(d)
The | 30 volt monitor monitors the output of the +30 volt and the -30 volt power supplies. If the output of either supply increases or decreases beyond specific limits, a warning output is supplied to the logic circuits.
(e)
The greater-than 2500 foot monitor indicates to the logic circuits whether the altitude signal frequency is above or below 115 kHz (2500 feet).
(f)
The dc altitude comparator monitors the two altitude output voltages from the operational amplifiers by comparing them. If the two voltages do not agree within 50 mv, an output is provided to the logic circuits.
(g)
The modulation monitor is used to monitor the transmitter modulation rate. A significant change in modulation rate will result in a warning output to the logic circuits.
B. Control
(1) Turn on Procedure
(a)
Provide electrical power (Ref 24-22-00).
(b)
Provide equipment cooling air (Ref 21-58-00).
(c)
Close ALTM LOW R1 and ALTM LOW R2 circuit breakers on P7 and ALTM LOW R3 circuit breaker on circuit breaker panel P126.
(d)
The height indicators should display an altitude between -3 and -11 feet with the warning flag out of view. The LRRA-3 failure annunciator should display a valid (black) indication.
EFFECTIVITY AZ ALL; IB 406-499
CONFIG 02 Page 14 Apr 25/88
34-33-00
LOW RANGE RADIO ALTIMETER SYSTEM - DESCRIPTION/OPERATION
________________________________________________________
1. General_______
A. The low range radio altimeter (LRRA) system supplies vertical position information for use by the pilots during approach and landing phases of flight operation. The LRRA system provides an accurate measurement of absolute altitude (height above terrain) from 2500 feet to touchdown. Flag alarm, dc altitude, and vertical terrain clearance (altitude trip) outputs are available for use by other systems.
B. On XA ALL EXCEPT IB 406-499, SN 351-399, two complete systems are installed in the airplane. Each system consists of a receiver-transmitter, height indicator, decision height (DH) light and rising runway display on an attitude director indicator (ADI), trip trim module, transmit antenna, and receive antenna. Location of components is shown on Fig. 1.
C. On SN 351-399, three systems are installed in the airplane. Systems 1 and 2 consist of a receiver-transmitter, trip trim module, height indicator, DH light and rising runway display on an attitude director indicator, transmit antenna, and receive antenna. System 3 consists of a receiver-transmitter, failure annunciator, transmit antenna, and receive antenna. Location of components is shown on Fig. 1.
D. On AT airplanes,
provisions for a third LRRA system are installed,
E. Power distribution to the LRRA equipment and the interface between the LRRA systems and other airplane systems is shown on Fig. 2.
2. Receiver-Transmitters and Trip Trim Modules___________________________________________
A. The receiver-transmitters are located side by side in center equipment center E9. A test connector with protective cover, three failure annunciators, and a control to reset the failure annunciators are located on the front panel. The failure annunciators identify a failure in the receiver-transmitter, height indicator, or antenna and coaxial cables. Two locking lugs secure the unit to its mount. A handle for carrying the unit is provided on the front panel.
Trip trim modules are located in center equipment center E9 behind their respective receiver-transmitter. Each module contains six potentiometers used for adjustment of the preset altitude trips.
3. Antennas________
A. The antennas are flush-mounted, probe-fed conical horns. Two identical antennas are used in each system, one for transmitting and one for receiving.
B. On ALL EXCEPT SN 351-399, the No. 1 and 2 system transmitting antennas are located to the left and right, respectively, of the lower fuselage centerline at body station
913. The No. 1 and 2 system receiving antennas are located to the left and right, respectively, of the lower fuselage centerline at body station
933. Coaxial cables connect the antennas to the receiver-transmitters. Each systems transmit and receive antennas are interconnected by a coaxial cable which provides a controlled leakage input signal to the receiver-transmitter integrity monitor circuits.
EFFECTIVITY
AF ALL; SN351-399; MD ALL; CONFIG GN ALL; AT ALL; VM ALL 08 Page 1 Apr 25/88
34-33-00
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AFT CENTER EQUIPMENT CENTER 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2(61)
