Protection Against Overloads; Crest Factor; Diode Test - Hameg Instruments HM8012 Mode D'emploi

F u n c t i o n s

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,
first 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
mea-surement 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
defined 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
capability of processing measurement signals
with a high peak value, without the converter
entering into saturation.
The HM8012 crest factor ranges from 1 to 7 (for
additional measurement error of <1%) and
depends 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, the
p
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 influenced
when there are no harmonic components in the
measurement signal placed outside the 100 kHz
(–3 dB) bandwidth of the converter.
Additional error Additional error due to high crest factor Additional error
Additional error Additional error
Error ± (% of reading)
CF 1-2 2-3
% 0.05 0.15
30
Subject to change without notice
/V
p RMS
3-4 4-5 5-6
0.3 0.4 0.5
Another factor influencing the measurement
precision 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
18 key. For diode measurements, connect
or
the device under test (DUT) between the COM
terminal and the V/ /T°/dB
There is a DC voltage across the connection
terminals. Accordingly, only voltage-free objects
need to be measured because any additional
voltages in the measurement path will distort the
result. It is preferable to remove, if necessary,
any components connected to the semicon-
ductor for precise results. It is possible to mea-
sure voltages up to 5 V. The maximum voltage
that the equipment will supply is 10 V in an open
circuit. If the cathode of the DUT is connected to
the ground (COM-terminal), the diode operates
in its conducting mode. If the anode of the DUT
is connected to ground, the diode operates in its
reverse mode. For measurements on Zener-
diodes, the anode of the device should be
connected to ground. Take care when making
measurements on sensitive circuits. The current
supplied by HM8012 is 1 mA constant for this
function. All keys except
OFFSET are inactive for this function.
19
using
terminal.
19 , 18 and HOLD/