TM 1-1500-204-23-4
4
Friction stop and jump test. The
altimeter shall be tested for friction in both ascending
and descending directions at the test points specified in
table 4-8. With the internal vibrator energized, the
pressure to the static port of the altimeter shall be
applied at the rates indicated for the test points in table
4-8. The change in the indicating position of the pointer,
due to apparent stopping and jumping as the counter is
turning or at any other place around the dial, shall be
recorded as friction and shall not exceed the tolerances
specified in table 4-8, column C. This test shall be
repeated with all electrical power off. The stop and
jump friction for the test as specified shall not exceed
the tolerances in specified table 4-8, column D.
5
Static friction test. At the
completion of the friction stop and jump test paragraph
4, and with all electrical power off, the altimeter shall be
subjected to a constant rate of decreasing pressure not
exceeding 3,000 feet per minute until the pressure is
within 100 feet of the tolerance listed in table 4-9 for
each test point. At this time, the rate of pressure
change shall be gradually decreased until the desired
test point is obtained. The pressure shall then be held
constant while two readings of the altimeter are taken,
the first without the integral vibrator operating and the
second with the vibrator operating. The difference
between the two readings shall be recorded as static
friction and shall not exceed the tolerances listed in
table 4-9.
6
Case leak test. The leakage of
the altimeter case, when the pressure within it
corresponds to an altitude of 30,000 feet, shall not
change the altimeter reading by more than the tolerance
shown in table 4-7 during an interval of one minute.
7
Barometric scale error test. At
constant atmospheric pressure, the barometric pressure
scale shall be set at each of the pressures (falling within
its range of adjustment) that are listed in table 4-10 and
shall cause the pointer to indicate the equivalent altitude
difference shown in table 4-10 within a tolerance of 25
feet.
8
Internal lighting test. Red and
white internal lighting shall be functionally tested in
accordance with applicable maintenance manual.
(c)
Replacement
criteria.
After
completion of tests, a tamper seal shall cover the
baroset locking screw. An inspection sticker with date of
completed bench test shall be placed on the outside of
the case. Compute reinspection date from date on the
inspection sticker.
h. Direct Reading Pressure Indicators. Principles
of operation, types, and testing of direct reading
pressure
indicators
are
described
in
following
paragraphs.
(1)
Principles
of
operation
and
types
indicators. Direct reading pressure indicators are
connected directly to pressure source by tubing or
flexible hose. Typical of the direct reading pressure
indicators are the fuel pressure, oil pressure, hydraulic
pressure, manifold pressure, and vacuum pressure.
(2) Testing. The following paragraphs
describe tests and replacement criteria for direct reading
pressure indicators.
(a) Pressure pointer oscillation test.
When pressure indicator pointers oscillate excessively
(more
Table 4-8. Friction Stop and Jump Error (Counter Drum Pointer)
Column A
Column B
Column C
Column D
test point
rate of ascent
tolerance
tolerance
altitude
or descent
vibrator
vibrator
(feet)
(feet per minute)
operative (feet)
inoperative (feet)
0
500
25
300
1,000
500
25
120
3,000
500
25
120
5,000
500
25
120
10,000
500
25
350
20,000
3,000
25
350
30,000
3,000
25
350
35,000
3,000
50
600
40,000
3,000
50
600
Change 1 4-19
