Magnification

TM-11-427 Barometers ML-102-B ML-102-E ML-102-F ML-102-G and ML-316/TM Manual
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1/8 inch in thickness. The lead exhaust tube through which the cell is

evacuated is pinched off and sealed at the end.

(2) The movement of the cell, caused by the varying pressure of

the atmosphere, is transmitted to the gear sector lever by thin strips

of beryllium copper which act as hinges. A fixed hinge serves as the

fulcrum of the gear sector lever. The teeth of the gear sector engage

a small pinion on the pointer shaft. A wire safety stop prevents the

teeth on the gear sector from becoming disengaged from the pinion

gear during severe vibrations or rough handling. A small auxiliary coil

spring is attached to the gear sector lever. The tension of the spring

can be varied by an adjusting disk which has a gear at its lower end

which meshes with a brass adjusting sector (fig. 9). The adjusting

disk is reached through a plugged opening in e plastic window. The

range of adjustment is approximately 10 millibars. Backlash in the

gears is removed by means of a small wire spring attached to the lower

side of the gear sector. The tension of this spring is transmitted to

the pointer shaft by a nylon thread looped once around a small lucite

drum at the base of the pointer shaft. A stop is provided to prevent

expansion of the cell below its lower limit during air transportation.

(3) The pinion is fastened to the pointer shaft which revolves in

a jeweled bearing at the bottom and extends through a hole in the

top bearing plate. The pointer, fastened to the end of the shaft, is

made of three sections of fine aluminum tubing and is clamped to

the shaft by a small setscrew.

b. Magnification. Magnification of the cell movement is accomplished

in three stages:

(1) The first stage is a simple lever magnification, being the ratio

of the distance between the fixed hinge (which acts as the fulcrum of

the lever) and the teeth of the gear sector to the distance between the

two hinges.

(2) The second stage is the ratio of the diameter of the gear sector

to the diameter of the pinion.

(3) The third stage is the ratio of the distance between the pointer

shaft and the scale being read to the radius of the pinion.