Db Measurements In Ac Volts Functions - Fluke 87 Series IV User Manual

dB Measurements in AC Volts Functions

The two ac volts functions allow you to display readings as
deviations in dB (decibels) above or below an established
level.
Set up dB measurements with the following procedure:
1. Make an ac volts measurement to be used as a
reference point.
2. Press to select dB. The dBm (or dBV) value
appears in the primary display and the ac volts
reading appears in the secondary display. A typical
dB display appears in Figure 3-2.
3. Press again to switch the ac volts and dB
readings. Press a third time to turn dB off.
Figure 3-2. dBm Display
Normally, dB is measured as dBm, which is a measure of
decibels relative to 1 milliwatt. The meter assumes a
resistance of 600 in making this calculation. This
resistance can be set for any value from 1 to 1999
using the meter's setup capabilities (see Chapter 5.)
When set to other than 600
resistance appears in the Index Display. (See Figure 2-4,
item 17.)
If dBm is displayed, check that the reference
resistance value closely matches the impedance
of the system being measured.
Making Measurements
Measuring Voltage
tc032f.eps
,
the dBm reference
Note
3
3-3