Design of a generic smart and wireless sensors network Benefits of emerging technologies

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Design of a generic smart and wireless sensors
network Benefits of emerging technologies
Laboratoire Central des Ponts Chaussées (LCPC)
French Public Works Laboratory Division for
Metrology and Instrumentation Vincent Le Cam,
L.M. Cottineau, L. Lemarchand, F. Bourquin
4th European Workshop on Structural Health
Monitoring 2-4 July 2008 in Cracow
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Synopsis

• Wireless sensors for civil engineering
  applications
• LCPC generic and wireless sensors platform
• Presentation and  philosophy 
• Wireless mode of communication
• Embedding µCLinux as Operating System
• An absolute time synchronisation
• 3. Applications
• Unmanned Aerial Vehicle for structures inspection
• Cable health monitoring
• 4. Conclusion and prospects

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Wireless sensors for civil engineerings
applications

• Need for wireless instrumentation in civil
  engineering situations is obvious for (at least)
  4 reasons
• Reason 1 Structures vulnerability (due to age,
  vibrations, weather) and complexity

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Wireless sensors for civil engineerings
applications

• Reason 2 Long structures (i.e. long distances
  between sensors), difficult to access,
  requirement of specific and expensive machine

 Epsilon  machine
Viaduct of Millau 2.460 Km !
Human cable inspection
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Wireless sensors for civil engineerings
applications

• Reason 3 No choice ! Wireless is imposed by the
  situation

• Control of an U.AV. for bridges inspection
  (instead of  epsilon  machine)
• Vehicles to Infrastructure communication for road
  safety applications
• Nomad water level measurements
• Etc

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Wireless sensors for civil engineerings
applications

• Reason 4 Electrical cables between wired
  sensors are
• Very expensive (48,8 kE of electrical cables on
  a total of the 297,9 kE for the Aquitaine bridge
  instrumentation. 16)
• Subject to fatigue, corrosion, E.M.
  disturbances,tightness of connectors, vandalism
• Synonym of limitations
• the number of sensors
• distances between sensors and/or supervisordue
  to linear capacity and resistivity
  effects.Examples
• Ethernet 80 m (1Mbps)
• RS485 1000 m (10Kbps)

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LCPC generic and wireless sensors platform

• Presentation and  philosophy 
• LCPC decided to design a platform that avoids
  recurrent problems when starting a new instr.
  development from scrach the un-reusability ,
  the cost (in time and money).
• LCPC goal is to propose a Wireless Sensors
  Network that
• Has a high level of functionnalities and services
  in terms of
• Wireless communications (rate, reliability)
• Software abstraction (from hardware)
• Synchronization
• Is fully generic (reusable in other contexts)

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LCPC generic and wireless sensors platform

• Presentation and  philosophy 
• The idea consisted in
• considering a sensor as the compilation of
  various functionnal layouts
• identifying application specific layouts from
  generic ones

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LCPC generic and wireless sensors platform

• Presentation and  philosophy 

• Thus, LCPC WSN solution is modular and consists
  of
• A  mother board  that integrates wireless
  communication, computation, data storage,
  synchronization mechanism.
• Numerous inputs/outputs (54 GPIO, CAN Bus, 2
  serial ports,1 SPI, 1PPI, 1 PWM) all drawn to a
  connector
• A pluggable (on the mother connector)  daughter
  board  that integrates application specific
  needs
• the physical sensor (accelerometer, strain
  gauge, tC sensor)
• the specific conditionning and filtering of the
  signals
• the analog to digital conversion task
• Inexpensive board !

