DSOXEDK Educator’s Oscilloscope Training Kit

Lab Guide and Tutorial

2 Basic Oscilloscope and

WaveGen Measurement Labs
Lab #1: Making Measurements on Sine Waves / 16
Lab #2: Learning the Basics of Oscilloscope Triggering / 22
Lab #3: Triggering on Noisy Signals / 27
Lab #4: Documenting and Saving Oscilloscope Test Results / 31
Lab #5: Compensating your Passive 10:1 Probes / 35
Lab #6: Using the WaveGen built-in Function Generator / 41

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Lab #1: Making Measurements on Sine Waves

In this 1st lab you will learn how to use the scope’s horizontal and vertical scaling
controls in order to properly setup the scope to display a repetitive sine wave. In
addition, you will learn how to make some simple voltage and timing
measurements on this signal.
1 Connect one oscilloscope probe between the channel-1 input BNC and the
output terminal labeled “Demo1” as shown in Figure 8. Connect this probe’s
ground clip to the center terminal (ground).

Figure 8 Connecting probes between the channel-1 and channel-2 inputs to the training
signals output terminals

2 Connect a second oscilloscope probe between the channel-2 input BNC and
the output terminal labeled “Demo2” as shown in Figure 8. Connect this
probe’s ground clip to the center terminal.
3 Press the [Default Setup] key near the upper right-hand section of the front
panel.

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Defaul t Setup will put the oscilloscope into a factory preset configuration. Not
only will this set the scope’s X and Y scaling factors to preset values, but it will
also turn off any special modes of operation that one of your fellow students
may have used.
4 Press the [Help] front panel key (near the channel-2 vertical controls).
5 Press the Training Signals softkey below the scope’s display.
6 Using the Entry knob, select the Sine signal (top of the list), then press the Output
softkey to turn it on.
There should now be a sine wave present on the Demo1 terminal, but it is not yet
recognizable using the scope’s default scaling factors. We will now adjust the
scope’s vertical and horizontal settings to expand and center this waveform on the
display.
7 Turn the channel-1 V/div knob clockwise until you see the displayed waveform
covering more than ½ of the screen. The correct setting should be 500 mV/d iv,
which is displayed as “500mV/” near the upper left-hand side of the display.
8 Turn the s/div knob (large knob in the Horizontal section) clockwise until you
observe more than two periods of a sine wave across the display. The correct
setting should be 50 ns/d iv, which is displayed as “50.00ns/” near the middle of
the top part of the display. Your scope’s display should now appear similar to
Figure 9. From this point forward we will simply refer to this as the scope’s
“timebase” setting.

Figure 9 Initial setup to view the sine wave training signal

9 Rotate the Horizontal position knob to move the waveform left and right.

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10 Press the Horizontal position knob to set it back to zero (0.0 seconds at
center-screen).
11 Rotate the channel-1 vertical position knob to move the waveform up and
down. Notice that the ground indicator on the left also moves up and down and
tells us where 0.0 Volts (ground level) is located on this waveform.
12 Press the channel-1 vertical position knob to set ground (0.0 V) back to
center-screen.
Let’s now make some measurements on this repetitive sine wave. Notice that the
oscilloscope’s display is basically an X versus Y graph. On our X-axis (horizontal)
we can measure time, and on our Y-axis (vertical) we can measure voltage. In
many of your EE or Physics class assignments, you have probably computed and
graphed electrical signals in a similar, but static, format on paper. Or, perhaps you
have used various PC software applications to automatically graph your
waveforms. When a repetitive input signal is applied to an oscilloscope, we are
able to observe dynamic (continuously updated) graphing of our waveforms.
Our X-axis consists of 10 major divisions across the screen with each major
division being equal to the sec/div setting. In this case, each horizontal major
division represents 50 nanoseconds of time, assuming that the scope’s timebase is
set to 50.0 ns/div as instructed earlier. Since there are 10 divisions across the
screen, then the scope is showing 500 ns of time (50.0 ns/div x 10 divisions) from
the left side of the display to the right side of the display. Notice that each major
division is also divided into 4 minor divisions, which are displayed as tick marks on
the center horizontal axis. Each minor division would then represent
1/4 div × 50 ns/div = 12.5 ns.
Our Y-axis consists of 8 major divisions vertically with each major division being
equal to the V/div setting, which should be set at 500 mV/div. At this setting, the
scope can measure signals as high as 4 Vp-p (500 mV/div x 8 divisions). Each
major division is divided into 5 minor divisions. Each minor division, represented as
tick marks on the center vertical axis, then represents 100 mV each.
13 Estimate the period (T) of one of these sine waves by counting the number of
divisions (major and minor) from the 0.0 V level of a rising edge (center-screen)
to the 0.0 V level of the next rising edge; then multiple by the s/div setting
(should be 50.0 ns/div).
T = _____________

