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How to select a probe?

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Post time 2016-5-17 11:49:41 | Show all posts |Read mode
Below is a list you need to consider when you choose a probe for a given measurement.

Input resistance

Input impedance is used to describe the loading effects of a probe. At DC and low frequency ranges, the probe's resistive component is the main factor that loads down the circuit under test. But as the frequency goes up, the capacitance of the probe tip, in parallel with the input impedance of the probe, resulting in greater loading and a more adverse effect to the target.
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 Author| Post time 2016-6-1 11:34:24 | Show all posts
Input Capacitance
Excessive input capacitance shows down the system's pulse response. Usually the least input capacitance possible is best.

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 Author| Post time 2016-6-2 12:25:56 | Show all posts
Maximum input voltage
To ensure user safety, help protect the oscilloscope input from destructive voltage, and avoid damage to the probe, select a probe that is rated for a higher voltage than the signal you intend to test.

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 Author| Post time 2017-4-20 09:29:13 | Show all posts
Bandwidth
The rated bandwidth of a probe should match the one of oscilloscope and be adequate for the test signal.But at higher frequencies, grounded lead inductance and input capacitance often influence system performance more than probe bandwidth.

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 Author| Post time 2017-5-3 15:56:19 | Show all posts
Attenuation
Choose the attenuation ratio of the probe (X1, X10, X100, X1000) to match the test signal amplitude to the vertical sensitivity range of the oscilloscope.

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 Author| Post time 2017-5-4 16:29:27 | Show all posts
Probe compensation range

Most passive probes have a specification that lists the oscilloscope input capacitance
range over which they can be used. When choosing a passive probe, be sure that the
oscilloscope's input capacitance lies within the probe's compensation range or you will
not be able to adjust the probe to chieve a correctly compensated square wave signal.


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 Author| Post time 2017-5-5 15:25:11 | Show all posts
Edited by WisdomAugust at 2017-5-5 15:27

Most oscilloscopes have 1 ohm input resistance. This input resistance
is in parallel with the input capacitance. Normally, high-frequency probes
with attenuation factors grater than X1 have adjustable compensation
networks built into them. Adjusting this compensation network provides
the best possible frequency linearity over the oscilloscope's desinged
frequency range. Operating instructions provided with probe explain
how to adjust the compensation network to obtain best signal fidelity.


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 Author| Post time 2017-5-8 11:47:29 | Show all posts
To select the appropriate probe, the first thing to do is to understand
the impact of the probe on the test, which includes the meaning of 2 parts:
1) the impact of the probe on the to be tested circuit;
2) The signal distortion caused by the probe.
The ideal probe should have no effect on the to be tested circuit, meanwhile
no distortion on the signal. Unfortunately, there is no such a probe to meet
these two conditions at the same time, usually need to do some trade-off
between the two parameters.

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 Author| Post time 2017-5-9 10:41:50 | Show all posts
In order to consider the impact of the measurement of probe,
usually we simply take the probe model as a R, L, C model,
and analysis the model and to be tested circuit together.



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 Author| Post time 2017-5-10 13:22:33 | Show all posts
First, the probe itself has an input resistance. The same theory as
testing voltage by multimeter, in order to minimize the impact of
the to be tested circuit, requires the input resistance (Rprobe) of
the probe itself as much as possible. However, because it's impossible
for Rprobe to be infinity, shunting will be generated with the to be
tested circuit, and the actual measured voltage may not be the
the real voltage on probe point, which is ofter encountered on some
power or amplifier circuit test. To avoid the impact of the load resistance
of the probe, there is the level required of Rprobe-10 times more than
Rsource and Rload. Most of the probe's input impedance is between
10K ohms and 10M ohms.

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