Ac-Coupled Ac Measurements; Ac And Dc Waveform Components - Fluke 8062A Instruction Manual

8062A
Instruction Manual
complex ac signals. Since rms is the dc equivalent to the original waveform,
it can be used in the relationships derived from Ohm's law (E = I x R), and
provides a reliable basis for comparing dissimilar waveforms.
Most meters in use today have average-responding ac converters rather than
true rms ac converters like the 8062A. Usually the gain in average-
responding meters is adjusted so that the reading gives the rms value,
provided the input signal is a harmonic-free sinusoid. However, if the signal
is not sinusoidal, the average-responding meter does not give correct rms
readings.
The 8062A ac converter actually calculates the rms value through analog
computation. This means that 8062A readings are accurate rms values not
only for harmonic-free sinusoids, but also for mixed frequencies, modulated
signals, square waves, sawtooths, 10%-duty-cycle rectangular pulses, etc.

2-13. AC-Coupled AC Measurements

Input signals are ac-coupled in the ac functions. One of the major advantages
of ac-coupling is that ripple measurements can be made on power supplies,
phone lines, etc. Ripple measurements cannot be made with dc-coupling.
Remember, however, that when the 8062A measures signals with the ac
voltage function, the reading on the display does not include the dc
component (if it exists). For example, consider the waveform in Figure 2-7.
The ac voltage function will measure the ac rms component. The dc voltage
function will measure the dc component. To obtain the total rms value for
such a waveform, first measure the ac and dc values separately, then
calculate the total rms value using the formula given in Figure 2-7.
AC Component
DC Component
0V
(ac rms component) 2 + (dc component) 2
RMS Total =
dy09f.eps
Figure 2-7. AC and DC Waveform Components
2-12