(2)
Root-Mean-Square
a n d
Peak Value Calculations
Y o u r V T - 1 7 3 , an voltmeter of absolute-mean value
indication type, reads root-mean-square values of
sinusoidal w a v e inputs. A l s o , it deflects the pointer in
proportion to the absolute-mean value of a given input
wave.
If the f o r m f a c t o r ( = root-mean-square v a l u e / a b s o l u t e
mean value) of the input wave and the crest ( = peak
value/root-mean-square v a l u e ) are known, then the
root-mean-square value and peak value can be cal-
culated as f o l l o w s .
Be sure to use the H O L D ( m a n u a l ) mode to measure
non-sinusoidal w a v e voltage.
a . Assume t h a t the meter reads x .
2 - v / T
• Absolute mean v a l u e = x = 0.9 x .
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• Root-mean-square v a l u e = ( A b s o l u t e mean v a l u e )
x ( f o r m f a c t o r ) .
• Peak v a l u e = (Root-mean-square value) x ( c r e s t ) .
b. F o r rectangular waves, their f o r m f a c t o r is unity
(1) and the crest unit (1).
2 ^/~2~
• Absolute mean v a l u e = x ^ 0 . 9 x .
71
• Peak v a l u e = 0 . 9 x .
c. F o r sawtooth w a v e s , their f o r m f a c t o r is
2
/ v ^ a n d
the crest A
/3".
• Absolute mean value = x ^ 0.9 x .
7Z
• Root-mean-square value =
2 v T
2
4 V T
—
x
7 ¥
x
=
^
x
%
1
0
4
x
"
• Peak v a l u e = ~ = x
v
/
T x = - ^ - ^ x = i . 8 x .
K
V
3
71
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