Keithley 2000 - Db Calculation

dB calculation
Expressing DC or AC voltage in dB makes it possible to compress a large range of measure-
ments 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, the value is converted to dB then REL is
applied to dB. If REL is applied after dB has been selected, dB has REL applied to it.
Configuration
To set the reference voltage, perform the following steps:
1. After selecting dB, the present reference voltage level is displayed:
REF: +0.000000
2. To change the reference level, use the and keys to select the numeric position.
Then use the ▲ and ▼ keys to select the desired value. Be sure to press ENTER after
changing the reference voltage.
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
=
1µV and V
REF
= 1000V.
dB= 20 log
V
IN
V
REF
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Basic Measurements 2-33