14 What is the frequency of this sine wave (F = 1/T).

F = _____________

Let’s now estimate the peak-to-peak voltage level of these sine waves, but first,
let’s make a few minor adjustments to our vertical settings that may help us
perform this measurement more accurately.

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15 Adjust the channel-1 vertical position knob (smaller knob below the lighted “1”
key) until the negative peaks of the sine waves intersect with one of the major
graticules (or grid lines).
16 Next, adjust the horizontal position knob (smaller knob near the top of front
panel) until one of the positive peaks of the sine waves intersect with the center
vertical axis that has the minor division tick marks.
17 Now, estimate the peak-to-peak voltage of this sine wave by counting the
number of divisions (major and minor) from the sine wave’s negative peak to
the positive peak; then multiply by the V/div setting (should be 1 V/div).
Vp-p = _____________

Let’s now use the scope’s “cursors” function to make these same voltage and
timing measurements; but without having to count divisions and then multiply by
scaling factors. First, visually locate the “Cursors” knob in the Measure section of
the front panel as shown in Figure 10.

Figure 10 Measurement Cursors knob

18 Press the Cursors knob; then rotate this knob until “X1” is highlighted; then
press again to select (if you don’t press the knob a second time after dialing to
the “X1” cursor, a time-out will occur and then the X1 cursor will automatically
be selected and the menu will close).
19 Rotate the Cursors knob until the X1 cursor (#1 timing marker) intersects with a
rising edge of a sine wave at a particular voltage level. Hint: Align the cursor at
a point on the waveform where it crosses one of the horizontal grid lines.
20 Press the Cursors knob again; rotate this knob until “X2” is highlighted; then
press again to select.
21 Rotate the Cursors knob until the X2 cursor (#2 timing marker) intersects with
the next rising edge of the sine wave at the same voltage level.
22 Press the Cursors knob again; rotate this knob until “Y1” is highlighted; then
press again to select.

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Figure 11 Using the scope’s cursor measurements

23 Rotate the Cursors knob until the Y1 cursor (#1 voltage marker) intersects with
the negative peaks of the sine waves.
24 Press the Cursors knob again; rotate this knob until “Y2” is highlighted; then
press again to select.
25 Rotate the Cursors knob until the Y2 cursor (#2 voltage marker) intersects with
the positive peaks of the sine waves.
26 What are the period, frequency, and peak-to-peak voltage of this signal (cursor
read-out is on the right-hand side of the display)?
X = _____________
1/ X = _____________
Y(1) = _____________

The most common method used to measure time and voltage on an oscilloscope
is the “division counting” method we used first. Although divisions must be
counted and then multiplied by scope settings, engineers that are familiar with
their scopes can quickly estimate of the voltage and timing parameters of their
signals… and sometimes a rough estimation is all that is required to know if a
signal is valid or not.
Using cursors should provide a slightly more accurate measurement and take the
guess work out of the measurement. Most of today’s scopes also provide an even
more accurate and faster way to make many parametric measurements
automatically. We will come back to using the scope’s automatic parametric

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measurements during lab #10 when we begin to make some measurements on

some digital signals. But for now, we need to take a step back and learn about
oscilloscope triggering.

