HT9012
EN - 4
2 GENERAL DESCRIPTION
HT9012 meter can performs the herewith measurements:
DC and AC voltage
Detection of AC voltage without contact
AC current
Resistance and test continuity
Diode test
Each parameter can be selected by rotating the 8-positions switch included OFF position.
To abilitate the hold function the
HOLD
key is available. There are also
key to
activate/desactivate the display backlight, the
RANGE
key for manual selction of
measurement ranges, the
MAX
key for maximum value measurement of some parameters
and the
MODE
key for the selection of different features common at the same position of
selector rotation. The selected quantity appears on a high-contrast liquid crystal display
with indication of measurement units and functions. The instrument disposes of an Auto
Power Off function consisting in an automatic switching off 15 minutes after last selector
rotation.
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 cur
rent having an intensity of 1A”. From this definition comes the numerical
expression: G=
T
t
t
dt
t
g
T
0
0
)
(
1
2
The effective value is indicated as RMS (
root mean square
).
The Crest Factor is defined as the ratio between the Peak Value of a signal and its
effective value: CF (G)=
RMS
p
G
G
. This value varies according to the waveform of the signal,
for a purely sinusoidal wave it’s worth
2
=1.41. In presence of distortions the Crest Factor
assumes higher values as long as the wave distortion is higher.
