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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