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UNIVERSITY OF CINCINNATI
Date:__February 4, 2005__ I, _____________________Daniel
Alford_______________________,
hereby submit this work as part of the requirements for the
degree of:
Master of Science
in:
Mechanical Engineering
It is entitled:
Lightweight, Low Cost, Automotive
Data Acquisition and Telemetry System
This work and its defense approved by:
Chair: _Dr. Randall Allemang________ _Dr. David
Brown_____________ _Dr. Allyn Phillips__________
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Lightweight, Low Cost, Automotive
Data Acquisition and Telemetry System
A Thesis Submitted to:
Division of Research and Advanced Studies Of The University of
Cincinnati
In Partial Fulfillment of the Requirements for the Degree
of:
MASTER OF SCIENCE
In the Department of Mechanical, Industrial, and Nuclear
Engineering Of the College of Engineering
2005
By:
Daniel Alford
B.S., University of Cincinnati, 2002
Committee Chair: Dr. Randall Allemang Committee: Dr. David
Brown
Dr. Allyn Phillips
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Abstract
Dynamically, testing small, lightweight automobiles can be very
difficult on a limited
budget. Several quality data acquisition systems exist that are
designed for automotive
applications, but most are large cumbersome units that require
an AC power inverter. It
would not be possible to use one of these systems on a small
lightweight vehicle, like a
Formula SAE racecar. A device powered from a 12 volt DC power
supply is required for
this type of application. Also, typical data acquisition systems
are far too bulky and
costly to be fitted to a Formula SAE vehicle. As with any
system, recording actual
operating conditions will provide useful information, leading to
system improvements.
In order to achieve these goals, several data acquisition with
telemetry systems were
investigated. The most interesting system, Dataq DI-720-EN and
Linksys wireless
router, were purchased and characterized through a barrage of
testing. The system was
first characterized by logging a random signal and transferring
the data through a typical
wired setup. The system was then methodically tested in the lab
with Ethernet wired and
wireless data transfer methods. The data acquisition and
telemetry system was also tested
dynamically, on the 2004 Bearcat Motorsports FSAE vehicle, using
wireless data transfer
methods. The testing results were promising, with minimal signs
of poor data. Some
gaps were seen in the data, but were deemed insignificant for
the majority of potential
testing. Lastly, several likely improvements are discussed.
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Acknowledgements
I would like to thank everyone that has been involved in the
development of this thesis.
To my committee members Dr. Randall Allemang, Dr. David Brown,
and Dr. Allyn
Phillips, I thank you all for your support, because without it
this research would not have
been completed.
I want to especially thank my advisor, Dr. Randall Allemang, for
his countless hours of
discussion and guidance at nearly any hour of the day. The
teaching assistant position for
Automotive Design I, II, and III not only paid the bills, but
has also enhanced my
engineering and leadership skills just as much if not more than
all of my years in the
undergraduate mechanical engineering program at the University
of Cincinnati. I am
amazed by your ability to find support for student projects and
research interests.
I want to thank PCB Piezotronics for their donation of six
single axis capacitive
accelerometers. Thanks to Todd Dahling and Brian Lewis of Manta
Corporation for
loaning the SoMat and Freewave equipment. To all of the students
and staff of the
SDRL, I want to wish the best of luck, you made the days more
enjoyable and there was
never a dull moment. Thanks to all my friends and family for all
the motivation to
complete this research. I should also thank the Bearcat
Motorsports teams of 2003, 2004,
and 2005 for the use of their race car for testing.
Thank you all.
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Oh, and thanks B.J. Stoney and Bill Wise for manufacturing those
parts.
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Table of Contents Table of
Contents.................................................................................................................
i List of Figures
....................................................................................................................
iii List of Tables
......................................................................................................................
v List of Tables
......................................................................................................................
v Chapter 1 Introduction
........................................................................................................
1
1.1 - Introduction
............................................................................................................
1 Chapter 2 Background
........................................................................................................
6
2.1 - Telemetry Systems
.................................................................................................
6 2.2 - Data Acquisition
Systems.......................................................................................
7
2.2.1 - Larson Davis DSS
...........................................................................................
8 2.2.2 - National Instruments Compact RIO
.............................................................. 10
2.2.3 - Motec
ADL....................................................................................................
13 2.2.4 - Pi Research Delta
System..............................................................................
14 2.2.5 - DaTaq DI-720-EN
.........................................................................................
15
2.3 - Data Acquisition Theory
......................................................................................
26 2.3.1 - Sampling Theory
...........................................................................................
26 2.3.2 -
Aliasing..........................................................................................................
27
Chapter 3 Applications
.....................................................................................................
29 3.1 - Lab Testing
...........................................................................................................
29
3.1.1 - Parallel Port:
..................................................................................................
30 3.1.2 - Local Area Network:
.....................................................................................
34 3.1.3 - Wireless Local Area Network:
......................................................................
41 3.1.4 - Wireless LAN w/Parabolic Antenna
.............................................................
44
3.2 - Onsite
Testing.......................................................................................................
46 3.2.1 - Static Testing
.................................................................................................
47 3.2.2 - Dynamic
Testing............................................................................................
56
Chapter 4 Conclusions & Future Work
............................................................................
59
References.........................................................................................................................
63 Appendix - A Instrumentation
.....................................................................................
66 Appendix - B Matlab
Script.........................................................................................
71
B.1 CSV
Converter..................................................................................................
71 B.2 Main Executable
...............................................................................................
73 B.3 Windows
...........................................................................................................
79 B.4 Load
Data..........................................................................................................
81 B.5 Cyclic Averaging
..............................................................................................
83 B.6
Overlapping.......................................................................................................
86 B.7
Autopower.........................................................................................................
88 B.8 Crosspower
.......................................................................................................
89 B.9
H1......................................................................................................................
92 B.10
Hv......................................................................................................................
93 B.11
H2......................................................................................................................
94 B.12 Multiple Coherence for H1
...............................................................................
95 B.13 Multiple Coherence for Hv
...............................................................................
95
i
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B.14 Plot Output
........................................................................................................
96 B.15 Plot Output 2
.....................................................................................................
99
ii
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List of Figures Figure 1.1 Basic System
.....................................................................................................
4 Figure 2.1 Channel
Selection............................................................................................
16 Figure 2.2 Max Sample Rate
Selection.............................................................................
17 Figure 2.3 Sample Rate
Selection.....................................................................................
17 Figure 2.4 Channel Settings Selection
..............................................................................
19 Figure 2.5 Sine Wave on +-10V Scale
.............................................................................
20 Figure 2.6 Sine Wave on +-5V Scale
...............................................................................
21 Figure 2.7 Fixed Calibration
.............................................................................................
22 Figure 2.8 Low
Calibration...............................................................................................
22 Figure 2.9 High Calibration
..............................................................................................
23 Figure 2.10 Sine Wave Phase
Shift...................................................................................
24 Figure 2.11 Parallel Sampling Example
...........................................................................
25 Figure 2.12 Multiplexed Sampling (Equal Sampling & Scan
Rates) ............................... 25 Figure 2.13 Multiplexed
Sampling (Non-equal Sampling & Scan
Rates)........................ 26 Figure 2.14 Sampling
Relationships
.................................................................................
27 Figure 2.15 Aliasing Example
..........................................................................................
27 Figure 2.16 Aliasing Contribution
....................................................................................
28 Figure 3.1 Parallel Port Testing Block
Diagram...............................................................
30 Figure 3.2 Parallel Port Frequency Response Functions
.................................................. 33 Figure 3.3
Typical
Coherence...........................................................................................
33 Figure 3.4 Parallel Port Random Time History
................................................................ 34
Figure 3.5 Wired Ethernet Block
Diagram.......................................................................
34 Figure 3.6 LAN Frequency Response
Functions..............................................................
36 Figure 3.7 LAN Sine Wave Time History
........................................................................
38 Figure 3.8 LAN Sine Wave Close Up
..............................................................................
39 Figure 3.9 Bellcrank
Rotation...........................................................................................
40 Figure 3.10 Basic Wireless System Block
Diagram......................................................... 41
Figure 3.11 WLAN Frequency Response Functions
........................................................ 42 Figure
3.12 WLAN Sine Wave Time History
..................................................................
43 Figure 3.13 Parabolic Testing Block Diagram
.................................................................
44 Figure 3.14 Parabolic Frequency Response Functions
..................................................... 45 Figure
3.15 Parabolic Sine Wave Time History
............................................................... 46
Figure 3.16 Vehicle Testing Block Diagram
....................................................................
46 Figure 3.17 Center Hill
FRFs............................................................................................
