Now that you know a little bit about the four basic instruments
that you'll be using for your lab experiments from Lesson 1,
let's now focus on how to properly scale waveforms on the oscilloscope.
Hi, I'm Johnnie Hancock, Product Manager for Keysight Technologies InfiniiVision oscilloscopes.
Let's pick up where we left off in Lesson 1.
Here, you can see our two waveforms from the resistive divider circuit,
but you're not likely to walk into your lab and see it already set up for you.
In fact, it could be in a very strange setup condition, special modes
that one of your fellow students used in the previous lab session.
My first recommendation is to press Default Setup.
On your scope, it may be called preset or maybe clear.
Here's Default Setup here.
When we press Default Setup, it's going to go to a standard configuration,
and it's not going to be set up right, but it turns off all special modes.
After pressing Default Setup, there are three main things you need to adjust:
The vertical scaling, the trigger level, and the horizontal.
Let's take a closer look at the front panel over here,
and those three adjustments are in three sections of the scope.
This section here is called the vertical scaling section.
It's usually located just above the input/DNCs.
Then, there's the horizontal section, that's this top section up here,
and the trigger section, and this is the trigger level knob.
These two sections, the horizontal and trigger, on different vendors' oscilloscopes,
they could be located in different places.
My suggestion to you is look at your scope and find those three sections,
vertical, horizontal, and trigger.
What do we mean by adjust the vertical scaling?
Here's the vertical section.
There's a big knob there.
Some scopes, there are dedicated scaling knobs for each channel.
In this particular scope, there's one set of scaling knobs,
and they're multiplex, so if I want to adjust Channel 1,
I press the 1 button, rotate the knobs, 2, rotate the knobs and so on.
Let's adjust the vertical scaling.
We can see our sine wave here from the default setup.
It's a bit too small, so let's expand it.
That's expanded too high.
You want it to fill up at least half of the screen.
If I click it, then I get a fine increment of adjustment.
Click the knob again, I get big jumps.
Notice as I'm changing this scaling, this number up here is changing.
We'll get back to that in just a minute.
The next step is to adjust the trigger level.
Triggering is really important, and we're going to get to that in a later lesson.
This is the trigger level.
As soon as I rotate the knob, a horizontal line pops up and shows me where the level is.
If I move it up above the waveform, the scope loses trigger.
I haven't explained what that is yet, but all you see is a blur of signals.
For now, just set it about the middle of the waveform.
The last step in setting up scaling is the horizontal,
how is it scaled horizontally.
If I rotate this large knob up here in the horizontal section,
rotate it clockwise, now it's spreading the signal out, showing less cycles.
If I rotate it the other way, it shows more cycles.
My suggestion is to get a couple cycles on screen.
If you rotate any of these knobs the wrong direction, just go back the other direction.
It's very easy.
Now, we've got the input signal.
This is Channel 1 of the oscilloscope, it's probing on the Vin of our circuit.
What about the output, the volage across R2 to ground?
Let's turn on Channel 2, so I'm probing it in the proper place,
and now we just do exactly like we did before, but now we only need to scale the vertical.
The horizontal is already scaled for us, and we're triggering on Channel 1.
We don't have to adjust those.
Now we just, again, adjust the vertical scaling knob.
Again, you can see this number change.
Now, you can see the Channel 2 waveform, which is Vout, across R2.
Back to those numbers at the top of the screen.
Up here, you can see this says 2.00 V/div.
It doesn't say division, but that's what it means.
That's telling you the scaling of the Channel 1 waveform.
We can use that to get an estimate of what the amplitude is of the Channel 1 waveform.
Let's see how big is the Channel 1 waveform.
I'm going to reposition it a little bit here, position it up here.
There are divisions on screen.
That's these white lines.
The distance between the white lines is called a division.
The yellow waveform, Vin, from top of R1 to ground,
one, two, three, four, five, it's about five divisions high,
times 2 V per division tells you that it's about 10 V pk-pk.
That's exactly what we expect.
What about the Channel 2 waveform?
It looks like it's the same size as the Channel 1 waveform, but it's not really,
because the scaling factor says 200 mV per division, or .2 V per division.
We can count the number of divisions, one, two, three, four, five,
times 200 mV per division is about 1 V.
Again, exactly what we expect based on the schematic, the circuit that we're probing.
What about timing?
This number up here, notice if I change the time scale, this one also changes,
tells me what the horizontal scaling is.
What is the period of one cycle?
I can see that it's about one, two, three, four, five divisions wide,
times 10 μs per division tells me that it's 50 μs for one period.
If you take the reciprocal of that, that tells you what the frequency is, it's 20 kHz,
and that's exactly what I have set as the output of the function generator.
I'll let you in on a little secret.
There's a special button that you shouldn't use.
It's called auto scale.
It will automatically set up the scope for you.
On your scope, it may be called auto set or something like that.
I suggest not using that button.
First of all, it doesn't always work.
If you have a very low frequency signal, it won't work.
If you have a very complex signal, it won't work.
Most of all, you're not going to learn how to use the oscilloscopes.
Your professors or lab coordinators,
there's a command that they can download into the scope
that they can get from our company that disables that button
so that you learn how to use the scope.
You've now got the basics on how to set up your oscilloscope and properly scale waveforms.
We also covered how to make quick estimated measurements of your signals
by counting divisions and multiplying by vertical and horizontal scaling factors,
which was the only way they could be performed
back when I was studying electrical engineering in college.
Later during this video series,
we'll talk about better and more automated ways to perform measurements on your waveforms.
In our next lesson, Lesson 3, we need to take a step back and talk about probing.
How do we get the signal into the oscilloscope in the first place?
Remember, Keysight has lots of technical resources on oscilloscopes for engineering students
that you can download at the URL listed on your screen.
One of those resources is this poster that you can download.
This poster summarizes what we just covered in Lesson 2.
You might want to talk your lab coordinator in to hanging this poster up in your circuits lab,
or, if you're a super engineering geek, you might want to hang it up in your dorm room.
Nothing wrong with being a geek.
Without us geeks, this would be a pretty dim world.
See you in Lesson 3.
Go North Carolina A&T Aggies!