TM 5-3895-363-13&P
16.3.3
16.3.4
DISPLAY MODE A
All strokes determined after “BAT” was
switched on or after “A” was depressed are
summed. When “A” is depressed. the
average stroke is computed and displayed
together with the number of strokes
averaged. The average mode of display is
identified by an A in the last position of the
stroke display. The average result is
displayed until either “B” or “A” is again
depressed.
In the “A” mode, triggering and
computation proceed exactly as in the “B”
mode An indication that triggering occurs
is given by the blinking of the A indicator.
The blow number is reset and the
summation of strokes is restarted at zero
with each depression of “A”. If “A” is again
depressed, a new average and
corresponding blow count will be given.
Note that the computation of the average
takes a brief but noticeable time and that
display of the average occurs
approximately one-half second after “A” is
depressed.
WARNING SIGNAL
Inconsistent hammer operation or erratic
triggering can cause varying stroke values
to be displayed by the SAXIMETERTM Stroke
Indicator. In order to warn the operator of
this condition, all decimal points in BLOW
NUMBER and the colon in STROKE are
displayed when any stroke reading differs
from the previous stroke by one foot or
more.
In the B mode, the warning signal will be
displayed only for blows with varying
strokes. In the A mode it will stay on until
resetting to the B mode occurs or until
another average is computed which did not
contain any consecutive strokes with more
than 9 feet difference.
A stroke difference of one foot may or may
not be an actual hammer condition and the
following should be considered.
At approximately a 7-foot stroke, a 0.10
second change of duration, At, causes a
l-foot stroke difference. A 1-foot stroke
difference may therefore result from rela-
tively small changes in duration mea-
surement. Unusual hammer-pile systems,
sound reflecting walls or other condi-
tions may effect erratic triggering and
therefore such small changes in the du-
ration measurement. It may then be ne-
cessary to find another microphone loca-
tion where steady triggering occurs.
It is easily determined by observation of the
ram travel whether or not the hammer
strokes inconsistently. If it does, the cause
(lack of lubrication, malfunctioning fuel
pump, poor hammer-pile alignment, etc.)
for the varying stroke should be determined
and corrected to improve the hammer
performance.
16.4 BATTERED PILE DRIVING
Driving battered piles causes increased ram fric-
tion and a gravity that is reduced in the axial
direction.
Figure 40 lists correct strokes, hb, given a SAX-
IMETERTM Stroke Indicator reading h and a batter
angle
a.
A friction angle of
J
= 1.1 degrees was as-
sumed for computation of the results and has little
effect on the correction
The results of Figure 40 indicate insignificant er-
rors of the uncorrected readings for batters less
than 1 5. Corrections for such small batters can
therefore be ignored For batters greater than 1-2
the results are greatly affected by the corrections
Even after correction. the SAXIMETERTM may be in
error due to the uncertainty of friction losses.
16.5 ACCURACY
SAXIMETERTM Stroke Indicator equations were de-
rived under the assumption of normal, i.e minimal.
ram friction. Of course, extreme friction would re-
duce the ram velocity. Then the stroke reading on
the SAXIMETERTM Stroke Indicator would be too
high. The ram surface should appear moist if it is
well lubricated. Scratches on the piston surface
caused by foreign matter may be an indicator of
extreme friction.
Another note: the built-in microphone easily picks
up “body-noise” of the SAXIMETERTM Stroke Indi-
cator. For example, working on the unit or switch-
ing the A, B or other controls may be interpreted
as hammer impact. Thus, for a reduced change of
erractic readings, switching and writing should be
limited to the trigger delay time of 0.7 seconds
after a blow.
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