HB 01-26-09 Oscilloscope (1) Lab 5 11
6.6 Scope Probes
In this experiment the function generator is connected to the scope by a cable with connectors
on both ends. Very often voltages in a circuit are of interest and a scope probe is used. This
is a cable with a connector on one end for plugging into the scope input. The other end of
the probe cable has an electrode for touching the point in the circuit whose voltage waveform
is desired. There is a clip for making a connection to ground. Probes often attenuate the
signal by a factor of 10 or a 100, but if they do, the resistance loading they present to the
circuit increases by a factor of 10 or a 100. Remember that in connecting a voltage measuring
device to a circuit the higher the resistance of this device the better. A probe is not used in
this lab.
7 Using The SWS Oscilloscope
One of the displays available with SWS is the oscilloscope. This is not actually an oscilloscope
but software that closely mimics an oscilloscope. In some respects the SWS scope is a more
powerful diagnostic tool than the BK scope. In particular:
1. There are 3 vertical inputs each of which has its own trace. (Three voltages can be
observed simultaneously as a function of time.) The 3 traces have different colors. The
input for each trace is selected by an input menu button.
2. This scope is a storage scope. When you stop monitoring data the last trace is stored
for further use and perusal.
3. There is a smart cursor which is used in a similar way as in the graph display.
On the other hand, the BK scope is a much faster scope. The highest frequency you can
examine with the BK scope is 30 MHz. With the SWS scope the highest frequency is 10 kHz.
The other main difference between using the BK and SWS scopes is that in the SWS scope
the controls are icon buttons, and a slider for the trigger level and slope. See page 178 of
the SWS manual for a description of adjusting the trigger level and slope. The picture in
the manual does not show this slider adequately. It is a small triangle in a vertical strip at
the very left of the scope screen. The default trigger voltage is 0 with positive slope.
There are only 2 trigger options in the SWS scope. The default is with the button at
the bottom of the scope display labeled TRIG in the in position. In this mode there must
be an appropriate input signal for a trace to be observed. This corresponds to NORMAL
for control 32 of the BK scope. If you are having trouble finding a trace, click the TRIG
button. With this button “out” the time base oscillator is free running and does not need
trigger pulses to produce a trace. This corresponds to AUTO for control 32 of the BK scope.
A difference here that that the TRIG button must be in to freeze the trace with the SWS
scope.
In using the SWS scope display, use MON rather than REC. An enormous amount of
data flows from the scope and if you use REC the storage capacity of SWS will be over
taxed.
7.1 Voltage From 750 Interface
In this section voltages from the SWS signal generator will be examined with the SWS scope.
In the right experiment setup window click the sample V button to open the signal generator
(44 pages)
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