To prepare you for later experiments in this course, we have designed a set of exercises to help you familiarize yourself with the capabilities of our oscilloscopes. Some of you have only briefly used 'scopes in your first year lab courses, while others may already be adept with them due to research experience. You should learn something either way, as the capabilities of scopes are truly impressive.

Before we get too far into how to use a scope, we should mention why we use them in the first place. After all, doesn't a multimeter measure voltage too? The answer, in short, is time. Multimeters are useful for measuring static quantities that change slowly, but if the phenomena we care about takes place in seconds or less it just can't keep up. Not to mention, even if it could update quickly enough you'd never be able to record the values to interpret what you were seeing. An oscilloscope solves both these problems by being able to capture a snapshot of changes over a timescale of our choosing.

While it may look rather like a largish electronic calculator that would be insanely complicated to operate with about a hundred tiny buttons and a 4.5“ wide screen, Don't Panic. Controls are put into reasonable groupings, and there is quite a bit of feedback given on the screen once you know how to look for it. As you work through these exercises, we'll introduce both the controls and the location of relevant feedback on the screen.

The front panel of our oscilloscopes. Get used to seeing it, we'll be using it a lot today.

The softkeys are the context-sensitive buttons just to the right of the screen. The Default Setup is usually towards the top-right corner of Tektronix instruments, but it varies from model to model.

• Start up the scope, then either wait for the time & date setup screen to pass or press one of the bottom 3 softkeys to get to the main screen
• Press the Default Setup button that's around the top right side of the scope.

Right now you should be seeing a yellow line in the middle of the screen with a bit of fluctuation to it. That's perfectly normal and the noise is probably some sort of 60 Hz signal that is picked up from power lines in the room.

• Press the yellow 1 button to select the first input channel
• Press it a second time to toggle the channel display off
• Press it a third time to toggle the display back on

As you do this, look at the left edge and bottom left corner of the screen. When the channel is turned on, the bottom part of the screen will display both the channel name and what the voltage scale is. In addition, a little yellow arrow indicates where the baseline of the signal is. (A blue arrow would indicate the baseline for channel 2).

• Turn the vertical position knob and watch the bottom part of the screen

The feedback text denoting the vertical offset is highlighted in pink

When you're turning the position knob, you can see that it shifts where the signal is displayed on the screen. This doesn't affect the values that you're measuring, but if you are trying to compare things and forget that you've shifted something then it can cause issues. Not only does it tell you what the offset is, it does so in both terms of a voltage and a number of divisions. This can be handy if you want to set a particular horizontal line on the screen as a reference point when you're looking at a signal.

• Turn the position knob just far enough that the signal can no longer be seen

The baseline of the trace is offscreen, denoted by the arrow in the top-left corner highlighted in pink.

Now, you'll see on the left-hand edge that instead of indicating a position, there will be a 1 with an arrow pointing down or up, depending on which way you shifted the signal.

• Change the vertical position to get your signal back on the screen, and note the number of divisions on the offset.
• Change the vertical scale up or down
• Tweak the vertical position just a bit to see what the new offset is

Our signal's back on the screen! Huzzah!

When you change the zoom level on a channel, the number of divisions that it is offset remains the same. So, if you were on a 1V scale with 1 division of offset and change to a 5V scale, you now have a 5V offset.

For a whole host of reasons that we won't get in to, there is often a good reason to use a cable that attenuates (reduces) the signal reading by a factor of 10 before it gets to the oscilloscope. This makes it the default assumption that you're using such a cable when you press Default Setup. However, when we're not doing that, we'll need to change one setting to properly read out voltages.

• Press the 1 button to bring up the channel 1 settings
• Press the fourth softkey to change the Probe 10X Voltage settings
• Press the middle softkey to change the Attenuation
• Use the multipurpose knob to set the attenuation to 1X

You'll need to do this any time you press the Default Setup button, unless you don't mind all your voltages being off by a factor of 10.

