TM 9-1829A, April 1944
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2021-07-07
e.
Calibrate:
All Stewart-Warner centrifugal tachometers are calibrated two to one (indicate twice the
revolutions per minute of flexible shaft). Therefore, use spindle No. 1 of calibrating machine (T-170645), as
master indicates twice the revolutions per minute at which this spindle turns (chapter 13). Place maximum
hand out of way by turning clockwise to maximum dial reading. Place unit on calibrating machine, run master
at 600 revolutions per minute, set pointer on staff at 650 revolutions per minute reading on unit being
calibrated and tap pointer lightly onto staff with handle of screwdriver (fig. 112). If unit being calibrated does
not have maximum hand, pointer should be set at actual master head reading and all points at which
instrument is checked should agree with master head. The 50 revolutions per minute difference is necessary
to offset the drag of the maximum hand. Run master at 1,800 revolutions per minute. Indicating pointer of
unit being calibrated should read 1,850 revolutions per minute. If instrument is too fast or too slow at 1,800
revolutions per minute master reading, slow down calibrating machine until master head reads zero. Turn
adjusting screw (I, fig. 105) clockwise if unit being calibrated is fast (turn counterclockwise if slow) one or
two turns. Run master at 600 revolutions per minute, loosen indicating pointer and reset again at 650
revolutions per minute (fig. 112). Again, run master at 1,800 revolutions per minute and if unit is still off,
repeat above procedure (refining all adjustments) until unit is correctly calibrated. Then tap pointer securely
onto staff.
Figure 112:Tapping pointer on staff while running on calibrating machine (T-170645)
f.
Replace bezel and case:
Place mechanism in case, replace glass, gaskets, and bezel, and fasten with screws.
Weatherize case with sealing or plugging cement.