Question: Could you provide me with a few simple examples on using an oscilloscope to measure voltages, both AC and DC?
I am a novice user and I need to learn skills on how to use the scope safely and correctly to measure AC and DC volts so that I can pass this information on to my students.
Can I connect an o’scope to the output of a DC power supply and calculate the voltage output using the calibration controls?
Or, what would be the easiest way to view an AC sine wave on the CRT? Are there other simple circuits that can be constructed using resistors and capacitors that will support my needs? Can you tell me where to find these directions or are there some examples you could share with me that you know work?
Sincere Thanks!
Answer: I see from your email address that you work with K-12 students; I’ll assume that your students are in high school, possibly in a basic electronics course.
Many basic oscilloscopes today offer features to make it really simple to operate the scope. Autoset is a popular one; when you push autoset, which is usually a button on the front panel, the scope will automatically identify the type of waveform and adjust controls to produce a usable display of the input signal. It’s one of my favorite buttons.
Auto-ranging is another common feature. With autoranging, the scope automatically scales each waveform as you move your probe from test point to test point. With these features, looking at a DC or AC voltage signal, is usually as simple as probing the signal and pressing “Autoset”. The scope will do the rest.
Most basic scopes also include a passive voltage probe for each channel of the scope. These probes can look at both AC and DC voltages. You’ll want to make sure you attach the ground lead of the probe to the ground of your circuit to provide an accurate reference point for the scope’s measurement. Then, you just touch the probe tip to the signal, press “Autoset” and voila, you’ll see your waveform.
Probes also provide many different probe tips to help you connect to your signal. A bare probe is usually a hard tip that you can jab in to a circuit board trace to probe the signal. The micrograbber tip can be put on top of the probe tip and allows you to “hook” on to a lead or bar or wire on your circuit. I imagine these will be the two tips you use the most.
In your application, my biggest concern would be safety. You could certainly look at the output of an AC/DC power supply to see a DC voltage; however, you’ll need to be extra careful to choose a low power output supply in case the student touches the signal. You could also use a basic function generator to produce a range of signals, including sine waves, to look at. With a function generator, you could connect the output of the generator directly to the scope with a BNC cable.
If your goal is to simply introduce students to the concept of voltage signals, and basic electronic components, have you considered using one of those children’s electronic toys where you create different circuits by snapping in different components? These toys have AC/DC power supplies, resistors, capacitors and a variety of other basic components, all clearly labeled. If you find one where the traces are exposed on the board, you can probe around the board with your scope and see how the different components work. You might want to add a current probe to your test setup so you can look at both current and voltage. This should be a safe option for use with students.
If you would like to build up a circuit, several EE professors at universities like UC Berkeley publish their lab courses. Tektronix also has an education site (www.tektronix.com/education) with lab resources to help you.
Good luck! It sounds like you are creating quite an interesting class. My high school didn’t offer an electronics class. However, my father who is also an engineer, did buy me my own “Create Your Own” electronic circuits toy when I was a kid. Perhaps I’ll bring my scope home this weekend and take a closer look at that toy.
Scope Guru 