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Oscilloscope Frequently Asked Questions

Updated on February 24, 2008
TDS3000B Series oscilloscope from Tektronix
TDS3000B Series oscilloscope from Tektronix

Oscilloscope Frequently Asked Questions (FAQ)

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 likely 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 an 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.

Lecroy WaveJet 300 Series Oscilloscope
Lecroy WaveJet 300 Series Oscilloscope

Any More Quesitons or Comments on Oscilloscopes?

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      5 years ago

      hello, i just want to ask, if i am using a current probe on an oscilloscope and get its measurement, is it really the specific amperes (current) that I measure. the physical measurement is in V, i need to make sure that it is also the current that I am measuring.

      say, i measure 400mV using current probe, is it really 400mA? Please advise. thanks.

    • profile image


      6 years ago

      hi, I need to measure switching speed from oscilloscope, can anybody suggest me?

    • profile image


      7 years ago

      how do i analyse a frequency spectrum FFT reading for a low-pass filter?

    • profile image


      8 years ago

      hi, i was wondering.

      im using an oscilloscope to investigate pulses from ultrafast femtosecond laser.

      first of all, i know the oscilloscope can't cope to measure the femtosecond pulse, however, i was told it can only capture the pulse trains, so my question is, what does the 'period' of the signal it the maximum period(duration of the pulse it can cope?) or what? thanks in advance.

    • profile image

      Function Generators 

      8 years ago

      I like the information give here about the ossilloscope. It can get quiet complicated, with very little information written in basic lay mans language. You have a great selection featured here.

    • profile image

      Mitch Albert 

      9 years ago

      I have an instrument that has 50 channels that outputs frequencies between 0.5 and 46000 hz. How can I identify the frequency for each channel? According to the manufacturer, it's a secret.


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