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User's Manual
True RMS AC Measurement
The AC measurement of the UT8806E has a true RMS response. The average heating power of
a resistor over a period of time is proportional to the square of the RMS of the voltage applied
to the resistor over that period of time, and is independent of the waveform. The UT8806E
can accurately measure the RMS value of a voltage or current waveform when it contains
negligible energy outside the effective bandwidth of the multimeter.
The AC voltage and AC current functions of the multimeter can measure "AC Coupling" true
RMS, that is, the RMS value of the AC component of the measurement signal (the DC
component is filtered out). Since the sine, triangle and square waves does not contain a DC
offset, their AC RMS and AC+DC RMS values are equal, as shown in Figure Table 3-1.
Table 0-35 TRMS AC Measurement of Sine, Triangle and Square Waves
Waveform
Sine Wave
Triangle
Wave
Square
Wave
Asymmetrical waveforms, such as pulse trains, contain DC components that are filtered out
by AC coupling TRMS measurement.
AC coupling TRMS measurement is very suitable or measuring small AC signals that contain
DC offsets, e.g., measuring AC ripple in the output of a DC power supply. However, in some
cases, it is necessary to measure the AC+DC RMS value. In this case, the user can use the DC
Voltage and AC Voltage functions to measure the DC and AC components of the signal
respectively, and then calculate its AC+DC RMS value according to the following formula. The
DC voltage measurement need to be made with 6.5-bit precision for optimal AC rejection.
Instruments.uni-trend.com
Crest Factor
(C.F.)
V
C
.
F
DC
AC RMS
2
1
1
.
C
.
F
.
AC
DC
UT8806E Desktop Digital Multimeter
AC+DC RMS
V
2
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