Oscilloscope Frequently Asked Questions

What is an oscilloscope?

An oscilloscope is a piece of test an measurement equipment for measuring time varying voltages

Can I measure currents with an oscilloscope?

Yes, there are two ways to measure a current with an oscilloscope.

1. The simplest way is to add a resistor in series with the current you are trying to measure, and then divide the voltage shown on the oscilloscope by the resistance to determine the current.

2. A much more expensive way of measuring current is to use a current probe. Current probes are basically a loop that goes around the wire that has the current you want to measure. They inductivly couple the current signal for measurement for an oscilloscope.

What is a trigger?

On an oscilliscope, the trigger is what tells the scope to start saving data. Usually it is simply a voltage level. When the voltage being measured goes either above or below the trigger level the oscilloscope saves the data before and after the trigger for display on the screen. There are also more complicated triggers, that respond to sequences or glitches, and most digital scopes have an auto trigger feature that will display waveforms with out the measured signal crossing the trigger level.

Why do I see a different frequency output depending on my sampling speed?

If you see a faster frequency on your oscilloscope display when you increase your sampling frequency, it is likly that you were subsampling the waveform. This occurs when you sample something slower than the actual waveform itself. You always need to have your sampling speed at least two times your signal freqency on a digital oscilloscope to get an idea of the frequency of the signal. However, to actually look at the waveform and get meaningful information beyond frequency, you will need to sample faster than this.

Can I use a XX MHz oscilloscope to measure a X Hz signal?

Yes, for most digital oscilloscopes you can reduce your sample speed down to look at signal in the Hertz range.

What is infinite persistance, and how do I use it on my oscilloscope?

Infinite persistance on an oscilloscope just means that it leaves all of the traces of the voltage waveforms on the screen until you decide to to clear it. You can use this feature to see if you have any waveforms that are different than the normal waveform, or in other words, you can look for glitches.