Fluke PM6690 - Rms

V
RMS
When the waveform (e.g. sinusoidal, triangu
-
lar, square) of the input signal is known, its
crest factor, defined as the quotient(Q
CF
)of
the peak (V
p
)andRMS(V
rms
) values, can be
used to set the constant K in the mathematical
function K
*
X+L. The display will then show
the actual V
rms
value of the input signal, as
-
suming that V
pp
is the main parameter.
V
Q
V
rms
CF
pp
=
1
2
EXAMPLE: A sine wave has a crest factor of
1.414 (
2
), so the constant in the for
-
mula above will be 0.354.
Press
MATH/LIM and after that
Math®Math(Off)®K
*
X+L Press K=
and enter 0.354 via the
NUMERIC
ENTRY
keys. Check that the L con-
stant is set to its default setting 0. Con-
firm your choices with the softkeys be-
low the display. If the input is AC cou-
pled and
V
pp
selected, the display will
now show the RMS value of any sine
wave input.
If the sine wave is superimposed on a DC
voltage, the RMS value is found as:
0.354
*
V
pp
+V
DC
.IfV
DC
is not known it can
be found as:
V
VV
DC
MAX MIN
=
-
2
To display the rms value of a sine wave super
-
imposed on a DC voltage, follow the example
above, but set L = V
DC
.
V
RMS
4-23
Measuring Functions