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Wireless Data Acquisition System Hasan Ozer and Mat Kotowsky An Application to Crossbows Smart Dust Challenge Contest Wireless Data Acquisition System
Hasan Ozer and Mat Kotowsky
An Application to Crossbows Smart Dust Challenge Contest
December, 2004
2

1 Project
Description ..................................................................................................... 3
2
Origin of Idea.............................................................................................................. 3
3 Objective..................................................................................................................... 4
4 Project
Function.......................................................................................................... 4
4.1
Description of Data to Be Acquired.................................................................... 4
4.2
Description of Installed System .......................................................................... 5
4.3
What Is Measured? ............................................................................................. 6
4.4
Operation of the System...................................................................................... 7
4.5
Presentation of Data on the Civil Data Systems Web Site ................................. 8

5 Outcome
of
Demonstration....................................................................................... 10
5.1
Installation of the System and Difficulties Overcome...................................... 10
5.2
Analysis of the Results...................................................................................... 11

6 Project
Benefit .......................................................................................................... 13
7 Project
Innovation..................................................................................................... 15
8
Product Specification Form ...................................................................................... 16
9
Required Documentation Supplements .................................................................... 17
10 Software
Disclosure.................................................................................................. 18

3
1

Project Description

The project is the first phase of a rapidly deployable Wireless Data Acquisition
system for surveillance of long-term structural health of critical infrastructure
components such as bridges, tunnels, buildings, pipelines, etc. The system described
herein uses Crossbow Mica2 motes to implement a wireless, autonomous, graphical
Internet display of data collected from sensors at an arbitrary number of locations
within a structure. There are two critical components of long-term structural health
monitoring: acquiring sensor response and communicating these data in a timely
fashion. Both of these components consume power, and thus power consumption
becomes a critical aspect of any wireless system designed for long-term use. Careful
selection of sensors and optimization of communication schemes will allow
sustained operation of the Wireless Data Acquisition system for a year or more.
2

Origin of Idea

The Wireless Data Acquisition system is an extension of ongoing projects in
Internet-enabled remote monitoring of critical infrastructure at the Infrastructure
Technology Institute and the Department of Civil and Environmental Engineering at
Northwestern University. The overall objective of Internet-enabled remote
monitoring is to provide timely information to parties interested in the structural
health of critical infrastructure components such as the crack in the bridge in Figure
1. Sensors on a structure are polled regularly so that responses may be compared
graphically with past readings to identify trends and automatically alert authorities of
impending problems. The main drawback of such a system of sensors is the extreme
cost in labor and materials for installation, wiring, and maintenance of such a system.
The natural extension of these wired systems is a wireless system that drastically
reduces the cost of installation and eliminates the impact of the sensor network on
the day to day use of a structure.

4
3

Objective

The objective of the project is to develop a system that will:
Eliminate hard-wired connections to each sensor
Operate for at least a month without human intervention
Records data at a given sample rate, including
o

Sensor output voltage
o

Temperature
o

Humidity
o

Mote battery voltage
Reduce cost, installation effort, and intrusion associated with a wired system.
4

Project Function
4.1

Description of Data to Be Acquired

This system is designed to record the response of any infrastructure component (such
as the fracture-critical bridge as shown in Figure 1) where the rate of data is slower
than 15 minutes. However, the proof of this system was established by measuring
the response of cosmetic racks in a house subjected to blasting at a nearby quarry.
As shown in Figure 2, sensors are attached across cracks to monitor long-term
changes in crack width with environmental conditions and blasting activity. The
same approach could be employed to monitor cracks in fracture critical bridges.

Figure 1: A bridge with a crack
5


Figure 2: MDA300 and Potentiometer mounted over crack with plan view and picture of house

4.2

Description of Installed System

The Wireless Data Acquisition system consists of a network that is comprised of one
base node and any number of sensor nodes. Each sensor node consists of one
Mica2 mote running MDA300Logger, one MDA300 sensor board, and one
ratiometric string displacement potentiometer which is connected to the screw
terminals of the MDA300 and installed across the crack. As shown in Figure 2, the
mote with its attached sensor board is then mounted a few inches away from the
crack. Though only one sensor node is pictured, any number of sensor nodes
maybe attached within radio range of the base node. At the time of the
CRACK
6
demonstration installation, only a single MDA300 board was available for testing.
The system was later successfully tested in the lab with two sensor nodes. Self-
assembling capability, though supported by the motes, is not necessary in this
application since locations of sensors are determined before deployment.

The base node consists of a mote running TOSBase mounted on an MIB510
interface board. The interface board is connected via a serial cable to a MOXA
NPort device which allows remote access to the system. This base node obviously
requires AC power, and it is hidden in a closet as shown in Figure 3. This base
node can be placed anywhere with in radio range of the sensor nodes as long as it
has power and either a phone line or some variety of Internet connection, including
cable modem, DSL, standard dial-up modem, or a cellular modem.

4.3

What Is Measured?

The system excites and records the voltage output of the ratiometric string
potentiometer, shown in Figure 2, which measures micrometer changes in crack
width. The potentiometer is optimal because of its high sensitivity, low power draw,
Figure 3: MOXA NPort (left) and MIB510 with mote running TOSBase (right)
7
and instantaneous response time. Such low-power devices are essential to the
success of any wireless sensor system. As the width of the crack changes, so will the
resistance of the potentiometer. The change in crack width is then a linear function
of the output voltage of the potentiometer given a known input voltage.
4.4

Operation of the System

At each sampling time (every hour in this test case), the Mica2 activates the
MDA300s 2.5 Volt excitation voltage to power the ratiometric string potentiometer.
The voltage output of the potentiometer along with temperature, humidity, and
battery voltage are stored locally on the sensor node motes onboard non-volatile
memory. It is necessary to utilize the precision input channels on the MDA300,
which have 12-bit resolution over the 0.5mm full scale travel length of the string
potentiometer to achieve a resolution of 0.12 micrometers.

Whenever data retrieval is required (every day at 11:00 PM in this test case) the
central PC autonomously communicates with the remote Wireless Data Acquisition
system from a remote location via the Internet via a modified version of BcastInject
to broadcast a read_log command and a mote address across the mote network.
The mote in question will then transmit all of its data back to the off-site PC where it
is recorded to the hard disk. This process is repeated for ea