Real world measurements
description
Transcript of Real world measurements
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 todayMichelson-Morley 1887
Large hadron collider
2011
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)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
Spring break
Project theme – The natural world
• Environment • Weather balloons• Lakes, rivers.• Weather, wind, rain.
• Bio-instrumentation• EEG• Pulse oximeter• Biomechanics (accelerometers)
Possible examples:
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
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
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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: 00101011101101214=16384 numbersResolution = range/16384
Eg: range is +10 to -10 V; 20/16384=1.2 mVrange is +1 to -1 V; 2/16382 = 0.12 mV
Aliasing error
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1
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Noise
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1.5
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What are sources of noise?
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
What’s this voltage?
R s o u rc e
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V s e n s o rV m e a s u re
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V s e n s o rV m e a s u re
R m e a s
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R s o u rc e
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V s e n s o rV m e a s u re
R m e a s
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==5VR
R
USB 6009 – input impedance
R s o u rc e
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V s e n s o rV m e a s u re
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R s o u rc e
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V s e n s o rV m e a s u re
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R s o u rc e
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V s e n s o rV m e a s u re
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==5VR
R
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i is not 0!
Analog output demo
R s o u rc e
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V s e n s o rV m e a s u re
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V s e n s o rV m e a s u re
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==1VR=10K and 100 Ω
Source impedance
R s o u rc e
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V s e n s o rV m e a s u re
R m e a s
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DAQ Analog Output
=1V =100 Ω
What is R source for our DAQ?
Generic sensor measurement
Sensor Measurement- DAQ
R s o u rc e
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V s e n s o rV m e a s u re
R m e a s
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If R source is small, and Rmeas is big, then you measure VsensorOtherwise, you might be measuring something else!
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.