Instruction manual

HB 01-26-09 Oscilloscope (1) Lab 5 12
window. Click auto. Drag the scope display icon to the terminals labeled V to open the
scope display. Observe the different signals from the signal generator with the scope display
and thoroughly familiarize yourself with the controls of the SWS scope.
You may have trouble getting a trace with the 3 positive only waveforms from the SWS
signal generator. This may be due to the fact that the default trigger level is 0. Try adjusting
the trigger level for a slightly positive voltage.
A nice feature of the SWS scope is the Smart Cursor. With a good stable trace investigate
investigate this capability.
7.2 SWS Scope and the Voltage Sensor
If you are using the SWS scope to measure voltages in a circuit, use the voltage sensor. To
set this up, drag the scope icon to the voltage sensor icon. The voltage censor is not used in
this lab.
8 Analog versus Digital Scopes
In an analog scope the input voltage, after amplification or attenuation, is applied to the
vertical deflection plates of the scope. The scope trace is smooth. In a digital scope, such
as the SWS scope, the input signal is sampled at the “sampling rate” and the scope trace is
these values usually connected by straight lines. You may have noticed this fact in looking at
the SWS scope trace. One of the important specifications for a digital scope is its sampling
rate, which may be hundreds of kHz or higher. This number is the maximum sampling rate
and is the rate used at the highest sweep speeds. In reality, the actual sampling rate is lower
and is usually adjusted so that there are about a few hundred to a thousand samples per
sweep. If the sampling rate is not high enough severe distortion of the signal can result. To
get a reasonable portrayal of the signal the sampling rate should be at least ten times the
frequency of the signal.
In the SWS scope the sampling rate is adjusted automatically and is displayed at the
bottom of the scope near the Trigger button and sweep speed. For the SWS scope determine
the sampling rate for a sweep speed of 1 ms/div and then calculate the samples per sweep.
A div or division is a large division as indicated by extended lines on the graticule.
A digital scope is often a storage scope. The sampled voltages are stored and the traces
viewed after the input voltage has ceased to be sampled. In an analog scope the trace will
disappear once the signal is no longer applied to the scope.
9 Optional Exercises- NO Credit
If you fully understand the operation of the scope and have extra time, feel free to explore two
additional features of the Wavetek generator; sweep and modulation. Look at the waveforms
on the scope and adjust the controls so as to highlight the features of these waves. Although
you can use any waveform you want, it is suggested that you start with sine waves and with
setting of the TIME/DIV control of 1 ms.
• SWEEP In the sweep mode, the wavetek repetitively sweeps from a lower frequency to
a higher frequency. Set the frequency knob of the Wavetek at about 1 kHz and pull out
this knob to start the sweep function. The higher frequency is selected by this knob.