48 Figure 3.18 Center Hill Coherence
...................................................................................
49 Figure 3.19 Bad Channels FRFs
.......................................................................................
50 Figure 3.20 Bad Channels
Coherence...............................................................................
51 Figure 3.21 Bad
Channels.................................................................................................
52 Figure 3.22 Throttle Position (Engine
Off).......................................................................
53 Figure 3.23 Throttle Position (Engine On)
.......................................................................
53 Figure 3.24 Typical Acceleration
.....................................................................................
54 Figure 3.25 Isolated Accelerometer Acceleration
............................................................ 55
Figure 3.26 Isolated
Accelerometer..................................................................................
55 Figure 3.27 Bad Channel FRF
..........................................................................................
57 Figure 3.28 Bad Channel Time
History............................................................................
57
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Figure 3.29 Dynamic Frequency Response Functions
..................................................... 58 Figure A.1
Wiring
Diagram..............................................................................................
67 Figure A.2 Damper Position
.............................................................................................
69 Figure A.3 Lateral Accelerometer
....................................................................................
70 Figure A.4 Accelerometers
...............................................................................................
71
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List of Tables Table 2.1 Performance Information of DSS DSIT
............................................................. 9
Table 2.2 Performance Information for RIO I/O Modules
............................................... 12 Table 2.3 Delta
Systems
...................................................................................................
14 Table 2.4 Data Acquisition Device Comparison
.............................................................. 15
Table 2.5 Channel
Comparison.........................................................................................
15 Table 2.6 IOS Example Parameters
..................................................................................
19 Table 2.7 Resolution Increases with applied
Gain............................................................ 21
Table 3.1 Vehicle
Sensors.................................................................................................
29 Table 3.2 Lab Test
Setups.................................................................................................
30 Table 3.3 Data Transfer Throughput
................................................................................
31 Table 3.4 Random & Sine Logging Parameters
............................................................... 35
Table 3.5 Vehicle Logging
Parameters.............................................................................
35 Table 3.6 MTS Test File Information
...............................................................................
39 Table 3.7 Onsite Test Setups
............................................................................................
47 Table 3.8 Center Hill Logging Parameters
.......................................................................
49 Table A.1 Suggested Sampling
Frequency.......................................................................
68
v
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Chapter 1 Introduction
1.1 - Introduction
Over the history of motor racing, racers have been looking for
the elusive perfect vehicle. In
reality a perfect vehicle does not exist, at least not for a
reasonably difficult course with varying
weather conditions. To be competitive, a team needs to know what
their vehicle will be doing on
track. In the early days of racing, the only feedback race
engineers had, was what they could see
and what the driver could see, feel, and hear. This seat of the
pants data logging was really the
only solution to perfecting a race car at the time, computers
were unheard of. Once computers
were invented, they were still too heavy and bulky to use on a
race car, so the seat of the pants
method was still utilized.
The major concerns when selecting a data acquisition device are
size, cost, expandability, and
capability. Some data acquisition devices are now small,
lightweight, and almost affordable, so
data logging has become the preferred solution to finding the
perfect vehicle, because a data
logger does not lie, or miss anything, like a driver might.
While a data logger is a great
improvement from the seat of the pants method, it can still be
improved. Data acquisition is not
all benefit, it has drawbacks too. Some of the drawbacks are
price, weight, and memory. Weight
is less of an issue when it comes to a racing series that has a
minimum weight rule, but in
Formula SAE there is no such rule, so every pound counts. Cost
of a data acquisition system can
be very overwhelming. Some systems cost well above $100,000,
sensors included, well beyond
the budget of most racers. Another downfall of a data logger is
that the data has to be
downloaded after the race and then processed. This means no
change can be made during a pit
stop to improve the vehicles performance and win the race; but
it can produce an abundance of
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information that the team could use to prepare a better vehicle
in the future. The typical racecar
data acquisition system contains an analog to digital converter
for each channel of data to be
collected and some form of memory. The memory, where all of the
digitized signals are stored
for later analysis, can be very pricey. To reduce the cost of
memory, the amount of data taken
could be reduced, by recording fewer channels or lowering the
sampling frequency. Either could
lead to many headaches for the race engineer; there may be
something important happening that
was not observed, which would lead to a large amount of wasted
time searching for a problem
that cannot be seen.
Telemetry is the transfer of data from the data acquisition
system to another data analysis system
in real time and wirelessly. If the race engineer could use
telemetry to analyze the vehicle data
as it comes in, the engineer could deduce improvements for the
vehicle-driver system. When the
vehicle comes in for a pit stop the team can make modifications
based on the data the engineer
analyzed from the last track stint. The current method in racing
is the use of a dual band UHF
radio frequency to telemeter data. Another popular option is to
log the data, and then transfer the
data once a lap. Telemetry is currently too costly for
widespread use outside of the top levels of
professional motorsports. This thesis will explore the
possibility of using a new technology,
wireless local area networks (Wireless LAN or WLAN) as a means
of transferring data at a much
lower cost. Wireless local area networks are not that different
from the dual band UHF radios
currently used. Their benefit is the lower cost structure, and
the drawback is the reduced range.
Looking back 50 years, it seems quite obvious on where the
biggest advantage to be gained was;
and 50 years from now it will be quite obvious where the biggest
improvement will be. But as of
right now, racecar engineers are spending enormous amounts of
time and money trying to find
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the smallest advantage. The top teams in Formula 1 (F1) are
spending in the range of $700
million a year to find any advantage they can. While the F1
teams may not be too concerned
with a budget, at least not a normal sized budget, club racers,
who are into racing only for the
thrill, are concerned with how every penny is spent, because
they are on a tight budget of their
own hard earned money. The wireless local area network
technology is not currently expected to
work at a range large enough to encompass a typical racetrack,
but it could be of use at a vehicle
dynamics testing area, or a parking lot used for testing.
Although the range is currently limited,
the wireless local area networking technology is rapidly
changing and may produce a
technological advance capable of significantly increasing the
range. This technology could also
be very useful to the SCCA Solo2 racers, as their autocrosses
typically run in open parking lots.
Where club racers may spend $10,000-20,000 a year, autocrossers
are more concerned with their
budget; they will probably only spend around $2,000 a year.
Figure 1.1 depicts the basic
concept, utilized to approach this lightweight, low cost,
automotive data acquisition and
telemetry system. A data acquisition and telemetry system of
this type would be in the $2,000
range where a professional motorsports data acquisition and
telemetry system is 5-10 times that.
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Wireless Game Adapter Sensors
Data Acquisition Device
Wireless Router
Wireless Link
Figure 1.1 Basic System
A Linksys wireless router, Linksys game adapter, Cisco access
point with parabolic antenna, and
Dataq DI-720-EN were chosen to be characterized by the testing
for this document, for their low
cost, small size and ability to be powered by a 12 volt DC power
supply. The IEEE has created
standards utilized by several manufacturers to create wireless
networking devices. The 802.11b
at 11 Mbps and 802.11g at 54 Mbps standards operate on a 2.4 GHz
frequency band, and differ
only by their throughput capability. Another standard, 802.11a
operates in a 5 GHz frequency
band and has capacity similar to the 802.11g standard, but had a
decreased range due to its
higher operating frequency. At the time of procurement, there
were no game adapters available
operating in the 802.11a and g wireless standards, therefore the
802.11b standard was chosen for
testing. The Cisco access point, also working in the 802.11b
standard, and parabolic antenna
were borrowed from the UCIT department, to test for the
additional range expected by using a
parabolic antenna. The Dataq unit was the chosen data
acquisition device, because of its
Ethernet output, low cost, small size, and ability to be powered
by the 12 volt DC power supply
4
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available on the test vehicle. The Dataq unit is a multiplexed
system, which means that the
multiple data channels are not being digitized
simultaneously.
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Chapter 2 Background
2.1 - Telemetry Systems
Historically, telemetry used an analog frequency modulation,
normally operating in the FM radio
broadcast band, to transfer data from one sensor to the data
logger. That meant if ten sensors
needed to be logged, ten distinctive FM radio frequencies were
required to transmit the data.
These systems have many disadvantages including interference
from FM radio stations, and
frequency shift issues. The FM broadcast band is fairly
populated, so finding a frequency band
large enough to transfer large amounts of data has become nearly
impossible. Frequency drift
issues arise when the transmitter is located in a thermally
active area, imposing another
limitation.
