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294 Keysight 34970A/34972A User’s Guide
AC Voltage Measurements
The main purpose of an AC “front end” is to change an AC voltage input into a DC
voltage which can be measured by the ADC.
Signal Conditioning for AC Measurements
Input signal conditioning for AC voltage measurements includes both attenuation
and amplification. An input coupling capacitor (C) blocks the DC portion of the
input signal so that only the AC component is measured. Ranging is accomplished
by combining signal attenuation from the first-stage amplifier and gain from the
second-stage amplifier.
The first stage implements a high input impedance (1 MΩ) switchable
compensated attenuator. The second stage provides variable-gain signal
amplification to scale the input to the AC converter to the full-scale level. Any
residual DC offset from the attenuator and amplifier stages is blocked by a
capacitor.
An AC voltage front end similar to the one discussed above is also used to
measure AC current. Shunt resistors convert the AC current into an AC voltage
which can then be measured. Current shunts are switched to provide selectable
AC current ranges.
C1MW
X 0.01
X1
A1
A2
X1
X10
X100
AC to DC
Converter
HI
LO
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