Page 1
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.
Page 2
Wiring:
During wiring it Is recomnnended that the
negative battery cable be removed from the
battery or the master switch{es) turned off.
The tachometer has a grounded case and is for
use on negative ground systems only (an
isolated case version is available for isolated or
positive ground use.) Connect the "Ground"
terminal to a point that is connected to the
negative {-) battery terminal.
Connect the "+12V" terminal to a point that is
energized when the ignition is switched on;
typically a purple wire. In most cases, power
and ground are available by wiring to the
terminals on an adjacent temperature or oil
pressure gauge, A one amp fuse must be
installed in series with the "+" (Pos) wire in order
to enable the internal surge protector function.
To use the Model 8402 on 24 volts connect a 30
ohm, 25 watt resistor (our Model 8924) in series
with the “+12V" tachometer terminal For 32
volts use a 47 ohm, 25 watt resistor (our Model
8932). Failure to use the appropriate ballast
resistor may damage the Model 8402
tachometer. The "+12V" terminal on the Model
8905 tach. may be safely connected to 12, 24 or
32 volt systems without a ballast resistor.
The "Points" (Sig.) terminal connects the RPM
information signal from the engine to the
tachometer. This connection should be made
using stranded two conductor twisted-shieided
wire. For multiple stations, two or more
tachometers may be connected in parallel
Diesel engines have no ignition and therefore
require a tachometer sender to generates the
digital impulses required by the tachometer.
Traditionally a mechanically driven sender was
mounted on the tachometer drive cable fitting on
the engine. Many newer engines do not have
such a fitting and instead use a magnetic pickup.
A “mag.*’ pickup is a device that senses the
passage of gear teeth in a non-contact manner,
it is screwed into a threaded hole in the gear
housing and adjusted so that the clearance is
approximately one-half turn back from contact
with the gear. The two sender wires are
connected to the signal and ground terminals at
the tachometer using a twisted/shielded cable.
Connect the two wires from the sender through
the two twisted inner conductors. Connect the
shield to the engine block. Do not connect the
tachometer end of the shield. If the signal is
continued on to another tachometer, carry the
shield connection through but do not connect it
to anything but the engine. Using a single wire
and the engine ground is not recommended and
will yield inferior results.
Diesel Sender Installation:
The Aetna Engineering Models 8910, 8912 and
8922 are magnetically coupled senders which
sense the passage of flywheel gear teeth or
similar items. They generates the electrical
RPM signal used by the tachometer. The 8910
and 8912 are housed in a diameter by 16
threads per inch case while the 8922 is
contained in a 5/8” by 18 threads per inch case.
Both the 8912 and 8922 have dual electrical
outputs.
Note that some engines built offshore have
metric sized sender mounting holes. Although
Aetna does not provide metric sized senders,
most metric “mag pickup” senders will
satisfactorily drive Aetna tachometers.
The sender is installed by screwing it into a
threaded hole on the flywheel bell housing or
other housing. It is screwed in until the end
contacts the gear then backed-off one-half turn
and secured in position with the jam nut. The
sender is connected to the tachometer using two
conductor twisted-shieided wire as previously
described.
This combination of tachometer and sender will
register the engine speed accurately to within +/one RPM when the sender is driven at exactly
the preset number of pulses-per-revolution rated
on the tachometer
Page 3
Testing;
Reconnect the battery and turn the ignition on.
The display should illuminate and show "0000"
indicating power is reaching the unit. Start the
engine and verify that the display indicates
engine RPM, When the engine is cold and idling
without load the right hand digits may seem to
"jump." This is due to fluctuation in the engine
speed and is pronounced because the readout
displays variations as small as one RPM. The
RPM's should steady when the engine is warmed
and operated above idle under a constant load.
Should the display continue to jump excessively
check engine tuning, look for a fouled injector or
a fuel suction line air leak. Contact the factory
for more suggestions.
K
If the tachometer shows all zeros with the engine
running, check the signal wiring from the engine.
If the tachometers digits fail to show at all, the
problem is in the power wiring to the tachometer
and not in the signal wiring. If the indicated
RPM is in error, check that the ratio select
switches are set properly.
