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

-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 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

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

==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

==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=10K and 100 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 =100 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.