Line Frequency; Measurement Principle - Hameg HM8118 User Manual

shown in the right panel and the essential parameters in
the left panel of the display. The four BNC sockets located
on the front panel can be connected to the component to
be measured with the appropriate measuring accessories.
Additionally, it is also possible to connect the measuring
instrument via ground socket on the front panel
ground potential. The socket is suitable for a banana plug
with a 4 mm diameter.
The front panel ground connector and the ground contact of the
trigger input are directly connected to the mains safety ground
potential through the line cord. The outer contacts of the front
panel BNC connectors –
20
axial cables attached) are connected to the GUARD potential
which has no connection to the safety ground! No external vol-
tages may be applied to the BNC connectors! The rear panel in-
terfaces and are galvanically isolated (no connection to
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ground)!
If there are undefined messages on the display or if the in-
strument fails to react to operation of its controls turn it
off, wait a minute and turn it on again in order to trigger a
reset operation. If the display remains unchanged or ope-
ration impossible, turn it off and take it to a qualified ser-
vice point (see Safety Instructions).
4.3

Line frequency

Prior to first measurements, the line frequency setting
must be set to the applied line frequency, 50 or 60 Hz. If
the line frequency is not set properly, depending on the
measurement range and the line frequency value, insta-
bilities may occur e.g. on the display. In order to set the
line frequency press the SELECT button
menu for accessing MAINS FRQ, use the knob
lecting the correct value.
4.4

Measurement Principle

The LCR meter HM8118 is not a traditional Wien, Maxwell
or Thomson measurement bridge. Rather, when connec-
ting a test object, the impedance |Z| and the correspon-
ding phase angle Θ (phase between current and voltage)
are always determined (see fig. 4.3). These measurement
values are frequency dependent and will be determined
by means of an AC test signal (which can be set manually
between 50mV and 1.5V). The test signal is induced in the
test item. This distinguishes a LCR bridge from a multime-
ter (DC measurement). Based on the measurement prin-
ciple, the measured impedance is always essential. Based
on the impedance (X axis) and the phase angel (angle), the
instrument is able to determine the missing value of the
Y axis. This means that it is not the DC component that is
being measured but rather the AC value. The issued values
are calculated digitally. This measurement of impedance
and phase angle is subject to a certain measurement inac-
curacy which will be described on the following pages.
In general, the HM8118 bridge can only determine the
ESR, ESC or ESL (= Equivalent Series Resistance / Capa-
city / Inductivity) according to the equivalent circuit dia-
43
(as well as the shields of any co-
23
, use the SYST
3
for se-
6
Imaginary
applied on the red terminal. The bias voltage works only
when the instrument on capacitance measurement
Axis
mode.
Measuring function selection
The desired test function is selected by push buttons (12)
and (14). The push button (12) gives access to the main
with
parameter (R, L or C), The push button (14) allows a
secondary parameter measurement
phase).
In order to measure D parameter the instrument needs at
first to be set to capacitance measurement mode, on the
other way, Q parameter will be displayed.
Auto-measurement function
The HM8018-2 is able to automatically determine the
component type in most cases. 3 different automatisms
exists: the automatic impedance range selection (see the
section « Auto-ranging»), the
(series/parallel) selection (see the section « passive
components »), and the automatic function selection. These
three automatisms are simultaneously activated when the
instrument is set in automatic mode with the RANGE
AUTO key (7). Then the user can change function or mode
that disables their respective automatism. The manual range
selection disables the three automatisms.
When the instrument is on automatic mode the function
choice depends on the impedance module, phase angle as
well as the quality factor .The diagram below shows the
choice made by the instrument.
Fig. 4.3: Measurement principle
gram of the component and is primarily used to measure
individual components. If a circuit with multiple compo-
nents is connected to the bridge, the instrument will al-
ways determine the ESR, ESC or ESL of the entire circuit
/ component group. This can potentially skew the measu-
rement result. The connected component / circuit is assu-
med to be the „Black Box". These values are available for
each component; however, please keep in mind that these
always describe the result of multiple, possibly overlapping
individual capacities, inductances and impedances. This
can easily cause some misunderstandings especially with
coils (magnetic field, eddy currents, hysteresis, etc.)
The LCR bridge HM8118 is primarily intended to determine pas-
sive components. Therefore, it is not possible to determine test
objects which are externally supplied with power.
Fig. 4.4 shows the link between capacity C
R ) and various test voltages that can be selected with the
s
bridge (0.2V
eff
measurement values of C
the selected test voltage. Point A shows the test point of
the instrument during the measurement of a single com-
ponent, point B shows the test point during the measu-
rement of a component group (in this case two capaci-
ties connected in parallel). In contrast to test point A, with
point B the bridge switches the measurement range due
to the impedance of the entire component group. As a re-
sult, the measurement results for point A and point B are
different.
jX
Q = 500
D = 0,002
above 45° = L
(Q/D, impedance or
Real
Axis
automatic mode
below -- 45° = C
Q = 500
D = 0,002
Calculation functions
Apart from displaying normal values as resistance, inductance or
Q = Quality factor
capacitance, the HM8018-2 can display relative deviations and
percentages. It is not possible to use these calculation modes for
D = Loss tangent
other functions than the three previous values. The deviations
and percentages are displayed in relation to the two stored values
A and B.
D = 1 / Q
The procedure to obtain relative measurement is as follows:
1) Connect the component corresponding to the reference
Q = 1 / D = 1 / tan delta
value.
(delta = Opposite angle of the phase angle)
2) Store the value (memory A) by pressing on the STORE key,
then press the A key.
3) Press on the A key. The indicator -A lights up and the
display shows the value (Measure – A).
A direct percentage measurement is possible, it is only to use the
÷B key instead of the –A key in the previous procedure. Then the
instrument displays the value 100*Measure/B in %.
To obtain a deviation in % proceed as follows:
1) Connect the component corresponding to the reference
value.
to 1.5V ). As can be seen in the figure, the
eff
or R are highly dependent on
s s
First-Time Operation
D = Q = 1
|Z| = 1000 Ω
D = 500
Q = 0,002
R
D = 500
Q = 0,002
D = Q = 1
(or resistance
s
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