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True-rms Digital Multimeters
Making Measurements
23
Using LoZ for Voltage Measurements (Model
289 only)
W Caution
Do not use the LoZ mode to measure voltages in
circuits that could be damaged by this mode’s low
impedance (≈3 kΩ).
To eliminate ghost voltages, the Meter’s LoZ function presents a
low impedance across the leads to obtain a more accurate
measurement.
To make a LoZ measurement, set the rotary switch to L. The
Meter displays the ac voltage in the primary display and the dc
voltage in the secondary display. During LoZ measurements, the
Meter’s range is set to 1000 volts in the manual ranging mode.
In LoZ, both R and M are disabled. There are no additional
modes for this function and the softkey labeled Menu is therefore
disabled as well.
Making dB Measurements
The Meter is capable of displaying voltage as a dB value, either
relative to 1 milliwatt (dBm), a reference voltage of 1 volt (dBV)
or a user-selectable reference value. See the “Setting a Custom
dBm Reference” section later in this manual.
Menu
41.83
dBm
VAC123.45
Save Setup
1000 Reference
Auto Range
500 VAC0 100 200 300 400
Ref
8:10pm
06/13/07
est08.eps
Figure 11. dBm Display
To set the Meter to display values in dBm, set the rotary switch
to V or T and press the softkey labeled Menu. Move the menu
selector to the menu item labeled dBm. Press the softkey
labeled dBm. The dBm, Hz menu selection replaces the
secondary display (123.45 VAC in Figure 11) with the frequency
measurement. All voltage measurements are displayed as a
dBm value, as shown in Figure 11.
A dBm measurement must use a reference impedance
(resistance) to calculate a dB value based on 1 milliwatt. When
set to 600 Ω (default), the reference impedance is not displayed
during a dBm measurement. When set to something other than
600 Ω, the reference impedance is displayed just above the
softkey labels.
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