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68 Operating the Meter
4. The left side of the display gives the status of the fixed
alarm. It indicates whether the fixed alarm is either on
or off and the current alarm threshold setting in terms
of percent of full scale of the probe in use (1% to 99%).
5. The right side of the display indicates whether the
variable tone alarm is either on or off.
6. The bottom line of the display indicates which function
key (F1-F4) is used to turn the two alarms on or off.
Fixed Alarm
1. Use F1 (ON)orF2 (OFF) to change the status of the
fixed alarm.
2. Use the numeric key pad to enter a two-digit alarm
threshold number. This number is equal to the percent
of full scale of the measurement range of the probe in
use. For example, to set the meter to sound its alarm
at 5 mW/cm
2
when using a Model 8721D probe, which
has a full scale measurement range of 20 mW/cm
2
, set
the alarm threshold to 25%.
3. If you want to turn the variable tone alarm on or off do
that next. See Variable Tone Alarm on the following
page.
4. When you are satisfied with all the alarm settings, press
ENTER and the meter will return to the measurement
screen.
Note
If you change to an
-
other probe with a
different full scale
measurement range,
the alarm threshold
will also change. A
setting that is often
used with shaped fre-
quency response
probes is 50% of
Standard. To set
the alarm for one of
the 8722 series
probes, which have
full scale measure
-
ment ranges of 300%
of standard, calculate
the threshold setting
by dividing the de
-
sired alarm level by
the full scale value.
In this case
50/300 = 16.66%.
Set the alarm thresh
-
old to 17% and the
alarm threshold will
be 51% of Standard
when using a
8722 series probe.