Important specifications of oscilloscope probe

Since oscilloscope probe is a vital addition to an oscilloscope, knowing its basic specifications are necessary to ensure that it will meet the requirements of the intended application.

One of the most important specifications is accuracy, which is the probe’s attenuation of the signal such as that of a 10X probe. Relying on the accuracy of the probe’s series resistor, oscilloscope probe’s accuracy is also dependent on the accuracy of the probe’s input resistance. The oscilloscope probe accuracy specification is only applicable when the probe is utilized with an oscilloscope featuring the assumed input resistance.

Attenuation refers to the output signal’s ratio to the input signal in respect of voltage. Usual oscilloscope probe attenuation levels are 10 and 1 (for no attenuation). Meanwhile, probes featuring attenuation levels of 100, which are rarely available, are ideal for specialist applications.

Another important specification of an oscilloscope probe is bandwidth. The maximum bandwidth refers to the frequency where the response falls by the low frequency value’s 3dB. When purchasing an oscilloscope probe, the bandwidth’s value should be higher than the expected maximum frequency. It should also be above the bandwidth of the oscilloscope itself, to allow oscilloscope users to maximize its full potential. To achieve accurate amplitude measurements, the oscilloscope probe’s bandwidth should be five times higher than the waveform’s frequency.

The length of the cable should also be considered when purchasing an oscilloscope probe. The longer the cable, the lower the bandwidth of the oscilloscope probes. Usual cable lengths are 1.3 m and 2 m, and higher voltage probes may require longer lengths.

Compensation range refers to the oscilloscope’s input capacitance that can be compensated by the probe, while IEC 1010 is the safety rating of the oscilloscope probe.

The input capacitance specification of the oscilloscope probe relies to some extent on the probe capacitor’s adjustment and the oscilloscope’s capacitance.

Input resistance refers to the sum of the resistor in the probe and the input resistance of the oscilloscope.

Input voltage includes both AC and DC components. The maximum input voltage or the highest voltage that can be connected to the oscilloscope probe should always be specified in the probe. Passive probes can support hundreds of volts, while active probes can only tolerate a few tons of volts.

Meanwhile, rise time is the period needed by the pulse’s leading edge to rise from 10 percent to 90 percent of its final value. To ensure accurate rise time and fall time measurements of the pulse, the system’s overall rise time — that is of the probe and the oscilloscope combined — should be faster by three to five times than the quickest transition to be measured.

Other important oscilloscope specification includes the readout detection and the tip or head style of the oscilloscope probe.

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