There are some more complex ways around the drawbacks of FM
telemetry, FM-FM and PWM-
FM. FM-FM modulation performs a frequency modulation of the
signal on a low frequency
carrier, and then on the radio carrier frequency. This works
well for near DC signals, but when
rapidly changing sensor signals, high bandwidth signals, are
being observed, FM-FM telemetry
is much less useful. Pulse width modulation-FM first modulates
samples of the signal as the
time duration of short pulses, and then frequency-modulates the
pulses.[19] The main
drawback is that when the signal to noise ratio of the recovered
signal becomes low, the receiver
cannot determine the precise frequency.
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2.2 - Data Acquisition Systems
Typically in motorsports and automotive testing several
different types of data are recorded.
They may range from various temperatures, pressures, positions,
accelerations, and many more.
These data types create an additional problem, knowing how to
record them. Many vehicle
signals are nearly DC, therefore very low frequency, while
others are very active, changing
several hundred thousand times a second, and some are on or off
(digital). The ideal system
would allow the user to set each channels sample rate, gain, and
calibration individually. Many
temperatures are slow to change, therefore a low sampling
frequency (1-2 Hz) would be desired
to reduce the amount of memory need, and eliminate extraneous
information. Brake rotor
temperatures may need to be sampled more frequently than other
temperatures, due to their quick
changes during braking, but it is unlikely to reach more than 10
Hz. Probably, the most extreme
case for the need to sample at high frequency would be to record
cylinder pressure. For a
motorcycle engine the speeds can reach above 15,000 rpm, and
attempting to capture the
pressure change of the explosion of fuel and air requires a
sampling frequency in the 100,000 Hz
range. It is highly unlikely cylinder pressures would ever be
recorded on a vehicle, as this is
much more common during engine dynamometer tuning. A multiplexed
data acquisition system
would not be recommended for measuring multiple cylinder
pressures, as in this case it is
important to know the relative time difference between peak
cylinder pressures, and a
multiplexed unit will not provide an accurate estimate. Much
more reasonable high frequency
signals likely to be measured on a vehicle are the damper
positions, and strain gauges placed on
particular parts. Strain gauges and damper positions are
typically sampled at 500 Hz. A
sampling frequency of 500 Hz and vehicle moving at 30 mph,
results in traveled distance of
about 1 inch between data points. Many motorsports data
acquisition devices contain inputs
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specifically for rpm measurements, which contain signal
conditioning that converts the rpm
sensors output to a recordable signal. Digital inputs are also
quite common in data acquisition
systems, and are used to record on/off situations. Digital
inputs are typically used to signify fan
and button/switch usage. Another requirement for a lightweight,
low cost, automotive data
acquisition and telemetry system is the ability to be powered by
a 12 volt DC power source.
Several data acquisition systems exist that will fit in the back
seat of a typical automobile, and
can be plugged into a power inverter, but these systems are far
too large, bulky, and heavy to be
used on a racecar, let alone a Formula SAE racecar.
There are several hundred, maybe thousand, data acquisition
systems available commercially.
The difficulty lies in finding a suitable low cost solution that
provides room for future expansion.
The comparison discussion for this thesis will be limited to
five systems, two popular
motorsports data acquisition systems, two lab systems, and the
chosen Dataq DI-720-EN. The
Motec ADL and Pi Research Delta systems are the motorsports
specific systems, while the
Larson Davis DSS and National Instruments Compact RIO are
oriented more towards the lab
testing environment.
2.2.1 - Larson Davis DSS
The Larson Davis Digital Sensing System (DSS) is typically used
to record structural dynamics,
sound pressure, and vehicle/engine noise. The DSS consists of a
Master Module with either a
parallel or Ethernet port for communicating with a personal
computer; it also stores the digitized
data. The Ethernet port allows this system to be used with the
same 802.11 wireless networking
technology explored throughout this thesis. The 8 slots of the
DSS can be filled with any
combination of receiver, source, and/or data acquisition
modules. A DSS full of data acquisition
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modules is capable of logging 64 channels. The DSS utilizes a
new technology, Digital Sensor
Interface Transmitters (DSIT), to reduce the cost of expensive
low noise cabling by locating a 24
bit ADC near the sensor. A 24 bit ADC could provide a
significant advantage over lower bit
units, as a higher number of bits increases the available
dynamic range and provides less need to
fill the entire dynamic range. The DSIT digitizes the signals
and sends the digitzed data to the
receiver card in the mainframe through inexpensive ribbon
cabling. The DSITs are capable of
sampling all channels simultaneously at sampling frequencies up
to 61 kHz. One, two, or three
sensor DSITs are available with direct voltage inputs. Many
sensors require an ICP power
source and some DSITs are capable of providing ICP power.
Another useful feature was the
ability to read the Transducer Electronic Data Sheets (TEDS)
data on the sensor. In todays
world of high channel data acquisition systems, it becomes
cumbersome and tedious to keep a
good record of test setups. TEDS sensors attempt to alleviate
this record keeping problem by
storing sensor specific information in the sensor. This
information ranges from the standard
information like serial number, model number, and calibration
sensitivity to user defined fields.
Table 2.1 describes the performance characteristics of the
available DSITs. For
Table 2.1 Performance Information of DSS DSIT
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2.2.2 - National Instruments Compact RIO
The National Instruments company produces several types of data
acquisition devices, from PC
card based applications to the mainframe and card systems. The
system of particular interest in
this application was the Compact RIO. One of the most
interesting features of the Compact RIO
was its size, only 3.5 by 3.5 by 10.75 inches for the premium
system. The Compact RIO is
developed around the RIO (Reconfigurable Input Output) FPGA
(Field Programmable Gate
Array) technology. The Compact RIO has a similar architecture as
the Larson Davis DSS. They
both contain a chassis integrated, real time processor with bays
for input-output modules. The
Compact RIO can operate as a control system as well as operating
as a data acquisition device.
The Compact RIO system utilizes National Instruments graphical
programming software,
LabVIEW, to control the input-output modules. This means that
the user must write a program
using LabVIEW to control the input-output modules. The real time
processor, the brains behind
the Compact RIO, controls the I/O modules independently which
allows the I/O modules to
operate in parallel. The real time controller also contains the
communication ports, serial and
Ethernet, again enabling the Compact RIO to be used with 802.11
wireless networking
technology. The Compact RIO allows the user to define the
measurement hardware circuitry
using FPGA chips and LabView. The field programmable gate arrays
are the major contributors
to the Compact Rios low cost, reconfigurability, and high
performance features. National
Instruments has developed several modules to be used with the
Compact RIO. Analog input
modules are available for small (+-80 mV), medium (+-10 V), and
large (+-60 V) voltage inputs,
as well as thermocouples and a +-5 volt module with simultaneous
sampling, antialias filtering,
10
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and TEDS capability. Table 2.2 lists all of the input-output
modules available for the Compact
RIO and their features.
11
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Table 2.2 Performance Information for RIO I/O Modules
12
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2.2.3 - Motec ADL
The Advanced Dash Logger (ADL) from Motec is one of the most
popular motorsports data
acquisition devices. It combines a data acquisition device with
a dash that can be used to display
vehicle information to the driver. The dash display is
configurable, allowing the user to
determine what information is important for the driver. It can
be used to replace many if not all
of the gauges found on a typical race car dash. The tachometer
has 70 segments that can be set
up to a maximum of 19,000 rpm, and the shift point can also be
programmed such that the
redline is dependent upon gear selection. The current gear is
also displayed. The dash has 3 user
definable numeric displays and 1 alpha numeric display; which
can be used to display any of the
200+ ECU (Engine Control Unit) or ADL channels available.
The standard Motec ADL comes with 6 (12 bit ADC) analog voltage
inputs, 4 analog
temperature inputs, 2 speed inputs, 2 digital inputs, 4 switch
inputs, and 4 auxiliary outputs for a
total of 22 I/O (input-output) channels. For an additional cost
it can be expanded to 50 I/O
channels as follows, 20 analog voltage inputs, 8 analog
temperature inputs, 4 speed inputs, 4
digital inputs, 4 switch inputs, 2 low voltage analog inputs,
and 8 auxiliary outputs. The analog
inputs have a signal input range of 0-15 volts. The ADL is
capable of sampling 8 channels at
1000 Hz, and the rest at 500 Hz, with the exception of the ECU
channels which can be sampled
at a maximum of 20 Hz. The standard system comes with 384
kilobytes of memory for digitized
signal storage and can be upgraded to 8 megabytes. All of the
systems allow 40 channels from a
Motec ECU to be input through an RS232 connection. Obviously, 50
ADL channels plus 40
ECU channels does not match the 200+ channels previously
mentioned. The additional Motec
ADL channels are derived from any combination of the 90 ADL and
ECU channels. These math
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channels provide additional flexibility to the ADL. The base
system has a cost of about $4600,
while the 50 I/O system sells for about $6500; Motec also sells
a 30 I/O system for about $5100.
