Download - Real world measurements
Real world measurements
Measuring things
• Making 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
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.
Leverage
• Sensors and 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.
Course structure (some details TBD)Week 1 Individual Lab: Intro to data acquisition - acceleration
Week 2 Individual Lab: Op-amps - lie detector
Week 3 Individual Lab: Instrumentation amp. – EKG
Week 4 Individual Lab: Mechanical – Stress/strain
Week 5 Individual Lab: Mechanical – Strain project (?)
Week 6 Individual Lab: Signal processing – EEG (brain waves)
Week 7 Individual Lab: Remote data collection (weather station)
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
• Environment • Weather balloons• Lakes, rivers.• Weather, wind, rain.
• Bio-instrumentation• EKG• EEG• Pulse oximeter• Biomechanics (accelerometers in your shoes)
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
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
time
sign
al
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
-0.5
0
0.5
1
time
sign
al
Noise
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-1.5
-1
-0.5
0
0.5
1
1.5
time
sign
al
What are sources of noise?
Types of noise• Thermal (Johnson) noise – due to thermal motion of charge
carriers. • 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 with Keithley
How close is the measured value to the actual one?
• Pressure sensor example:
Simple voltage divider demo
What’s this voltage?
R s o u rc e
21
V s e n s o rV m e a s u re
R m e a s
2
1
R s o u rc e
21
V s e n s o rV m e a s u re
R m e a s
2
1
R s o u rc e
21
V s e n s o rV m e a s u re
R m e a s
2
1
==2.5VR
R
USB 6009 – input impedance
R s o u rc e
21
V s e n s o rV m e a s u re
R m e a s
2
1
R s o u rc e
21
V s e n s o rV m e a s u re
R m e a s
2
1
R s o u rc e
21
V s e n s o rV m e a s u re
R m e a s
2
1
==2.5VR
R
i
i is not 0!
Analog output demo
R s o u rc e
21
V s e n s o rV m e a s u re
R m e a s
2
1
R s o u rc e
21
V s e n s o rV m e a s u re
R m e a s
2
1
==1VR=20K and 200 Ω
Source impedance
R s o u rc e
21
V s e n s o rV m e a s u re
R m e a s
2
1
DAQ Analog Output
=1V =200 Ω
What is R source for our DAQ?
Generic sensor measurement
Sensor Measurement- DAQ
R s o u rc e
21
V s e n s o rV m e a s u re
R m e a s
2
1
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.
• Try to create a virtual scope, where data is collected and plotted continuously. Hint: collect an infinite number of samples.