ABM-4083
30
Model DMM will display measurement result of calculation. If the value of “Input” is larger than that of
“Reference”, displayed result will be positive; contrarily, it will be negative if the value of “Input” is smaller
than that of “Reference”.
3.8.3 dB Calculation
Expressing DC and AC voltage in dB makes it possible to compress a large range of measurements into a
much smaller scope. The relationship between dB and voltage is defined by the following equation:
Where: V
IN
is the DC or AC input signal
V
REF
is the specified voltage reference level
The instrument will read 0dB when the reference voltage level is applied to the input.
If a relative value is in effect when dB is selected, this relative value will be converted to dB value before
REL is applied. If REL is applied after dB function has been selected, dB has REL applied to it directly.
To set the reference voltage, perform the following steps:
1. Press
Shift
+
mX+b
for dB math operation and the present reference value is displayed:
REF
：
+0.000000
2. Use
and
keys to choose a numerical place and use
and
keys to increment
or decrement the digits. Enter a value and units prefix.
3. Press
Auto
(ENTER) to confirm the reference voltage, the message “
CHANGE SAVED
” will be dis-
played for a moment. DMM returns back to the measurement status.
4. DMM will display the result of the dB calculation.
If you want to change the parameter values when dB function is in effect, you can take actions as below:
1. Press
Shift
→
to enter the command level, “
4: dB REF
“ will be displayed.
2. Press
to enter the parameter level, and the present reference value will be displayed:
REF: +1.000000 .
3. Use
and
keys to choose a numerical place and use
and
keys to increment
or decrement the digits. Enter a value and units prefix.
4. Press
Auto
(ENTER) to confirm the reference value, the message “
CHANGE SAVED
” will be displayed
for a moment, and DMM will return to the command level. Press
Trig
(ESC) to cancel the reference
value input, DMM returns back to the command level without changing the reference value.
5. Press
Shift
→
key to exit the menu and return to the dB math operation status.
Notes: The dB calculation takes the absolute value of the ratio V
IN
/V
REF
. The largest negative value
of dB is -160dB. This will accommodate a ratio of V
IN
= 1uV, V
REF
= 1000V.
3.8.4 dBm Calculation
dBm is defined as decibels above or below a 1mW reference. With an user-programmable reference impedance,
Model DMM reads 0dBm when the voltage needed to dissipate 1mW through the reference impedance is applied.