The memory expansions also add significant cost to the system,
ranging from $900 to $1875 for
1 to 8 Mb respectively. Telemetry, which enables the user to
view real time data, is an additional
cost of $5300 for the radios and $1100 to enable this option in
the ADL. The total cost of a
system with telemetry could range from $11,000 to almost
$15,000.
2.2.4 - Pi Research Delta System
Pi Research is one of the most respected data logging companies
in motorsports. They sell a
variety of systems from their entry level System 1 to their top
of the line Sigma Elite system.
The System 1 contains 6 analog inputs, wheel speed, rpm, lap
time and lateral acceleration. The
System 1 provides a good start into race car data acquisition,
but it does not provide enough
flexibility to be appropriately compared with the previously
mentioned systems. The Sigma
Elite comes standard with 40 analog channels and 8 digital
channels with 128 Mb of memory; it
can be expanded to 64 analog channels and 12 digital channels.
This system was eliminated
from discussion due to its complexity and expected cost. It is
typically only used in the highest
levels of professional motorsports. The Delta and Delta Lite
systems are very similar. They
only differ in expandability, storage memory and telemetry, seen
in Table 2.3.
Delta Lite Delta Expandable No Yes Telemetry No Yes
Memory (Mb) 2 8
Table 2.3 Delta Systems
The basic Delta system contains 10 analog inputs, 2 wheel
speeds, lap time, rpm, 2 accelerations,
and ECU signals. The system can be expanded to provide an
additional 24 analog inputs and 2
wheel speeds. For additional costs, the Delta system can be
attached to a dash and/or a telemetry
14
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system. The radios for the telemetry option, operate in the
450-470 MHz frequency range, and
require an appropriate license from the FCC. The Delta system is
capable of logging 0-5 volt
signals at sampling rates up to 500 Hz. Table 2.4 provides a
general system comparison of the
five devices, while Table 2.5 details the quantity of the
different type of channels.
Device ADC (bits)
Channel Count
Max Sampling Frequency (Hz)
Size (in X in X in)
Type Price
DSS 24 64 61,000 6 X 9.25 X 14.5 Simultaneous Unknown Compact
RIO 12-24 64 800,000 3.5 X 3.5 X 10.75 Both ~$6,000
Motec ADL 12 22-50 1,000 1.5 X 3.5 X 7 Simultaneous
$4,600-$6,500
Pi Delta 10 42 500 1.5 X 4 X 4 Unknown Unknown Dataq 16 44
250,000 1.5 X 7 X 9 Multiplexed $1,500
Table 2.4 Data Acquisition Device Comparison
Device Analog Input
Temperature Input
Digital Input
ECU Input
Speed Input
Auxilary Outputs
DSS 0-64 0 0 0 0 0-32 Compact
RIO 0-64 0-32 0-64 0 0-64 0-64
Motec ADL 6-20 4-8 4-8 40 2-4 4-8 Pi Delta 10-34 0 0 Unknown 2-4
0 Dataq 32 0 8 0 0 4
Table 2.5 Channel Comparison
2.2.5 - DaTaq DI-720-EN
The data acquisition device chosen was the DI-720-EN, from
Dataq. The Dataq device was
chosen for its low price tag, number of channels, and because it
can use the Ethernet to transfer
data. The cost of the device and the software was about $2500.
The DI-720-EN can transfer
data from the real time controller to the logging computers hard
disc by a parallel cable or, it can
be set up as a network device and the data can be transferred
over a local area network. This
Ethernet data transfer method made it particularly interesting,
because of the possibilities of
coupling the Dataq device with existing 802.11 wireless
networking technologies. The DI-720-
EN only records voltage signals, so some sensors will not work
directly with the DI-720-EN.
15
-
Two such examples are thermocouples and strain gauges, these
sensors will require signal
conditioning. The DI-720-EN contains 32 single-ended or 16
differential channels as well as 8
digital inputs and 4 digital outputs. A differential channel is
a channel that has a positive signal,
and a negative signal; these signals are then referenced against
each other. A differential channel
should only need to be used when a potential exists between the
ground for the data acquisition
device and the ground for the sensor. Figure 2.1 shows the
channel selection window.1
Figure 2.1 Channel Selection
WINDAQ/Pro was the version of Dataqs software used throughout
the testing for this paper,
which allows for a maximum sample rate of 250 kHz. The Dataq
system utilizes multiplexed
data acquisition which means that the maximum sampling frequency
must be divided
1 To setup channels follow the path and directions at the bottom
of the window: Edit Channels
16
-
(multiplexed across) each channel. The maximum sample rate is
the rate at which the analog to
digital converter (ADC) digitizes the signal. The rate at which
each channel is being digitized is
the maximum sample rate divided by the number of channels
enabled. The maximum sample
rate is often referred to as the scan rate in a multiplexed
system, Figure 2.22.
Figure 2.2 Max Sample Rate Selection
The maximum sample rate should not be confused with the sample
rate; an example will be
presented after the discussion of Dataqs intelligent over
sampling (IOS) feature. The sample
rate is the frequency that the software displays and records the
digitized signal. It should be
noted that this sample rate is the total sample rate or
throughput rate. For example, if sixteen
channels were enabled and the sample rate was set to 16,000
samples per second then each
channel would contain 1000 data points per second recorded or
the analog signal of each channel
would be digitized every 1 thousandth of a second. Figure 2.3
shows the sample rate window3.
Figure 2.3 Sample Rate Selection
2 Set the maximum sample rate by following this path: Edit
Preferences Max Sample Rate or Ctl+F3 3 Setup can be performed by
following this path: Edit Sample Rate or F3
17
-
The DI-720-EN is equipped with a feature, Dataq calls
intelligent over sampling. Intelligent
over sampling is a feature of the DI-720-EN that allows the data
that was digitized between
sample points to be used. When the sample rate and the maximum
sample rate are not set equal,
the analog to digital converter will digitize the signal at the
maximum sample rate divided by the
number of enabled channels; then the processor will down sample
digitized data to the user
defined sample rate divided by the number of enabled channels.
There are several processes that
can be used while down sampling: average, last point, maximum,
minimum, root mean square,
and frequency. The average acquisition method will sum the value
of all of the points between
the sample rate points and scale it by the number of points;
while the last point method will only
retain the last point. Logically, the maximum and minimum
methods will retain the maximum or
minimum value. The RMS acquisition method will take a root mean
square average of the
points. Figure 2.4 shows the window used to select the
acquisition method and gain level.4
4 To setup the acquisition method and/or gain follow this path:
Edit Channel Settings
18
-
Figure 2.4 Channel Settings Selection
As mentioned earlier, an example will be discussed to further
clarify the intelligent over
sampling topic, the parameters of which are shown below in Table
2.6.
Maximum Sample Rate 50000 Channels 2
Sample Rate 100
IOS Method Last Point
Table 2.6 IOS Example Parameters
A signal sent into each of the two channels will be digitized by
the ADC at a rate of 25,000 times
per second. The software will then be set to sample at 100 Hz,
which means the hardware
created 500 times more data points than required. With the last
point method this means every
500th point will be recorded to the logging computers hard
disk.
19
-
The DI-720-EN allows each channel to have a gain applied to it.
Applying a gain to a sensor
signal is useful to maximize the amount of the dynamic range
being used. For example, a sine
wave characterized by the equation below, which would look like
Figure 2.5, when recorded on a
+-10 volt scale.
2)sin( += xy (2.1)
0 1 2 3 4 5 6 7 8 9 10-10
-8
-6
-4
-2
0
2
4
6
8
10
Time
Am
plitu
de
Sine Wave on +-10V Scale
Figure 2.5 Sine Wave on +-10V Scale
But, if the same signal was gained so that the dynamic range was
+-5 volts, it would appear as
Figure 2.6 shows. A quick comparison of the two figures shows
that the amplitude of the sine
wave was much more defined in Figure 2.6, therefore more of the
dynamic range is being used
and the resolution of the signal is better.
20
-
0 1 2 3 4 5 6 7 8 9 10-5
-4
-3
-2
-1
0
1
2
3
4
5
Time
Am
plitu
de
Sine Wave on +-5V Scale
Figure 2.6 Sine Wave on +-5V Scale
Gain Scale (V)
Resolution (mV/bit)
1 10 1.22
2 5 0.61
4 2.5 0.31
8 1.25 0.15
Table 2.7 Resolution Increases with applied Gain
Table 2.7, shows the maximum resolution of a signal on each
scale. There are two ways
available to calibrate the channels. The first method, called
Fixed Calibration, requests the
engineering value equivalent to a +10 volt signal and a -10 volt
signal from the sensor, as shown
in Figure 2.7.5
5 The fixed calibrator can be found by following this path: Edit
Fixed Calibration or F12
21
-
Figure 2.7 Fixed Calibration
The second method uses a low and high calibrator value
(sometimes called a two-point method).
