Aetna SM Versions - Manual

PRECISION SENSITIVE DIGITAL TACHOMETER
INSTALLATION INSTRUCTIONS
Special Instructions for ‘-SM’ & ‘-SH’ Versions
Aetna Engineering Precision Sensitive Digital
Tachometers are premium quality instruments.
They use "LSI" digital circuitry to provide an
instrument guaranteed accurate to one RPM,
that, never requires calibration, and performs
reliably in the marine environment.
The ‘-S_’ version tachometers are supplied with
a special ratio setting designed to operate from
the signal provided from a “mag-pickup" or other
sensor which receives a particular number of
pu!ses-per-revoIuiion (PPR) from the rotating
device to be measured. The PPR ratio refers to
the preset number of pulses the tachometer
must detect for each revolution of the apparatus
to be measured. The -SM' version is rated for
use between 28 and 90 PPR and the '-SH'
version is rated for use between 90 and 255
PPR. The overall tachometer performance
involves functions beyond the PPR ratio, such as
filter constants and signal sensitivity. Therefore,
the correct version. '-SM' or '-SH' must be used
for the specific PPR ratio desired or satisfactory
performance will not be realized.
The tachometers are available with either Light
Emitting Diode (LED-Model 8402) or Liquid
Crystal Display (LCD-Model 8905) readouts.
The LED is best suited for use in shaded
sunlight while the LCD should be used in
applications where the tachometer will be
exposed to direct unshaded sunlight. Both are
self-iiluminated for night viewing.
The tachometers are supplied with a choice of
black or polished stainless steel bezel. The
black bezel tachometer includes a trim ring
which can be optionally used as required to
match
existing instrumentation. Aetna
tachometers also fit perfectly inside both the
round and square VDO Blue Line cases (contact
us for detailed instructions).
Mounting:
Select a mounting location where the tachometer
may be easily read. The front of the tachometer
has a gasketed glass-to-metal seal making it
suitable for use in locations exposed to rain and
spray. It uses only non-ferrous materials so it
can be located in close proximity to a compass
without significantly affecting the compass
(nevertheless, the compass adjustment should
be checked after installation; particularly
because the removed tachometers may have
been influencing the compass). The unit may be
installed in an existing standard 3-3/8 inch
diameter hole. It will fit holes up to 4 inches
when used with the optional black trim ring. If
placing the tachometer under a protective glass
cover, be sure that it is adequately ventilated to
keep the maximum temperature of the case
below 175 degrees Fahrenheit. Exceeding this
case temperature may damage the tachometer.
Mount the tachometer using the clamp and
hardware provided. In exposed locations it
should be bedded down with a bead of sealant
behind the flange. Place the tach in the raised
trim ring if it is to be used, if the trim ring is
positioned so that it will collect water, drill a
3/16" drain hole at the lowest point in the ring.
The clamp legs may be bent over or cut off to
accommodate thicker panels. An O'ring is
included for use as a centering aid when
installing the unit in 3-3/8 inch holes. If the hole
is tight, roll the O'ring back from the flange then
insert the tach so that the O'ring rolls into the
hole as the tach is inserted. For larger holes an
Oaring type spacer may be made from a length
of appropriate diameter wire.