TM 1-1520-238-T-58–248–7.SYSTEM DESCRIPTION (cont)8–7(d) The barometric altimeter (fig. 8–17) is connected to the static port. Sea level barometric pressure isset using the zero–set locking screw. The zero set knob is then used to set the altitude pointer to zero. A changein outside air pressure acts instantly on the two opposed aneroids (elastic metal disks). The aneroids (elasticmetal disks) expand or contract as air pressure changes, which causes the rocking shaft to rotate. This rotation ismultiplied by the gear train, which moves the altitude pointer and counters.STATICPORTM68-127STATICAIRPRESSUREGEARTRAINOPPOSEDANEROIDSBAROMETRIC ALTIMETERSTATICPRESSUREFITTING P1OUTSIDEAIRZEROSETKNOBROCKING SHAFTCPG INTR LT ORPILOT EXT LT/INTR LT PANELS0 - 5 VDCAIR PRESSURE(INCHES OF MERCURY)IN.HGZERO - SETLOCKING - SCREWPOINTERFigure 8–17.Barometric Altimeter Functional Block Diagram
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