Real world measurements
(not ModCon II there will be no
modeling or control)
Measuring things
• Making accurate measurements is an essential part of
all branches science and engineering.
• Much (all?)of our understanding of the world was born
from experimental measurements (often ones that
disagreed with the current theory).
• Models of systems are useless without validation.
• Performance of engineered systems must always be
measured and tested.
“Experiment is the sole judge of scientific truth” Feynman
Healthcare
Modern engineering systems
Physics – classical and today
Michelson-Morley 1887
2011
Large hadron collider
And corporations want to instrument
your life (this is a conspiracy)
What you will learn (hopefully)
•
•
•
•
Make a set of physical measurements.
Analyze and present experiment data.
Conduct basic error analysis of data.
Design a basic computer based experimental
system.
• Use measurements test physical models.
This class is just the beginning
Leverage
•
•
•
•
•
Electronics keep getting cheaper.
Wireless keeps getting cheaper and better.
Sensors getting smaller.
GPS is getting easy and cheap.
IPhone and Wii are driving down complex sensor
costs.
• Ability to interface to computers keeps getting
easier.
• PCBs are fast and cheap.
Course structure (some details TBD)
Spring break
Week 1
Individual Lab: Intro to data acquisition - acceleration
Week 2
Individual Lab: EKG
Week 3
Individual Lab: Mechanical – Stress/strain
Week 4
Individual Lab: Signal processing
Week 5
Individual Lab: Pulse Oximeter
Week 6
Individual Lab: Mechanical vibrations
Week 7
Individual Lab: TBD
Week 8
Team Project
Week 9
Team Project
Week 10
Team Project
Week 11
Team Project
Week 12
Team Project
Week 13
Team Project
Project theme – The natural world
Possible examples:
• Environment
• Weather balloons
• Lakes, rivers.
• Weather, wind, rain.
• Bio-instrumentation
• EEG
• Pulse oximeter
• Biomechanics (accelerometers)
Projects can focus on building a reasonably challenging
sensor/circuit or using commercial sensors and focus on the
experiment and the data.
A few things….
•
•
•
•
This is not an EE course.
Ninjas.
Lab reports – focus mainly on results.
Weekly labs will be individual, we will try to
minimize the sharing of equipment.
• Team project will be in groups of about 4.
• Significant changes in labs from last years
class.
Grades – yes we have to give them
• Storey conjecture: If you turn everything in on
time, come to class, spend a reasonable
amount of time on homework, and put forth a
reasonable effort, the lowest grade you will
receive is a B.
• Corollary: You can easily get a C, D, or F by not
doing the above mentioned tasks.
So… let’s get down to business
Hardware – USB data acquisition
Analog to digital conversion
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signal
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-1
0
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time
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What is the sample rate?
Our system has a 14 bit ADC, if we set the range to ±10 V, what is resolution?
Resolution
14 bit ADC: 00101011101101
214=16384 numbers
Resolution = range/16384
Eg:
range is +10 to -10 V; 20/16384=1.2 mV
range is +1 to -1 V; 2/16382 = 0.12 mV
Aliasing error
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signal
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time
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Noise
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signal
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What are sources of noise?
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time
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Types of noise
• Thermal (Johnson) noise – due to thermal motion of electrons
• Shot noise – discrete nature of electrons
• 1/f noise or flicker noise
Interference
• Electromagnetic interference – (man-made or natural)
• Cross-talk – coupling between different signal lines
How accurate is the DAQ?
• If we measure 1 V, should we believe it?
• Test it
Simple voltage divider demo
1
2
R source
2 2
1
Vsensor
1
2
R source
Vmeasure
R source
R
=5V
Vsensor
=
1
2
Vsensor
1
Rmeas
2
Vmeasure
Rmeas
R
What’s this1voltage?
Rmeas
Vmeasure
USB 6009 – input impedance
2
source
2 2
1
2
source
R source
i
=5V
Vsensor
=
1
2
Vmeasure
R
Rmeas
i is not 0!
R
Rmeas
1
2
Vmeasure
Rmeas
1
Vmeasure
Analog output demo
1
2
R source
Vsensor
2 2
1
Vmeasure
R source
=1V
Vsensor
=
R=10K and 100 Ω 2
Rmeas
Vmeasure
1
Rmeas
1
Source impedance
DAQ Analog Output
1
2
R source
2
Vmeasure
Vsensor
=100 Ω
Rmeas
=1V
1
What is R source for our DAQ?
Generic sensor measurement
If R source is small, and Rmeas is big, then you measure Vsensor
Otherwise, you might be measuring something else!
1
2
R source
2
Vmeasure
Vsensor
Rmeas
1
Sensor
Measurement- DAQ
This week: Accelerometers
Matlab data acquisition toolbox
In class exercises
• See Data Acq. Toolbox tutorial, try exercises 1,
2, and 3. Work with the person next to you.