TM 1-1500-204-23-4
than one-half of the minimum scale division), examine
lines and connections for security and anchorage.
When lines are secure and anchored properly and
pointer still oscillates, replace indicator.
(b)
Zero
check
test.
At
zero
indication, errors must not exceed tolerances specified
in table 4-11. When tolerances listed in table 4-11 are
exceeded, indicator shall be replaced.
i.
Remote
Reading
Pressure
Indicators.
Principles of operation, types, and testing of remote
reading pressure indicators are described in the
following paragraphs.
(1) Principles of operation and types.
Remote reading pressure indicators are connected
indirectly
to
the
pressure
source
by
electrical
transmitters and wiring. The transmitters are connected
directly to the pressure source by tubing or hose. As the
pressure increases or decreases, the mechanism in the
transmitter is displaced. When the mechanism is
displaced, a signal is sent to the indicator through the
electrical wiring which causes the mechanism in the
indicator to turn to a corresponding position as that of
the transmitter, thus giving an indication of the pressure
being measured. This type system is called self-
synchronous (autosyn), and may be adapted to
practically all pressure measuring needs. The autosyn
system of transmitting pressure readings may be
incorporated for use with oil pressure, fuel pressure,
multi-purpose,
hydraulic
pressure,
and
manifold
pressure indicators.
Table 4-9. Static Friction Error (Counter Drum
Pointer) (Vibrator Inoperative)
Test point
altitude
Tolerance
(feet)
(feet)
500 ..........................................
70
1,500 ..........................................
70
2,500 ..........................................
70
3,500 ..........................................
70
7,500 ..........................................
80
12,500 ..........................................
90
17,500 ..........................................
110
22,500 ..........................................
120
32,500 ..........................................
180
35,500 ..........................................
300
42,500 ..........................................
300
(2) Testing. The following paragraphs
describe tests and replacement criteria for remote
reading pressure indicators.
(a) Continuity check test. Test wiring
for proper continuity as specified in applicable wiring
diagram.
(b) Master transmitter test. Test
indicators and transmitters with a synchro test set.
When either indicator or transmitter is faulty, it will be
replaced.
(c) Zero check test. With ac power on
(26V, 400Hz), error at zero indication must not exceed
tolerances specified in table 4-12. When errors exceed
tolerances listed in table 4-12 and wiring and transmitter
are in correct working order, the indicator will be
replaced.
j. Tachometer Systems. Principles of operation,
types, and testing of tachometer systems are described
in the following paragraphs.
(1) Principles of operation and types.
Tachometer
systems
are
independent
instrument
systems which furnish their own operating power. A
tachometer system consists of an indicator, a generator,
and connecting wiring. Synchronous rotor three-wire,
synchronous rotor two-wire, dual synchronous rotor
three-wire,
and
dual
synchronous
rotor
two-wire
tachometer systems are the most common types.
(2) Testing. The following paragraphs
describe tests and replacement criteria for tachometer
systems.
Table 4-10. Pressure Altitude Difference (Counter
Drum Pointer)
Pressure
Altitude
(inches of
difference
mercury (Hg))
(feet)
28.10 .................................................
-1727
28.50 .................................................
-1340
29.00 .................................................
-863
29.50 .................................................
-392
29.92 .................................................
0
30.50 .................................................
+531
30.90 .................................................
+893
31.00 .................................................
+983
4-20
