41
Instrument Functions
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 resistan-
ces and thermoelectric voltages between different metals
have been intentionally eliminated by this offset correc-
tion. The compensation values will not be stored after the
¸HMC8012 has been switched off and have to be rede-
termined. 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 se-
cond), 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. This
applies to a low pass filter. A lower setting (Slow) ensures
more stable measurement values. However, the measure-
ment is slow and signal elements 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
<
50 kHz, and select Fast for a set-
ting of
>
1 kHz.
If the second 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.
Value). 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.
The maximum accuracy in measurements is achieved when using
the setting „Slow (ADC Rate).
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 measurement time can vary between 10ms,
100 ms and 1s and is shown below the frequency informa-
tion 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 measurement per second, for MEDIUM
it is 10 measurements per second and for FAST it is 100
measurements per second.
5.4 Measuring Resistance
For the resistance measurement, connect measurement
cables with clamps to the respective connectors on the
front panel of the instrument. A two-wire measurement
only requires the COM and V connectors. A four-wire
measurement also requires the LO/HI connectors (SENSE).
After connecting the cables and connecting with a resis-
tance, press the Ω key. The resistance value will show on
the display. During a resistance measurement, the cable
resistance (cable offset) requires particular attention. Espe-
cially for small resistances which may be close to the cable
offset it is recommended to zero the measurement section.
A zero measurement is also called a relative measurement,
i.e. each measurement value indicates the difference be-
tween a saved zero value and the input signal.
+ -
frequency source
Fig. 5.3: Measuring frequency
+ -
current source
(AC/DC)
Fig. 5.2: Measuring a DC or AC current
Fig. 5.4: Measuring resistance (2-wire)
- +
resistance 2-wire
(Ω)
