Tektronix TDP0500, Быстрый старт Руководство пользователя

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Probing principles
Input impedance and probe loading
When you connect the probe inputs to a circuit, you are introducing new resistance, capacitance, and inductance into the circuit.
Each input of the differential probe has a characteristic input impedance of 500 k
Ω to ground in parallel with less than 2 pF.
For signals with low source impedance and
frequency, the 500 k
Ω input impedance on
each input is large enough to prevent the inputs
from loading the signal sources. The greater
the source impedances and the higher the
signal frequencies, the more you should take
these factors into account.
The more the impedance of the signal source
on an input increases, the more the probe loads
the source and reduces the signal amplitude.
The frequency of the signal also affects signal
measurement. As the frequency of the signal
increases, the input impedance of the probe
decreases. The lower the impedance of the
probe relative to that of the source, the more
the probe loads the circuit under test and
reduces the signal amplitude.
42 TDP0500 & TDP1000 Quick Start User Manual