Keysight DAQ970A Guia Del Usuario página 240

4 Measurement Tutorials
Current measurements
Only supported on the DAQM901A multiplexer 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, Rs 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 Rs 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.
240 Keysight DAQ970A/DAQ973A User's Guide