FLASHMETER
EN - 4
2. GENERAL DESCRIPTION
The instrument carries out the following measurements in full Autorange:
DC
voltage
AC
TRMS
voltage
Detection of AC voltage without contact
Resistance and Continuity test
According to the quantity present at the input, the instrument automatically switches
between voltage and resistance measurement. The instrument is also provided with the
following function keys:
AutoHold/
to enable freezing the measured value on the
display and to activate the white light torch,
ON/OFF
and a central
V/
Ω
/
to manually
select resistance measurement and continuity test. The selected quantity appears on the
LCD display with the indication of the measuring unit and of the enabled functions. The
instrument is provided with a display backlight function which automatically deactivates
after approximately 2 minutes' idling. The instrument is also equipped with an Auto Power
OFF device which automatically switches it off approx. 15 minutes after the last time the
instrument was used.
2.1. MEASURING
AVERAGE
VALUES ANDTRMS VALUES
Measuring instruments of alternating quantities are divided into two big families:
AVERAGE-VALUE meters: instruments measuring the value of the sole wave at
fundamental frequency (50 or 60 Hz).
TRMS (True Root Mean Square) VALUE meters: instruments measuring the TRMS
value of the quantity being tested.
With a perfectly sinusoidal wave, the two families of instruments provide identical results.
With distorted waves, instead, the readings shall differ. Average-value meters provide the
RMS value of the sole fundamental wave; TRSM meters, instead, provide the RMS value
of the whole wave, including harmonics (within the instruments bandwidth). Therefore, by
measuring the same quantity with instruments from both families, the values obtained are
identical only if the wave is perfectly sinusoidal. In case it is distorted, TRMS meters shall
provide higher values than the values read by average-value meters.
2.2. DEFINITION OF TRUE ROOT MEAN SQUARE VALUE AND CREST FACTOR
The root mean square value of current is defined as follows:
“
In a time equal to a period,
an alternating current with a root mean square value of 1A intensity, circulating on a
resistor, dissipates the same energy that, during the same time, would be dissipated by a
direct current with an intensity of 1A
". This definition results in the numeric expression:
G=
T
t
t
dt
t
g
T
0
0
)
(
1
2
The root mean square value is indicated with the acronym RMS
.
The Crest Factor is defined as the relationship between the Peak Value of a signal and its
RMS value: CF (G)=
RMS
p
G
G
This value changes with the signal waveform, for a purely
sinusoidal wave it is
2
=1.41. In case of distortion, the Crest Factor takes higher values
as wave distortion increases.
