TM 1-1520-238-T-5
8–24
8–7.
SYSTEM DESCRIPTION (cont)
8–7
(d) The barometric altimeter (fig. 8–17) is connected to the static port. Sea level barometric pressure is
set using the zero–set locking screw. The zero set knob is then used to set the altitude pointer to zero. A change
in outside air pressure acts instantly on the two opposed aneroids (elastic metal disks). The aneroids (elastic
metal disks) expand or contract as air pressure changes, which causes the rocking shaft to rotate. This rotation is
multiplied by the gear train, which moves the altitude pointer and counters.
STATIC
PORT
M68-127
STATIC
AIR
PRESSURE
GEAR
TRAIN
OPPOSED
ANEROIDS
BAROMETRIC ALTIMETER
STATIC
PRESSURE
FITTING P1
OUTSIDE
AIR
ZERO
SET
KNOB
ROCKING SHAFT
CPG INTR LT OR
PILOT EXT LT/
INTR LT PANELS
0 - 5 VDC
AIR PRESSURE
(INCHES OF MERCURY)
IN.
HG
ZERO - SET
LOCKING - SCREW
POINTER
Figure 8–17.
Barometric Altimeter Functional Block Diagram
