1 wireless structural sensors using reliable communication protocols for data acquisition and...

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Wireless Structural Sensors using Reliable Communication Protocols for

Data Acquisition and Interrogation

Yang Wang, Prof. Kincho H. Law

Department of Civil and Environmental Engineering, Stanford University

Prof. Jerome P. Lynch

Department of Civil and Environmental Engineering, University of Michigan

IMAC XXIII, Orland, FL, February 2, 2005

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AgendaAgenda

Research background Hardware design of the latest wireless

sensing unit prototype Software design of the latest wireless SHM

system Laboratory validation tests Field validation tests Future direction

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AgendaAgenda



system Lab validation tests Field validation tests Future direction

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Structural Health Monitoring (SHM)Structural Health Monitoring (SHM)

S. Chase (2001), National Bridge Inspection Program (NBIP): Nearly 60,000 bridges in U.S. evaluated as structurally deficient.

Over 580,000 highway bridges in U.S. mandated by Federal Highway Administration for biannual evaluations.

Human Visual Inspection: resource consuming; visible damages only

Advanced Sensing Technology for Autonomous SHM:

Rapid, accurate, low-cost

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From Wire-based Sensing to Wireless SensingFrom Wire-based Sensing to Wireless Sensing

E. G. Straser, and A. S. Kiremidjian (1998), Installation of wired system can take about 75% of testing time for large structuresM. Celebi (2002):

Estimation for each sensor channel and data recording system: $2,000; Installation (cabling, labor, etc.) per wired channel: $2,000. (Total: $4000)

Traditional DAQ System: wire-based

Future Wireless DAQ System

This wireless SHM prototype system is Jointly developed by researchers in Stanford University and the University of Michigan

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Challenges in Wireless SHM (1)Challenges in Wireless SHM (1)

Limited power consumption: The wireless units most likely run on batteries.

BETTER PERFORMANCE: Long-distance high-speed wireless acquisition; Extensive local data processing.

LOWER POWER: Wireless communication consumes lots of power; Likewise for extensive local data processing

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Challenges in Wireless SHM (2)Challenges in Wireless SHM (2)

Synchronization for data collected from multiple sensing units

Communication range

Limited bandwidth of wireless communication: impedes high-speed real-time data collection from multiple sensors

Failures in wireless data transmission

Communication protocol for the network: real-time data collection; multiple sensing units; synchronization; robust data transmission

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Dr. E. G. Straser, Prof. A. Kiremidjian (1998)

Dr. J. P. Lynch, Prof. K. H. Law et al. (2002)

Y. Wang, Prof. J. P. Lynch, Prof. K. H. Law (2005)

Wireless SHM Unit Prototypes from Stanford and UMichWireless SHM Unit Prototypes from Stanford and UMich

L. Mastroleon, Prof. A. Kiremidjian et al (2004)

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Design ObjectiveDesign Objective

Relatively low power

Long communication range for civil structural applications

Robust communication protocols for reliable data acquisition

Near-real-time, non-stopping wireless data collection, from multiple sensors, at an acceptable sampling frequency

Near-synchronized data collection

High-precision analog-to-digital conversion from multiple heterogeneous analog sensors

Considerable local data processing capability

Point-to-multipoint, and peer-to-peer communication

Low cost

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AgendaAgenda




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Parallel Port4-channel 16-bitAnalog-to-Digital

ConverterADS8341

4-channel 16-bitAnalog-to-Digital

ConverterADS8341

40 kbps 9XCiteWireless

Modem with 900MHz Tranceiver

8-bit Micro-controllerAtmega128

Sensing Interface Computational CoreWireless

Communication

0 - 5VAnalog

Sensors

SPIPort

128kB External SRAMCY62128B

UARTPort

Functional Diagram of the Latest PrototypeFunctional Diagram of the Latest Prototype

Major power consumption when components are active:

9XCite – 45mA average between transmitting and receiving.

Atmega128 – 15mA running at 8MHz

CY62128B – 15mA

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Power consumption: 75 – 80mA when active; 0.1mA standby

Communication range: 90m indoor, 300m outdoor

Near-real-time, non-stopping wireless data collection, from multiple sensors: up to 24 sensors at 50Hz sampling frequency

Near-synchronized data from multiple wireless sensing units

16bit Analog-To-Digital conversion, 4 A2D channels, 100kHz Fs

Local data processing: 4096-point float-point number FFT


Total hardware cost: $130.00 each for small quantity production

Hardware Performance SummaryHardware Performance Summary

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Picture of the Prototype with Wireless ModemPicture of the Prototype with Wireless Modem