Using the low and high calibrator method requires the lowest and
highest voltage level as well as
the appropriate engineering value for that voltage, setup seen
in Figure 2.8 and Figure 2.9.6 7
Figure 2.8 Low Calibration
6 The low calibrator can be found following this path: Edit Low
Calibration F9
7 The high calibrator can be found following this path: Edit
High Calibration or F11
22
-
Figure 2.9 High Calibration
The DI-720-EN is a multiplexed data acquisition device, meaning
each channel is not digitized at
the same instance as the other channels. This leads to a phase
shift, which is most easily seen by
logging the same sine wave on multiple channels. Once the
channels are overlaid, as in Figure
2.10, it is quite obvious that the sine wave is shifted (delayed
in time). It should be noted that
channel one is the curve furthest to the right and the channel
number increases moving to the left.
It is important to note, because this implies channel one was
the last to be logged, but this was
not the case. It is a function of how the data was plotted; a
single time array was used for all of
the channels. At first glance this seems backwards, that channel
two leads channel one, but upon
a closer look at the details it makes perfect sense. If a signal
is logged at time t0 on channel one
and again at t0+t on channel two, and so on, and the channels
are then plotted against the same
time array it will appear as if channel two leads channel one,
as in Figure 2.10. While this shift
is not detrimental, it must be known so that the data can be
corrected and plotted appropriately.
23
-
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
Time
Vol
t
Time History
Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8 Ch 9 Ch 10Ch 11Ch 12Ch
13Ch 14Ch 15Ch 16
0.018 0.019 0.02 0.021 0.022 0.023
0.52
0.53
0.54
0.55
0.56
0.57
0.58
0.59
0.6
Time
Vol
t
Time History
Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8 Ch 9 Ch 10Ch 11Ch 12Ch
13Ch 14Ch 15Ch 16
Figure 2.10 Sine Wave Phase Shift
Many high priced data acquisition systems sample all channels
simultaneously, while the lower
priced systems contain fewer ADCs and must sample each channel
separately. The ideal data
acquisition system utilizes a parallel sample and hold technique
that samples all channels at one
instant, seen in Figure 2.11. Figure 2.12 depicts a multiplexed
system digitizing a sine wave on
four channels with the scan rate and sample rate equal to one
another, notice the time delay
between data points from channel to channel. This delay is the
scan rate and in this case it was
also the sample rate. Figure 2.13 shows the sampling
characteristics of a multiplexed system
when the scan rate and sample rate are not equal. In this
figure, the scan rate is the time delay
from channel to channel and the sample rate is related to the
time elapsed between the data
points of one channel.
24
-
0 1 2 3 4 5 6 7 8 9 10-1
0
1
Sig
nal
Parallel Sampling
0 1 2 3 4 5 6 7 8 9 10-1
0
1C
h 1
0 1 2 3 4 5 6 7 8 9 10-1
0
1
Ch
2
0 1 2 3 4 5 6 7 8 9 10-1
0
1
Ch
3
0 1 2 3 4 5 6 7 8 9 10-1
0
1
Time (s)
Ch
4
Figure 2.11 Parallel Sampling Example
0 1 2 3 4 5 6 7 8 9 10-1
0
1Multiplexed Sampling (Sampling = Scan)
Sig
nal
0 1 2 3 4 5 6 7 8 9 10-1
0
1
Ch
1
0 1 2 3 4 5 6 7 8 9 10-1
0
1
Ch
2
0 1 2 3 4 5 6 7 8 9 10-1
0
1
Ch
3
0 1 2 3 4 5 6 7 8 9 10-1
0
1
Ch
4
Figure 2.12 Multiplexed Sampling (Equal Sampling & Scan
Rates)
25
-
0 1 2 3 4 5 6 7 8 9 10-1
0
1
Sig
nal
Multiplexed Sampling (not equal)
0 1 2 3 4 5 6 7 8 9 10-1
0
1
Ch
1
0 1 2 3 4 5 6 7 8 9 10-1
0
1
Ch
2
0 1 2 3 4 5 6 7 8 9 10-1
0
1
Ch
3
0 1 2 3 4 5 6 7 8 9 10-1
0
1
Time (s)
Ch
4
Figure 2.13 Multiplexed Sampling (Non-equal Sampling & Scan
Rates)
2.3 - Data Acquisition Theory
2.3.1 - Sampling Theory
Sampling theory is defined by Shannons Sampling Theorem, which
states:
21 =
= Nyqsamp FtF (2.2)
maxFFNyq (2.3)
These equations describe the maxim frequency content that can be
described by data logged at
any chosen sampling frequency. Figure 2.14 depicts the previous
equations of Shannons
Sampling Theorem. The Nyquist frequency is the frequency where
foldback begins, and aliasing
becomes an issue.
26
-
Figure 2.14 Sampling Relationships
2.3.2 - Aliasing
Aliasing is exactly what the term implies; multiple signals can
be characterized by a single set of
data points, i.e. has an alias or another name. Figure 2.15
shows a high frequency sine wave that
is characterized by the same data points that were digitized
from the low frequency sine wave.
Figure 2.15 Aliasing Example
Figure 2.16 depicts the frequencies that will be aliased back to
frequency of interest.
27
-
Figure 2.16 Aliasing Contribution
The Dataq DI-720-EN does not contain any anti-aliasing filters,
so care must be taken when
logging real world sensor signals. A filter must be added to all
sensor signals to reduce the
frequency content above the maximum frequency of interest. The
random data that was logged
for this thesis was passed through a basic RC low pass filter
which was all that was available in
the 12 VDC environment of the moving vehicle.
28
-
Chapter 3 Applications
3.1 - Lab Testing
The 2004 University of Cincinnati Formula SAE car was used as
the test vehicle
throughout the evaluation of the data acquisition system. For
the initial tests, a pink noise
generator with a rudimentary 200 Hz filter provided the signal
to be measured on 16
single-ended channels. An anti-aliasing filter was added to the
output of the pink noise
generator to limit the frequency content; this was controlled by
a cascaded pair of
resistor-capacitor (RC) filters tuned to 200 Hz. A single RC
filter would reduce the
signal by about 6 dB per octave; with the addition of a second,
cascaded RC filter, the
signal is reduced another 6 dB per octave to a total of 12 dB
per octave. The second set of
tests measured a 50 Hz sine wave, again on 16 single-ended
channels. For the third set of
tests the Bearcat Motorsports vehicle was instrumented according
to Table 3.1.
Description Sensor Type Left Front Bellcrank Travel Rotary
Potentiometer Right Front Bellcrank Travel Rotary Potentiometer
Left Rear Bellcrank Travel Rotary Potentiometer Right Rear
Bellcrank Travel Rotary Potentiometer Throttle Position Rotary
Potentiometer Front Lateral Acceleration Capacitive Discharge
Accelerometer Front Longitudinal Acceleration Capacitive Discharge
Accelerometer Front Vertical Acceleration Capacitive Discharge
Accelerometer Rear Lateral Acceleration Capacitive Discharge
Accelerometer Rear Longitudinal Acceleration Capacitive Discharge
Accelerometer Rear Vertical Acceleration Capacitive Discharge
Accelerometer
Table 3.1 Vehicle Sensors
All of these sensors were then used to observe the vehicle
during a test on a MTS four
post road simulator. The test vehicle provided the power for the
Dataq DI-720-EN, a
pink noise generator, accelerometers, and a sine wave generator
all from the standard 12
29
-
volt motorcycle battery. The game adapter and potentiometers
required a 5 and 10 volt
regulated power source. The system was tested using four
different types of data
transmission, the standard parallel cable transmission, Ethernet
cable transmission or
local area network, wireless local area network transmission,
and wireless local area
network transmission with a parabolic antenna, which concluded
the lab testing. Table
3.2 contains the details of each lab test setup.
Transfer Method Signal Setup
Parallel LAN WLAN WLAN-
ant Random 200 Hz
Sine 50 Hz
Car
1
2
3
4
5
6
7
8
9
10
Table 3.2 Lab Test Setups
3.1.1 - Parallel Port:
Dataq DI-720-EN
Random Noise
Figure 3.1 Parallel Port Testing Block Diagram
30
-
The parallel port data transfer method, while not the current
standard, is still used in
industry today. The purpose of testing this type of data
transfer was to provide a standard
to measure the performance of all other data transmission
techniques. The current
method of data transfer in most data acquisition systems is
through either a firewire
interface (IEEE 1394) or an Internet interface, both of which
provide very fast data
transfer speeds, in comparison to the parallel port method. The
block diagram in Figure
3.1 describes the test setup used for the parallel port testing.
