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2 GENERAL DESCRIPTION
The instrument carries out the following measurements:
• DC and AC voltage.
• Detection of AC voltage without contact (VoltSense)
• AC current
• Resistance and test continuity.
• Diode test
The instrument, depending on the measured parameter, automatically switches between
these functions. Is there also a key which performs two features: the switch on/off of the
instrument and the HOLD function (see § 4.2.1 for details). The selected quantity appears
on a high-contrast LCD display with indication of measurement units and functions.
2.1 TRMS AND MEAN VALUE MEASURING INSTRUMENTS
Safety testers for alternate quantities are divided into two big families:
• MEAN VALUE instruments: instruments which measure only the value of the wave at
the fundamental frequency (50 or 60 Hz).
• TRUE ROOT MEAN SQUARE instruments, also defined as TRMS: instruments which
measure the true root mean square value of the quantity under test.
In presence of a perfectly sinusoidal wave, both families provide identical results. In
presence of distorted waves, instead, the readings are different. Mean value instruments
provide only the value of the fundamental wave while True RMS instruments provide the
value of the entire wave, including harmonics (within the passband of the instrument).
Accordingly, if the same quantity is measured with both kinds of instruments, the
measured values are identical only if the wave is purely sinusoidal. Should it be distorted,
True RMS instruments provide higher values than medium value instruments.
2.2 TRUE ROOT MEAN SQUARE VALUE AND CREST FACTOR DEFINITIONS
The current effective value is defined as follows: "In an interval of time equivalent to a
period, an alternate current with effective value having an intensity of 1A, by passing on a
resistor, disperses the same energy which would be dispersed in the same period of time
by a direct current having an intensity of 1A". From this definition comes the numerical
1
expression: G=
T
The Crest Factor is defined as the ratio between the Peak Value of a signal and its
effective value: CF (G)=
for a purely sinusoidal wave it's worth
assumes higher values as long as the wave distortion is higher.
+T
t
0
2
The effective value is indicated as RMS (root mean square).
g
) (
t
dt
t
0
G
p
. This value varies according to the waveform of the signal,
G
RMS
2 =1.41. In presence of distortions the Crest Factor
EN - 4
HT100
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