Relative Readings Modifier (Rel); Decibels And Auto Power Modifier - Fluke 8808A User Manual

8808A
Users Manual
After a function modifier is selected, pressing any function button turns off all modifiers,
causes the secondary display to go blank, and returns unmodified readings to the primary
display.

Relative Readings Modifier (REL)

The relative readings modifier displays the difference between the relative base and the
input measurement. For example, if the relative base is 15.000 V and the present input
measurement is 14.100 V, the display will show -0.900. Readings are shown on the
primary display.
To avoid electrical shock or damage to the Meter, do not touch
the input terminals or test leads during measurement. Relative
readings may not indicate the presence of dangerous voltages
at the input terminals or test leads.
Relative readings modifier cannot be selected if the display shows 0L
(overload) or is blank.
To make a relative reading, press T to select the relative readings modifier. The last
valid reading taken is stored as the relative base, the primary display zeroes out, and
RELX is shown on the primary display. (The secondary display is unaffected.)
To edit the relative base, use the number editor as described in the "Using the Number
Editor" section later in this chapter.
Selecting the relative readings modifier turns off autoranging and locks the present range.
Make sure you are in the correct range before pressing T. If you press Uor V
after pressing T, the Meter exits the relative readings mode.

Decibels and Auto Power Modifier

The decibels modifier takes a voltage measurement, converts it to dBm (measure of
decibels relative to one milliwatt), and displays the result on the primary display.
Press dB to toggle in and out of the decibels modifier. When the decibels modifier is
selected, "dB" is shown on the primary display.
Decibels can be selected only when a voltage function is selected on the primary display
(volts ac, volts dc, or volts ac + dc). Decibels are always displayed in a single, fixed
range with 0.01 dB resolution. However, the basic measurement itself (volts ac for
example) autoranges.
A voltage measurement is converted to dBm using the following formula (value is the
measurement value):
The reference impedance can be set to any of 21 reference impedances listed in Table 3-5
by using the list editor as described in the "Using the List Editor" section later in this
chapter.
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