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HB 01-26-09 Oscilloscope (1) Lab 5 1

Oscilloscope Lab 5

Equipment SWS, BK Precision model 2120B oscilloscope,Wavetek FG3C function generator,

2-3 foot coax cable with male BNC connectors,

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 to use the scope 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

such as 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 An Analogy, or the Case of the Vanishing Ink

A slowly varying periodic voltage is observed on a voltage meter. A curve of the voltage

versus time is desired. On a long strip of paper are put a vertical axis for voltage and a

horizontal axis for time. At time t

a plot of voltage versus time is started when the voltage

has the value V

and a positive slope (voltage increasing). See Fig. 1. At time t

it is noticed

that the ink around the point at time t

has started to fade. There is good reason to believe

that after not too long a time the ink will vanish. The plotting is stopped at time t

. The

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Inhaltsverzeichnis

Seite 1 - 1 Introduction

HB 01-26-09 Oscilloscope (1) Lab 5 1Oscilloscope Lab 5Equipment SWS, BK Precision model 2120B oscilloscope,Wavetek FG3C function generator,2-3 foot co

Seite 2

HB 01-26-09 Oscilloscope (1) Lab 5 10The controls you have just used are the ones most frequently employed in adjusting thetrace.It is instructive to

Seite 3

HB 01-26-09 Oscilloscope (1) Lab 5 116.6 Scope ProbesIn this experiment the function generator is connected to the scope by a cable with connectorson

Seite 4

HB 01-26-09 Oscilloscope (1) Lab 5 12window. Click auto. Drag the scope display icon to the terminals labeled V to open thescope display. Observe the

Seite 5

HB 01-26-09 Oscilloscope (1) Lab 5 13You will ﬁnd that the two knobs labeled SWEEP TIME and MOD/DEPTH-SWEEPRATE aﬀect the waveform. Can you ﬁgure out

Seite 6

HB 01-26-09 Oscilloscope (1) Lab 5 14Figure 1:Figure 2:

Seite 7

HB 01-26-09 Oscilloscope (1) Lab 5 15Figure 3:Figure 4:

Seite 8 - 6 Using The BK Oscilloscope

HB 01-26-09 Oscilloscope (1) Lab 5 16Figure 5:

Seite 9

HB 01-26-09 Oscilloscope (1) Lab 5 2time interval plotted is P = t2− t1. In Fig. 1 the curve to the right of t2is dotted. Noplotting is done for a tim

Seite 10

HB 01-26-09 Oscilloscope (1) Lab 5 3passes to the outside of the tube and can be observed. If the electron beam is suddenlycut oﬀ, the light from the

Seite 11 - 7 Using The SWS Oscilloscope

HB 01-26-09 Oscilloscope (1) Lab 5 4screen. When the ramp voltage across the horizontal deﬂection plates is VL, the electronbeam is at the left of the

Seite 12

HB 01-26-09 Oscilloscope (1) Lab 5 5voltage and always tracing out the same curve. The result is a stationary trace of the inputvoltage on the scope s

Seite 13 - 10 Finishing Up

HB 01-26-09 Oscilloscope (1) Lab 5 6• POWER(1,3)-Button (3) turns the scope on and oﬀ. LED (1) indicates when the scopeis on.• CRT(4-6) (cathode ray t

Seite 14 - Figure 2:

HB 01-26-09 Oscilloscope (1) Lab 5 712. VERTICAL MODE switch. Set to CH1 (channel 1 or X input).13. CH1 AC-GND-DC switch. Set this switch at AC. This

Seite 15 - Figure 4:

HB 01-26-09 Oscilloscope (1) Lab 5 8When this control is in the CAL position, control 23 is calibrated. Set in CAL position (fullyclockwise).27. HORIZ

Seite 16 - Figure 5:

HB 01-26-09 Oscilloscope (1) Lab 5 9the eﬀect of turning the variable sweep rate knob (26). Increase the sweep speed one clickat a time and note how t