An oscilloscope, formerly known as an oscillograph, is a benchtop instrument that graphically displays electrical signals and shows how those signals change over time. They are used by engineers to troubleshoot circuits and check signal quality. Most engineers use a digital oscilloscope, which is what we’re going to focus on here. Digital oscilloscopes acquire and store waveforms, which show a signal’s voltage, frequency, the portion of the signal that is noise, whether the signal is distorted, the timing between signals and more.
But when it comes to choosing the best oscilloscope, how do you know which oscilloscope is right for your application? There are some primary factors to consider when you buy an oscilloscope.
Oscilloscope bandwidth
System bandwidth determines an oscilloscope’s ability to measure a signal. Specifically it determines the maximum frequency that the instrument can accurately measure. Bandwidth is also a key determining factor in the oscilloscope price.
Oscilloscope rise time
Rise time describes the useful frequency range of an oscilloscope, and this is a critical measurement in the digital world. Rise time is often considered when measuring digital signals like pulses and steps.
Oscilloscope sample rate
The sample rate of an oscilloscope is similar to the frame rate of a movie camera. It determines how much waveform detail the scope can capture.
Determine what you need – use the ‘five times rule’
Sample rate (samples per second, S/s) is how often an oscilloscope samples the signal. Again, we recommend a ‘five times rule’. Use a sample rate of at least 5x your circuit’s highest frequency component.
Oscilloscopes come with a wide variety of sample rates, from 1 to 200 GS/s, to meet the needs of your application.
The faster you sample, the less information you’ll lose and the better the scope will represent the signal under test. However, fast sampling will also fill up your memory quickly, which limits the time you can capture.
Channel density of an oscilloscope
Digital oscilloscopes sample analog channels to store and display them. In general, the more channels the better, although adding channels adds to the oscilloscope price.
Determine what you need
Your application will determine whether you need to choose an oscilloscope with two, four, six, or even eight analog channels. Two channels let you compare a component’s input to its output, for example. Four analog channels let you compare more signals and provides more flexibility to combine channels mathematically (multiplying to get power, or subtracting for differential signals, for example). Oscilloscopes with six or eight channels allows for multiple bus analysis while simultaneously viewing voltage or current type signals in a power related environment.
A Mixed Signal Oscilloscope adds digital timing channels, which indicate high or low states and can be displayed together as a bus waveform. Whatever you choose, all channels should have good range, linearity, gain accuracy, flatness, and resistance to static discharge.
Some instruments share the sampling system between channels to save money. But beware: the number of channels you turn on can reduce the sample rate.
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