The DI-720-EN has two
methods of transferring data, parallel port or Ethernet.
Parallel port communications
have four different operating modes standard; bi-directional,
enhanced parallel port
(EPP), and extended capabilities port (ECP). The mode of
communication depends upon
the age and sophistication of the data acquisitions and
computers parallel ports. The
extended capabilities mode of communication was used to take the
parallel port data used
throughout this document. The throughput sampling frequency
(sample rate times the
number of enabled channels) used throughout the testing was
16,000 samples/second, so
this type of communications limit was not approached. Dataq has
tested the throughput
of these modes of communication for the DI-720-EN; the results
can be seen in Table
3.3.
Data Transfer Mode Maximum Data Throughput
Standard 40,000 Samples/second Bi-directional 80,000
Samples/second
EPP 250,000 Samples/second ECP Not Tested
Ethernet 50,000 Samples/second Wireless Ethernet 42,000
Samples/second
Table 3.3 Data Transfer Throughput
31
-
The frequency response functions (FRFs) were computed, assuming
the input was logged
on channel one. The FRFs were plotted in Figure 3.2, below, and
show that each channel
was logging the same signal. This can be determined by three
methods, observation of
the FRF, coherence, and the time history. Observation of the
FRFs shows the magnitude
to be nearly one, up to the point where the filter starts
rolling off. The coherence was
analyzed as a check; it also has a magnitude of one up to about
half the filter cut off
frequency, Figure 3.3. Since there was only one signal
considered the input, this is really
ordinary coherence. This was attributed to the rudimentary
filtering method, and a more
robust filter would extend the point of initial roll off. Figure
3.4 shows the time history
of all the channels. Because the DI-720-EN is a multiplexed
unit, the time history from
channel to channel will not lay on top of one another without
adjusting for the
multiplexer. Randomly generated data is not the best suited
signal for observing this, or
determining the phase shift, so discussion of the phase shift
has been delayed until sine
wave data has been discussed and documented. This should be
discussed here since the
phase shift for a multiplexed system is a good way to document
the actual time/phase
relationship for the multiplexer.
32
-
0 50 100 150 200 250 300 350 400 450 500-200
0
200Block size = 1024 :Uniform Window P000 :Overlap = None
:Cycles ave. = None
Pha
se (
Deg
rees
)
FRF Hv -- Input 1 On Each Output
0 50 100 150 200 250 300 350 400 4500.5
1
1.5
Frequency (Hz)
Am
plitu
de X
/F
Figure 3.2 Parallel Port Frequency Response Functions
H1 Ordinary Coherence -- On Each Output
0 50 100 150 200 250 300 350 400 4500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1Block size = 1024 :Uniform Window P000 :Overlap = None :Cycles
ave. = None
Frequency (Hz)
Coh
eren
ce
Figure 3.3 Typical Coherence
33
-
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
Time
Vol
t
Time History
Figure 3.4 Parallel Port Random Time History
3.1.2 - Local Area Network:
Figure 3.5, seen below, depicts the system setup utilized for
the testing performed
throughout this section, with the data recorded block
alternating between random noise,
sine wave, and vehicle sensors.
Random Noise
Figure 3.5 Wired Ethernet Block Diagram
Dataq DI-720-EN
Linksys Wireless
34
-
The wired local area network data transfer method was the next
step in the process. The
goal was to determine if a local area network would affect the
data being transferred. A
data acquisition box being used as network device is a concept
still just emerging in the
commercial data acquisition market. The University of Cincinnati
Structural Dynamics
Research Lab (UC-SDRL) has been working with a developmental
network device called
the Digital Sensor System (DSS) from Larson Davis. UC-SDRL has
had success using
the DSS as a network device in vibrations testing, so logging
data over a local area
network was not expected to cause any issues. Three different
forms of data logged over
the local area network were 200 Hz limited random noise, 50 Hz
sine wave, and vehicle
data excited by a road simulator. The 200 Hz random noise and 50
Hz sine wave were
logged using the parameters seen in Table 3.4, while the logging
parameters for the
vehicle data are shown in Table 3.5.
Max Sample Rate 16000 Throughput Rate 16000
Channels 16 Sample Rate 1000
Table 3.4 Random & Sine Logging Parameters
Max Sample Rate 16000 Throughput Rate 16000
Channels 11 Sample Rate 1455
Table 3.5 Vehicle Logging Parameters
The random data spreads information across the entire frequency
range allowing the
computation of frequency response functions to be useful.
Computing the frequency
response function of a signal relative to itself yields a value
of one:
( ) ( )( )
Input
OutputH = (3.1)
This allows for a simple observation of the frequency response
functions to determine if
channel two, three, four, etc, was logging the same signal as
channel one. Note that
while this the conceptual definition of the frequency response
function, the Hv algorithm
35
-
from Reference [1], utilizing auto and cross power spectra
between the input and
response channels, was actually used to compute the FRF. Figure
3.6 compares nicely to
Figure 3.2, so it appears local area networking (internet
interface) does not adversely
affect the data being transmitted.
0 50 100 150 200 250 300 350 400 450 500-200
0
200Block size = 1024 :Uniform Window P000 :Overlap = None
:Cycles ave. = None
Pha
se (
Deg
rees
)
FRF Hv -- Input 1 On Each Output
0 50 100 150 200 250 300 350 400 4500.5
1
1.5
Frequency (Hz)
Am
plitu
de X
/F
Figure 3.6 LAN Frequency Response Functions
A 50 Hz sine wave was logged according to the parameters in
Table 3.4, above. The 50
Hz sine wave was tested for two reasons, observation and
location of gaps in the time
history, and determination of the gap length. A gap is a
location in the time data stream
where the data was either not digitized or not recorded during a
specified time period.
Gaps occur because of three known reasons: large amounts of disk
activity, large
amounts of network traffic, and lost communication in which the
buffer overruns.
36
-
The DI-720-EN contains a 7500 sample buffer, which in
combination with the
throughput rate determines how fast the data must be transferred
from the DI-720-EN to
disk. Large amounts of disk activity can be eliminated by
reducing multitasking,
allowing the computer to only write the information from the
DI-720-EN. Reducing the
gaps due to large amounts of network traffic can be achieved
with the application of a
dedicated network. The data acquisition systems software knows
when a gap occurred,
but does not know how long the gap lasted. The gap information
can be exported into a
modified comma separated variable format, but this modified
format is not readily
compatible with Matlab. When the hardwares buffer overflows, it
sends a packet with
an odd number of bytes to signify that a gap has occurred.
Several runs were performed
to check for gaps in the data; the results indicated that no
gaps occurred when the system
was adequately powered. The test vehicles 12 volt battery was
inadvertently drained and
a significant number of gaps were seen during this low power
testing. Figure 3.7 shows a
few seconds of the total 3 minutes of data collected. Notice the
lack of jumps/spikes in
the waveform; this indicates that no gaps occurred in the data
during that time frame.
While it is possible for the system to produce a gap exactly N
times the wavelength,
where N is any integer number, it is highly unlikely. Therefore,
a gap in the data should
produce a noticeable irregularity in the sine wave.
37
-
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
Time
Vol
t
Time History
Figure 3.7 LAN Sine Wave Time History
Zooming in on a particular area of Figure 3.7 will produce
Figure 3.8. In this close up,
notice the shift in the wave form from channel one to channel
two and so on. As
discussed earlier, this is to be expected with a multiplexed
data acquisition device. The
phase shift can be calculated from either the measured time
delay seen in Figure 3.8 or
from the phase plot in Figure 3.6.
38
-
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
Time
Vol
t
Time History
Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8 Ch 9 Ch 10Ch 11Ch 12Ch
13Ch 14Ch 15Ch 16
0.018 0.019 0.02 0.021 0.022 0.023
0.52
0.53
0.54
0.55
0.56
0.57
0.58
0.59
0.6
Time
Vol
t
Time History
Ch 1 Ch 2 Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8 Ch 9 Ch 10Ch 11Ch 12Ch
13Ch 14Ch 15Ch 16
Figure 3.8 LAN Sine Wave Close Up
The next portion of testing measured signals generated from
vehicle movements. The
MTS four post road simulator was utilized as the method of
excitation. The signal sent to
each hydraulic shaker can be characterized by the parameters
seen below in Table 3.6.
