Section 3: Basic DMM operation
Model 2110 5½ Digit Multimeter Reference Manual
3-56
2110-901-01 Rev. C/August 2013
dBm
The dBm math function is defined as decibels above or below a 1 mW reference. With a user-
programmable reference impedance, the instrument reads 0 dBm when the voltage needed to
dissipate 1 mW through the reference impedance is applied. The relationship between dBm, a
reference impedance, and the voltage is defined by the following equation:
Where:
V
IN
is the input signal voltage
Z
REF
is the reference impedance
The reference resistance (Z
REF
) can be set from 50
Ω
to 8000
Ω
and can be set from the front panel
or by using remote programming. Changing the reference resistance does not affect a stored null
(relative) value.
The reference resistance value is stored in volatile memory. The reference resistance defaults to 600
Ω
when power to the instrument is cycled.
This feature is available for DCV and ACV only.
Front-panel operation
Perform the following steps to use the dBm function:
1. Select the
DCV
or
ACV
function.
2. Press the
SHIFT
and
NULL
(
MATH
) keys.
3.
Use the ◄ and ► keys to display
dBm
and press
ENTER
.
4.
Use the ◄ and ► keys to display
REF RES
and press
ENTER
.
Note that if you select the
RUN
menu option instead, the percent function will enable using the
current target value.
5.
Use the ◄, ►, ▲, and ▼ keys to enter the reference resistance and press
ENTER
.
6. With
RUN
displayed, press
ENTER
. The MATH indicator turns on.
You can disable the math operation by pressing a different function key. You can also disable it from
the math menu as follows:
1. Press the
SHIFT
and
NULL
(
MATH
) keys.
2.
Use the ◄ and ► keys to display
OFF
and press
ENTER
.