User manual

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.