Many other signals were tested, but none seemed to excite the
system as well.
Front Rear Source: Random Random Shape: 1/F 1/F
RMS Amplitude: 0.8 0.8 Min Frequency: 0.4 0.4 Max Frequency: 2.5
4
Table 3.6 MTS Test File Information
Figure 3.9 shows the signals captured for the four bellcrank
potentiometers. This data
serves as a baseline for the data that will be taken in later
data acquisition tests when the
39
-
car is running with a wireless Internet interface. Notice the DC
offset of the signal, this is
because the potentiometer was set with the middle of its travel
roughly at the middle of
the bellcrank travel. The minimum potentiometer travel should
have been set to the
minimum bellcrank travel, to optimize the dynamic range. AC
coupling and analog
summing are two other methods used to remove DC offsets from
signals. AC coupling is
essentially a high pass filter which corrupts data from zero to
about five Hz and hence
affects many of the interesting signals in vehicle dynamics. The
second option, an analog
summing amplifier, would add the negative value of the DC offset
to the signal, thereby
centering the signal on zero. If the data acquisition devices
ADC contained more bits
the DC offset would be less of an issue.
0 0.5 1 1.5 2 2.5 3 3.54.4
4.6
4.8
5
5.2
5.4
5.6
5.8Left Front Right FrontLeft Rear Right Rear
Figure 3.9 Bellcrank Rotation
40
-
3.1.3 - Wireless Local Area Network:
The testing performed throughout this section was obtained
utilizing a Linksys wireless
router to transfer the data from the test vehicle to computer;
the system diagram is shown
below in Figure 3.10.
Linksys Game Adapter Random Noise
Dataq DI-720-EN
Linksys Wireless
Wireless Link
Figure 3.10 Basic Wireless System Block Diagram
Wireless local area network data was logged according to Table
3.4 and Table 3.5. As
before, the random data was transformed using Fourier transform
techniques, and
analyzed. The FRFs magnitude and phase plots were overlaid,
shown in Figure 3.11.
The FRFs are flat with a magnitude of one up to 200 Hz, this
shows that each channel
was logging nearly the same signal, because of the filter on the
random noise generator
information above 200 Hz was expected to be partially corrupted.
The phase linearly
increases from 0 to 200 Hz, described by:
t= (3.2)
41
-
0 50 100 150 200 250 300 350 400 450 500-200
0
200Block size = 1024 :Uniform Window P000 :Overlap = None
:Cycles ave. = None
Pha
se (
Deg
rees
)
FRF Hv -- Input 1 On Each Output
0 50 100 150 200 250 300 350 400 4500.5
1
1.5
Frequency (Hz)
Am
plitu
de X
/F
Figure 3.11 WLAN Frequency Response Functions
Figure 3.12 depicts a 50 Hz sine wave that has been captured
using a wireless local area
network. It was in Figure 3.12 that the first sign of a
potential problem arose; notice the
jump in the sine wave at about 27.72 seconds.
42
-
27.68 27.7 27.72 27.74 27.76 27.78 27.8 27.82-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
Time
Vol
t
Time History
Figure 3.12 WLAN Sine Wave Time History
This is a gap or loss of data, which could be a major problem
depending upon the type of
data and the nature of the analysis of the data that is
required. Consider a vehicle moving
at 30 miles per hour and gap of one second, this equates to
about 44 feet traveled or about
4.5 car lengths. The software for many motorsports data
acquisition systems calculates a
track map from lateral acceleration, longitudinal acceleration,
longitudinal velocity, and
elapsed time. If a gap occurs, this method of track map
generation would fail in that
vicinity. If a very low frequency sine wave is always logged on
one channel, the gap can
be determined by realigning the data after the spike based upon
where it is expected to
be. Although it will not be known what happened during that time
period, at least the
length of time or distance traveled will be known, and can be
linked to a certain sector of
the course.
43
-
3.1.4 - Wireless LAN w/Parabolic Antenna
Figure 3.13, below, describes the test setup used throughout
3.1.4 - which discusses the
characteristics of testing with a parabolic antenna in the
lab.
Linksys Game Adapter Random Noise
Dataq DI-720-EN
Cisco Access Point
Parabolic Antenna
Linksys Wireless
Wireless Link
Figure 3.13 Parabolic Testing Block Diagram
The final lab testing task was to test the wireless local area
network with a parabolic
antenna. The purpose of a parabolic antenna was to focus the
wireless Internet signals
and therefore, optimize the incoming and outgoing data signals
between the data
acquisition system and the computer. Essentially, power is being
wasted when the signal
is being sent out in all directions. Focusing the signal should
increase the range and will
be discussed more elaborately in the onsite testing section. As
in the previous FRFs, the
frequency response functions of Figure 3.14 have a magnitude of
one up to the filter cut
off which was the limit of reliable data. The phase angle plots
show similar results to
previous testing as well.
44
-
0 50 100 150 200 250 300 350 400 450 500-200
0
200Block size = 1024 :Uniform Window P000 :Overlap = None
:Cycles ave. = None
Pha
se (
Deg
rees
)
FRF Hv -- Input 1 On Each Output
0 50 100 150 200 250 300 350 400 4500.5
1
1.5
Frequency (Hz)
Am
plitu
de X
/F
Figure 3.14 Parabolic Frequency Response Functions
The sine wave time history, Figure 3.15, shows that gaps still
occurred with the antenna.
Upon further examination of the two data sets shows that the
number of gaps was
reduced.
45
-
25.67 25.68 25.69 25.7 25.71 25.72 25.73 25.74 25.75-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Time
Vol
t
Time History
Figure 3.15 Parabolic Sine Wave Time History
3.2 - Onsite Testing
Linksys Game Adapter Random Noise
Dataq DI-720-EN
Cisco Access Point
Parabolic Antenna
Linksys Wireless
Wireless Link
Figure 3.16 Vehicle Testing Block Diagram
46
-
The onsite testing was preformed with similar inputs as used in
the lab and only with
wireless data transmission methods. Two types of onsite testing
were performed, static
and dynamic. The static testing provided a baseline for onsite
testing. The dynamic
testing was used to determine the real world range. Table 3.7,
seen below, depicts the
onsite testing performed. A diagram of the parabolic antenna
test setup used in this
section can be seen in Figure 3.16, above, while the
non-parabolic antenna setup can be
seen in Figure 3.10.
Transfer Method Signal Location Engine
Setup WLAN
WLAN-ant
Random 200 Hz
Car Onsite (Static)
Onsite (Dynamic)
On Off
1
2
3
4
5
6
7
8
Table 3.7 Onsite Test Setups
3.2.1 - Static Testing
A variety of types of static testing were performed using either
a standard wireless
antenna or a parabolic antenna. The primary signal recorded was
a random 200 Hz wave,
vehicle data was also recorded. Both of these types of signals
were recorded with and
without the engine running to determine if the noisy radio
frequency characteristics of a
vehicle would have a significant impact. The initial static
testing was performed at the
University of Cincinnati Center Hill Research Facility. The test
vehicle and computer
were placed at opposite ends of the facility, a distance of 70
meters. A random signal
47
-
was then logged on 16 channels using the wireless local area
network transmission
method. As expected, Figure 3.17 had a magnitude of one up to
the filter cutoff
frequency, but interestingly above the filter cutoff is more
closely matched than
previously seen.
0 50 100 150 200 250 300 350 400 450 500-10
0
10Block size = 1024 :Uniform Window P000 :Overlap = None :Cycles
ave. = None
Pha
se (
Deg
rees
)
FRF Hv -- Input 1 On Each Output
0 50 100 150 200 250 300 350 400 4500.5
1
1.5
Frequency (Hz)
Am
plitu
de X
/F
Figure 3.17 Center Hill FRFs
Note the different shape and magnitude in the phase plot of
Figure 3.17, compared to
Figure 3.11. Further investigation shows that the phase shift in
Figure 3.11 was about 2
degrees and 0.3 degrees in Figure 3.17 at 100 Hz. Figure 3.18
corroborates the data seen
in Figure 3.17 with a coherence level of 0.9 for the entire
frequency range. These
differences can be associated with a change in the test setup,
note the difference in
maximum sample rates of Table 3.8 and Table 3.4. The difference
in FRF phase and
magnitude characteristics above the low pass filter cutoff was
not investigated.
