How to select the right oscilloscope probes

• Single Ended Active Probes. As the name implies, an active probe is equipped with active circuitry in the probe head. Where passive probes meet their performance limitations, active probes shine. Due to their low capacitance, single ended active probes can deal with high frequencies, high speeds and avoid excessive loading. As you are moving into those ranges of measurements and need more accuracy, you likely will find yourself reaching for an active probe.

• Differential Active Probes Theseprobes are specifically designed to take differential measurements. Although they cost more upfront, this investment quickly pays off with accuracy and ease of use. Differential active probes remove common mode noise, have a much higher bandwidth, require no grounding and reduce probe loading by about 50% compared to a single ended probe. As these advantages translate into a significant performance boost, you might even end up using them when measuring single ended signals.
• Current Probes While the probes mentioned above all belong to the voltage probe family, these probes measure current and come both in active and passive varieties.While you can measure current from the voltage drop across a shunt resistor, current probes give a much cleaner picture of the current waveform. They eliminate measurement uncertainty and the need for complicated calculations by making measuring, documenting and sharing easy. Depending on their specifications, current probes can measure anything from very low to very high currents.

• Other types of probes High voltage probes can cover measurements in the kV range, provide high attenuation ratios and extra user safety. Optical probes convert optical signals to electrical ones so they can be viewed and analyzed on the scope screen. Logic probes are a great tool for debugging analog issues in digital systems. These and many other specialist probes available guarantee you will find the one for your specific measurement needs.

Next, you will want to consider what bandwidth your probe needs. For optimal performance, it needs to be equal to or exceed the bandwidth of your oscilloscope. Probe bandwidth should also be at least three times the signal frequency, but take rise times into account as well. Faster rise times greatly increase the bandwidth needed. Lastly, your probe and oscilloscope now form a system, make sure to calculate if the system bandwidth is sufficient to capture the full bandwidth of your signal.

You might also be thinking about compatibility. Most basic probes are BNC-terminated and compatible between scopes regardless of brand. Specialist probes might not be interchangeable, but have added features for ease of use. The AutoProbe interface on some Keysight probes, for example, can automatically detect which probe is being plugged in, and adjust the units the probe is measuring in accordingly.

However, any probe’s input resistance and capacitance should match those of the oscilloscope. You can make good use of a probe’s attenuation factor to extend the dynamic range of your oscilloscope. The probe itself will also have a dynamic range translating into a maximum input voltage, so make sure you are operating within those limits.

Lastly, don’t forget about the probe tip form factor. You will need to connect the probe to your circuit, and the right oscilloscope probe tip design will not only make your job easier but also improve measurement accuracy.