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Tutorial
302
Keysight 34970A/34972A User’s Guide
Current Measurements
Current measurements are allowed only on the 34901A module.
An ammeter senses the current flowing through its input connections –
approximating a short circuit between its input terminals. An ammeter must be
connected in series with the circuit or device being measured such that current
flows through both the meter and the test circuit.
A resistor, R
s
in the diagram below, is connected across the input terminals such
that a voltage drop proportional to the input current is generated. The value of R
s
is selected as low as possible to minimize the instrument’s
burden voltage
, or
IR
drop. This voltage drop is sensed by the internal DMM and scaled to the proper
current value to complete the measurement (
see the discussion on the following
page
).
AC current measurements are very similar to DC current measurements. The
output of the current-to-voltage sensor is measured by an AC voltmeter. The
input terminals are direct coupled (ac+dc coupled) to the shunt so that the
internal DMM maintains DC continuity in the test circuit. Performing AC current
measurements demands additional care. The
burden voltage
(loading) varies with
frequency and input inductance, often causing unexpected behavior in the test
circuit (
see the discussion on the following page
).
On-Card
Fuse
S1
Rs
LO
I
±VDC to Input Amplifier and
Analog-to-Digital Converter
