(2)
Both the indicator and air data computer are designed to give correct readings at a ground level barometric pressure of 29.92 inches of mercury. An independent mechanical system, controlled manually by the BARO set knob (figure 7), corrects the main rotating shaft through a differential and the servo repeater system by rotating the synchro stator. Current position of the barometric correction system is indicated on two numerical counters in the instrument face.
(3)
The servo repeater system is controlled from the central air data computer by a three-wire synchro signal representing corrected pressure altitude. (Refer to figure 7.) This signal is translated into a mechanical input to the instruments main rotating shaft. Placing the mode switch to STBY opens the servo repeater loop and allows pneumatically derived forces (alone) to operate the counters and pointer. With the mode switch in the CADC position, the servo repeater loop is closed and the counters and pointer are positioned by the higher resolution and more accurate corrected pressure altitude signal from the air data computer.
(4)
A vibrator is mounted on the instrument frame to reduce friction errors during pneumatic mode operation only. The only tie-in the vibration system has with other instrument subsystems is power on-off switching, which is controlled by the mode switch (Kl, figure 7)
(5)
Four areas are monitored for possible failure; central air data computer power and servo operation, and altimeter power and servo repeater loop operation. (Refer to figure 7.) Upon detection of a malfunction in any of these areas by the failure monitor, a red STBY flag appears in the altimeter face, the mode automatically shifts to standby (disabling servo loop), a vibrator is turned on, and the 26 volt ac excitation supplied to the air data computer altitude servo is disconnected. All these operations occur whenever the mode switches are placed in the STBY position.
(6)
The autopilot/flight director system directs a coarse and a fine altitude error signal from its altitude select system through differential transformers in the captain's altimeter to the pitch computers and to the altitude alert system from the first officer's altimeter. The barometric correction system mechanically positions the two transformers as it corrects the other altimeter systems (Fig. 7). This signal conditioning service is independent of other altimeter systems.
EFFECTIVITY
ALL 30 Page 14 Dec 25/8434-13-00
AIRSPEED ERROR (OUTPUT TO AUTO THROTTLE COMPUTER)
26V AC (FROM AUTO THROTTLE COMPUTER)
AUTO THROTTLE AIRSPEED SELECT COMMAND (FROM MODE SELECT PANEL)
28V DC (FROM AUTO THROTTLE COMPUTER
INDICATED
T33514
XA
DC POWER NOT CONNECTED ON
AZ 221-225, 231-233, 281
Indicated Airspeed Indicator - Simplified Command Airspeed Circuit
Figure 6 (Sheet 1)
EFFECTIVITY ALL XA EXCEPT;
LH 011-030,051-070,082-099;
AF 152-199; MD 501-599;
GN 601-699; AT 701-750;
799 Page 15
34-13-00
IB 406-499; VM 751-799 Dec 25/83
T33525
..... .......XA
AIRSPEED ERROR (OUTPUT TO AUTO THROTTLE COMPUTER FROM CAPTAIN'S INDICATOR)
26V AC (FROM AUTO THROTTLE COMPUTER)
AUTO THROTTLE AIRSPEED SELECT COMMAND (FROM AUTO THROTTLE COMPUTER)
28V DC (FROM AUTO THROTTLE COMPUTER)
AUX FUEL SW INSTALLED ONLH 014-050; IB 406-499, AND AF 181-182,197-199 AFTER INCORP OF SB 28-2119
DC POWER NOT CONNECTED ON LH 011-013,051-070,082-099
Indicated Airspeed Indicator - Simplified Command Airspeed Circuit
Figure 6 (Sheet 2)
EFFECTIVITY
LH 011-099; AF 152-199;
MD 501-599; GN 601-699;
AT 701-750; IB 406-499;
799 Page 16
VM 751-799
34-13-00
Dec 25/88
C. Primary altitude indicators receive 26 volt ac power controlled by circuit breakers in electronic circuit breaker panel P7. Captain's altimeter power comes from the essential flight instrument bus (115 volts ac) through flight instrument transformer No. 3 and circuit breaker CADC 1, SVO PNEU ALTM IND 1. First officer's power comes from flight instrument bus No. 2 through flight instrument transformer No. 6 and circuit breaker CADC 2, SVO PNEU ALTM IND 2.
D. The vibrator circuit in each altimeter is powered by 28 volts controlled by circuit breakers in electronic circuit breaker panel P7. The captain's altimeter draws its power from the essential transformer rectifier unit, through the 28 volt dc essential flight instrument bus and circuit breaker ALTM VIB 1. The first officer's altimeter draws its power from transformer-rectifier unit No. 2 through the 28 volt dc flight instrument bus No. 2, and circuit breaker ALTM VIB 2.
XA 8. _________________________
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：747飞机维护手册AMM CHAPTER 34 - NAVIGATION 第34章导航1(80)
