Instruction manual

HB 08-18-2010 8

helpful to refer to previous sections during these exercises. Reminder: the VOLTS/DIV and

TIME/DIV switches are not calibrated unless the knobs in the center of these switches are

fully clockwise in the calibrated positions.

5.1 Preliminaries

Remove any input cables to the scope. Turn on the scope (control 3) and observe LED (1).

In a few seconds you should see a trace which is a horizontal line (it takes the cathode a

few seconds to warm up). If you do not, check your initial control settings. Adjust the

INTENSITY (4) and FOCUS (6) controls for a sharp trace which is easy to view but not

brighter than necessary. Too bright is hard on the phosphor. Move the trace about the

screen with the 2 POSITION controls, 17 (vertical) and 27 (horizontal). Leave the trace

centered. Turn the time base switch (23) to 0.2 s and note the light spot move slowly across

the screen until it gets to the right hand side of the screen. What happens then? Investigate

the eﬀect of turning the variable sweep rate knob (26). Increase the sweep speed one click

at a time and note how the moving spot becomes a solid line. Observe that there is a range

of sweep speeds for which the trace “ﬂickers.” This is due to the persistence of the phosphor

or of the human eye, or perhaps both.

When you need to make measurements of an input signal (peak voltage, period, etc.), it

is useful to use the two position controls (17, 27) to move parts of the trace onto the gridlines

of the screen that have ﬁner divisions.

Try setting the Trigger COUPLING switch (32) to NORMal. The trace should disappear,

as there is no input signal for the scope to trigger on. Set this switch back to AUTO to

retrieve the trace.

5.2 Observing Voltage From The Wavetek FG3C Function Generator

This function generator produces sine, square and triangular waveforms which are selected

by three pushbuttons. The frequency of these waveforms can be adjusted from 0.3 Hz to

3 MHz by means of a knob marked frequency and 7 pushbuttons. The output frequency

appears in the middle of the display panel. At the bottom of the display panel to the right

appear Hz, and in the middle of the bottom there may a multiplier for Hz such as k or

M. It is important to check for the k or M to determine whether the stated frequency is

in kHz or MHz. The multiplier appears and vanishes automatically as you cross certain

threshold frequencies such as 1 kHz. The amplitude of the output is varied by a knob at

the right marked AMPL. The knobs have “in” and “out” positions. The functions for the

knobs are marked in black for the “in” position and blue for the “out” position. In using

this instrument as a simple function generator be sure all the knobs at the bottom of the

front panel are in and that the only two green LED’s that are on are one for the waveform

chosen and one for the frequency range (buttons at top).

Connect the 50 Ω output of this oscillator to the CH1 vertical input (14) of the BK scope

using the coaxial cable. Set the AMPL knob full CCW and turn on both the oscillator and

scope. Adjust the Wavetek for about a 1 kHz sine wave and turn the AMPL knob CW until

you see a reasonable signal.

Vary all of the controls listed below leaving the parameters of the input voltage constant.

Note the eﬀect on the trace of varying a control and understand why the trace changes in

the way it does. In answering the following questions make sketches of a trace if it will help

your explanation. How does the trace change if: