Hameg HM8118, Руководство пользователя, Страница: 27 / 36

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Measuring Equipment
The HM8118 calculates a „virtual“ impedance
Z = V
s
/ I
p
. V
s
is the secondary voltage, I
p
is the primary
current (all complex values). The mutual inductance is cal-
culated using the mutual inductance definition:
V
s
= R
s
* I
s
+ L
s
dI
s
/dt + M dI
p
/dt
If no current is applied to the secondary winding (I
s
= 0),
the following is true:
V
s
= M dIp/dt or M = Im{Z}/w .
In this case, the value for M can also be negative. It is pos-
sible to use a BIAS current if necessary. However, BIAS
is not used to improve the accuracy. Some coils may be
subjected to a strong bias current BIAS. In this case, the
measurement must be performed under the same condi-
tions as they are to be used for the circuit.
8.3.4 Determining the Leakage Inductance
The short circuit principle is applied to determine the
leakage inductance for the HM8118 bridge. The wiring to
determine the leakage inductance does not differ from a
conventional inductance measurement. The component /
transformer is connected to the instrument via BNC con-
nectors on the HM8118 instrument front panel. The HZ186
is not mandatory for this purpose. You can also use the in-
cluded standard cable which is suitable for inductance
measurements.
Before determining the leakage inductance, it is re-
commended to first perform a conventional inductance
measurement of the primary transformer winding. In this
case, the secondary side remains open (see fig. 8.10).
Fig. 8.9: Measuring the mutual inductance
Contrary to a conventional inductance measurement, de-
termining the leakage inductance requires the secondary
transformer side to be short-circuited (see fig. 8.11). If the
secondary side is short-circuited, the measured values of
the primary side correspond to the leakage inductance.
8.4 4-Wire SMD Test Adapter HZ188
The SMD test adapter HZ188 is suitable to qualify SMD
components. The test adapter converts the configuration
of a 4-wire measurement to a 2-wire measurement. Due to
its net weight, it is recommended to mount the measure-
ment adapter and bridge to a flat surface (e.g. a table). The
test adapter is directly connected to the front panel BNC
connectors of the bridge via the four BNC sockets. For the
measurement, insert the SMD component to be measu-
red with its connectors between the two provided contact
pins (measurement contacts). This equipment is included
in delivery.
8.4.1 Compensation HZ188
Fig. 8.12: 4-wire-SMD test adapter HZ188
H CUR
H POT
L POT
L CUR
L C
OPEN
R
H CUR
H POT
L POT
L CUR
SHORT
primary secondary
primary secondary
Fig. 8.10: Primary inductance measurement
H CUR
H POT
L POT
L CUR
L
C
OPEN
R
H CUR
H POT
L POT
L CUR
SHORT
primary secondary
primary secondary
Abb. 8.11: Leakage inductance measurement
Technical Data HZ188
Function: Test adapter to operate (via 4-wire connec-
tion) with LCR bridge HM8118
Measurable components:
SMD resistances, coils or capacitators
Frequency range: 20 Hz to 200 kHz
Maximum voltage: ± 40 V maximum value (AC+DC)
Connectors: BNC sockets (4), measurement contacts (2)
Safety standards:
EN61010-1; IEC61010-1;
EN61010-031; IEC61010-031
Environmental conditions: Contamination Class 2, internal use
Operating temperature:
+5 °C to +40 °C
Temperature limits: -20 °C to +70 °C
Weight: approximately 300 g