Cubic 156-PMD, Operation Manual

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NOTE: At each end point, a distance of about
6
inches ( is blanked out. This
feature prevents alarms caused by tilting of the search head at the sweep reversals,
observed as a natural tendency in most operators.
d. A sudden short-duration increase of the click rate (chirp) followed by a
lower click rate (anywhere between 3 and clicks per second) indicates an initial
alarm and simultaneous automatic switchover to the POINT mode, when the search
head is swept over an anomaly in the soil, such as at point A in figure 3-1.
3-3 Investigation of Initial Alarms (Chirps).
a. After a chirp has signaled the presence of a possible mine with the
switchover to POINT mode, the click rate drops to a lower rate (anywhere between 3
and 50 clicks per second). Quickly return the search head to the approximate location
where the alarm first occurred and sweep the search head from side to side over the
area in short slow sweeps of 1.5 to 2 feet (0.5 to
in length. An increase in click
rate will be heard from the headset as the side of the search head passes over the
edge of the buried object. (The click rate response sounds similar to a Geiger Counter.)
The click rate will decrease when the search head is centered over the object and will
increase again as the other side of the search head passes over the other edge of the
buried object. By moving the search head slightly forward or backward from sweep to
sweep, the outline of a large buried object can be exactly determined. (For example: In
figure 3-1, higher click rates are obtained at points B through G.)
As
long as an alarm
indication, signified by a higher click rate, is periodically encountered, automatic reset
to the SEARCH mode will not occur. However, when leaving the area of the buried
object, the click rate drops to about ??? clicks per second and then stops after 3.5
seconds. Automatic reset to the SEARCH mode occurs when the POINT mode clicks
stop. If operations are continued, start sweeping immediately after automatic reset to
SEARCH mode occurs and synchronize sweeps again with the metronome clicks (one
click every 2.5 seconds).
b. If after a chirp a repeatable alarm indication cannot be obtained in POINT
mode, investigate the same area again in SEARCH mode. Repeatable chirps obtained
in the same spot indicate a possible mine.
3-4