A sensor's output stage is characterised

PHYSICS · Multi-part · Fermi University Physics · Electronics, Instrumentation & Communication · Circuit foundations and passive networks · Circuit foundations and passive networks

Electronics for Measurement, Ch The bench: probes, cables, grounds and what the instrument shows

Problem

A sensor's output stage is characterised, in Thevenin form, by an open-circuit voltage

V_{\rm th}=2.00\,\mathrm{V}

(peak, sinusoidal) and an output resistance

R_{\rm th}=250\,\mathrm{k}\Omega

. It is observed with a

\times1

oscilloscope probe presenting

1\,\mathrm{M}\Omega

in parallel with

120\,\mathrm{pF}

at a signal frequency of

5.0\,\mathrm{kHz}

. ((a)) Using only the resistances (ignoring the probe's capacitance), estimate the fraction of

V_{\rm th}

that would appear at the scope. ((b)) Using the impedance divider with the probe's capacitance included, find the actual fraction of

V_{\rm th}

displayed at

5.0\,\mathrm{kHz}

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