That's enough playing with the position of the signal, let's actually look at something. We'll use a function generator to start off with, since 'scopes are quite good at measuring periodic signals. We'll start with our faithful companion of periodic signals, the sine wave.

• Use a BNC cable to connect the first output channel of your function generator to the first input channel of your oscilloscope
• Turn the function generator on, and wait a bit for it to finish starting up
• Turn the function generator output on by pressing the Output1 button. It should light up green when you do this.
• Press the Default Setup button to restore your scope settings to a baseline state
  • Remember to change the Attenuation settings afterwards!

At this point, you should see something like the following on your scope:

The default state of the scope and function generator when both are on. Note that the Output1 button on the function generator is lit up

There are a few things that have changed, even though you can't see the whole signal yet.

• The trigger frequency detection has kicked in, and shows that you likely have a 1 kHz signal input.
  • See the pink highlight on the image of the scope
• The triggering system is active, as indicating by the Trig`d in green in the top center of the screen.
  • See the orange highlight on the image of the scope

The frequency estimation acts as a nice sanity check sometimes, but may not be the best way of reading out an unknown signal. More important is the fact that the scope is now properly triggering.

Now its time to get a better look at out signal. Thanks to the function generator, we already know what we should expect: a 1kHz sine wave that has a 5V difference between the peaks.

• Turn the Vertical Scale knob counter-clockwise to zoom out so that you can see the whole waveform. It should work well at a 1V scale.
• Adjust the horizontal scale to zoom in and out on the waveform

The same setup with the trace scaled to be visible. Note that the scale in the bottom-left says 10V; I forgot to reset the attenuation settings before taking the picture.

You'll eventually want to actually get some numbers out of the scope, rather than just looking at the squiggly lines.

• Count the number of vertical divisions that the sine wave spans. A division is the space between two of the dotted lines; each dot in the vertical lines is 20% of a division.
  • If you're a factor of 10 high, go check the probe attenuation like we showed you how to do earlier
• Count the number of horizontal divisions in one period. The spacing is given in seconds the bottom center of the scope.

This is how all measurements on oscilloscopes were made in ye olde days. Sure, you might use a ruler or means of magnifying the image, but for a good few decades that was it. With a digital scope, we've got some additional options that can make life easier.

Writing on the face of a scope is a good way to invoke the wrath of its owner, but we can do one better. The Cursor button will let us pick vertical or horizontal lines that we can draw across the screen and read out values with 50% less squinting.

The basic cursor menu. The location of the cursor button is outlined in pink, while the multipurpose knob is outlined in orange.

• Press the Cursor button, on the top row of buttons.
• Use the top softkey to change the Type to Amplitude.
• Use the multipurpose knob to move one cursor to the top of the sine wave.
• Select the other cursor by pressing the bottom softkey.
• Use the multipurpose knob to move the other cursor to the bottom of the sine wave.

Your screen should look something like the following:

The difference between the cursor positions is shown on the middle-right of the screen.

All that being done, you'll probably have something that's around a 5 volt difference. You'll also probably notice that the cursors only move one pixel at a time, so the readout is quantized. Long story short, that quantization factor is 4% of the voltage division you have selected.

• Push the top softkey again to change the cursors to Time.
• Move the first cursor to a peak of the sine wave.
• Push the bottom softkey to select the second cursor.
• Move the second cursor to the next peak of the sine wave.

Cursors being used for a time measurement

From here, you'll notice that there are some additional features to the time cursors. Not only do you get a readout of the time since triggering for each cursor, you get the voltage at that point as well as the frequency and period associated with the interval. Neat!

Another option we have is to use some of the scope's built in measurement features. This can be handy when there are multiple things you need to keep track of across both signals and the cursors won't cut it.

• Press the Measure button in the top middle row of the controls.

The measurement controls, with the button outlined in pink.

The right-hand side of the screen should now have options for measurement gating, the two input channels, the Math channel, and a Snapshot option.

