HT9021
EN - 4
2. GENERAL DESCRIPTION
HT9021 meter can perform the herewith measurements:
•
DC and AC TRMS Voltage up to 1000V
•
DC and AC TRMS Current up to 1000A
•
Resistance and continuity test with buzzer
•
Capacitance
•
Frequency with test lead and jaws
•
Duty
cycle
•
Diode
test
•
Temperature with type K probe
•
AC voltage detection with and without contact with integrated sensor
Each parameter can be selected by rotating the 8 positions switch. To abilitate the hold
function the HOLD key is available. There are also the following keys: “
MODE
"
MAX/MIN
",
“
Hz%
“, “
PEAK/REL
” and “ ”. For their use please see § 4.2. The selected quantity
appears on a LCD display with indication of measurement units and functions. An
analogical bargraph it is also availbale
2.1. TRMS AND MEAN VALUE MEASURING INSTRUMENTS
Safety testers for alternate parameters 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 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
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.
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