Physics 434 Module 5Lab & writeup thanks to Prof. Toby Burnett

1

Module 5 – Serial devices using VISA (LabView for “Virtual Instrument Software Architecture”)

An application to measure capacitance

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Examples of “serial interfaces”

RS232 (dumb terminal) HPIB GPIB (general purpose instrument bus) “Fire wire” USB

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The Agilent (nee HP) 43310Avoltmeter: example of a GPIB instrument

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You could measure in the frequency domain: A low-pass RC filter

100 1 103 1 104 1 1050.01

0.1

1

10Bode plot for a low-pass RC filter

frequency (Hz)

|H(f

)|

1

2

1

2R C

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You could measure in the time domain (à la Module 4)

Apply a square wave, measure response, charge or discharge

May not seen serial device; at least use Agilent to measure resistor

0 1 104

2 104

3 104

4 104

5 104

0

0.2

0.4

0.6

0.8

dischargecharge

RC circuit

time (s)

volta

ge a

cros

s ca

paci

tor

R 1 103

C 1 107

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Main points (see the doc)

Understand the Agilent instrument Build the RC circuit (you might want to use the signal

generator and scope to get a quick understanding). Two options (or your own ideas)

Frequency domain: Get and use the SweptSineGenerator (in the Module5 llb). Generate the sweep.

Time domain: use the Vi from Module 4 to create a long square-wave pulse

Analysis either inline, or write out the data to fitGenerate a final vi to calculate the frequency.

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Example Fitting:Levenberg-Marquartd.vi

This VI has a nice interface to specify a model. It is a cluster of 3 items: the formula, an array of parameters to fit, (a,f) and the independent variable (x).

Package it into a subVI, inputs X, Y, “Initial Guess”, output “Best Fit” and “Best Fit Coefficients” (really parameters). Make a LED light up if there is an error. The graph comparing data with best fit can be generated here

(But note that this is already done: there is a fit_bode.vi you can use)

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The final project

We will be coming around to discuss this. See the list of suggestions on the web site

Can be individual or joint (will probably be joint): if joint, the individual contributions need to be specified

(specific sub-vis, for example.) It will still be a joint grade. Make a proposal, perhaps by e-mail. I want to have a title

and a short description.