
Keysight E1412A Digital Multimeter User Guide
xliii
True RMS AC Measurements
Keysight E1412A Multimeter Application Information
AC Turnover Errors
Errors are generated when the multimeter's input LO terminal is driven with an
ac voltage relative to earth. The most common situation where unnecessary
turnover errors are created is when the output of an ac calibrator is connected to
the multimeter “backwards.” Ideally, a multimeter reads the same regardless of
how the source is connected. Both source and multimeter effects can degrade
this ideal situation.
Because of the capacitance between the input LO terminal and earth
(approximately 200 pF for the E1412A), the source will experience different
loading depending on how the input is applied. The magnitude of the error is
dependent upon the source's response to this loading. The multimeter's
measurement circuitry, while extensively shielded, responds differently in the
backward input case due to slight differences in stray capacitance to earth.
Because of this, the 100Vac and 300Vac ranges may latch up for high voltage,
high frequency “backward” inputs. Therefore, only drive the high terminal when
measuring ac voltages. You can use the grounding techniques described for dc
common mode problems to minimize ac common mode voltages (see Common
Mode Rejection (CMR)).
Содержание E1412A
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