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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
 (2)

(3)

(4)

(5)

A 737-300/400/500MAINTENANCE MANUAL
The display unit is powered by the EIS circuit breakers on the P6-2 panel. The EIS PRIMARY 1 and EIS PRIMARY 2 circuit breakers power the left channel; the EIS PRIMARY 3 and EIS PRIMARY 4 circuit breakers power the right channel.N1, FF and maintenance (on the left channel only) modules are powered by EIS PRIMARY 1 and EIS PRIMARY 3 circuit breakers on battery bus; EGT and N2 modules are powered by EIS PRIMARY 2 and EIS PRIMARY 4 circuit breakers on standby bus.Power Supply
 (a)  
The EIS Primary Display contains six internal power supplies that are powered from P6 LOAD CONTROL CENTER panel. These six internal power supplies are configured in two groups, one group powers the left channel for engine 1, the other powers the right channel for engine 2. With this arrangement, power supply 1 (PSU1) connects to the N1 and the fuel flow/fuel used parameter displays, power supply 2 (PSU2) connects to the N2 parameter display, and the power supply 3 (PSU3) connects to the EGT parameter displays per side (see Fig. 4 sheet 2).

 (b)  
These power supplies are identical. They supply 28v dc to electronic modules and their associated displays. The 28v dc power supplies are internally monitored to provide three output signals, power interrupt, power monitor and microprocessor system and the required control action taken if any output is invalid.

 (c)  
The power supplies also contain a light sensor and its associated amplifier circuit. The light sensor circuit supplies a correction signal, which is dependent upon the voltage level of 5v integral lighting supply to the autodimming control.

Microprocessor System

 (a)  
The microprocessor system contains the devices which execute the central processing and control functions of a module. The microprocessor, in conjunction with a programmable read only memory (EPROM), a random access memory (RAM) and an interrupt control, processes the digitized parameter input signal values to provide the sequential formatted data stored in RAM. The microprocessor system also provides the control lines required to operate the individual displays and refresh them at a rate in excess of 200 Hz to ensure flicker-free operation, in sychronism with the interrupt control.

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 (b)  
The microprocessor system interrogates the discrete input signals and modifies the action of the control system to suit the discrete input signal conditions.

 (c)  
The digitized parameter values are also supplied as real time data to the maintenance module via a parallel to serial data interface.

 (d)  
The overlimit annunciator and relay drive (approach idle and starter cutout) circuits are controlled by output signals from the microprocessor system (where applicable).

 (6)  N1 Module
 (a)  
The N1 input consists of actual N1 as frequency input and limit N1 as a voltage ratio input.

 (b)  
The actual N1 input signal is derived from an engine-mounted sensor and is a frequency input proportional to engine speed. The frequency is measured, digitized, formatted and stored in RAM, in readiness for transmission to the display driver, under interrupt control of the microprocessor. The actual N1 parameter value is displayed on an LED counter and pointer. An N1 valid output signal is provided to show validity of N1 real time output (analog). A nominal 28v dc indicates a valid output; nominal 0v indicates invalid output.

 (c)  
The automatic limit N1 input signal is a ratiometric dc voltage derived from the flight management computer via the digital analog adaptor. The input signal is converted to digital format by an analog to digital (A/D) converter. The digitized data is processed in the same manner as the actual N1 signal and is displayed on an LED bug provided that the limit N1 valid input is 28v dc nominal (valid input condition).

 (d)  
The manual set limit N1 is selected by pulling out the Manual Set knob. This action signals the microprocessor that automatic mode signals are to be ignored. That the manual set limit ratiometric dc voltage from an internal potentiometer is to be digitized and processed in the same manner as automatic mode. The parameter is displayed by means of a 7 segment LED display in addition to the LED bug. The 7 segment display is "blanked" in the automatic mode (i.e. Manual Set knob pushed in).
　
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