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Atmega128 Micro-

controller

Sensor Connector

4 Channel, 16-bit A2D Converter

Address Latch for the External

Memory

128kB External Memory

Power Switch

Connector to Wireless Modem

Prototype Double-layer Circuitry BoardPrototype Double-layer Circuitry Board

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Container Dimension

4.02” x 2.56” x 1.57”

(10.2cm x 6.5cm x 4.0cm)

Antenna Length: 5.79” (14.7cm)

Wireless Sensing Unit Prototype PackageWireless Sensing Unit Prototype Package

Power supply requirement: 5V

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AgendaAgenda




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Wireless Sensing NetworkWireless Sensing Network

Server-side software: Computer server manages network of multiple wireless sensing units

Firmware: Atmega128 micro-controller organizes different hardware modules of the wireless sensing units

Simple star topology

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Objectives of Communication Protocol DesignObjectives of Communication Protocol Design

Major Challenge: Address Unreliability of Wireless Communication

Sufficiently reliable: detect the wireless communication failures; Successfully recover the system whenever a communication failure happens

Central server: active – responsible for reliability

Sensing units: passive – save power

Synchronization among different wireless sensing units

Retry and acknowledgement protocol to ensure the fidelity of data transfer

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Reliable Beacon Signal Synchronization ProtocolReliable Beacon Signal Synchronization Protocol

•Straser and Kiremidjian (1998)

BroadcastBeacon signal to

all WSUs Begin sensor datasampling and

storage

Verify with eachWSU if it

received theBeacon signal

A WSU didn't receivethe Beacon signal

Inform WSUs* oneby one to restart

* WSU: Wireless Sensing Unit** CS: Central Server

Y

Receivedbeacon signal

Wait andRespond to

Beaconverification

Restart andacknowledge with

CS**, wait forBeacon signal

Wait for datacollection

command from CS

Receive restartcommand

Y

Start data collection fromWSUs one by one, and

round by roundTransmit data to

CS

Received datacollection request and

data is ready

Central Server Wireless Sensing Unit

Finish one round ofdata transmission

Wireless communicationand its direction

Y

Y

Approximate beginningsynchronization error:

20 micro-Seconds.

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System complexity incurred by the unreliability of the wireless communication -> state machine concepts

A set of states A set of transitions among these states. At any point in time, the state machine can only be in one of the possible

states. In response to different events, the machine transits between its discrete

states. Visualize the communication protocol

State Machine Concept for Software DesignState Machine Concept for Software Design

State 2State 1Action

Condition

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Communication State Diagram for Wireless Sensing UnitCommunication State Diagram for Wireless Sensing Unit

State1Wait forBeacon

State0Bootup

State2Wait forBeaconVerifi.

State3Wait for

DataCollect.

Initialize memory

No condition

Send LostBeacon

Received BeaconVerification

Start data collection

Received Beacon

Send BeaconConfirmation


Send BeaconConfirmation


Send AckRestart

Received Restart

Send AckRestart

Received Restart

Send DataReady

Received Request for datacollection and data is ready

DataTransfer

Send AckRestart

Received Restart

Service

Event

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Dual Stack Memory Allocation for Non-stopping DAQDual Stack Memory Allocation for Non-stopping DAQ

Instant 1

Storingsensor data

Storingsensor data

Memory Map for Sensor 1 Memory Map for Sensor 2

Currently transfering

Storingsensor data

Storingsensor data

Instant 2

Stack 1-1 Stack 2-1

Stack 1-2

Stack 1-2

Stack 1-1 Stack 2-2Stack 2-1

Stack 2-2

Currently transfering

•Straser and Kiremidjian (1998)

•Lynch and Law et al. (2002)

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AgendaAgenda




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Wireless Sensing Unit

Crossbow CXL01LF1

Accelerometer

Wireless Modem Receiving Data from

Wireless Sensing Units

Lab Validation TestsLab Validation Tests

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Sampling frequency: 200Hz. Sampling resolution: 16 bits

Real-time non-stopping data collection from four wireless sensing units

Crossbow CXL02LF1 accelerometer, RMS noise floor of 1mg

Bosch SMB110 accelerometer, RMS noise floor of 7mg

Some Test ParametersSome Test Parameters

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Discrete Fourier Transform of the third-floor acceleration during free-vibration

Three theoretical natural frequencies: 2.08Hz, 5.71Hz, and 8.18Hz

First Lab Test: Free VibrationFirst Lab Test: Free Vibration

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Figure 7 – Ground acceleration time history

Second Lab Test: Chirping-signal Ground MotionSecond Lab Test: Chirping-signal Ground Motion

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Comparison of measured and theoretical absolute acceleration at third floor

Absolute Acceleration at Third FloorAbsolute Acceleration at Third Floor

Measured

Computed

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1st floor 2nd floor 3rd floor