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LCPC generic and wireless sensors platform

• Presentation and  philosophy 

(Right) 2 sensors inside outdoor boxes under test
(Left) The both (mother daugther) boards
plugged one to the other.
7 cm
2.5 cm
11 cm
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LCPC generic and wireless sensors platform

• Wireless mode of communications

While making an active technological survey on
wireless protocols LCPC selected TCP/IP - the
standard simple worldwide protocol- that allows
accurate transmissions (no loss of data), hight
rate (often MB/s), and that simplifies the
network topology and cost. Self-made protocols
were excluded.
Using the TCP/IP protocol for W.S.N.
communications makes exchanges between sensors
as simple as in a traditionnal network of
computers. Moreover, any kind of sensor network
topology can be considered
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LCPC generic and wireless sensors platform

• Wireless mode of communications

• TCP/IP is a software stack whose physical
  implementation could be found on small devices
  under low-level standards that are
• wired Token Ring, Ethernet,
• wireless Wifi, Wimax, GPRS, UMTS,

3 cm
4 cm
LCPC WSN mother board

• TCP/IP dissemnination makes it ubiquitous,
  especially through the Wifi implementation
• Numerous hotspots in hotels, airports,
  streets,workshops
• 50 of US companies
• That makes TCP/IP solutions very cheap (compared
  to others) and easily scalable.
• Simple and unexpensive Wifi Access Points ensure
  a wireless area even around a bridge

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LCPC generic and wireless sensors platform

• Wireless mode of communications

Example easy and cheap deployment of a wireless
Wifi area on a 400m long cable suspended bridges
by means of a simple Access Point (800 Euros)
Supervision
A two antennas outdoor A.P.
A.P. is fixed at the bridge extremity
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LCPC generic and wireless sensors platform

• Wireless mode of communications

• LCPC WSN TCP/IP solution is based on the Wifi
  802.11g standard.For many years Wifi for WSN
  was precluded because of its  heavyweight  and
  the consequent power consumption.
• Appreciables works have been lead to make TCP/IP
  viable for wireless sensor network. Refer to
• 2 Adam Dunkels, Juan Alonso, Swedish Institute
  of Computer Science Making TCP/IP Viable for
  Wireless Sensor Networks. 2004.
• 3 Ariz Scottsdale, ABI Research, 2008, Wi-Fi
  Moves into the Sensor Networking.
• To save power and to reach long monitoring
  duration, the platform has the restriction to use
  very short and rare periods of wireless
  communications. No continuous communication can
  be considered over fews weeks running. Between
  two comm. periods the platform can store up to
  250 MBytes and has the capacities to process data.

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LCPC generic and wireless sensors platform

• Embedded uCLinux as Operating System

LCPC WSN platform integrates an Operating System
uCLinux. uCLinux is dedicated (in terms of
size, memory energy ressources) to the embedded
world. After long and hard works to implement it
on the processor (a Digital Signal Processor
Blackfin BF537), uCLinux offers very important
advantages As each OS, uCLinux offers to
developper a large collection of drivers to
control inputs/outputs, to set interrupt and
real-time algorithms linked to I/O activity of
the mother board. One driver recognizes our Wifi
module Then algorithms could be wrote using the
standard ANSI C language independently from
Blackfin hardware registers, architecture... Softw
ares are consequently simplified and reduced,
really portable to other systems. No need to be
an electronic engineer to implements his own
programs.
Pinguin inside !
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LCPC generic and wireless sensors platform

• Embedded uCLinux as Operating System

An honest demonstration of source code
simplification and reduction
Left no operating system, extract of the
specific source code to open the RS232 port of a
specific processorRight source code under
uCLinux O.S. to open a RS232 serial port.
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LCPC generic and wireless sensors platform

• Embedded uCLinux as Operating System

The most important benefit delivered by the O.S.
implementation in WSN resides in the fact that
sensor behavior can be remotely modified whitout
physical (un)mounting expensive, long and
dangerous operations. uClinux is first running as
a middle-ware between the processors physical I/O
and the software user-application, when its Wifi
is on, sensor is directly and remotely
addressable via the Local Area Network through
web browsers (Ex. Firefox) or the Telnet
universal deamon. Sensors are remotely
re-configurable !
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LCPC generic and wireless sensors platform

• Absolute time synchronisation between sensors

• Synchronization often forgotten when moving
  from wired to wireless world. Nevertheless,
  making collected datas of WSN able to be compared
  is strategic.
• Examples in vibration or wave propagation
  applications, needed accuracy could reach up to 1
  Microsecond ! In other words a same event must
  be dated by two sensors with a difference that
  musnt exceed 1 µS.
• Solutions could be classified in three categories
  
• Distributed solutions a Supervisor sends
  periodically a beacon in the WSN
• Post-facto synchronization the Supervisor try
  to correct event datation after it occured
• Self-synchronization each sensor is able to
  recover a common hour independently from the
  network. This is the one retained by LCPC, the
  technique is based on the GPS.