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Lab #2: Learning the Basics of Oscilloscope Triggering

As mentioned earlier, oscilloscope triggering is probably the most important
capability of an oscilloscope that you should understand if you want to get the
most out of your oscilloscope measurements. This is especially important when
attempting to make measurements on many of today’s more complex digital
signals. Unfortunately, oscilloscope triggering is often the least understood aspect
of oscilloscope operation.
You can think of oscilloscope “triggering” as “synchronized picture taking”. When
an oscilloscope is capturing and displaying a repetitive input signal, it may be
taking tens of thousands of pictures per second of the input signal. In order to view
these waveforms (or pictures), the picture-taking must be synchronized to
“something”. That “something” is a unique point in time on the input signal, or
perhaps a unique point in time based on a Boolean combination of input signals
(logic “pattern” triggering) while using multiple channels of the oscilloscope.
An analogous situation to oscilloscope triggering is that of a photo finish of a horse
race. Although not a repetitive event, the camera’s shutter must be synchronized
to the first horse’s nose at the instant in time that it crosses the finish line.
Randomly taking photos of the horse race sometime between the start and end of
the race would be analogous to viewing untriggered waveforms on a scope.
To better understand oscilloscope triggering, let’s make some more
measurements on our familiar sine wave that we used in Lab #1.
1 Ensure that your two oscilloscope probes are still connected between the
terminals labeled Demo1 & Demo2 and Channel-1 & Channel-2 input BNCs
respectively.
2 Press [Default Setup] on the scope’s front panel.
3 Press [Help]; then press the Training Signals softkey.
4 Select the “Sine” training signal using the Entry knob; then press the Output
softkey to turn it on.
5 Set channel-1’s V/div to 500 mV/d iv.
6 Set the scope’s timebase to 50.00 ns/d iv.
7 Press the [Trigger] front panel key.

Your scope’s display should now look similar to Figure 12. Using the scope’s
default trigger conditions, the scope should be triggering on a rising (slope
selection) edge (trigger type selection) of the sine wave that is being probed and
captured by channel-1 (source selection) as this signal crosses the 0.0 V level
(trigger level setting). This point in time is shown at center-screen (both
horizontally and vertically) if the horizontal position control is set to 0.0 sec
(default setting). Waveform data captured before the trigger point (left side of
display) is consider negative time data, while waveform data captured after the
trigger point (right side of display) is considered positive time data.

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Ì®·¹¹»® б·²¬

Figure 12 Triggering the oscilloscope on a rising edge of channel-1 at 0.0 Volts

Note that the “filled” orange triangle near the top of the display indicates where
the trigger time point (0.0 s) is located. If you adjust the horizontal delay/position,
this orange triangle will move away from center-screen. The “hollow” orange
triangle at center-screen (only visible if the delay/position is not 0.0 s) indicates
the time location of the delay setting when using the scope’s default “center”
reference.
8 Rotate the trigger level knob clockwise to increase the trigger level voltage
setting.
9 Rotate the trigger level knob counter-clockwise to decrease the trigger level
voltage setting.
As you increase the trigger level voltage setting, you should observe the sine wave
shifting in time to the left. If you decrease the trigger level voltage setting, the sine
wave will shift to the right. When you initially turn the trigger level knob, a
horizontal orange trigger level indicator will appear, and the exact trigger voltage
setting is always displayed in the upper right-hand corner of the scope’s display. If
you stop rotating the trigger level knob, the orange trigger level indicator will
time-out and disappear after a few seconds. But there is still a yellow trigger level
indicator shown outside the waveform graticule area on the left to indicate where
the trigger level is set relative to the waveform.
10 Rotate the trigger level knob to set the trigger level to exactly 500 mV (1 division
above center-screen). Note that the exact trigger level is displayed in the upper
right-hand corner of the display.
11 Press the Slope softkey and then select a Falling edge trigger condition.

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The sine wave should now appear to be inverted 180 degrees with a falling edge of
the waveform synchronized to center-screen as shown in Figure 13.

Ì®·¹¹»® б·²¬

Figure 13 Triggering on the falling edge of the sine wave at + 500 mV

12 Increase the trigger level voltage setting until the orange level indicator is
above the positive peaks of the sine wave (approximately +1.5 V).
With the trigger level set above the sine wave, the scope’s acquisition and display
(repetitive picture taking) is no longer synchronized to the input signal since the
scope can’t find any edge crossings at this particular trigger level setting. Your
scope’s display should now look similar to Figure 14. The scope is now “auto
triggering”.

