Voltage Probes
Voltage probes are intended to measure or display voltages on the DUT. Ideally, the test instrument and its probe will not affect the voltage being measured. Practically, that translates into the test instrument and its probe presenting a high impedance that will not load the DUT. In many situations, an impedance with a resistive component of a megohm is adequate. For AC measurements, the reactive component of impedance may be more important than the resistive.
Because of the high frequencies often involved, oscilloscopes do not normally use simple wires to connect to the DUT. Instead, a specific scope probe is used. Scope probes use a coaxial cable to transmit the signal from the tip of the probe to the oscilloscope, preserving high frequencies for more accurate oscilloscope operation.
Scope probes fall into two main categories: passive and active. Passive scope probes contain no active electronic parts, such as transistors, so they require no external power.
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