Rohde & Schwarz HMC8012G, Руководство пользователя

Страница: 51 / 74

46
Instrument Functions
5.2 Measuring a DC / AC Current
To measure a DC or AC current, you can connect a power
supply unit to the ¸HMC8012 multimeter via silicon
test leads, for instance. Use the COM and A connectors on
the bottom. Once the DC I / AC I key on the front panel of
the instrument is used, the DC or AC current value will be
shown on the multimeter display.
In addition, it is possible to show a second function (2nd)
on the display. The soft menu key 2nd FUNCTION and
the knob allow you to select AC I, DC V, dB or dBm. The
selected function is shown above the main measurement
value display. The menu display changes depending on the
selected second function. The soft menu key REMOVE 2nd
allows you to hide the second function from the display. To
compensate for the line resistance of measurement cables,
it is necessary to short circuit the measurement cables and
press the NULL key. This triggers the offset correction of
the entire measurement section. This value will be shown
next to the soft menu key NULL and on the display below
the main measurement value. The line resistance of the
measurement cable, contact resistances and thermoelec-
tric voltages between different metals have been intentio-
nally eliminated by this offset correction. The compensation
values will not be stored after the ¸HMC8012 has been
switched off and have to be redetermined. In addition, you
may also enter the NULL value numerically or via knob.
The soft menu key ADC RATE and the knob allow you to
set the display refresh rate to SLOW (5 measurements per
second), MEDIUM (10 measurements per second) or FAST
(200 measurements per second).
You can select the option SLOW, MEDIUM or FAST via
soft menu key AC FILTER (main function AC I) and knob. A
lower setting (SLOW) ensures more stable measurement
values. However, the measurement is slow and signal ele-
ments of higher frequency will be attenuated. Depending
on the input frequency, this function will smoothen the
displayed value. The setting MEDIUM is saved as default
value. Select the setting SLOW for an input frequency of
+ -
current source
(AC/DC)
Fig. 5.3: Measuring a DC or AC current
The maximum accuracy in measurements is achieved when using
the setting SLOW (ADC Rate).
<
50 kHz, and select FAST for a setting of
>
1 kHz. If the se-
cond function (2nd FUNCTION) is activated (dB or dBm),
you have the option to define a reference value. For the
function dB, the reference value is the current (REF. VA-
LUE). You can set the reference value numerically or via
knob. If a
reference value is defined, you can reset the pre -
viously selected reference value via soft menu key NULL.
For the function dBm, the reference value is 1mW and is
often used for RF signal measurements. If the dBm func-
tion is activated, the multimeter performs a measurement
and calculates the power supplied to a comparator resis-
tance. The reference value (REF. VALUE) in this case is 50,
75 or 600 Ω. In addition, you can set a user-defined value
(USER) either numerically or via knob.
5.3 Measuring Frequency
The frequency display can be added in the main function
AC V and AC I as the second measurement function (2nd).
The measurement time can be set via soft menu key GATE
TIME. The gate time can vary between 10ms, 100 ms and
1s and is shown below the frequency information on the
display.
The display refresh rate is dependent on the selected ADC
rate in the AC V or AC I mode. For the setting SLOW, the
measurement rate of the frequency measurement is 1
+ -
frequency source
Fig. 5.4: Measuring frequency
Fig. 5.5: Gate Time
The AC filter is only a display filter and not a low-pass filter. The si-
gnal will be not circumcised. Fluctuating signals can be better read.