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Figure 14 Auto triggering with the trigger level set above the input signal

Auto Trigger is the scope’s default trigger mode. When the scope is using the Auto
Trigger mode, if the scope doesn’t find a valid trigger condition (edge crossing of
the sine wave in this case) after a period of time (time varies and depends on the
scope’s timebase setting), then the scope will generate its own asynchronous
trigger and begin taking pictures (acquisitions) of the input signal at random
times. Since the “picture taking” is now random, rather than synchronized to the
input signal, all we see is a “blur” of waveforms across the screen. This “blur” of
waveforms should be a clue to us that our scope is not triggering on the input
signal.
13 Press the trigger level knob to automatically set the trigger level to the
approximate 50% level.
14 Disconnect the channel-1 probe from the Demo1 terminal.

With the channel-1 probe disconnected from our signal source, we should now
see a baseline 0.0 V DC signal. Since with this 0.0 V DC signal we no longer have
any edge crossings, and hence the scope has nothing to trigger on; the scope
again “auto triggers” in order to show us this DC level signal.
In addition to the default Auto Trigger mode, the oscilloscope also has another
user-selectable trigger mode called the Normal Trigger mode. Let’s now see how
the Normal Trigger mode differs from the Auto Trigger mode.
15 Re-connect the channel-1 probe to the Demo1 terminal. You should see the
triggered sine wave again.
16 Press the [Mode/Coupling] front panel key (to the right of the trigger level knob).

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17 Rotate the Entry knob to change the trigger mode selection from Auto to Normal.
At this point you should not see any difference in the displayed waveform.
18 Disconnect the channel-1 probe from the Demo1 terminal again.

You should now see the last acquisition (last picture) that occurred before the
probe was disconnected. We do not see the 0.0 V DC level trace that the Auto
Trigger mode displayed. When the Normal Trigger mode is selected, the scope will
only display waveforms if and only if the scope detects valid trigger conditions
(edge crossings in this case).
19 Rotate the trigger knob clockwise in order to set the trigger level at +1.50 V
(which is above our sine wave).
20 Re-connect the channel-1 probe to the Demo1 terminal.

The sine wave is now connected and being input to the scope, but where is our
repetitive display of this signal? Since we are using the Normal trigger mode, the
scope still requires valid edge crossings, but since the trigger level is set above the
waveform (@ +1.50 V), there are no valid edge crossings. So as you can see with
the Normal trigger mode, we don’t have any clue as to where our waveform is, and
we can’t measure DC.
21 Press the trigger level knob to automatically set the trigger level to the
approximately 50% level. Your scope should begin to show repetitive
waveforms again.
Some older scopes use to refer to what we today call the Normal trigger mode as
the Triggered trigger mode, which may actually be a more descriptive term for this
triggering mode since in this mode the scope only triggers when it finds a valid
trigger condition, and will not generate an automatic trigger (asynchronous
trigger to generate asynchronous picture taking). And it is a bit of an oxymoron
that the Normal trigger mode is not the “normally” used trigger mode, and it is not
the scope’s default trigger mode. The trigger mode that is normally used is the
Auto trigger mode, which is the scope’s default trigger mode.
As this point you may be wondering when to use the Normal trigger mode. The
Normal trigger mode should be used when the trigger event occurs very
infrequently (including single-shot events). For example, if you had the scope
setup to display a very narrow pulse, but if this pulse occurs at just a 1 Hz rate
(once per second), if the scope’s trigger mode was set to the Auto trigger mode,
then the scope would generate lots of asynchronously-generated automatic
triggers and would not be able to show the infrequent narrow pulse. In this case
you would need to select the Normal trigger mode so that the scope would wait
until obtaining a valid trigger event before displaying waveforms. We will connect
to such a signal a bit later during Lab #8 and Lab #9. But for now, let’s learn more
about triggering on noisy signals.

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Lab #3: Triggering on Noisy Signals

A repetitive sine wave is about the simplest type of signal for a scope to trigger on.
But in the real world, signals are not so simple. In this lab we will learn how to
trigger on signals in a noisy environment (a real-world condition), as well as learn
how to eliminate noise on digitized waveforms using waveform averaging.
1 Ensure that your two oscilloscope probes are still connected between the
terminals labeled Demo1 & Demo2 and the Channel-1 & Channel-2 input BNCs
respectively.
2 Press [Default Setup] on the scope’s front panel.
3 Press [Help]; then press the Training Signals softkey.
4 Using the Entry knob, this time select the “Sine with Noise” signal; then press the
Output softkey to turn it on.
5 Set channel-1’s V/div to 500 mV/d iv.
6 Set the scope’s timebase to 200.0 µs/d iv.