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LCPC generic and wireless sensors platform

• Absolute time synchronisation between sensors

• Synchronization using a small GPS receiver
• Ultra low-power consumption (few mW)
• Can combine active/sleep modes.
• As each GPS receiver does, it delivers
• - a serial sequence of bytes containing absolute
  timeand position,
• A binary signal  PPS  at a period of 1S /-
  20nS
• By connecting the PPS signal to the reset input
  of theµS counter of the processor, mother board
  couldreach accurate time stamping up to 5 µS.

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LCPC generic and wireless sensors platform

• Absolute time synchronisation between sensors

Test campaigns have been leaded and provided very
good results. As expected, the accuracy only
depends on the latency of the uCLinux O.S. to
raise the interrupt associated to the µS
counter-reset event.
RESULTS Ti Tj lt 5 µS ?t.
Sensor  i  and sensor  j  under sync. tests
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Applications

• Application 1 Unmanned Aerial Vehicle
  Instrumentation

• In order to evaluate the potentialities of
  bridges inspection by means of an U.A.V. the
  system has been implemented.
• The onboard system controls many devices
• Cameras,
• Laser-meter devices,
• Differencial GPS receivers,
• Angles variations
• Vibrations by means of accelerometers
• and communicates in real time with a remote
  Supervisor.

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Applications

• Application 2 Cable Health Monitoring

In view of safety, structure durability and cost
efficiency, monitoring cables and particulary,
detection and localization of wire breaks in
cables is strategic. LCPC developped a method
based on the acoustic emission of the wave
generated when a wire break occurs. By means of a
distribution of sensors detecting and dating each
acoustic waves, a Supervisor that collects those
informations is able to localize the rupture.
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Applications

• Application 2 Cable Health Monitoring

LCPC generic wireless platform has been specified
to developp the new generation of this acoustic
system. Each wireless sensor records and
transmits to a Supervisor the full shape of the
signal (including a pre-trigger period), ensures
an absolute time stamping (µS thanks to its GPS)
and is able to adapt its behavior according to
its transactions with the supervisor.
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Applications

• Application 2 Cable Health Monitoring

• Results and prospects
• Large scale campaigns have been lead on real
  bridges,
• Simulated ruptures were well detected and
  localized,
• Correlation with the previous (wired) system is
  good,
• Platform subject to industrial transfers.

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Conclusion and prospects

• LCPC has developped an efficient generic
  Wireless Sensor Network platform,
• Modular  mother /daughter  boards design
  reduces industrial costs and simplify evolutions
• Thanks to the uCLinux, it is able to be remotly
  and wirelessly updated. This provides a
  breakthrough when thinking structure monitoring.
  Consequent costs can be reduced,
• Embedded algorithms can be easily implemented in
  std. C language without expertise
• Thanks to the GPS technique, the platform
  ensures absolute time stamping up to 1 µS. In
  case of indoor applications, GPS re-emitter can
  be considered.
• Energy consumption is a point to perform.
  Platform power autonomy fully depends on the
  application needs (from days to weeks). Works
  that aim at recovering energy (sun, wind,
  vibrations) are actually leaded by LCPC and will
  be integrated to reach the unlimited autonomy.
• The efficiency and the genericty of the platform
  is already prooven by its various disseminations
  and the first industrial transfers

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Conclusion and prospects
Thus LCPC clearly wants to makes its platform a
reference in Civil Engineering instrumentation
world and appreciate any kind of cooperation
THANK YOU !!!