Hameg Instruments HM8011-3 Manual De Operación página 15

Current measurements
For current measurements, the device to be tested
is connected to the mA socket (3) or the 10A socket
(11). The HMS011-3 module should be inserted
into the line which carries the lowestpotential
to ground. To ensure safety of operation, the
voltage to ground across the COMMON
terminal should not exceed 500 V
AC currents are determined by their true rms value
(see "Crest factor"). When measuring AC currents,
a DC component is suppressed.
The current measurement ranges are microfuse-
protected from overload condition (2000mA range:
up to 2A; lower ranges: up to 200mA). The 10A
input is not fuse protected. If a fuse has blown,
firstly eliminate the overload cause. Then re-
establish the operating condition of the H M 8011-
3 multimeter.
At currents which exceed 10A (max. 20A) the
max. admissible measuring time is 30sec.
Resistance measurements
For resistance measurements, the device to be
tested is inserted between the COMMON terminal
(5) and the V/kΩ socket (11). A DC voltage is applied
across the connecting terminals. Therefore only
devices which are not under voltage should be
measured, because any voltage present in the test
circuit will give an erroneous result. If very small
resistances are measured, the line resistance of
the connecting leads must be taken into
consideration. When the resistance measurement
inputs are shortened (approx.0Ω) the buzzer beeps
continuously.
Overload protection
All measurement ranges of the HM8011-3
multimeter are protected against different types
of overload conditions. General procedure: When
measuring unknown magnitudes, firstly select
the highest measurement range, before
switching over to the optimum readout range.
If a failure of the HMS011-3 module is detected,
firstly eliminate the failure cause, before
performing any further measurement.
Fuse replacement: If overload occured in a current
measurement range, one of the two microfuses
must be replaced before re-startingoperationof the
HM8011-3 module. For this purpose, the set must
be opened, the fuses being only a cessible from
the inside. In any case, only fuses of the specified
type shall be used to avoid damaging of the
HM8011-3 multimeter and to ensure continuity of
specification in the current measurement ranges.
Crestfactor
The evaluation of complex or distorted signals
requires detection of the true rms value. The HM
Sous réserve de modifications / Reservado el derecho de modificación
8011-3 multimeter permits to measure AC values
and indicate their true rms value. . . . . The crest factor
is an important magnitude for test value
interpretation and accuracy evaluation. It is defined
by the signal peak voltage to signal rms value:
Crest factor = CF = V
.
This factor is a measure of the dynamic input
p
voltage range of an AC/DC converter and expresses
its capability of handling test signals having a high
crest factor without reaching the converters
saturation limit.
The crest factor of the HM8011-3 multimeter
ranges from 1 to 7 (for errors of < 1%) and depends
on the rms value of the signal to be measured. The
crest factor has a maximum value of 3.5 at full-
scale reading, e.g. of 7 at the mid-scale point of
the selected measurement range. The reading
accuracy is reduced for signals having a higher crest
factor.
additional
AC error
[%]
Fig. 1
Crest factor
Among others, the reading accuracy depends on
the band width of the rms converter.
Measurements of complex signals are hardly
affected, unless important harmonics of the
measured signal are beyond the converter
bandwidth of 150 kHz (- 3 dB).
Another magnitude acting upon the reading
accuracy is the duty factor of the test signal. It is
related to the crest factor as follows:
T = period duration
t = pulse duration
u = pulse voltage
The shown waveform with a 1% duty factor for
example has a crest factor of 10. The accuracy
specified in Fig. 1 is given for such a waveform
and a constant pulse voltage of 1V.
Operational check
To obtain the normal operating temperature, the
mainframe with inserted module should beturned
on at least 60 minutes before starting the test.
Measuring equipment required
Fluke 51 01 B calibrator/Rotek 600 AC/DC calibrator
1 Resistor 180 kΩ ± 0.01 %
/V
p rms
µ
√
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