Even though the scope’s default setup condition configures the scope to trigger on
rising edges at 0.0 V, it appears that the scope is triggering on both rising and
falling edges of this noisy sine wave as shown in Figure 15. The scope is actually
triggering ONLY on rising edges. However, when the scope appears to be
triggering on a falling edge of the sine wave, it is actually triggering on a rising
edge of the random noise that is riding on the sine wave.

Figure 15 Attempting to trigger on signals in a noisy environment

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7 Verify that the scope is triggering on rising edges of noise by setting the
timebase to 200.0 ns/d iv.
8 Set the scope’s timebase back to 200.0 µs/d iv.

So how can we make the scope trigger during instances that are only coincident
with the rising edge of the sine wave (without noise)? Let’s now learn more about
some of the scope’s user-selectable trigger coupling options.
9 Press the [Mode/Coupling] front panel key (near the trigger level knob).
10 Press the HF Reject softkey to turn on a “high frequency reject” filter.

The input signal to the scope is actually split and sent down two different analog
paths inside the scope. The signal going down one path is captured by the scope’s
acquisition system (picture taking system). A similar signal is sent down a separate
path to be processed by the scope’s analog trigger circuitry. (Refer to the
oscilloscope block diagram shown in Appendix A.) When HF Reject has been
selected, the signal that is processed by the scope’s analog trigger circuitry is first
passed through a 50 kHz low-pass filter. Since the noise consists of a broad
spectrum of frequencies, including high frequency elements, the trigger circuitry
then “sees” a sine wave with most of the noise removed/attenuated, while the
signal that is sent down the acquisition path is unaffected (noise retained). This
way we see the noise, as shown in Figure 16, but the scope’s trigger circuitry does
not see the noise. But there are limitations.

Figure 16 Triggering on a noisy sine wave using HF Reject

Since the HF Reject filter is based on a fixed 50 kHz low-pass hardware filter, it
can’t be used on higher frequency signals. This 50 kHz low-pass filter does not
affect our 1 kHz sine wave training signal. But if we were attempting to use trigger

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HF Reject on a noisy 20 MHz sine wave, the 50 kHz filter would “kill” both the noise
and the fundamental 20 MHz sine wave making it impossible to trigger on
anything. But we have two more options.
11 Press the HF Reject softkey again to turn it off. The scope should appear to
trigger on the rising and falling edges of the sine wave again.
12 Press the Noise Rej softkey to turn on the “noise reject” filter.

The Noise Rej filter is not based on frequency, but is based on amplitude. Although
we have been talking about a single trigger level, there are actually two levels that
a signal must cross through in order to qualify as a valid trigger. This is called
“trigger hysteresis”, or sometimes referred to as “trigger sensitivity”. The default
trigger sensitivity of most scopes is 0.5 divisions. This means that input signals
must swing at least 0.5 divisions peak-to-peak in order to qualify as valid trigger
conditions. But this also means that scopes will trigger on noise if the noise
exceeds approximately 0.5 divisions peak-to-peak. When Noise Rej is selected, the
scope’s hysteresis is expanded to approximately 1.0 division peak-to-peak. For this
particular noisy sine wave, 1.0 divisions of trigger hysteresis solves our problem
most of the time. You may notice some “flickering” on the scope’s display. This
means that the 1.0 divisions of hysteresis is not quite enough. Another solution is
to use the scope’s trigger holdoff feature, which we will talk about during lab #7.
Before we depart from making measurements on this sine wave with noise, what if
we wanted to view and perform measurements on this sine wave, but without the
random noise?
13 Press the HF Reject softkey. Now both high frequency reject filtering, as well as
noise reject filtering should be turned on to provide us with a very stable
trigger.
14 Press the [Acquire] key in the Waveform section of the front panel (just below
the cursors knob).
15 Rotate the Entry knob to change the scope’s acquisition mode from Normal to
Averaging.
When the Averaging acquisition mode has been selected, the scope averages
multiple waveform acquisitions together. If the noise riding on the signal is
random, then the noise component will average out so that we can then make
more accurate measurements on just the fundamental signal component as shown
in Figure 17.

