second-reduction pinion. The gear train pinion is
driven by the drive ring and in turn drives the three
spur gears. Two of the spur gear drive the two
tachometer generators through quill shafts (the
third gear drives the revolution counter and
elapsed time indicator).
The output signal from each tachometer
generator consists of voltage pulses generated at
the rate of 512 pulses for each propeller shaft
revolution. The signal voltage and pulse width are
determined by the rotational speed of the
tachometer drive assembly. The tachometer
signals pass through separate amplifiers located
on the MRG casing near the tachometer enclosure.
After being amplified and converted to 256 pulses
per shaft revolution, the tachometer signals
enter the signal conditioning enclosure (S/CE).
Comparison circuitry, within the S/CE selects
the strongest tachometer signal and sends it on
to the rest of the ECSS for logging and display
of shaft speed. The tachometer (quill) shaft
Figure 8-14.--Revolution counter and elapsed time
must be turning at least 30 rpm for a reliable
indicator.
reading.
pinion. It contains provisions for connecting
a tachometer generator, a revolution counter,
and a magnetic speed sensor. The tachom-
DANGER
eter generator and revolution counter are
driven at exactly 50 percent of the propeller shaft
Do not attempt to work on the ta-
speed.
chometer system while it is in the
automatic propulsion mode. A loss of
signal from the tachometer could cause an
MRG Instrumentation
undesirable or dangerous propulsion plant
response.
A liquid sight indicator (fig. 8-15) is provided
at each main bearing. Each indicator has a
fitting containing a window (bull's eye) through
Revolution Counter and
which a stream of oil can be observed flowing
Elapsed Time Indicator
from the bearing, a fitting for a dial-type
thermometer, and a well for installation of a
The revolution counter is mounted adjacent
remote-reading RTE.
to the tachometer generators and is driven by
the same drive assembly. The unit provides a
L u b e oil pressure at the inlet to the
local, digital display of total propulsion shaft
header is sensed by both a pressure transducer
revolutions and elapsed time at specific shaft
and a pressure switch. The transducer sends
speed ranges. Figure 8-14 shows the face of the
signals to the ECSS for METER/DDI dis-
unit.
play, pump logic operation, data logging,
and HEADER PRESS HI/LO alarming at the
PACC and the PLCC. The pressure switch
Tachometer Generator, Revolution
provides the permissives for the turning gear and
Counter, and Magnetic Speed Sensor Drive
GTE starting.
On the FFG class ships, the tachometer
The most remote bearing lube oil pressure is
generator, revolution counter, and magnetic speed
sensed by a transducer located at the lower
sensor drive are driven by the starboard HS
8-24
