True-Rms Ac Measurements - Rigol DM3068 User Manual

Chapter 5 Measurement Tutorial

True-RMS AC Measurements

The AC measurement of DM3068 has true RMS response. The power dissipated in
a resistor over a period of time is proportional to the square of the measured true
RMS voltage, whatever the waveform shape is. The DM3068 can accurately
measure the true RMS voltage and current if the waveform shapes whose energy
beyond the effective bandwidth of the multimeter can be negligible. The effective
AC voltage bandwidth of DM3068 is 800 kHz and the effective AC current
bandwidth is 100 kHz.
The multimeter's ACV and ACI functions measure the "AC coupled" true RMS value,
that is to measure the RMS value of AC component (DC component is filtered)
from the input signal. As shown in table 5-1, since the sine, triangle and square
waves (50% duty cycle) do not have DC offset; each wave has an equal value in
AC and AC+DC.
Table 5-1 True- RMS AC Measurements of Sine, Triangle and Square waves
Waveform
V
0
V
0
V
0
t
-V
T
Non-symmetrical waveforms such as pulse trains contain DC component which will
be filtered during the AC coupled true RMS measurements.
The AC coupled true RMS measurement is especially useful for measuring small AC
signals having DC offset such as the AC ripple from DC power supplies. However, in
fewer cases the AC+DC true RMS value must be measured. First you can
User's Guide of DM3068
Crest Factor (C.F.)
2
3
1
AC RMS
V
2
V
3
V
C .F .
RIGOL
AC+DC RMS
V
2
V
3
V
C .F .
5-3