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Figure 17 Using the scope’s Averaging acquisition mode to eliminate the noise

16 Using the measurement techniques you learned in Lab #1, determine the
following:
Period = _____________
Freq = _____________
Vp-p = _____________

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Lab #4: Documenting and Saving Oscilloscope Test Results

When you complete your various circuits lab assignments, your professor may
require you to write up a test report. Including images (pictures) of your
measurements in your lab report may be required. In addition, if you can’t
complete a lab assignment during one session, you may want to continue testing
at a later time. But it would really be great if you could pick up where you left off;
without having to re-setup your scope or possibly re-acquire waveforms. In this lab
you will learn how to save and recall various oscilloscope file types including
images, reference waveforms, and setups. For this lab you must have access to a
personal USB memory device.
1 Ensure that your two oscilloscope probes are still connected between the
terminals labeled Demo1 & Demo2 and Channel-1 & Channel-2 input BNCs
respectively.
2 Press [Default Setup] on the scope’s front panel.
3 Press [Help]; then press the Training Signals softkey.
4 Using the Entry knob, select the “Sine” waveform; then press the Output softkey
to turn it on.
5 Set channel-1’s V/div to 500 mV/d iv.
6 Set the scope’s timebase to 100 ns/d iv.

At this point you should see five cycles of a sine wave as shown in Figure 18. Let’s
now save this image (picture), save the waveform, and save the setup.

Figure 18 Five cycles of a sine wave that we want to save for documentation and later
analysis

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7 Insert your personal USB memory device into the scope’s front panel USB port.
8 Press the [Save/Recall] key in the File section of the front panel below the
Cursors knob.
9 Press the Save softkey; then press the Format softkey.
10 Using the Entry knob, select PNG 24-bit image (*.png).
11 Press the Save to (or possibly Press to go) softkey; then point to \usb using the
Entry knob.
12 Press the File Name softkey; then rotate the Entry knob and give this file a name.
For now, let’s call it “test”.
13 When you rotate the general-entry knob, an alpha-numeric string will pop up.
Simply dial to the first letter, “t” in this case, and then either press the Enter
softkey, or press the Entry knob.
14 Repeat step #13 for each remaining character in this file name.
15 Press the Delete softkey to delete any remaining characters from the default file
name.
16 Press the Increment softkey to turn off auto-increment (box should be black).
Note that if auto-increment is turned on, the scope will automatically increment
a number associated with the file name. This can be useful if you intend to save
multiple images without needing to manually re-enter different file names
between each save operation.
17 Press the Press to Save softkey.

Your USB memory device should now have a stored image of the scope’s display
similar to Figure 18. The file name should be “test.png”. You can open this file or
insert it into a Microsoft-Word document later to see if it is really there. Let’s now
save the scope’s setup configuration.
18 Press the [Save/Recall] front panel key.
19 Press the Save softkey; then press the Format softkey.
20 Using the Entry knob, select Setup (*.scp).
21 Press the Save to (or possibly Press to go or Location) softkey.
22 Point to \usb using the Entry knob; then press the Entry knob.
23 Press the File Name softkey. You will see that the previous file name you entered
will become the new default file name. Since the “setup” file format uses a
different file name extension, we can use the same file name.
24 Press the Press to Save softkey.

Your USB memory device should now have the file named “test.scp” that contains
the scope’s current setup configuration. We will recall this setup configuration
later. Note that you can also save setups to one of the scope’s internal flash
memory registers. However, one of your fellow students that may use this
oscilloscope next could overwrite this memory register with his/her setup. So it is

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always good practice as a student using a shared scope to save oscilloscope

setups and waveforms using your own personal memory device. Let’s now save a
reference waveform data file.
25 Press the [Save/Recall] front panel key.
26 Press the Save softkey; then press the Format softkey.
27 Using the Entry knob, select Reference Waveform data file (*.h5).
28 Press the Save to (or possibly Press to go) softkey.
29 Point to \usb using the Entry knob; then press the Entry knob.
30 Press the File Name softkey. Again, we don’t need to define a new name since
this file format will also have a unique file name extension (test.h5).
31 Press the Press to Save softkey.

