Real world measurements

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

Berkeleyearth.org Measurements are debated

Measurements are important in healthcare

Transportation is not safe without measurements

Measurements can tell us how the universe is built Michelson-Morley 1887 Large hadron collider

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

Course structure (some details TBD) Week 1Individual Lab: Intro to data acquisition - acceleration Week 2Individual Lab: EKG Week 3Individual Lab: Mechanical – Stress/strain Week 4Individual Lab: Ballistocardiograph Week 5Individual Lab: Pulse Oximeter Week 6Individual Lab: Pulse Oximeter Week 7Individual Lab: Mechanical vibrations Week 8Team Lab: Remote experiments - arduino Week 9Team Project Week 10Team Project Week 11Team Project Week 12Team Project Week 13Team Project Week 14Team Project Spring break

Projects Projects can focus on a reasonably challenging sensor/circuit using commercial sensors and focus on the experiment and the data.

A few things. This is not an EE course – but many measurements are electronic (all in this course). Ninjas. Lab reports – focus mainly on results. Weekly labs will be individual. Team project will be in groups of about 4.

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 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: =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

Aliasing error

Noise What are sources of noise?

Simple voltage divider demo What’s this voltage? = =5V R R

USB 6009 – input impedance = =5V R R i i is not 0!

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

The electrocardiogram

Me Time (sec) V (arb)

EKG The EKG is a powerful diagnostic tool. Regularly used by cardiologists.

Disclaimers We are not real doctors. Neither are you. Do not try to interpret your EKG.

Safety

We will review this in lab, but basically – 100 K resistors between you and breadboard. – Unplug your laptop while collecting data.

Privacy Your EKG could be considered private medical information under Federal HIPAA laws. If using this data makes you at all uncomfortable – then use one of the instructors as your subject.

The circuit AD623 – Instrumentation amplifier

The Op-Amp

Simplification for op-amp circuit analysis 1.Assume no current flows into the inputs. 2.If the op-amp is wired with negative feedback, and other circuit dynamics are “slow” (less than ~100 kHz), then Then the two input voltages are equal.

What does this circuit do?

The instrumentation amplifier Wikipedia

AD623 Data sheet

AD623 – Instrumentation amplifier Let’s look at the filters now

Linear circuits – Double the input, double the output. – A sinusoidal input results in a sinusoidal output of the same frequency.

How to characterize a linear circuit (at sinusoidal steady state) We can fully characterize the system with two parameters: Magnitude of output/Magnitude of input (B/A) Phase difference between input and output (theta) Your linear circuit

The Bode plot Developed 1930s Published 1945