Resistance Measurements; Protection Against Overloads; Crest Factor; Diode Test - Hameg Instruments HM8012 Manuel

F u n c t i o n s
alternating voltage height with the measuring
range choice.

Resistance measurements

For resistance measurements, connect the object
to be measured between the COM terminal
the V/ /T°/dB terminal
across the connection terminals. Accordingly,
only voltage-free objects need to be measured
because the voltages in the measurement circuit
will distort the result. In the case of low resistance
measurements, the OFFSET key
compensate, where applicable, for measurement
cord resistance.
For high resistance measurements, it is ad-
visable to place the resistance to be measured as
close as possible to the measurement terminal or
to use a shielded measurement cable connected
to ground.

Protection against overloads

All the HM8012 measurement ranges are pro-
tected against various forms of overload. Precise
indications are given in the technical charac-
teristics.
In general: during the measurement of unknown
quantities, always begin with the highest mea-
surement range and, from then on, switch ranges
using optimum display. If HM8012 malfunctions,
fi rst eradicate the cause before going on to make
the following measurement.

Crest factor

To evaluate complex or deformed signals, the
determination of a true rms value is necessary.
The HM8012 digital multimeter will allow the
measurement of AC quantities with a display of
the true AC or AC + DC value. The crest factor
is important data for interpreting measurement
values and for evaluating its accuracy. It is defi ned
as the ratio between the peak voltage and the rms
value of the signal.
Crest factor = CF = V
It is a measurement of the dynamic input voltage
range of the AC converter and expresses the ca-
pability of processing measurement signals with
a high peak value, without the converter entering
into saturation.
28
Subject to change without notice
and
. There is a DC voltage
can be used to
/V
p RMS
The HM8012 crest factor ranges from 1 to 7 (for
additional measurement error of <1%) and de-
pends on the magnitude of the rms value of the
signal to be measured.
To avoid saturation of the HM8012 input stages,
make sure that the input signal peak value does
not exceed 3 times the value of the range, or
850 V . At the middle of the measurement range,
p
the maximum crest factor is 7. The accuracy of
the displayed value depends, among other things,
on the rms value converter bandwidth. Complex
signal measurements will barely be infl uenced
when there are no harmonic components in the
measurement signal placed outside the 100 kHz
(–3 dB) bandwidth of the converter.
Additional error due to high crest factor
Error ± (% of reading)
CF 1-2 2-3 3-4
% 0.05 0.15 0.3
Another factor infl uencing the measurement pre-
cision is the duty cycle of the measurement signal.
The crest factor in this relation becomes:
V
T = period duration, t = pulse duration
V = pulse voltage.
Accordingly, a rectangular signal having a duty
cycle of 1% has a crest factor of 10. The minimum
pulse duration should be approximately 10 μs.

Diode test

Choose the diode test function
key. For diode measurements, connect the
device under test (DUT) between the COM termi-
nal and the V/ /T°/dB
4-5 5-6
0.4 0.5
using or
terminal. There is