Making Accurate DC Voltage Measurements in the Presence of Series Mode AC Signals

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Making Accurate DC Voltage Measurements in the Presence of Series Mode AC Signals. (86.33 KB)

Accurate DC voltage measurements are not normally made in the presence of significant series mode AC signals. Unwanted interference signals are avoided by use of appropriate lead and guarding configurations, and other best measurement practices. However, there are some applications where AC content is present – one example being the output of multijunction thermal converters, where relatively high coupling between the heater and temperature sensing elements results in a significant AC content on the DC output voltage. Another is measuring the DC offset at the output of an AC source. This paper explores typical precision digital multimeter (DMM) responses to and rejection of series AC mode signals, considers how their design architecture influences the response, and suggests useful avoidance tactics to preserve measurement accuracy.