• Press the second softkey to select Ch1
• Use the multipurpose knob to toggle on the Period measurement.

The scope with period and frequency measurements turned on. The period measurement it highlighted in pink.

There should now be a box in the lower-left side of the screen showing you the period of your signal.

• Rotate the multipurpose knob and turn on the Frequency option

You can turn measurements off by toggling them again. These scopes can show up to 6 automatic measurements at once.

• Use some of the other free slots to measure the Peak-Peak voltage, the Minimum voltage, and the Maximum voltage.

You might notice some more fluctuation going on here than you had with the cursors. That's because the scope is continuously calculating values based off of the current set of data it has gathered. The frequency in particular seems susceptible to wandering like this. Thankfully, the scope has a handy tool that helps us smooth out these fluctuations: the Averaging option.

Multiple measurements simultaneously selected for our signal.

Averaging is just what it says on the tin: It will collect data from multiple triggering events and average out the readings. For something with a well-defined period, this is amazing for eliminating random noise. Let's check it out.

• Press the Acquire button in the middle of the Horizontal control group
• Select the Average option
• Press Acquire again to toggle the menu off

The Oscilloscope's Acquire menu. The button is in the middle of the horizontal control knobs, highlighted in pink.

Even averaging only 16 times should be enough to get a rock solid reading on the measured values here. In fact, the scope manufacturer essentially expects that you'll use averaging when making measurements. To go back to normal:

• Select the Sample option

The middle choice (Peak Detection) is something that is used for hunting noise or fast events, we'll get to its uses later. You'll also notice that you can toggle the number of waveforms averaged from 4 to 128, with the downside being that you'll have to wait a while for things to settle for high averaging values

• Turn the cursors off before you continue

We only mentioned triggering earlier, but its time to go back to it again since it will be the cause of many of your scope woes. The problem is that the scope gathers data too quickly to be able to display it continuously on a screen. One way of dealing with this might be to set a refresh rate (e.g. 50 times a second), but that would become a headache if you were even slightly off from the frequency you wanted to look at. Instead, what we do is specify when to gather data. We do this by selecting a voltage (positive or negative) and a slope (again, positive or negative). Modern digital scopes are able to buffer data continuously, so they can effectively show you what happened before the trigger event! On the other hand, analog scopes could only start drawing after the trigger and thus started on the far left side of the screen instead of the center. Hopefully it will start making sense as we play with the controls

The trigger controls on our scope are grouped together on the right-hand side, consisting of a knob and two buttons. Well, that's not quite true. The Run/Stop and Single buttons on the top-right corner of the scope are somewhat related.

• Toggle the Run/Stop button a few times and observe what changes

The scope toggled down to stop. The control button is in the upper-right corner and turns red when the scope is stopped. Note that the triggering text now reads Stop in red, shown in the orange highlight.

The most obvious thing should be that the waveform stops changing. You'll also see that the indicator in the top center of the screen will change to red text reading Stop. At some point in your career you may very well spend time debugging things only to discover that the problem was you stopping the scope display.

• Press the Single button once

This should get the scope to gather a single trigger event and then stop, with the text Acq Complete in the top center of the screen.

• Press the Run/Stop button to go back to the regular operating mode.
• Change the Horizontal scale back to 500$\mu$s

Now let's play with the triggering itself a bit.

• Turn the Level knob on the far right side of the scope controls and observe what happens to the waveform
• Look at how the indicator arrow on the right side of the screen moves as you change the knob
• Look at how the triggering display in the bottom right level changes as you change the knob

The place the scope centers your signal should shift as you move the trigger level. If you look at the center of the screen, the voltage of the sine wave should match your triggering voltage as you shift things about. There's a caveat here…

• Turn the Level knob until it is above/below the waveform
• Turn it back and forth a few times to overlap or miss the waveform, watching the triggering indicator in the top center of the screen

You'll see that when you first move off the waveform, the status will change to Ready before switching to Auto and your screen turning into wiggly soup. This is a feature, not a bug! The idea is that if you don't have your triggering set up to work for your signal, you might still want to see something to get an idea of what you're looking at. Hence, the screen will be snapshoting your waveform at intervals that won't line up with its period. The specific rate isn't specified in the manual, and depends on what your timescale setting it. Enough of that for now; I'm getting dizzy.

