In electronic measurements, probes are critical components that connect circuits to instruments. Selecting the wrong probe can result in inaccurate measurements or even pose a safety hazard. When choosing a probe, consider the following four factors:

1. Voltage

Ensure that the maximum voltage rating of the probe and oscilloscope is significantly higher than the highest possible voltage of the signal (including peaks and overshoots), leaving sufficient safety margin.

2. Frequency

The probe bandwidth must be at least three times the highest frequency of the signal. For digital signals, the formula is: Bandwidth (MHz) ≥ 350 / Rise Time (ns). The probe bandwidth must not become a bottleneck in the entire measurement system.

3. Check the impedance

Probes can “load” the circuit, affecting measurement results: High-impedance circuits: Use probes with high input resistance and low input capacitance (such as active probes) General circuits: Standard passive probes are sufficient

4. Consider the measurement point

Measuring voltage to ground: Use passive/active voltage probes Measuring voltage difference between two points or floating ground systems: Must use differential probes

Remember: The performance of the entire measurement system depends on its weakest link. A good oscilloscope paired with poor probes is like a good car with poor tires—it cannot perform to its full potential.