51
Setting of Parameters
surement value (reference value) is displayed. The measu-
rement value deviation is shown in the appropriate units
(Ohm, Henry, etc.).
6.3 Reference Value (REF_M, REF_S)
The menu function REF_M or REF_S enables the user
to enter a reference value which will be used as a basis
for the measurement result ∆ % or ∆ ABS. Press the SE
-
LECT key
3
to use the SETUP menu function and the set-
ting REF_M (for the main measurement value display) and
REF_S (for the secondary measurement value display) to
enter a reference value each. The applicable units will be
selected automatically depending on the selected measu-
rement function for the main measurement value display
(H, F, Ω or S) or for the secondary measurement value dis
-
play (Ω, S or °). You can enter a reference value numerically
with up to five digits after the decimal point. Alternatively,
you can press the TRIG key
27
to perform a measurement,
and the resulting measurement value will be adopted as
reference value.
6.4 Selecting the Measurement Range
The measurement range can be selected automatically or
manually. In some cases, it is useful to lock the automa-
tic measurement range function as it can take a complete
measurement cycle to determine the appropriate measure-
ment range. This can also be useful when switching similar
components. The bridge HM8118 automatically switches
to the measurement range 6 and subsequently back to the
adequate measurement range if a component has been
connected to the instrument. If the automatic measure-
ment range function has been locked and the impedance
of a component equals more than 100 times the nominal
value of the measurement range, the bridge will display an
OVERRANGE measurement error. In this case, it is neces-
sary to select a suitable measurement range for the mea-
surement. Press the AUTO/HOLD key
17
to switch bet-
ween the automatic and the manual measurement range
selection.
6.4.1 Automatic range selection (AUTO)
If the automatic measurement range function is activated,
the bridge automatically selects the most suitable mea-
surement range for an exact measurement in accordance
with the connected component. The instrument will switch
to the next measurement range level below if the measure-
ment value is smaller than 22.5% of the selected measure
-
ment range or 90% higher than the end value of the mea
-
surement range. An integrated switching hysteresis of ap-
proximately 10% prevents the instrument from constantly
switching the measurement range if the measurement va-
lue is close to the switching threshold of a measurement
range. The following table shows the switching thresholds
for switching the measurement range (if the constant vol-
tage CST V is switched off):
Measurement Range
Component Impedance
1 to 2
Z > 3.00 Ω
2 to 3
Z > 100.00 Ω
3 to 4
Z > 1.60 kΩ
4 to 5
Z > 25.00 kΩ
5 to 6
Z > 1.00 MΩ
2 to 1
Z < 2.70 Ω
3 to 2
Z < 90.00
Ω
4 to 3
Z < 1.44
kΩ
5 to 4
Z < 22.50
kΩ
6 to 5
Z < 900.00
kΩ
6.4.2 Manual Measurement Range Selection
The bridge HM8118 includes 6 measurement ranges (1–6).
The measurement ranges can be preselected manually or
automatically. The following table indicates the source re-
sistance and the impedance of the connected component
for each measurement range. The specified ranges are im
-
pedance ranges, not resistance ranges. Capacitators or in-
ductances are frequency-dependent components.
Measure-
ment range
Source
Impedance
Component
Impedance
1
25.0 Ω
10.0 µΩ bis 3.0 Ω
2
25.0 Ω
3.0 Ω bis 100.0 Ω
3
400.0 Ω
100.0 Ω bis 1.6 kΩ
4
6.4 kΩ
1.6 kΩ bis 25.0 kΩ
5
100.0 kΩ
25.0 kΩ bis 2.0 MΩ
6
100.0 kΩ
2.0 MΩ bis 100.0 MΩ
Additionally, the impedance of capacitators is inversely
proportionate to the frequency. Therefore, larger capaci-
tators will be measured in the lower impedance measure-
ment ranges. Consequently, the measurement range for
any given component may change as the measurement
frequency changes. If you wish to measure multiple si-
milar components, it is possible to shorten the measure-
ment time by using the AUTO/HOLD
17
key to switch from
the automatic measurement range selection to the manual
measurement range selection with the DUT (= Device Un-
der Test) connected. The AUTO/HOLD key will no longer
be illuminated. It is recommended to primarily use the ma-
During the measurement of an inductance in the AUTO mode, it
may occur that the HM8118 is constantly changing the measure-
ment range. This is based on the fact that the source impedance
is dependent on the selected measurement range so that after
switching the measurement range, the newly measured value is
outside the range of the 10% hysteresis. In this case, it is recom-
mended to use the manual measurement range selection.
The LCR bridge HM8118 does not create a 50Ω system. Instead,
it changes its internal resistance dependent on measurement
function and measurement range. Every cable shows losses and
distorts the original measurement result because of inductive and
capacitive properties (particularly because of its length).
The input impedance changes dependent on the selected
measurement range and the connect load impedance between
25Ω and 100kΩ.
Содержание HM8118
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