• Adjust the trigger level to 0V by watching the readout in the bottom-right corner of the screen as you turn the knob.

Now that we're back to a know state, let's mess with some of the other options.

• Press the Triger Menu Button, just above the knob
• Toggle the Slope option a few times using the multipurpose knob and see what happens

Unless you've done something quite strange, your sine wave should be centered on a point where it is at 0V and decreasing. The little indicator in the corner will also flip directions.

• Toggle back to a Rising Slope
• Change the Mode to Normal
• Use the Level knob to set the trigger level off the edge of your waveform

New behavior! Now, instead of just showing you whatever, the scope will keep the last image that triggered it on the screen while it waits. You'll see that the indicator in the top-center of the screen will now read Ready instead of Auto. Normal triggering is generally more useful for intermittent events, when you don't know when the next one will happen but you don't want to look at dead time inbetween. But, if you want to see something anyways…

• Press the Force Trig button (below the level knob) a few times

This lets you demand a refreshed signal now, which can help if you're not sure what's going on but don't want to tweak the trigger settings.

The other options here don't really make sense for this signal, so we'll save them for later.

We're going to be asking you to characterize signals both in these exercises and throughout the quarter during your experiments. So, let's define what that means.

• What type of waveform (or other thing) is it?
• What relevant voltages can you characterize it with?
• What relevant times can you characterize it with?
• What else is there to know about it?
• Include a photo (or screenshot, sketch, or plot) of the waveform
  • Annotation is not expected this week, but is generally helpful

For a sine wave, this would be (at a minimum) noting that it is a sine wave, what the amplitude is, if there's an offset (i.e. if the baseline is centered around 0V or something else. For a periodic signal this would be the difference between the maximum and minimum), and what the period is. Basically, enough information that someone would be able to tell if the thing they were looking at was the same or not.

The first waveform you were looking at. It could be characterized as “A sine wave with a 2.5V amplitude (or 5V peak-to-peak amplitude), no offset, and a frequency of 1 kHz.”

Next, disconnect your UChicago Signal Blackbox™ and re-connect the function generator.

Let's look at something a bit different: a square wave! Press the Home button on the function generator and select the Square option from the listing of continuous waves. You can do this either via the touch screen or using the blue right arrow beneath the dial on the function generator to change menus and then turning the dial and using it as a pushbutton.

• Using the cursors and measurement menu, characterize the frequency & amplitude of the square wave

Unless you've been playing with settings, it should match your sine wave here. However, we might also want to know something about just how “square” that square wave is. Do do that, you'll need to zoom in on the time scale. A lot.

• Adjust the horizontal scale until the transition between high and low voltages is visible and spans a division or more.

The screen should look something like the following:

A close-up view of a square wave's transition. Note the timescale here

There are any number of metrics you could use here to characterize how long the transition is, but one is to look at the time taken to go from one fraction of the initial value to a fraction of the final value. For electronic signals, 10% - 90% is standard.

• Using the cursors, measure the time it takes for the voltage to change from 10% above the baseline to 90% of its final value
  • Hint: Since the amplitude should be 5V, 10% of that is 0.5V. For the default settings, this means we would be measuring the time to change from -2V to 2V

You should get something on the order of a few to tens of ns here. You can also do this measurement via the built-in functions.

• Using the Measure menu, select the Rise Time option

The value you get here is probably pretty unstable, as on this scale there's likely to be some noise on your signal.