Measured (m/s2) 2.14 3.35 4.74

Theoretical (m/s2) 2.07 3.76 4.93

Relative Difference 3.32% 11.5% 3.93%

Comparison of measured and theoretical maximum absolute acceleration

Maximum Absolute Acceleration at Three FloorsMaximum Absolute Acceleration at Three Floors

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Acceleration Data and FFT Results of the Shake-table Excited by 5.7Hz Sinusoidal Input

Sampling Frequency: 100Hz. Total time: 40.96 Seconds. Total Number of Pts: 4096

Third Lab Test: Sinusoidal Ground MotionThird Lab Test: Sinusoidal Ground Motion

0 5 10 15 20 25 30 35 40 45-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15Time History

Acc

eler

atio

n (g

)

time (Sec.)

0 1 2 3 4 5 6 7 8 9 100

100

200

300

400

500Absolute Values of FFT to Time History Computed Onboard By Unit No.1

Mag

.

Freq.(Hz)

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Third-floor Acceleration Data

Sampling Frequency: 100Hz. Total time: 40.96 Seconds. Total Number of Pts: 4096

Third Test: Sinusoidal Ground MotionThird Test: Sinusoidal Ground Motion

0 5 10 15 20 25 30 35 40 45-0.5

0

0.5Time History

Acc

eler

atio

n (g

)

time (Sec.)

0 1 2 3 4 5 6 7 8 9 100

200

400

600

800

1000

1200

1400Absolute Values of FFT to Time History Computed Onboard By Unit No.3

Mag

.

Freq.(Hz)

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AgendaAgenda




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Geumdang Bridge Test, KoreaGeumdang Bridge Test, Korea

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14 12

11 10 9 8 7 6 5 4 3

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NORTH

Pier Pier PierAbutment

46.0m18.7m 18.7m

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Sensor PropertyPCB Piezoelectric

(Cable System)PCB MEMS Capacitive

(Wireless System)

Maximum Range 1 g 3 g

Sensitivity 10 V/g 0.7 V/g

Bandwidth 2000 Hz 80 Hz

RMS Resolution (Noise Floor) 50 g 0.5 mg

Wire-based System versus Wireless SystemWire-based System versus Wireless System

Sampling Frequency 200Hz 70Hz

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Bridge Traffic ExcitationBridge Traffic Excitation

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155 160 165 170 175 180 185 190-0.04

-0.02

0

0.02

0.04KAIST Data Aquisition System

Time (sec)

Acc

eler

atio

n (g

)Sensor Location #8

155 160 165 170 175 180 185 190-0.04

-0.02

0

0.02

0.04Wireless Data Aquisition System

Time (sec)

Acc

eler

atio

n (g

)

Sensor Location #8

Time History Comparison Between Two SystemsTime History Comparison Between Two Systems

Wireless System

Wire-based System

Difference in sensor and signal conditioning

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0 2 4 6 8 10 12 14 160

1

2

3

4

FFT - KAIST DAQ

Frequency (Hz)

Mag

nitu

de

Sensor Location #8

0 2 4 6 8 10 12 14 160

0.2

0.4

0.6

0.8

FFT - Wireless DAQ

Frequency (Hz)

Mag

nitu

de

Sensor Location #8

Comparison of FFT to Time HistoryComparison of FFT to Time History

Wireless System

Wire-based System

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Validation Results SummaryValidation Results Summary

Rapid installation, and low cost

Communication range: 50 – 60m in box girder

Networked real-time and non-stopping data collection: 14 wireless sensors at 70Hz sampling frequency

Data is near-synchronized

Robust communication protocols for reliable data acquisition

Local data processing capability

Analog-to-digital precision


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AgendaAgenda




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Future DirectionFuture Direction

To be improved for current prototype system:

Power design, anti-noise circuits design

Accommodation for digital sensors

Greater wireless communication range, higher data rate

Multiple receivers at different channels to improve data rate

Large-scale data collection from densely allocated sensors

More local data analysis and damage identification algorithm

Handling mal-functioning sensing units

Further field validation tests

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AcknowledgementAcknowledgement

National Science Foundation CMS-9988909 and CMS-0421180.

The University of Michigan Rackham Grant and Fellowship Program

The Office of Technology Licensing Stanford Graduate Fellowship

Smart Infrastructure Technology Center at Korean Advanced Institute of Science and Technology (KAIST), Korea Highway Corporation

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The EndThe End

1 wireless structural sensors using reliable communication protocols for data acquisition and...

Documents

wireless units

wireless shm prototype

wireless structural

future wireless daq

wireless shm unit prototypes

data recording system

reliable data acquisition

university of michigan