Hameg HM8018 Bedienungsanleitung Seite 8

Selection of the test
The desired test function
selection buttons@)/@/@and @. The dimensions allo-
cated to the corresponding test functions are indicated
in the display. Beside L and C measurement,
for determination of the
inductor coils and parallel conductance values of capaci-
tors are available. Measurement
these additional functions
and loss factor of the tested component. The correspon-
ding formulas are specified in the chapeter entitled
"Dissipation Factor and Q-factor".
measurement function, the range selection knob @ is
used to adjust the corresponding measurement range.
The appropriate dimension is indicated in the display.
Connection of the test object
The components under test can be connected in two
different ways to the HM8018 unit. Two 4mm banana
jacks are available for quick and rough measurements.
The test object is either plugged in or fixed below the
screw-type terminals. Under different conditions, this
fast procedure is not sufficiently precise (please refer to
the chapter entitled "Dissipation Factor and a-factor"
for further information). In case of measurements
ring higher accuracy, the HZ18 Kelvin probe offered in
the HAMEG accessory line should be used.
Zero adjustment
Normally the HM 8018 unit is zero-adjusted. However,
the display may indicate some digits due to aging or
varying environment temperatures, even when no test
object is connected. This display error can be eliminated
with the "Display Zero" trimmer
ranges. When using the Kelvin input and the HZ18 test
lead, the lower measurement
the used cable with the "Probe Compensation"
mer. This has no influence upon the adjustement perfor-
med with the "Display Zero" trimmer.
Measuring accuracy
The HM8018 unit offers a basic of 0.5% of reading. To
make full use of this measuring accuracy, the compo-
nents under test should be very carefully connected.
Basically, care has to be taken of good contact making,
and the connecting wires between
the component to be measured should be as short as
possible. To increase measuring accuracy and reliability
of the test results, the HM 8018 unit has three different
test frequencies. These are automatically switched over
via the range selector for better practical handling. The
test frequencies are 160 Hz in the highest measuring
ranges, 1600 Hz in the 20 nF/20mH and 200nF/200mH
ranges and 16kHz in the lowest range.
In case of losses in the test leads due to comparably
high test currents —which occur especially in case of
low inductance and high capacitance —the HZ 18 Kelvin
cable is recommendable.
racy of L and C measurements
M4 — 8018
function
is selected via the function
functions
series resistance values •of
of these values with
permits to calculate quality
After selecting the
requi-
in all measurement
ranges can be adapted to
trim-
the terminals and
Its influence upon the accu-
is not very important.
However, when series and parallel components
determined, test errors of more than 100% may occur
without the HZ18 cable. Furthermore
permits to connect components which are difficult to
access.
DC bias
The test voltage of the HM8018 unit is sinusoidal with
frequencies between 160 Hz and 16kHz. The amplitude
is about I Vss.When capacitors are connected without
biasing, they are negatively poled at every second half-
wave. This may lead to irreversible damage, particularly
when tantalum capacitors are used. For this reason a 2 V
DC voltage can be applied to the test object. This will
prevent any negative polarization. However, correct
polarity should be observed, when connecting the capa-
citor. The positive pole of the DC voltage is applied to
the red banana socket.
Dissipation factor and Q-factor
Any passive electronic part is subject to losses when
operated. In case of capacitors, the losses depend on
the type of dielectric material, capacitance, temperature
and operating frequency. In the equivalent circuit diæ
gram, the losses are shown as a first approximation by
an equivalent shunt resistor of the capacitor. This resi-
stance can be determined
with the HM 8018 unit by using the "G" test function.
Beside the dissipation of the core material used, the
quality of an inductance coil is essentially dependent on
the ohmic resistance of the winding.
circuit diagram, these losses are characterized by a resi-
stor connected in series with the induction
stance is determined with the HM8018
"Rs" test mode.
When measuring Rs or G, it is possible to use a smaller
measuring range. However, the measuring value of ima-
ginary parts may not be exceeded by a factor of 2.5 (e.g.
determination of Rs or G is allowed in the 2000 pF range
for capacitors up to 5nF).
The formlulas required to evaluate quality and loss fac-
tor are as follows:
tanö= G/m•Cx Q= l/tanö
tanö= Rs/o•L Q= 1 /tanö
where:
= tan = dissipation factor (no dimension)
D
= loss factor (no dimension)
G = parallel conductance in S (1 S = I/Q)
= series resistance
= measured value
2xnxf in rad/sec (f=test frequency)
The test principle of the HM8018 module permits to
determine the equivalent components
Ies 450 (tan delta ö S 1) with a deviation of < 1%. This
exceptionally good result is achieved due to a special
test procedure which has not been used in sets of this
price category up to now. However, when measuring
iron core coils, no reliable result can be achieved in many
cases in spite of the used test procedure. This is largely
due to the saturation behaviour
used. For this reason, the result should be checked with
an approximate calculation,
inductance values of iron
the Kelvin probe
as a parallel conductance
In the equivalent
coil. Its resi-
by using the
in Q
in F or H
up to phase ang-
of the core material
when determining
core transformers and coils.
Subject to change without notice
are
the