The tachometer includes special circuitry to
minimize loran interference from the digital
processor. Nevertheless, if a loran set is
aboard, it should be checked for interference by
observing the loran SNR when the ignition is on
without the engine running. Be sure any
interference isn't from an alarm buzzer or bell. If
interference is detected, check the loran antenna
& ground or install a filter, such as the "MAR-P5"
from Marine Technology (562) 595-6521, in the
+12 voit power and ground leads to the
tachometer.
The tachometer is now ready to use. No
adjustment is ever necessary. The circuitry
employs a piezoelectric crystal to permanently
maintain calibration.
On the Mode! 8402 the built-in dimmer senses
the ambient light and adjusts the display
intensity for comfortable viewing. When
operated in bright light the case will feel vrarm to
the touch. This is normal and will not damage
the unit provided the case temperature does not
exceed 175 degrees.
The Model 8905 has internal backlighting
provided by solid state lamps that do not require
routine replacement, The 8905 consumes less
than one-half watt and does not create
significant heat.
A special anti-fogging compound is applied to
the inside of the glass during manufacture.
Internal fogging of the glass may be reduced by
removing the ratio switch cap. In cases of
persistent fogging, contact the factory for
additional help. No routine maintenance of the
tachometer is required. Clean the glass with a
soft cloth. The sensor end of the sender should
be cleaned periodically of any accumulation of
magnetic particles which can shunt the magnetic
sensitivity.
The sender may be tested with an ohmmeter.
Measurement of the resistance on the leads
should be between 100 and 1000 ohms. During
installation, wiring can be verified by temporarily
running a separate wire pair directly from the
sender to the tachometer.
Limited Warranty
Aetna Engineering warrants its tachometers to
be free of defects in material and workmanship
for a period of two years from the date of
purchase as shown on the original consumers
purchase receipt.
Warranty service will be provided free of charge
if the unit is delivered to Aetna Engineering
during the warranty period accompanied by
original consumer proof of purchase. Any
transportation, removal, or reinstallation charges
will be paid by the purchaser whenever incurred
in connection with this warranty. In absence of
proof of purchase receipt, the warranty period
shall be two years from the date of manufacture.
This warranty does not apply to units subjected
to misuse, neglect, accident, incorrect
installation wiring, improper installation, water
damage, or units used in violation of the
installation instructions furnished by us. This
warranty excludes any incidental or
consequential damages connected with failure or
defect in the product. Aetna Engineering
products are not designed, intended or approved
for use on or involving aircraft or in hazardous
locations.
This warranty gives you specific legal rights and
you may have other rights which vary from state
to state.
Page 4
Aetna Digital Tachometers
SWITCH SETTING INSTRUCTIONS
For use by Factory A uthorized Personnel ^ Only
PPR
28
29
30
31
32
33
' 34
35
36
37
3B
40
41
42
43
44
45
46
47
43
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
66
67
68
69 off
70
71
72
73
74
75
76
77
78
79
60
61
62
63
84 off
85 off
66
87 off
88
89
90
Version ‘-SM'
Switch
4
1 2
off
off
off
off
off
off off
off
off off
off
off
off
off
off
off
off
off
off
off off
off
off
off off
off
