Top Tips for Buying an Oscilloscope

Before purchasing an oscilloscope, consider the following tips and guidelines:

  1. Stay away from analog. Unless you are a collector, don't buy an analog oscilloscope. An analog oscilloscope has few, if any, advantages over that of a digital oscilloscope. No manufacturers make new analog scopes nowadays and they often have limited performance and availablity of parts.

  2. Bandwidth. As a general rule of thumb, purchase an oscilloscope with a bandwidth five times (5X) higher than the maximum frequency of the signal you need to measure. This ensures an accurate representation of the waveform. High-bandwidth scopes can be quite expensive, so you may have to compromise somewhat on this.

  3. Sampling rate. Most oscilloscopes have two different sampling rates or modes: real-time sampling (RTS) and equivalent-time sampling (ETS). These are specified in mega- or giga-samples per second (MS/s or GS/s). When evaluating oscilloscopes, make sure you know which type of sampling the specification applies to. Manufacturers often list the higher specification in order to look good. However, ETS sampling only works with repetitive signals as it builds the waveworms over successive acquisitions. If your signals are mosly single-shot, transient or varying, you can only use RTS sampling, which is typically a couple of magnitudes lower in sample rate than ETS.

  4. Memory depth. Digital oscilloscopes store captured sample points in memory. The amount of memory the scope has determines how long it can store the signal before having to dump it. This can limit the effective sampling rate of the oscilloscope if there is insufficient memory. This is most apparent when zooming in on a signal. Memory depth = sample rate x time across display

  5. Channels
  6. . In today's digital world, a traditional 2-channel or 4-channel oscilloscope may not be enough to view all signals of interest. A mixed-signal oscilloscope (MSO) provides 2 to 4 analog channels and 16 digital channels for logic timing. This eliminates the need for a combined logic analyzer and oscillopcope solution or special software to isolate activity.

  7. Resolution. Many digital oscilloscopes are designed for digital signals and hence have an 8-bit resolution. If you need to view analog signals (such as for audio, automotive, or environmental monitoring), you will need to get a 12-bit or even 16-bit scope. At the higher resolutions, accuracy of 1% can be achieved, verus 3% - %5 accuracy for 8-bit oscilloscopes.

  8. PC vs. handheld scopes. If you need to take your oscilloscope out in the field, consider getting an external PC-based oscilloscope module that plugs into your laptop computer. Handheld oscilloscope can suffer from small displays that are hard to read outdoors, have a limited battery life, and are quite expensive for what they offer. Their main advantage is they are small and rugged and as such can be used in environments where a laptop would be too fragile.

  9. Probes
  10. . Some manufacturers skimp when it comes to oscilloscope probes. Probes should at least match, if not exceed, the bandwidth of the scope. Also make sure you get the right probe for the application. For very fast signals, consider getting an active FET-amplifier probe. For high voltages, buy a differential isolated probe.