Note that when we saved the .png file type earlier, this was just a pixel map of the
scope’s display. This type of file cannot be recalled back into the scope, and
measurements cannot be performed on data stored in this type of file. This type of
file, as well as a .bmp file type, is primarily useful for documentation purposes,
such as inclusion in your lab reports. But the “Reference Waveform” data file (.h5)
that we just stored saves voltage versus time data as X-Y pairs. This type of file can
be recalled back into the scope for later analysis. You can also recall this type of
file into many PC applications for more extensive off-line analysis.
Now that we have saved the scope’s setup configuration, as well as saved the
waveform (4 cycles of a sine wave), let’s see if we can recall these files. But first we
will begin with a default setup in order to destroy the current setup and waveform
that you see on-screen.
32 Press [Default Setup].
33 Press [Save/Recall].
34 Press the Recall softkey; then press the next Recall softkey.
35 Select Setup as the type of file to recall using the Entry knob.
36 Press the Location (or possibly Press to go or Load from) softkey; then point to
“test” using the Entry knob.
37 Either press the Press to Recall softkey, or press the Entry knob.

We should have just restored the scope’s setup to its previous configuration.
However, the scope does NOT save the status of the training signals. So at this
point the only waveform we should see is a baseline (0.0 V) signal since there are
no signals present at the inputs of our probes. Let’s now recall the waveform that
we previously saved.
38 Press the Recall softkey; then select Reference Waveform data (*.h5) using the
Entry knob.
39 Press the Load from (or possibly Press to go or Location) softkey; then point to
“test” using the Entry knob.
40 Either press the Press to Recall softkey, or press the Entry knob.

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You should now see the stored version of our sine wave (along with the live 0.0 V
baseline signal) using the previous setup configuration as shown in Figure 19. At
this point you can change the setup if you like, and you can also continue making
measurements on this stored waveform. Note that you can remove your USB
memory device at any time after saving/recalling your data.

Figure 19 Recalling the scope’s setup configuration and waveform

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 Basic Oscilloscope and WaveGen Measurement Labs 2

Lab #5: Compensating your Passive 10:1 Probes

Now that you’ve completed the first four labs in this oscilloscope training guide
and should be somewhat familiar with how to use an oscilloscope to make basic
voltage and timing measurements, let’s take a step back and talk about probing
again. In the Getting Started section of this guide we briefly discussed probing and
showed the electrical input model of the combination of a passive 10:1 probe and
the oscilloscope’s input. This electrical model of the probe and oscilloscope is
shown again here in Figure 20.

Figure 20 Simplified schematic of a passive 10:1 probe connected to the scope’s 1 M

input impedance

If you remember, you were instructed to ignore the capacitive components in this
electrical model and consider just the resistive components. When we looked at
just the resistive components, we determined that the combination of the probe’s
9 M probe tip resistor plus the scope’s 1 M input impedance established a
10-to-1 voltage-divider ratio. For low-frequency or dc applications, ignoring the
capacitive elements is appropriate. But if you need to measure dynamic signals,
which is the primary measurement application for oscilloscopes, the capacitive
elements of this electrical model can’t be ignored.
Inherent in all oscilloscope probes and scope inputs are parasitic capacitances.
These include the probe cable capacitance (C cable), as well as the scope’s input
capacitance (C scope). “Inherent/parasitic” simply means that these elements of the
electrical model are not intentionally designed-in; but are just an unfortunate fact
of life in the real world of electronics. And the amount of inherent/parasitic
capacitance will vary from scope-to-scope and probe-to-probe. But without
additional designed-in capacitive components to compensate for the inherent
capacitive elements in the system, the reactance of the system under dynamic
signal conditions (non-dc) can change the overall dynamic attenuation of the
probing system to something different than the desired 10:1 ratio. The purpose of
the additional/designed-in probe tip capacitor (C tip) along the adjustable
compensation capacitor (C comp) is to establish a capacitive reactance attenuation
that matches the resistive attenuation of 10:1. When the compensation capacitor

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is properly adjusted, this also ensures that the time constant of the probe tip
capacitance in parallel with the 9 M resistor matches the time constant of the
inherent and compensation capacitances in parallel with the scope’s 1 M input
resistor.
Rather than spending a lot more time talking about the theory of this, let’s just
connect to a signal and see the affect of under-compensation, over-compensation,
and proper-compensation. But first be aware that we will be connecting our
channel-1 probe to a different terminal from the previous labs.
1 Connect both of your oscilloscope probes to the terminal labeled Probe Comp.
Note that this is the same terminal that is also labeled Demo2.
2 Press [Default Setup] on the scope’s front panel.
3 Set channel-1 to 1.0 V/d iv.
4 Set channel-1 offset/position to 0.0 V (default setting).
5 Press the trigger level knob to set the trigger level to approximately 50% on
channel-1.
6 Press the [2] front panel key to turn on channel-2.
7 Set channel-2 to 1.0 V/d iv.
8 Set channel-2 offset/position to approximately +3.5 V.
9 Set the scope’s timebase to 200.0 µs/d iv.

