Lab 10_ Building a Hot Wire Anemometer

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```					Franklin W. Olin College of Engineering Introduction to Modeling and Control: Engineering of Compartment Systems Lab 10: Building a Hot Wire Anemometer Part 2 of 2 In this lab you will construct, test, and model a working hot wire anemometer. This lab will be the final lab in thermal systems and will require you to use your new knowledge of heat transfer and circuits. The final product of this lab will be a working scientific instrument which can measure wind speed with very good temporal resolution. Create the circuit shown below. NOTE THAT PIN 4 OF THE OP-AMP GOES TO -12V.

U1

1

6 OUT

OPA551

OS1

OS2

5

+12 7 R1 Lamp

4 -12 R3

V-

V+

2

5K

3

+

-

R2 50

We will discuss how this circuit works in class, but by now you should be able to get some idea by thinking about how this circuit works at steady state. HINT: the voltage dividers on the left and right of the op-amp are fed identical voltages at their tops from the op-amp output. If their mid-point taps are at the same voltage, then their resistance ratios must also be equal. From this description, and imagining what happens if the lamp resistance goes up or down, you should be able to deduce what this circuit is trying to do. The circuit has stable equilibria at two output voltages, one positive – the other negative. It has an unstable equilibrium at zero volts. Leave the glass light bulb intact. Check that the circuit is working by turning the potentiometer. You should see the light bulb brighten and darken as you turn the potentiometer up and down. Finally, turn the potentiometer all the way down so that the light turns off. Take the light bulb out of the circuit. Wrap the bulb in a sheet of paper. Slowly crush the bulb in the vice that is in the lab. Carefully discard the broken glass and carefully remove the bulb from the paper. Carefully place the bulb back into the circuit (the glass is sharp