(2)
Platform heading input

 (3)
Heading servo null

 (4)
Servo loop control transformer (CT) rotor continuity

 (5)
Magnetic field sensor excitation current

 G.  Failure of the monitored functions results in loss of the super flag output voltage (28 volts dc nominal) from the coupler. In addition, a latching indicator on the front of the coupler trips when heading servo loop failure occurs.
 6.  Horizontal Situation Indicator (HSI) and Radio Magnetic Indicator (RMI)
_______________________________________________________________________
 A.  The HSI's and RMI's are on the captain's and first officer's instrument panels. Heading information from data transmitters in the compass coupler is fed to resolvers in the indicators. The resolvers develop a signal relative in phase and magnitude to the heading signals. The resolver signal is amplified and drives a synchro-motor which positions a rotating compass card to indicate the heading against a fixed index at the top of the indicator. The synchro-motor also drives a rate generator which provides a rate signal to the resolver to null the heading signal as the rotating compass card is positioned to the correct heading.
 EFFECTIVITY

 

 ALL  12 Page 9  Aug 25/8234-21-00
 B.  A flag logic circuit in the indicators senses indicator resolver outputs and heading valid signals from the compass couplers. As long as all signals are present, the heading flag is held out of view. If any of the signals are lost, the heading flag will appear at the fixed heading marker at the top of the indicator.
 7.  Flight Instrument Switching Relays__________________________________(See figure 3.)
 A.  The MHRS interfaces with the flight instruments through a network of flight instrument relays and switches which consists of the following:
 (1)  
Captain's compass transfer switch and relay.

 (2)  
First officer's compass transfer relay.

 (3)  
Captain's VOR/ILS-INS switch and VOR/ILS-INS relay.

 (4)  
First officer's VOR/ILS-INS switch and VOR/ILS-INS relay.

 (5)  
Captain's attitude/compass stabilization transfer switch and relay.

 (6)  
First officer's attitude/compass stabilization transfer relay.

 B.  The relays are standard stepping relays and are located in the flight instrument relay panel (P73), which is attached to the left side of the equipment rack (El) in the main equipment center. (See figure 3.)
 C.  Arc suppression diodes are connected across each relay coil to eliminate high voltage transients which may damage the coil. These diodes are contained in the instrument switching accessory box.
 D.  Magnetic heading outputs from the compass coupler are controlled through the compass transfer and RADIO/INS switching networks. Platform heading input to the coupler is controlled through the attitude/compass stabilization switching network.
 8.  Operation
_________
 A.  Functional Description, Flight Instrument Switching (See figure 4.)
 (1)  
Platform heading and platform heading valid signals from the inertial navigation systems are transferred through the attitude/ compass stabilization switching network to the compass couplers. The platform heading gyro signals are used to damp the magnetic heading signals from the magnetic field sensors.

 (2)  
The gyro stabilized magnetic heading outputs from the compass couplers are transferred through the compass transfer and RADIO/INS switching networks to compass cards in the horizontal situation indicators and radio magnetic indicators.

 (3)  
INS 1 normally provides stabilization signals to compass coupler 1 which in turn supplies stabilized magnetic heading to the captain's HSI and VOR RMI plus the first officer's ADF RMI. INS 2 normally supplies stabilization signals to compass coupler 2 which supplies stabilized magnetic heading to the first officer's HSI and VOR RMI plus the captain's ADF RMI. However, the switching is arranged so that INS 3 may be switched to provide stabilization to either compass coupler 1 or 2. Either compass coupler may be selected to drive the captain's and first officer's flight instruments.

 B.  Functional Description, Slaved Mode
 (1)  Input Signals
 (a)  In the slaved mode, the 800-Hz three-phase signal from the field sensor (representing the earth's magnetic field) is compensated and applied to the compass coupler (Fig. 5). The INS platform heading signal is also a three-phase synchro signal, applied to the coupler.
　
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