48
-
Max Sample Rate
200,000
Throughput Rate
16,000
Channels 16 Sample Rate 1000
Table 3.8 Center Hill Logging Parameters
H1 Ordinary Coherence -- On Each Output
0 50 100 150 200 250 300 350 400 4500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1Block size = 1024 :Uniform Window P000 :Overlap = None :Cycles
ave. = None
Frequency (Hz)
Coh
eren
ce
Figure 3.18 Center Hill Coherence
Since the Center Hill facility was deemed too small to test the
potential range of the
system, the test vehicle was taken to Raymond Walters, a
University of Cincinnati
satellite campus, for more conclusive testing. It was during
this phase of testing that an
erratic and unexplainable system fault occurred. The logging
parameters were set as
stated in Table 3.8. The vehicle was set at one end of the
parking lot and the computer
and routers at the other; then a random signal was logged for
three minutes, same as the
Center Hill test. When the frequency response function
magnitudes and phases were
49
-
plotted it became obvious that something was different or
possibly wrong. Figure 3.19
shows that five of the sixteen channels logged were different,
channels 9-13. The bad
channels had a different magnitude from 50 Hz and above. They
also had an inconsistent
phase characteristic that was a significant difference in
magnitude.
0 50 100 150 200 250 300 350 400 450 500-100
0
100Block size = 1024 :Uniform Window P000 :Overlap = None
:Cycles ave. = None
Pha
se (
Deg
rees
)
FRF Hv -- Input 1 On Each Output
0 50 100 150 200 250 300 350 400 4500.5
1
1.5
Frequency (Hz)
Am
plitu
de X
/F
Figure 3.19 Bad Channels FRFs
The coherence of those five channels started dropping off at
about 100 Hz and continued
much faster than the other channels, which can be seen in Figure
3.20, below.
50
-
H1 Ordinary Coherence -- On Each Output
0 50 100 150 200 250 300 350 400 4500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1Block size = 1024 :Uniform Window P000 :Overlap = None :Cycles
ave. = None
Frequency (Hz)
Coh
eren
ce
Figure 3.20 Bad Channels Coherence
The time history of all sixteen channels can be seen in Figure
3.21 for 1/10th of a second
of the three minutes logged. It was not possible to notice a
difference in the 1/10th of a
second time history, so the first peak was magnified to show
that five of the channels
were indeed not following the others. This test setup was
retested in the UC-SDRL, as
well as in several additional tests, attempting to reproduce the
results to no avail.
51
-
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
Time
Vol
t
Time His tory
4 6 8 10 12 14 16
x 10-3
0.1
0.12
0.14
0.16
0.18
0.2
0.22
0.24
0.26
0.28
Time
Vol
t
Time History
Figure 3.21 Bad Channels
Before dynamic testing began it was decided to evaluate the
level of noise to be expected
in a motorcycle engine powered race car environment. The first
step was to instrument
the car with the sensors detailed in Table 3.1. The sensor
signals were then logged for
three different test setups, engine not running, engine running,
and engine running with
one accelerometer isolated. The test setup with the engine not
running was performed
with the ECU (Engine Control Unit) power turned off, thus the
throttle position sensor
was un-powered. Figure 3.22 shows one second of the throttle
position, where the signal
randomly oscillates between 41 and 34 milli-volts. The possible
quantization error was
12 milli-volts, as seen in Table 2.7, therefore the oscillation
was from the ADC setting its
bits. Unshielded wires potentially act like antennas creating
noise. Figure 3.23 shows
the noise level has increased to about 100 milli-volts, from
engine vibration, power
source fluctuation, or RF noise from firing engine coils. The
majority of the DC offset in
Figure 3.23 was from the sensor power.
52
-
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.033
0.034
0.035
0.036
0.037
0.038
0.039
0.04
0.041
0.042Throttle Position (Engine NOT Running)
Time (s)
Vol
tage
Figure 3.22 Throttle Position (Engine Off)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
3
3.5
4
4.5
Throttle Position (Engine Running)
Time (s)
Vol
tage
Figure 3.23 Throttle Position (Engine On)
53
-
Figure 3.24 shows the significant differences seen in magnitude
between the engine
running, engine not running, and the engine revving test. Figure
3.25 compares the
acceleration of the isolated accelerometer for the three
different tests. Figure 3.26 was
created to show the detail that was easily lost in the noise of
Figure 3.25. The engine not
running accelerometer magnitude oscillates between about 0.925
and 0.965 volts, a
difference of 40 milli-volts which was above the level
attributable to quantization error.
The vehicle was very mechanically noisy because of the rigidly
mounted accelerometers,
as seen in Figure 3.25. The accelerometers could be filtered at
a much lower frequency
in order to eliminate some of this noise since the primary
interest in these signals is to
document the low frequency performance of the vehicle.
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-5
-4
-3
-2
-1
0
1
2
3
4
5
Time (s)
Vol
tage
Typical Acceleration
Engine Reving Engine Running Engine Not Running
Figure 3.24 Typical Acceleration
54
-
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2
-1
0
1
2
3
4
Time (s)
Vol
tage
Isolated Accelerometer Accleration
Isolated AcclerometerEngine NOT Running Engine Running
Figure 3.25 Isolated Accelerometer Acceleration
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.85
0.9
0.95
1
1.05
1.1
Time (s)
Vol
tage
Isolated Accelerometer Accleration
Isolated AcclerometerEngine NOT Running
Figure 3.26 Isolated Accelerometer
55
-
3.2.2 - Dynamic Testing
For actual vehicle data, the maximum frequency of interest was
expected to be below 500
Hz, so a sampling rate of 1000 Hz was used throughout the
testing. The dynamic testing
was performed at the University of Cincinnati Raymond Walters
campus parking lot and
at the Transportation Research Centers Vehicle Dynamics Area
(VDA), in Marysville
Ohio. The parking lot used at Raymond Walters contains several
islands with small trees
that can affect the range. The VDA at the Transportation
Research Center (TRC) was
used to setup a typical FSAE endurance course for testing. The
VDA is a vast wide open
paved area where there are no obstructions for the RF equipment.
It was common for one
or two gaps to occur per lap during the TRC testing, but one
data set produced zero gaps
and several of the gaps could be attributed to a person walking
between the antenna and
the car. A solution for the pedestrian traffic gaps could be a
higher mounted computer
antenna. A second day of testing at Raymond Walters revealed
another system fault.
Figure 3.27 shows the frequency response characteristics of the
system fault, while
Figure 3.28 shows 0.1 seconds of the time history. It was quite
obvious from these plots
that the magnitude of one channel was not captured accurately.
Dataq was contacted
about this and the previously mentioned system fault but they
were unable to provide an
answer. Since the two faults were different and no supplier
answer could be provided, it
was assumed that these faults were hardware problems with the
relatively low cost
system that was used for the data acquisitioning. It is advised
that any future user be
aware of potential hardware problems, and therefore analyze the
logged data carefully.
56
-
0 50 100 150 200 250 300 350 400 450 500-200
0
200Block size = 1024 :Uniform Window P000 :Overlap = None
:Cycles ave. = None
Pha
se (
Deg
rees
)
FRF Hv -- Input 1 On Each Output
0 50 100 150 200 250 300 350 400 4500.5
1
1.5
Frequency (Hz)
Am
plitu
de X
/F
Figure 3.27 Bad Channel FRF
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
Time
Vol
t
Time History
Figure 3.28 Bad Channel Time History
57
-
The 200 Hz random waveform was logged once more on sixteen
channels with the FSAE
racecar driving around a small course at Raymond Walters. Even
though the course was
small, five gaps still occurred, which were linked to the small
trees in the middle of the
course. The phase and magnitude are plotted below in Figure
3.29, this figure was very
typical for what was considered a good frequency response
function plot.
0 50 100 150 200 250 300 350 400 450 500-200
0
200Block size = 1024 :Uniform Window P000 :Overlap = None
:Cycles ave. = None
Pha
se (
Deg
rees
)
FRF Hv -- Input 1 On Each Output
0 50 100 150 200 250 300 350 400 4500.5
1
1.5
Frequency (Hz)
Am
plitu
de X
/F
Figure 3.29 Dynamic Frequency Response Functions
58
-
Chapter 4 Conclusions & Future Work
Motorsports is highly competitive industry where a minute
increase in performance could
mean the difference between first and second place. An engineer
in this type of
environment must utilize every tool at his fingertips at a level
of proficiency that is
unrivaled. To achieve such a high level of performance from a
motor vehicle a data
acquisition system is a requirement. The data acquisition
methods employed in
motorsports today, include the use of a complex data logger and
several sensors,
positions, accelerations, pressures, temperatures, and strains
to name a few. Data
acquisition systems have advanced significantly since their
inception, but most are still
not very affordable. The purpose of this thesis was to
investigate the possibilities and
ca