Modern scopes add a variety of new measurement and math features to the vertical, horizontal, and trigger controls used over a span of decades.
In part 1 of this series, we looked at the features, such as the vertical, horizontal, and trigger controls that have appeared on oscilloscopes since the mid-20th century and that remain in use today. Now, we’ll take a look at recent additions that boost measurement speed and improve measurement accuracy.
Q: Before we move on, could we quickly review the vertical, horizontal, and trigger controls?
A: Sure. For this demonstration, I’m using a PicoScope 2204A from Pico Technology along with PicoScope 7 software running on Windows. Oscillocopes from other manufacturers offer a similar user interface and math features, but of course, the implementation details will vary. In Figure 1, I’ve set the scope’s internal signal generator to generate a 1-V peak 1-kHz sine wave, which is displayed on the instrument’s channel A. For vertical sensitivity, the PicoScope software asks you to enter the full-scale voltage range, or ±2 V in this case, equivalent to 400 mV per division. For horizontal sweep speed, I have chosen 500 µs per division. So we can eyeball the Figure 1 waveform and see that it measures 1 V peak, or 2 V peak-to-peak. Each cycle takes two divisions, or 1 ms, so the frequency is 1 kHz, confirming our settings on the signal generator.
Q: What about triggering?
A: Triggering is a complicated topic. You can trigger on various aspects of your time-domain signal or even on events occurring in the frequency or protocol domains. We’ll take a closer look in a subsequent article, but for this demonstration, each sweep triggers when a rising portion of the channel A signal exceeds zero.
Q: Wait, it looks like Figure 1 triggers when the input goes negative.
A: Good observation, and one that illustrates one of the differences between modern digital scopes and older analog versions. If you look at the horizontal axis labels at the bottom, you’ll see the times range from -2.5 ms to +2.5 ms. Triggering occurs at t = 0, indicated by the yellow diamond in the center of the display. Everything to the left occurred before the trigger. This pre-trigger information can be invaluable. If you set your scope to trigger on a fault condition (an overvoltage, for example), the pre-trigger information can help show you what led to the fault.
Q: What else can modern oscilloscopes do?
A: They have cursors or rulers that help take the guesswork out of interpreting displayed waveforms. PicoScope, for example, has rulers as shown in Figure 2, which help measure peak values and waveform periods. I’ve grabbed two horizontal rule lines from the top left and positioned them at the peaks of the sine wave, and I have dragged vertical rulers from the bottom left and positioned them at the rising zero crossings of successive cycles of the sine wave. The ruler function presents a table showing the deltas between the sets of ruler lines, showing that the peak-to-peak voltage is 1.986 V and the cycle width is 997.1 µs.
Q: What are the icons below the vertical and generator controls on the left?
A: Those represent measurement, math, and other functions that can speed your test applications. For example, I could have skipped the ruler lines in Figure 2 and simply clicked the measurements icon, which presents a menu of measurement functions related to amplitude, time, and other categories. In Figure 3, I have selected peak-to-peak voltage, RMS voltage, frequency, and cycle time, which you can see in boxes below the waveform display. Note that other manufacturers’ scopes have similar features, but you would access them differently.
Q: What else can we measure?
A: If you have a signal with high harmonic content, you may be interested in crest factor, the ratio of peak to RMS voltage. Figure 4 shows the crest-factor measurement for a triangle waveform.
Q: What about multichannel measurements?
A: Multichannel measurements are very important. Frequently, for example, you’ll want to compare a device under test’s input and output. In a subsequent article, we’ll look at multichannel measurements and demonstrate how to perform math operations on multiple channels of waveform data.
Continue to Part 3.
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Part 2 of getting the most from an oscilloscope focuses on optimizing measurements with digital features and proper vertical control. Modern digital scopes use automated tools like cursors and on-screen readouts for accuracy, while traditional controls like volts per division must be carefully set for scaling. It is also crucial to ensure your setup is correct, including using the right probe and performing a proper probe compensation.