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Berkeley PHYSICS 111 - Lab 9 LabView Programming

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Block DiagramLast Revision: August 2008 Page 1 of 32 ©2008 Copyrighted by the Regents of the University of California. All rights reserved. University of California at Berkeley Physics 111 Laboratory Basic Semiconductor Circuits (BSC) Lab 9 LabView Programming ©2008 by the Regents of the University of California. All rights reserved. References: View sections 1-5 LabView 7.1 Basic interactive training CD, or the 6 hour tutorial on-line available; also Review the LabView Power Point Lecture; http://socrates.berkeley.edu/~phylabs/bsc/LV_Programs/Lecture-LV_9 then click on “Modern Experimental - - -“ Wells & Wells Entire Book on LabView Programming. Horowitz & Hill Chapter 7.11 and Chapter 15. In this lab you will learn how to acquire data using LabVIEW, and use your knowledge to investigate Johnson Noise. Before coming to class complete this list of tasks: • Completely read this Lab Write-up • Answer the pre-lab questions utilizing the references and this write-up • Perform any circuit calculations or anything that can be done outside of lab. • Begin and if possible complete programming tasks in this lab write-up • Plan out how to perform Lab exercises in this write-up. Pre-lab questions: 1. What are the properties of a good data acquisition environment? 2. At room temperature, what would be the RMS noise across a 100k resistor sampled between 1kHz and 10kHz? 3. What is the predicted gain of the circuit in used in Exercise 9.4? NOTE: Use LabView only on PC’s running Windows 2000/NT/XP Several LabView programs are used in this lab. Some of these programs do not use data acquisition hardware and can be run on your own computer. Download and install the LabVIEW Development system 7.1 from http://socrates.berkeley.edu/~phylabs/bsc/LabView it is password pro-tected,.available from the GSI’s in the 111-LAB. If you run the original program you will have full privileges; you will be able to examine and edit the LabVIEW code. If you run the executable, you will not be able to examine or edit the code. All LabView programs discussed that do not use the data acquisition hardware, and can be downloaded from http://socrates.berkeley.edu/~phylabs/bsc/LV_Programs The following files are in Programs.ZIP • Noisy Signal Generator.vi • Visual Noise.vi LabVIEW Training CD (LV_Tutorial.ZIP) The majority of the exercises do not require the data ac-quisition hardware, and can be done on your own computer.The exercises requiring the DAQ are 2-2, 3-4, 4-5, 6-4 and all of section 7. The tutorial is located in the 111 Lab Share on the 111-Lab Net-work.Physics 111 BSC Laboratory Lab 9 LabVIEW Programming Last Revision: August 2008 Page 2 of 13 ©2008 Copyrighted by the Regents of the University of California. All rights reserved. Background Data Sources Originally, physicists made measurements by hand; we measured lengths with rulers, counted events by penciling in tick marks, and timed events with stopwatches. But as the experiments be-came more sophisticated, hand and eye techniques failed; they were too slow, too inaccurate, and too imprecise. Experiments began making measurements electronically. In some experiments, the measurements are intrinsically electrical; for instance: • Measurements of the charge collected on a plate from a cosmic ray. • Measurements of the resistance of a semiconductor. • Measurements of the radio signal from a pulsar. • Measurements of the potential across a nerve cell. Other experiments produced data that is not intrinsically electrical, but are best measured by con-verting the data to an electrical signals. Devices which convert a non-electrical measurements to an electrical signal are called transducers, and some typical examples include: • A spectral line converted to an electrical signal by a photomultiplier tube. • The passage of an energetic particle converted to an electrical signal in a spark chamber. • The separation between two masses in a gravity wave experiment measured by light inter-ferometry and converted to an electrical signal with a photocell. • The temperature of a liquid helium bath converted to an electrical signal by measuring the resistance of a semiconductor. • The pressure in vacuum chamber measured with an ion gauge. Perhaps the last important non-electrical observations were photographs of astronomical images, and particle tracks in bubble chambers. Now even astronomical “photos” are taken electronically with CCD cameras, and bubble chambers have been replaced by silicon detectors. Computerized Data Acquisition For many decades, it was sufficient to read the signal on a meter, or display the signal on an oscillo-scope. Sometimes hybrid methods were used; for my Ph.D. thesis, I took about ten thousand photo-graphs of oscilloscope screens, and analyzed the information on the photos with calipers. Nowadays, most data is collected by computer. Computers have become astonishingly powerful, and data acqui-sition hardware has become cheap, fast and accurate. Data acquisition by computer has many ad-vantages over hand collection: • It is generally more precise and accurate. • The much larger data sets that can be collected by computers are far more amenable to so-phisticated analysis techniques. • It is much less tedious. • When properly programmed, there are no recording errors. Noise, Signal Processing, and Data Acquisition Unfortunately, it’s a rare experiment that produces noise-free data. Noise comes from many sources. Some are intrinsic, like the Johnson Noise discussed later in these Background notes, while others are extrinsic, like the 60Hz harmonics picked up from the power lines. It is always best to minimize noise before collecting data, but inevitably we would like to “see into the noise”…to recover a valid signal from a noisy signal. Powerful signal processing techniques, like filtering, averaging and Fou-rier Transforms, have been developed to do this. Most of these techniques require extensive data sets. Frequently, computerized data acquisition is the only way to acquire enough data. Data Acquisition Devices Modern instruments like oscilloscopes, signal sources, and digital multimeters can often send their measurements to computers. The most common hardware interface protocol is called the GPIB bus, sometimes known as the HP-IB or IEEE bus. Powerful in its time, the GPIB interface is slow,


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