Real world measurements

1. Real world measurements

2. 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

6. Healthcare

7. Modern engineering systems

8. Physics – classical and today Michelson-Morley Large hadron collider

9. And corporations want to instrument your life (this is a conspiracy)

10. 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.

11. 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.

12. Course structure (some details TBD)

13. Project theme – The natural world Possible examples: • Environment • Weather balloons • Lakes, rivers. • Weather, wind, rain. • Bio-instrumentation • EKG • EEG • Pulse oximeter • Biomechanics (accelerometers in your shoes) Projects can focus on building a reasonably challenging sensor/circuit or using commercial sensors and focus on the experiment and the data.

14. 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.

15. 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.

16. So… let’s get down to business

17. Hardware – USB data acquisition

18. Analog to digital conversion What is the sample rate? Our system has a 14 bit ADC, if we set the range to ±10 V, what is resolution?

19. 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

20. Aliasing error

21. Noise What are sources of noise?

22. 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

23. How accurate is the DAQ? • If we measure 1 V, should we believe it? • Test with Keithley

24. How close is the measured value to the actual one? • Pressure sensor example:

25. Simple voltage divider demo R =2.5V = R What’s this voltage?

26. USB 6009 – input impedance i R =2.5V = i is not 0! R

27. Analog output demo R=20K and 200 Ω =1V =

28. Source impedance DAQ Analog Output =200 Ω =1V What is R source for our DAQ?

29. Generic sensor measurement If R source is small, and Rmeas is big, then you measure Vsensor Otherwise, you might be measuring something else! Sensor Measurement- DAQ

30. This week: Accelerometers

31. Matlab data acquisition toolbox

32. 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.