off
off off
off
off
off
off
off
off off
off
off off
off
off
off off
off
off
off on
off
off on
off
off
off
off
off
off
off
off
off on
off
off on
off
off on off
off
off
off on off
off
off
off on off on
3
off
off
off
off
off
off
off
off
on
off
on off
on
off
on
on
off
on off
off
on
off
on off
off
on
off
on off
off
on off
off
on
off
on off
off
on
on
off
off on
on
on
off
on on
off
on
on
off
on
off
on on
off
on
off
off on
on
on
off
on
off on
on
off
on
on on
off
on off
on off
on
on
on off
on off off
on off
on off
on off
on off off
on off
on off
on off on
on off
on off on
on off
on off
on off
on off on
on off
off off
off off
off
off off
off off
off
off off
off off
off off
off on
off
off on
off on
off off
off on on
off off on
on off
on off
on off
on off
on off
on off
on
on
on
on
on
off
off
off
off
off off
off
off
off
off on
off
on
on off
on
on off
on off
on off
on
on on
on on
on
on
on on
on
Position
5
on
on
on
on
off off
off
off
off
off
off
off
on off
on
on
on off
on
on
on
off off
off off
off
off
on off
on off
on
on on
on
off on
off
off
on off
on
on on
off off
off off
on
on
on
6
on off
off
on
on
on
on on
on
off
off
off
on
off
on
off
on off
on off
on
on
on
on
off
off
off
on off
off
on
on off
on off
on off
on
on on
on
off
off
off
on off
off on
on off
off
on
on off
on
on
on
off
off
off
on off
off
on on
on off
on off
on off
on on
off off
off off
on off
off
off on
off
on off
on on
on on
off off
off
off
on off
off
off on
on off
off
on off
on
on
off
off on
off
on
off
on
off off
on
off
on
on off
on
on
on
off
off
off
off
on
off
Version ‘-SH’
1
Switch Position
3
2
off
on
off
on
off
on
on off
on off
on
on
on
on
on
on
on off
on
on on
on off
on
on
on
on off
on
on off
on
on off
on
on
on
on
on
on
on
on off
on
on
on
on
on
on
on
on
on
on
on
on
on
on
on
on on
on on
on on
on
on
on
on
on on
on on
on
on
on
on on
on
on
on
on
on
off
off
off
off
off off
off
off
off
off
off
off
off
off off
off
off
off off
off
off
off
off
off
off
off
off
off
off on
off
off off
off
off
off on
off
off on
off
off off
off on
off on
A 5
on oft
on
on
on
on
on
on on
on
on on
off off
off
off off
off
off off
off
off
off
off
off
off on
off
off
on
on off
off on
on off
off
on on
off
on
on
off
on on
off
on off
off off
on
on off
off off
on
off
on
off
on
off
on
off
on
on
on
on off
on
on
on
on
on on
on
on
on
on on
off
off
off
off
off off
off
off
off on
off
off
off
off off
off
off
on
off
off on
on
off on
on
off
on
off
on
off
on
off
off off
on
off
off
on
on off
off
off
on off
off
on off off
on
on
6
on
on off
on off
on
on
on
off
off
on
on
off
on oft
on off
on
on on
off off
off
off
on off
off
on
off
off on
on
on on
on
off off
off
off
on
off
on
on off
on off
on off
on
on on
on
off off
off
on
off
on
off
off
on
off
on
on off
on
on
on
off off
off
off
on
on
off
off
on off
on
on
on on
on
off off
off
off
off
on off
off
on
off
on off
on off
on on
on
on
off
off
off
on off
off
on on
off
off off
on
off on
on
on on
on
on
off off
8
7
on
off
on
off
on
off
on
off
on
off
on
off
on
on
on
off
off
on
on
off
on
off
on
off
on
off
on
off
on
on
off
on
off
on
off
on
off
on
on
off
on
off
on
off
on
off
on
off
on
PPR
8
7
off
on
off
off
on
off
on
off
on
off
on
off
on
on
off
on
off
on
on
off
on
on
off
on
off
on
on
off
on
on
off
on
off
on
on
on
off
on
on
off
off
on
on
on
off
on
off
91
92
93
94
95
96
97
98
eg
100
101 off
102
ICG
104
105
106
107
106
109
110
111
112
113
114
115
116
117
116
119
120
121
122
123
124
125
126
127
128
w
129
130
131
132
133
134
135
135
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152 on off
153 on off off
off
off
off
off
off
off
off
off
off
off.
