19
If the input differs significantly from a sine wave, the reading is
incorrect as a different conversion factor would relate the average
value of the signal to its rms value (see table as below).
Correct measurements of non- sinusoidal wave forms can be made
directly with the true- RMS models.
The parameter which defines the degree of distortion of the wave
form and influences the measurement accuracy is the crest- factor
defined as the ratio of the peak value to the rms value.
AC Coupling
Input
Wave form
Peak
value
Vdc
+Vac
(TRMS)
Vac
Average
value
Vdc
Crest
factor
Sine wave
1.414 1.000 1.000 1.000
0
1.414
Full-wave
1.414 1.000 0.435 0.421 0.900
1.414
Half - wave
2.000 1.000 0.771 0.764 0.636
2
Square wave
1.000 1.000 1.000 1.110
0
1
Pulse
D= X / Y
K
D
D
=
−
2
2.000
2
D
2K 2.22K 2D
1
D
Triangle
wave
1.732 1.000 1.000 0.960
0
1.732
