Measuring Range; Auto-Ranging; Manual Range - Hameg HM8018 Handbuch

O p e r a t i o n o f t h e H M 8 0 1 8
resistance, thus the voltage at the component
terminals will be always below 0.5 V. The source
resistance is as a function of the impedance ran-
ge. The graph shows the voltage evolution at the
component terminals as function of its impedance
and the measuring range (R1 range 15 Ω, R6 range
100 MΩ).

Measuring range

The HM8018 offers 6 impedance ranges (R1-R6).
The measuring range can be selected either
manually or automatically. Each range has a
source resistance approximately equal to half of
the impedance of the current range. The extreme
ranges R1 and R6 use the source resistances of
the R2 and R5 ranges.
Note: The measuring ranges determine the impe-
dance ranges (and not capacitance or inductance
value ranges), the ranges of capacitance and
inductance depend upon the test frequency. The
high capacitance values as the low inductance
values will be measured on a low impedance
range, whereas the low capacitance values as
the high inductance values will be measured on
the higher ranges.
The chart below gives the measurement range
according to the component type and the fre-
quency range.
Range R Re-
source sistance
R1 100 Ω 1mΩ –
15Ω
R2 100 Ω 15Ω –
330Ω
R3 1 kΩ 330Ω –
3.3 kΩ
R4 10 kΩ 3.3 kΩ –
33 kΩ
R5 100 kΩ 33 kΩ –
330 kΩ
R6 100 kΩ 330 kΩ –
100 MΩ
f is the test frequency (Hz)

Auto-ranging

In normal operation the HM8018 selects the most
appropriate range for an accurate measurement.
When the instrument measures impedance that it
is out of its current range, the instrument switches
one range up or one range down and makes a new
22
Subject to change without notice
Induc- Capaci-
tance (H) tance
0.01 μH – 99.9 mF –
2.4/f 10.6/f mF
2.4/f – 10.6/f mF –
52.5/f 482/f μF
52.5/f – 482/f μF –
525/f 48.2/f μF
525/f – 48.2/f μF –
5252/f 4.82/f μF
5252/f – 4.82/f μF –
52520/f 0.48/f μF
52520/f 0.48/f μF –
9999 0.001 pF
measurement. If this measurement is within the
validity domain of this new range the instrument
will display the value. If not, the range change
process will be repeated. There is a built in hys-
teresis in the order of 10% to prevent multiple
range changes if a component is on the limit of
range boundary. The chart below gives the limits
of range changes.
Range
|Z|
Change
1 to 2
|Z| > 15 Ω
2 to 3 |Z| > 330 Ω
3 to 4 |Z| > 3.3 kΩ
4 to 5 |Z| > 33 kΩ
5 to 6 |Z| > 330 kΩ
Remarks:
If certain types of inductors are measured it
may occur that the HM8018 switches indefi nitely
between two ranges. Due to the fact that generally
the inductor value depends of the current going
through, the HM8018 will give different values
from one range to an other because the source
resistance changes. This variation from one range
to another may be higher than the automatic mode
hysteresis that creates irresolution. So it is neces-
sary to switch to manual mode to fi x the range

Manual range

When an important quantity of similar components
has to be tested, the automatic mode process
duration time can be avoided. While a component
is measured in automatic mode, press the AUTO
button. The current range (selected by the ins-
trument) is hold and displayed for a short time. It
is possible to save the confi guration settings for
a further use by pressing the STORE button and
then CONFIG key. If the impedance of the com-
ponent is higher than 50 times the nominal value
for the range (given by R source resistance), the
message OFL is displayed. Then you must change
the range. This not applies to the 15 Ω range for
which overtaking is obtained for an impedance of
approx. 18 Ω. As far the higher range R6 allows
measurements up to 99.9 MΩ.
The manual range mode, thus, is to be reserved to
precise cases. To avoid measurement instability
and additional uncertainty the instrument should
be ever working in automatic range mode.
Range
|Z|
Change
2 to 1 |Z| < 13.5 Ω
3 to 2 |Z| < 300 Ω
4 to 3 |Z| < 3 kΩ
5 to 4 |Z| < 30 kΩ
6 to 5 |Z| < 300 kΩ