TM 1-1500-204-23-4
the barometric dial is immaterial. The vibrator must be
energized throughout this test. Beginning with the
barometric pressure at 31.018 inches of mercury the
altimeter shall be subjected to successively decreasing
then increasing pressures corresponding to altitudes
specified in table 4-6. The reduction m pressure shall
be made at a rate not in excess of 10,000 feet per
minute to within approximately 300 feet of the test point.
The test point shall be approached at a rate compatible
with
Table 4-5. Pressure Altitude Difference
(Three 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
30.99 ..........................................
+974
Table 4-6. Scale Error (Counter Drum Pointer)
Altitude
Equivalent pressure
Tolerance
(feet)
Inches of mercury-Hg)
±(feet)
-1000
31.018
±30
0
29.921
±30
500
29.385
±35
1000
28.856
±35
2000
27.821
±40
3000
26.817
±45
5000
24.896
±50
8000
22.224
±60
10000
20.577
±65
12000
19.029
±70
15000
16.886
±80
18000
14.942
±90
20000
13.750
±95
25000
11.103
±105
30000
8.885
±115
35000
7.041
±125
38000
6.097
±140
40000
5.538
±140
45000
4.355
+185
50000
3.425
±500
the test equipment. The altimeter shall be kept at the
pressure corresponding each test point for at least one
minute, but not more than five minutes before a reading
is taken. The error at all test points must not exceed the
tolerance specified in table 4-6.
2
Hysteresis test. The hysteresis
test shall begin not more than 15 minutes after initial
exposure of the altimeter to the pressure corresponding
to the upper limit of the scale error test prescribed in
paragraph 1. While the altimeter is at this pressure, the
hysteresis test shall commence with vibrator operative.
Pressure shall be increased at a rate simulating a
descent in altitude at the rate of 5,000 to 20,000 feet per
minute until within 3,000 feet of the first test point, table
4-7. The test point shall then be approached at a rate of
approximately) 3,000 feet per minute. The altimeter
shall be kept at this pressure for at least 1 minute, but
not more than 15 minutes, before the test reading is
taken. After the reading has been taken, the pressure
shall be increased further, in the same manner as
before, until the pressure corresponding to the second
test point table 4-7, is reached. The altimeter shall be
kept at this pressure for at least 1 minute, but not more
that 10 minutes, before the test reading is taken. When
the reading has been taken, the pressure shall be
increased further, in the same manner as before, until
third test point table 4-7 is reached. The reading of the
altimeter at either of the three test points shall not differ
by more than the tolerance specified in table 4-7 from
the reading of the altimeter for the corresponding
altitude recorded during the scale error test prescribed in
paragraph 1.
3
After-effect test. With vibrator
operative and not more than five minutes after
completion
of
the
hysteresis
test
prescribed
in
paragraph 2 the altimeter reading (corrected for any
change in atmospheric pressure) shall not differ from
the original atmospheric pressure reading by more than
the tolerance specified in table 4-7.
Table 4-7. Test Tolerances (Counter Drum Pointer)
Tolerance
Test
(feet)
Case LeakTest ......................................
100
Hysteresis Test:
First Test Point (25,000)........................
60
Second Test Point (20,000) ...................
60
Third Test Point (0) ...............................
30
After-Effect Test....................................
30
Change 3 4-18