• Use the Acquire button to turn averaging on and observe the result

The utility of averaging in this case is the same as before, but it may not be sufficient to completely stabilize the readings. While doing this measurement I watched the rise time change by more than 10% of the average value. However, it took long enough that I couldn't see any difference visually. That, however, ties nicely into another scope feature we can use.

• Turn averaging off before you continue

Sometimes we want to compare a signal to itself under a differing set of circumstances. In other words, we want to create a Reference image. Thankfully, there's a handy way to do that in the form of a little white button on the scope!

Before we can view a reference, we need to first chose what trace to save. We can do so as follows:

• Press the Save/Recall button
• Use the top button or knob to change the Action to Save Waveform
• Make sure that the Save To destination is Ref
• Make sure that the source is Ch1 and the To option is RefA
• Save your trace with the Save softkey

The bottom of the screen should read “Ch1 waveform saved to Ref A” after you do this.

Now that we've saved a waveform, we can recall it using the Ref button.

• Press the Ref' button (just to the left of Channel 1's vertical scale knob)
• Use the softkeys to toggle Ref A to On

The scope displaying a saved reference. The Reference button is outlined in pink.

The scope will now draw the saved trace in white, behind any other signals. This is handy to have when you're trying to optimize some difficult to characterize feature by being able to see how it changed relative to a baseline.

• Watch for a while to see how the transition of the square wave changes with time

There are limits to the reference feature; specifically that you can't make actual measurements with it. It only captures the image, not the underlying voltage & time measurements.

• Turn the reference off by going to the Refernce menu and toggling it via the softkey

There is another useful tool for comparing signals that's better for sporadic events

Since our scope has digitized its data, it is straightforward for it to be able to show us an image of what the trace has been doing in the past. To access this feature, do the following:

• Press the Utility button (Just above the horizontal controls)

The utility button, outlined in pink, and the display option, outlined in orange.

• Select the Display option via softkey
• Find the 'Persist' option's softkey
• Use the knob to cycle between no persistance, 1,2,5 seconds, or infinite
  • Set the option to Infinite for the moment

This will keep a darkened copy of every trace that's been displayed in the background. This is again only a visual indicator; you can't make measurements based off of the persistent image. But you can do things like use cursors to get a range of values, or estimate the frequency of events

• Use the cursors to estimate the amount of drift in the start & end of the signal's rise
  • Time cursors and counting boxes is fine here

An example of using time cursors and persist to make a measurement. Here I'm using the voltage division grid to identify when the persistent signal is at $\pm2$ V and placing the time cursors at those locations. In this instance, the fastest transition time is being identified. The pink lines on the screen indicate the intersection points.

To turn persistence off again, use the Utility Menu ⇒ Display option and change the Persist option to off

Detection of singular events is not as relevant to the electronics course this quarter. If you want practice you can jump to the PHY211 Tutorial page.

There are two kinds of data you can export from the 'scope. A *.jpg screenshot of what is currently shown on the screen, and a *.csv file with the voltage vs time data.

The lab computers are already set up so that you can copy a screenshot or data from them by using some Tektronix software. To do so:

• Connect the USB socket on the back of the scope to a jack on a computer with a cable
• Open up the Open Choice Desktop program from the desktop
• Press the Select Instrument button and select whatever option starts with USB
• Use the Get Screen button to capture a screenshot
  • Use the Waveform Data Capture if you want to pull numerical information from the scope

Alternatively, if you have a USB flash drive, you can plug it into the socket on the front of the scope to save your data. To configure what to save, do the following:

• Press the Save/Recall button
• Use the softkeys to set the Action you want.
  • Save All lets you save both an image and the voltage vs time data
  • Save Image gives you exactly what's on the screen when you press the button
  • Save Setup is used for saving all of the scope settings (offsets, zoom levels, trigger settings)
  • Save Waveform you've seen
  • Recall Setup is used for recovering settings you've saved in the past
  • Recall Waveform is an alternative to the Recall button menu
• You can change the behavior of the Print button here to either save all or save images.