Tektronix - Probe Considerations for Low Voltage Measurements such as Ripple

Our thanks to Tektronix for allowing us to reprint the following article.

The probes that ship with an oscilloscope may not be the right choice for low voltage measurements

Nearly all oscilloscopes ship with 10X attenuation passive probes because this type of probe is the best choice for making measurements across a broad range of applications. To cover the widest range of applications, a general purpose probe is usually rated from DC to 500 MHz and is generally capable of measuring up to a few hundred volts. Users making low voltage measurements will often fall into the trap of using the 10X probe that came with their oscilloscope and they end up with inaccurate results because a 10X passive probe is not capable of making accurate measurements in the low millivolt range.

Probe Considerations when making Low Voltage Measurements

When making low voltage measurements, it is important to consider oscilloscope sensitivity, probe attenuation, system noise, probe grounding, probe input impedance, AC coupling, probe offset, and probe bandwidth.

1. Use probes with a low attenuation factor to maximize the oscilloscope’s vertical sensitivity

Vertical sensitivity indicates how much the oscilloscope’s vertical amplifier can amplify a signal. On most Tektronix oscilloscopes, the most sensitive vertical setting is 1 mV/division when no probe is attached. As shown in Figure 1, the measurement system’s smallest vertical scale factor will be 2 mV/division when a 2X probe is attached (Channel 1) is, and the smallest vertical scale...

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