Voltage Lev; Preload/ Bias Current Bias - Hameg R&S HM8118 Benutzerhandbuch

7.1.2 Voltage LEV

The LCR bridge R&S®HM8118 generates a sinusoidal mea-
surement AC voltage between 50 mV
resolution of 10 mV . You can set the measurement AC
eff
voltage either in the SETUP menu via LEV or via LEVEL
key by means of the knob
. You can select the decimal point to be changed via ar-
7
row keys. Using the SETUP menu additionally provides
you with the option to select the measurement AC voltage
by means of the numeric keypad. The amplitude accuracy
is ±5 %. This voltage is applied to the component through
a source resistance. Depending on the impedance of the
connected component, the source resistance may auto-
matically be selected in accordance with the following ta-
ble. The source resistance is dependent on the selected
measurement range.
Component Impedance
10.0 µΩ to 3.0 Ω
3.0 Ω to 100.0 Ω
100.0 Ω to 1.6 kΩ
1.6 kΩ to 25.0 kΩ
25.0 kΩ to 2.0 MΩ
2.0 MΩ to 100.0 MΩ

7.1.3 Preload/ Bias Current BIAS

The constant voltage (CST V function) must be switched on for
measurements with bias current or external preload.
To permit a forecast on how a component will behave in
the circuit at a later point, you can preset a DC BIAS which
corresponds to the subsequent supply voltage (current).
Fig. 7.2: Constant voltage CST_V activated
The BIAS function offers the option to overlap a DC with
the AC measurement range voltage. Components such as
electrolytic or tantalum capacitors require a positive
preload for an accurate measurement. An internal preload
of 0 to +5 V with a resolution of 10 mV or an external
DC
preload of 0 up to +40 V
DC
power supply (instrument back panel) allow reality-orien-
ted measurements (function C-R / C-D). Additionally, the
Is is necessary to unload coils before removing them, i.e.after
switching off the bias current, it is required to wait for the coils
to discharge before the component is disconnected from the
measuring instrument. During the discharge, "Please wait..." is
shown in the LCD display. The bias current (BIAS) is only availa-
ble for the inductance measurement.
and 1.5 V with a
eff eff
or the arrow keys
6
Source Resistance
25.0 Ω
25.0 Ω
400.0 Ω
6.4 kΩ
100.0 kΩ
100.0 kΩ
/ 0.5A through an external
internal preload helps measurements on semiconductor
components.
For measurements of inductances, (function L-R / L-Q),
only an internal bias current is available which can be set
9
from 0 to +200 mA (DC) with a resolution of 1mA. An ex-
ternal bias current is not possible in this case.
Use the BIAS key to select the value for the preload or
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the bias current. Press the BIAS key again after entering
the value to complete the process. You can use the knob
and the arrow keys
6
lect the amount of the preload / bias current. You can acti-
vate the internal preload or bias current (BIAS) by pressing
the BIAS / key. If the preload or bias current is ac-
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tivated, the BIAS /
the BIAS / key again, the preload / bias current will be
deactivated and the key will no longer be illuminated.
The error message "DCR too high" indicates that the resistance
of the connected DUT is too high for the selected bias current. In
this case, the bias current cannot be activated.
Example for internal BIAS preload:
Unipolar capacitators must be connected with the correct pola-
rity, i.e. the positive capacitator pole must be connected to the
left contact and the negative pole to the right contact. The pre-
load (BIAS) is only available for the capacity measurement.
In this example, a 1000µF (20V) electrolytic capacitator
was measured with a measurement voltage of 5kHz. The
C-R mode is activated as function and the BIAS
used via knob or arrow keys
6
to select the value for the internal preload. The BIAS /
is used to activate the internal BIAS preload.
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Fig. 7.3: Internal BIAS preload
Example for external BIAS preload:
Fig. 7.4: Connectors for external BIAS preload
Instrument Functions
(decimal point) to se-
7
key will be illuminated. By pressing
(decimal point)
7
key is
10
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