Instruction manual

HB 01-26-09 Oscilloscope (1) Lab 5 9

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.

6.2 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:

1. the VOLTS/DIV controls are changed (15 and 16)?

2. the TIME/DIV controls are changed (23 and 26)?

3. the trigger level (33) voltage is changed (33)? Note that if the trigger voltage is set too

high or too low the trace does not “freeze” but “runs” to the right or the left if the

trigger coupling switch is on AUTO.

4. With the trigger COUPLING switch in the NORMal mode, can you make the trace

disappear by rotating the TRIG LEVEL knob (33) both ways? Explain.

5. the triggering slope is changed from + to − (pull control 33).

6. the position controls 17 and 27 are changed?