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Unformatted text preview: HB 08-18-2010 1 Oscilloscope Equipment SWS, BK Precision model 2120B oscilloscope,Wavetek FG3C function generator, 2-3 foot coax cable with male BNC connectors, 2 voltage sensors Reading How To Use Science Workshop, pp. 170-183 (scope display). Review the Voltage, Current, and Resistance writeup for the use of the SWS signal generator. Remark The oscilloscope is a difficult instrument to understand, but it is also a very impor- tant instrument. Studying this write-up carefully before the lab will be worthwhile. This lab cannot be approached casually. 1 Introduction The standard instrument for examining time dependent voltages in a circuit is the oscillo- scope, or scope for short. Even if you are doing a DC experiment it is a good idea to look at the circuit with a scope. You might find a large AC signal symmetric with respect to ground that does not show up on DC instruments but is affecting your experiment in undesirable ways, such as overloading a sensitive amplifier. Oscilloscopes are ubiquitous in the medical profession. They are seen next to hospital beds showing the electrical output of a heart. They are used extensively in operating rooms. A voltage which depends on time can be drawn on graph paper with the voltage on the vertical axis and the time on the horizontal axis. If the voltage is periodic (repeats itself after one cycle) an oscilloscope will present a similar curve. By adjusting the scope it is possible to display part of one cycle or many cycles of the waveform. Properties of a periodic voltage, such as shape, peak-to-peak amplitude and period, can be measured. Is that sine wave from your signal generator distorted? Feed it into a scope and find out. Scopes have other uses, but these are the primary subjects of this lab. The oscilloscope is a sophisticated instrument. Competent use depends on understanding how this instrument works. It is often necessary to consult the instruction manual for a particular scope in order to use it effectively. The basic ideas are usually the same but are implemented in different ways. In this lab you will become familiar with 2 oscilloscopes, the model 2120B made by BK Precision, and the SWS scope. Both these instruments do very much the same thing except that the controls on the BK are mostly knobs and switches and those on the SWS are icons and buttons. The SWS scope is digital. The input waveform is digitized and stored, at least for awhile. The BK scope is analogue. The input voltage may be amplified, but it is not digitized and stored. 2 Analogue Oscilloscope Basics The heart of an analogue scope is a cathode ray tube (CRT). See Fig. 2. A cathode ray is an historical name for a beam of electrons. The tube refers to the glass vacuum envelope....
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