If your probes are properly compensated, you should see two 1 kHz square waves
with a very flat response on your scope’s display similar to Figure 21. Let’s now
adjust the probe compensation on each probe.

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 Basic Oscilloscope and WaveGen Measurement Labs 2

Figure 21 Using the scope’s 1 kHz probe compensation signal to compensate 10:1 passive
probes

10 Using a small slotted screw driver, adjust the variable capacitor located on the
body of each probe. Note that this adjustment is sometimes located near the
BNC connection end of some probes.
Figure 22 shows an example of the channel-1 probe (yellow waveform)
over-compensated, and an example of the channel-2 probe (green waveform)
under-compensated. If you don’t observe a near-perfect square wave, then
re-adjust the probe compensation on your probes until the waveforms on your
scope are similar to Figure 21.

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Figure 22 Improperly compensated probes

After your probes have been properly adjusted, so long as you continue to use
these probes on this scope, you shouldn’t need to re-adjust them the next time
you use the scope.
At this point you have completed the hands-on portion of this lab. If you are
running short on time and need to complete the last lab in this chapter, then skip
to Lab #6 and then read the content of the remainder of this lab later.

Computing the Proper Amount of Capacitive Compensation

If you are up for a challenge, compute the amount of compensation capacitance (C
comp) required for proper compensation using the following assumptions:

R tip = 9 M
R scope = 1 M
C scope = 15 pF
C cable = 100 pF
C tip = 15 pF
C parallel = C scope + C cable + C comp
C comp = ?

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 Basic Oscilloscope and WaveGen Measurement Labs 2

To compute the required amount of compensation capacitance (C comp), the

easiest method is to equate the time constant (1/RC) of the parallel combination
of R tip and C tip with the time constant of the parallel combination of R scope and C
parallel:

ã
R tip I C tip R scope I C parallel

Remember that C parallel is the combination of three capacitive elements in the

probe/scope model.
Another computational method would be to equate 9X the capacitive reactance of
C parallel with 1X the capacitance reactance of C tip. This will establish the same
attenuation factor contributed by capacitive reactances as the attenuation factor
contributed by the resistive-only network (10:1):

ã I
fC tip fC parallel

C comp = _______

Probe Loading
Besides properly compensating your 10:1 passive probes in order to achieve the
most accurate oscilloscope measurements, another issue that must be considered
is probe loading. In other words, will connecting the probe and scope to your
device-under-test (DUT) change your circuit’s behavior? When you connect any
instrument to your circuit, the instrument itself becomes a part of your DUT and
can “load” or change the behavior of your signals to some degree. If we use the
given values of resistances and capacitances listed above (along with the value of
C comp that you computed), we can model the loading affect of the probe and
scope together as the parallel combination of a single resistor and capacitor as
shown in Figure 23.

Figure 23 10:1 passive probe and scope loading model

For low frequency or dc applications, loading is dominated by the 10 M

resistance, which in most cases should not be a problem. But what if you are
probing a 100 MHz digital clock signal? The 5th harmonic of this digital clock,

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which is a significant component in creating the shape of this signal, would be

500 MHz. Now compute the reactance contributed by the 13.5 pF capacitance of
this loading model shown in Figure 23:

Xc ã ã ã
fC I I I I
Š

Although 13.5 pF may not sound like much, at higher frequencies this amount of
loading capacitance can be significant. For higher frequency applications such as
this, most scope vendors provide optional active probing solutions that have
significantly lower input capacitances (sub pF). But these types of special probes
cost significantly more than the typical 10:1 passive probe.
Lastly, be aware that the probe + scope models presented in this lab are very
simplified. More accurate models would include inductive elements as well. Wire,
especially your ground lead, should be considered as an inductive element,
especially for high frequency applications.

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