Learning to use an oscilloscope involves learning the measurement and performance terms of an oscilloscope. Understanding the terms help users compare and evaluate an oscilloscope with other models, and choose the proper oscilloscope for his application.
Among the important performance terms and considerations are bandwidth, rise time, sample rate, waveform capture rate, triggering capabilities, record length, effective bits and frequency response.
One of the important terms is bandwidth, which determines the basic ability of the oscilloscope to measure a signal. The oscilloscope’s capability to display a signal decreases as the frequency of the signal increases. This specification represents the frequency range an oscilloscope can measure accurately.
The oscilloscope can not resolve high-frequency changes if it does not have sufficient bandwidth. Edges will vanish, while amplitude will be distorted and details may be lost. Without sufficient bandwidth, the oscilloscope’s features will mean nothing.
Describing the oscilloscope’s useful frequency range, rise time measurement is critical in the digital world. It is an important performance consideration when measuring digital signals, such as steps and pulses. The oscilloscope must have adequate rise time to capture the details of rapid transitions accurately.
Specified as samples per second (S/s), sample rate is the number of times a digital oscilloscope takes a sample of the signal. The higher the sample rate (i.e., the faster the oscilloscope samples), reduces the chances of losing critical information or events, while offering the displayed waveform more detail and resolution. Minimum sample rate is important when viewing slow changing signals over longer periods of time. Generally, changing the horizontal scale control will also alter the displayed sample rate.
The waveform capture rate of the oscilloscope is expressed in waveforms per second (wfms/s). It indicates the speed at which the oscilloscope acquires waveforms.
Varying greatly, the waveform capture rate depends on the oscilloscope’s type and performance level. Those with high waveform capture rates offers more visual insight into the behavior of the signal, while significantly increasing the probability that the oscilloscope will easily capture transient anomalies such as runt pulses, jitter, transition errors and glitches.
Vital for clear signal characterization, the trigger function of an oscilloscope synchronizes the horizontal sweep at the signal’s proper point. Trigger control enables users to capture single-shot waveforms and stabilize repetitive waveforms.
The number of points comprising a complete waveform record, waveform length determines the number of data that will be captured with every channel. Since an oscilloscope can only store a limited amount of samples, the sample rate will be inversely proportional of the waveform duration (time) of the oscilloscope.
Effective bits indicate the ability of the oscilloscope to accurately reconstruct the shape of the sine wave signal. It compares the actual error of the oscilloscope to that of an “ideal” digitizer. Since the actual errors include distortion and noise, the amplitude and frequency of the signal must be specified.
Other oscilloscope performance terms that users have to be familiar with include frequency response, vertical sensitivity, sweep speed, gain accuracy, horizontal accuracy (time base) and vertical resolution (analog-to-digital converter).
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