Chapter 8 Tutorial

Measurement Fundamentals

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dxu yq” MWW’s ac voltage measurement section performs input signal conditioning. All frequency counters are susceptible to errors when measuring low-voltage, low-frequency signals. The effects of both internal noise and external noise pickup are critical when measuring “slow” signals. The error is inversely proportional to frequency. Measurement errors will also occur if you attempt to measure the frequency (or period) of an input following a dc offset voltage change. You must allow the internal MWW’s input dc blocking capacitor to fully settle before making frequency measurements.

Error

1%

 

Input

10 mV, 10 Hz

0.5%

 

 

10 mV, 100 Hz

 

100 mV, 10 Hz

1 mV

2 mV

3 mV

Input Random Noise (RMS)

 

If the external noise pickup becomes large enough to exceed the hysteresis of the measuring circuitry, the frequency function may actually become unusable. External shielding and low-pass filtering may help.

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HP 34970A manual Measurement Fundamentals