How to select a probe?

WisdomAugust

We can see all the excellent features of the active probe are

brought by the front amplifier, but this high bandwidth amplifier

is expensive and need to be placed in a limited space in the

front of the probe, resulting in high cost.
General passive probe prices are hundreds of dollars or so,

while the price of active probes usually are thousands of dollars.
So the active probe is generally used in the need for the

occasion pf high measurement bandwidth.

WisdomAugust

However, the active probe is not no shortcomings, limiting the wide

usage of active probes besides price factors, the other reason is its

limited dynamic range. The input voltage range like this high bandwidth

amplifier is not very large, so its measurement range can not be as big

as the passive probe. Commonly used 10: 1 passive probe, its dynamic

range usually at hundreds of volts, and it’s just a few volts for common

active probes. So there will be some limiation for its application.

WisdomAugust

There is also a branch of the active probe, that is differential active probe.

The difference is that the front amplifier is a differential amplifier.
The advantage of the differential amplifier is that it can directly test the

high-speed differential signal, while its common mode rejection ratio is higher,

the common mode noise rejection ability is better.

WisdomAugust

Current probe is another kind of active probe. There’s a magnetic ring

on the front end of the current probe, when measure, the magnetic ring

cover on the measured power line. Because the generated magnetic

field when the current flowing through the wire, which was collected by

the magnetic ring, the magnetic flux in proportion to the current flowing

through the wire.

WisdomAugust

There’s a Hall sensor inside magnetic ring, which can detect

the magnetic flux and its output voltage in proportion to magnetic

flux. Therefore, the current probe output voltage is in proportion

to the measured current flowing through the wire. The conversion

factor for a typical current probe is 0.1V / A or 0.01V / A.

WisdomAugust

The main advantage of the current probe is that it can measure current without

disconnecting the power line. Based on the Hall effect, it can  measure both DC

and AC. Typical applications of current probes are system power measurement,

power factor measurement, and switching machine impact current waveform

measurements. The main drawback of the current probe is that its small current

measurement capability is limited by the bottom noise of the oscilloscope, so the

small current measurement capability is limited. Generally less than 10mA of

current is difficult to measure.