54
Instrument Functions
Contrary to the internal preload, in this example an exter-
nal DC preload is generated on the HM8118 back panel.
Component and measurement mode are identical to the
example with the internal preload. The external DC preload
is generated for the HM8118 by a power supply unit (here:
Hameg HMP2020) in this example. The voltage is applied
to the power supply unit at 20V and the current is limited
to 250mA.
The C-R mode is also activated as function and the BIAS
10
key is used via knob
6
or arrow keys
7
(de-
cimal point) to select the voltage value. Press the BIAS
MODE
24
key to select the EXT (= external) function via
knob. Use the BIAS /
26
key to activate the external
BIAS preload.
Example for internal bias current BIAS:
The process for an internal bias current is similar to that
for an internal preload. In this case, the L-R or L-Q function
is selected and any given inductance is connected to the
bridge. Use the BIAS
10
key via knob
6
or the arrow keys
7
(decimal point) to select the value for the in-
ternal bias current. The BIAS /
26
key is used to acti-
vate the internal BIAS bias current.
Fig. 7.7 shows an example for a typical waveform of a bias
current that is adjustable to a maximum value in connec-
tion with a connected load.
Fig. 7.5: Activate external BIAS preload
Fig. 7.6: Activate external BIAS preload
7.1.4 Measurement Range RNG
The measurement range can be selected automatically or
manually. If the measurement range is changed, the inter-
nal measurement circuit (replacement circuit) will be mo-
dified and internal relays will be switched. Therefore, a
change in the measurement range depends on multiple
factors, such as phase angle, impedance, measured va-
lue, etc.
The measurement range can be set manually via knob
6
in the range of 3 Ω to 500 kΩ. In the SETUP menu, use the
arrow keys
7
to select the RNG function, press
the knob (editing mode) and select the desired measure-
ment range via knob. Press the knob again to confirm the
selected value. Use the AUTO/HOLD key to then switch
between automatic (AUTO/HOLD key is illuminated) and
manual measurement range selection.
7.1.5 Measurement Speed SPD
The measurement speed can be set in three increments:
❙
SLOW
(slow),
❙
MED
(medium)
❙
FAST
(fast).
In the SETUP menu, use the arrow keys
7
to
select the SPD function to set the measurement speed,
press the knob
6
(editing mode) and select the measure-
ment speed via knob. Press the knob again to confirm the
selection.
The number of measurements for a continuous triggering
(CONT) is approximately 1.5 per second at the SLOW set-
ting, 8 per second at MED or 14 per second at FAST. The
Fig. 7.7: Maximum setting for bias current in connection with the
connected load (typical waveform)
If the measuring instrument permanently toggles between two
measurement ranges (limit of the automatic measurement range)
or if the component to be measured is known, select the manual
measurement range selection (see chapter 6).