Fluke 287 Fluke 287 and 289 Multimeter Users Manual - Page 33

Using LoZ for Voltage Measurements (Model 289 only), Making dB Measurements, dBm Display

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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. 8:10pm True-rms Digital Multimeters Making Measurements 06/13/07 41.83 dBm Auto Range 0 100 200 300 400 500 VAC 123.45 VAC 1000 Reference Menu Save Ref Figure 11. dBm Display Setup est08.eps 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. 23

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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 k
Ω
).
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
VAC
123.45
Save
Setup
1000
Reference
Auto Range
500 VAC
0
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.