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HEWLETT-PACKARD
JOURNAL
T E C H N I C A L I N F O R M A T I O N F R O M T H E h p - L A B O R A T O R I E S
5LISHED BY THE HEWLETT-PACKARD COMPANY, 1501 PAGE MILL ROAD, PALO ALTO, CALIFORNIA JANUARY, 1964
An RMS-Responding Voltmeter
With High Crest Factor Rating
IN TYPICAL electronics work, measurements of
ac voltage are most often made with voltmeters
that respond to the average value of the rectified
voltage waveform or to the peak. In most cases
such measurements are completely satisfactory,
as confirmed by the popularity of such voltmeters.
At the same time, however, there are occasions
when a measurement based on the true rms value
of a voltage is desired. Measurements of electrical
or acoustic noise, of low-duty-cycle pulse trains,
and of voltages of undetermined waveform are
instances wherein an rms-responding voltmeter
is valuable.
A new voltmeter has now been developed that
both responds to the rms value of the ac waveform
and has a high crest factor rating. This rating is
the measure of the voltmeter's ability to read the
rms value of waveforms that have a high peak-
to-rms ratio such as low-duty-cycle pulse trains
(see pp. 4, 5).
Fig. 1. Hewlett-Packard Model 3400A RMS Volt In other respects the new voltmeter is as con
meter indicates root-mean-square value of complex
waveforms having frequency components within 10 venient to use and has as wide a measuring range
cps to 10 Me passband. Large crest factor of 10 to 1 as the best average-responding types. Its voltage
enables accurate rms voltage measurements on nearly
all waveforms, including impulse noise and narrow range extends from 100 microvolts to 300 volts
pulse trains (see text). and its frequency range from 10 cps to 10 mega
cycles. Its crest factor rating is 10:1 which en
«.«S. VOLIS ables it to read at full scale the rms value of pulse
trains that have only a 1% duty cycle. At l/10th
of full scale, it will read pulse trains of only 0.01%
duty cycle.
-
SEE ALSO:
Cresf factor, pp. 4, 5
Fig. 2. Temperature-compensated taut-band meter has 7000-hr. Stability curves, p. 6
linear scales individually calibrated for each meter U. S. Frequency Standard p. 7
movement on -hp- servo-controlled meter calibrator.