Fluke 189 - Manual (Page 40)

Model 187 & 189
Users Manual
3-4
dB is calculated with the following formula:




=
Vr
Vx
dB
10
log * 20
•
For dBm, Vr is the voltage across the reference
resistance at 1 mW. For example, Vr would be
0.7746 V with a 600
Ω
reference resistance.
•
For dBV, the reference voltage (Vr) is 1 V.
Measuring DC Voltage
Set up the meter for dc voltage measurement as shown in
Figure 3-4. All pushbutton features are available for a
standard dc volts reading.
Both AC and DC Voltage Measurements
When a dc volts function is selected, the meter can
display ac and dc components of a signal separately or
the combined ac + dc (rms) value.
To select separate ac and dc signal components:
•
Press % once to display ac voltage in the primary
display and dc voltage in the secondary display (ac
over dc).
•
Press % a second time to reverse the displays (dc
over ac).
•
Press % a third time to display the ac + dc rms value
in the primary display. (FAST MN MX is unavailable in
this state.)
•
Press % a fourth time to return to the normal dc volts
display.
Figure 3-3 shows some typical displays.