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.