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
off
on off
on off
on
on
on
on off
on
on off
on
on
on
on
on off
on off
on off
on off
on
on
on
on
on
on
on
on off
Page 5
PPR
1 2
154
156
156
157
1^
159
160
161
162
163
164
1Й
166
167
1Ш
1Ю
170
171
172
173
174
ITS
176
177
178
179
180
181
182
183
184 on
185 on
186
187
188
199
190
191
192
193
194
195
196 on
197
193 on
199 on on
200
201
202
203
204 on
on off
on
on
on off
on off
on off
on off
on
on off
on
on
on
on off
on
on
on
on off
on off
on
on off
on off
on
on
on off
on off
on off
on off
on
on
on off
on off
on
on off
on
on off
on off on
on
on on
on on off
on on
on on
on on
on
on on
on on off
Aetna Digital Tachometers
SWITCH SETTING INSTRUCTIONS
For use by Factory Authorized Personnel Only
■ Version ‘-SH’
Switch Position
4 5
3
off
off
off
off off
off
off
off
on
on off
off
on
on off
off
on off
off
off on
on oft
off on
off on
off on
on
on off
off on
on off
on off
off on
off on on
on on
on on
on
on on
off on
off on
on on
off on
off on
on on
off on on
on on
off on on
on on
on off off
off off
off off
on off
off off off
on off
off off
off off on
on off off on
off off on
on off
on off
on
on on
on
on
on
on
on on
on
on
on
off off
off
off off
off off
off on
off off
off
off on
off
on off
off
on off
off
off on
on off
on on
off
on
on on
off on
off
off off
off off
on off
off on
on off
on off
off
on on
on on
on off
on
on on
on
on on
on on
off off
off off
off off
off off
off off on
off off
off on
off on off
off on on
6
on
on
off
off off
on
on off
on
on on
off off
off
off off
on off
off
on on
off
off
on
on off
on
on
off
off on
on off
off
on
off off
on off
on
on
on
off off
off
on off
off on
off
off on
on
on on
on on
off off '
off
off on
off
on off
off on
off off
on off
on
on on
off
off on
off on
on on
off
off on
on
on on
on on
off off
off on
off
off on
on
off off
PPR
8
7
off
on
on
off
on
on
off
on
on
off
on
on
off
on
off
on
on
off
off
on
on
on
off
on
off
off
off
off
off
off
on
206
206
207
206
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
226
226
227
228
229
230
■ 231
232
233
234
235
236
237
238
239
240
241
242
243
244
245 on
246
247 on
248
249
250
251
252
253
254
255
1
on
on on
on
on on
on on
on
on
on
on
on on
on on
on
on
on on
on on
on
on on
on
on on
on
on
on on
on
on
on on
on on
on
on on
on
on
on
on
on on
on on
on
on
on
on on
on
on on
on
on
on
on
on on
on on
on
on
on on
Switch Position
3
2'
on off
off off
off off
on
off
off
on off
off on
on
on off
off
on
off
off on
off on
on
on off
off
off on
on off
off
off on
on
off
on off
on
on off off
on
on
on off
on
on off
on
on
on off
on on
on off
on off
on
on on
on off
on
on on
on off
on
on on
on on
on
on on
on
on
on on
on
on on
on
on on
on
on
on on
on
on on
on
on on
on on
on
on on
on
on on
on on
4
on on
off
on
on
off off
on
on off
on off
off off
on off
on off
on off
off
on off
on on
on on
on
on on
on
on on
on
on on
off
off off
off off
off on
off off
off
off off
on
on off
on off
off
on
off on
on
off on
off on
off off
off off
on off
off off
on
off on
on
off on
off on
on
on off
on off
on off
on on
on
on on
on
on on
on on
on on .
5 6
off
on
on
on on
on
oft
off on
off
on
off
on
off off
on
on off
on off
on
on on
off
off on
off
off on
off on
off off
on off
on on
on on
off off
off on
off
on off
off
on
off
off on
on ,
on on
on on
on
off off
off
on off
off on
off
on
on off
on on
on on
on
off
off
off on
on on
off off
off
on off
on on
off off
off
on off
off
off on
off
off
on
on
on
8
7
on
off
off
off
on
on
on
off
off
on
on
off
on
off
on
off
off
off
on
on
off
on
off
off
on
off
on
on
on
on
off
on
off
on
Procedure: Position the switches according to the table using a thin stylus such as the metal
filler from a ball point pen. Care should be taken to use only moderate pressure in actuating the
individual switches to avoid damaging them. Use of pienty of light and magnification can be
helpfui. Switch #1 is on the left, #8 on the right; up is on and down is off.
Loading...