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 C.  The electronics section of the NU includes assemblies which control and convert input power, produce precision frequency signals, charge the battery unit, control temperatures, buffer pitch and roll synchro output signals, amplify stabilization and accelerometer loop signals, and control moding and warning flag signals. The pitch and roll synchro signals are buffered in the gimbal electronics and transmitted to the autopilot and weather radar for stabilization.
 D.  Warning flag logic circuits in the electronics section receive signals from the IRU, DCU, and other assemblies in the electronics section. The logic circuits control warning flags in the attitude director indicator and the horizontal situation indicator. The logic circuits also produce a master warning signal for the WARN lamp on the control display unit.
 E.  The electronics section furnishes power, timing and control signals to the IRU and DCU. Horizontal and vertical acceleration signals are processed in the electronics section and transmitted to the DCU.
 F.  The DCU of the navigation unit consists of assemblies which make up a digital computer with input/output circuits to perform necessary conversion between analog and digital signals. The latitude and longitude of the flight origin, waypoints, and destination are inserted into the DCU using the control/display unit keyboard. True airspeed and barometric altitude are signal inputs to the DCU from the central air data computer. The latitude and longitude inputs, air data computer inputs, constants contained in the DCU memory, and inputs from the IRU and electronics are used to continuously solve navigation equations and produce signals for control and display during the NAV mode of operation. The DCU also performs self-tests and comparisons between its output data and the output data of the other INS computers and produces warning signals if tolerances are exceeded.
 G.  The DCU output signals are the gyro positions, sent to the electronics section control so that the IRU will be properly oriented with respect to the earth as present position is changed. Mode control, alert, and warning flag signal outputs from the DCU are also transmitted to the electronics section.
 EFFECTIVITY

 AIRPLANES WITH DELCO INS  CONFIG 1  02 A Page 32  Apr 25/8734-41-00
 H.  The DCU computes cross track deviation and track angle error which are transmitted to the autopilot to maintain the airplane on the desired track during automatic navigation. Navigation data signals are transmitted from the DCU to the horizontal situation indicator (HSI) and the control/display unit for visual displays and to other INS DCU's for comparison and remote loading.
 7.  Battery Unit
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 A.  The battery unit (BU) provides auxiliary power to initiate INS turn on and to supply essential power to maintain INS operation when the 115-volt input power is interrupted or drops below the required voltage. The battery unit contains 19 nickel-cadmium cells which are connected in series to furnish 24 volts dc. A 20-ampere circuit breaker on the front of the battery unit protects it from excessive current flow if a short circuit develops. Power from the battery unit is used momentarily to close a relay which turns on the INS, and also is used for a 10-second battery test period during automatic INS alignment. Battery unit power is connected to the INS power circuits so that it will sustain INS operation in any operating mode if primary power fails. The battery unit will sustain INS operation for periods of up to 15 minutes.
 B.  The INS will automatically transfer to battery power if ground power is removed from the airplane with the INS turned on. In order to protect the INS batteries from inadvertent discharge, a ground crew call horn, located in the nose wheel well, activates 30 |10 seconds after the INS transfers to battery power with the airplane sitting on the ground.
 8.  Horizontal Situation Indicator (Fig. 11)
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 A.  Two horizontal situation indicators (HSI) are installed in the airplane, one on each pilots' instrument panel. Each indicator is a composite instrument used primarily to display airplane heading with respect to true north, or magnetic north as determined by its mode of operation. The HSI also displays information from conventional sources such as the VOR/ILS and magnetic heading reference systems as well as from the inertial navigation system.
 B.  On ATLAS ALL EXCEPT AT 701-750, the captain's HSI receives INS navigation information from INS No. 1 or No. 3 and the first officer's HSI receives INS navigation information from INS No. 2 or No. 3 as selected from the INS transfer switch on the captain's flight instrument panel. An illuminated annunciator adjacent to the switch shows which two of the three INS systems are supplying information to the HSI's (Fig. 1). On AT 701-750, both HSI's receive INS navigation information from INS No. 1, No. 2 or No. 3 as selected from their respective INS transfer switches.
　
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