioningcalculation

Position、Time

（4 satellites）

・Satellites tracking

・Check of satellite’s clock

・Control of satellites

・Update of navigationmessage

Atomicclock

Crystal clock

GPS System Structure

Simplified GPS Receiver

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Single Point Positioning

Code-Phase Differential GPS （DGPS)

Carrier-Phase Differential GPS

GPS Positioning

10m～100m＊

10cm～10m＊

mm～10cm＊

Accuracy

GPS Positioning Methods

SV1

SV2 SV3

SV4

S Unknown Point (X, Y, Z)

（ X1, Y1, Z1)

（X2, Y2, Z2) （ X3, Y3, Z3 ）

（ X4, Y4, Z4 ）

Single Point Positioning

)offsetclockreceivertodueerror(s)rangetrue(rrangePsudo ii +ρ=

τ∆×= cs τ∆(C: Light speed, : Clock bias)

1r

1ρ

2ρ3ρ

4ρ

GPS Satellite

Antenna

Receiver

Ionosphere

40cm～10m

Troposphere 2～3m

（Vapor～40cm）

Multi-path

Error Factors in GPS Positioning

Satellite Position

Satellite Clock

Receiver NoiseReceiver Clock Offset

Noise

Multi-path

Multi-path

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Error Factors

Reference Station

True range ρR

Receiver

Antenna

GPS Satellite

Correction for Pseudo range ΔｒR

Rover Station

Correction for Pseudo range ｒC

Pseudo range ｒR

Pseudo range ｒ

Correction for Pseudo range and rate

Corrected range ｒ’

Code-Phase Differential GPS （DGPS)

Phase count Φ＝Δ φSR｜

tt0

Carrier-phase pseudo range

λΦ ＋Ｎλ ＝ρ＋ｃΔδ

epoch t0

epoch t1

epoch t2

ＮＮ

Ｎ

Φ2

φSR(t0)

fraction

φSR(t0)

Phase Count and Integer Ambiguity

φSR(ｔ2) ＝ Φ2 ＋Ｎ

＝ρ2/λ＋cΔδ2/λ

Φ1

Carrier-Phase Differential GPS

Epoch: The instant of time at which a give data set (e.g., satellite ephemeris) is valid

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Marine Application (RTK-GPS)GPS Satellites

Rover StationReference Station

Data Trans.

Reference Station Rover Station

GPS ReceiverGPS Receiver

PCTeleTele

Marine Application (RTK-GPS)

Applications of GPS/GNSS: Geodetic Survey, Construction, Marine Control Systems, etc.

User Segment

Airplane, spaceship

Survey Engineering

Marine ApplicationsCar, Train…

GPS/GNSS can be applied in many fields Hitech Navigation Systems

Real-time Structuring MonitoringAtmosphere StudiesPrecision FarmingYield MonitoringTelematics (car-navigation)Animal & People Tracking (S&R)Personal Digital AssistantsAutomated Berthing/Docking SystemAircraft Tracking and LandingOther Applications…

Remoted Observer Construction

GPS MobileNew technology

Machine ControlGIS (Graphics)

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Plumbing

Dredging

Riplap

Gut ship

Caisson

Reference station

GPS Satellites

Survey ship

Marine Applications

Installation of Offshore Structure

Ship Control Systems (DPS)

Further Information1. Institute of Navigation (US)

http://www.ion.org2. GPS Receiver Manufacturers:Garmin: http://www.garmin.com/Trimble: http://www.trimble.com/Novatel: http://www.trimble.com/Magellan: http://www.magellangps.com/en/3. Others:

http://www.colorado.edu/geography/gcraft/notes/gps/gps_ftoc.html

Summary of GPS/GNSS

• GNSS: GPS, GLONASS, and GALILEO• GPS: 3 segments (space, control, user)• User segment: Antenna, Receiver, Display –

position, time, velocity, and other information• Many applications (civilian and military):

navigation (marine, space, air, and land), survey engineering GIS (graphics), machine control, GPS mobile, etc.

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Any Questions?

Activity

• Module 5