EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH EIS ú
31-42-00
ú ú 04 Page 13 ú Mar 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
(7)
EGT Module
(a) Exhaust gas temperature (EGT) is measured by six or nine chromel alumel thermocouples located in the LP turbine. An average temperature signal is provided for input to the EGT module. The EGT signal is amplified and applied to a voltage controlled oscillator (V/F conversion), to produce a frequency proportional to the dc input signal level. 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 EGT parameter is displayed on an LED counter and pointer.
(8)
N2 Module
(a)
The N2 module receives an analog signal from the engine high pressure (core) rotor speed transmitter. The frequency of the signal is proportional to the core rotor speed.
(b)
The N2 input signal is processed in the same manner as the actual N1 parameter in N1 module.
(9)
FF Module
(a)
The fuel flow (FF) input signals are derived from an engine-mounted sensor. The mass flow rate input signal consists of start and stop pulses independently transmitted over three wires, the time interval between the start and stop pulses being proprotional to mass flow rate. The start and stop pulses are used to gate a clock frequency (derived from the microprocessor crystal) into a binary counter. Since the gating period is equal to the time interval between the start and stop pulses the binary counter holds a binary number proportional to the mass flow rate. The binary number is processed by the microprocessor system, formatted and stored in RAM in readiness for transmission to the display driver, under interrupt control of the microprocessor. The FF parameter is displayed on an LED counter and pointer.
(b)
The fuel used (FU) indication is obtained on the FF LED counter by depressing the bezel-mounted FUEL USED pushbutton and remains displayed for 10 seconds.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH EIS ú
31-42-00
ú ú 04 Page 14 ú Mar 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
(c)
The totalized value of the fuel used is obtained by integrating the FF rate against time. A real time clock divides down the timing pulse train to produce a series of integrate command pulses having a constant time interval (dt) between each pulse. The microprocessor detects each integrate command pulse and computes the product of FF and dt, adds this value to the previous total of fuel used and then stores the current value. This process is repeated for each integrate command pulse.
(d)
Another bezel-mounted pushbutton (FUEL USED RESET) is used to reset the fuel used value to zero.
(10)
Maintenance Module
(a)
The maintenance module receives from both engine channels (left and right) the real time inputs of actual N1, N2, EGT and fuel flow via each computing module. The input data is processed and then transmitted onto a single ARINC 429 data bus.
(b)
The real time inputs are checked for any exceedance or Abnormal Start condition. All parameter information for an engine will be stored in non-volatile RAM when there is either an exceedance or abnormal start condition. The exceedance values can be presented on the parameter display before power is removed or transmitted via the ARINC 429 data bus.
(c)
An ARINC 429 input supplies total air temperature (TAT) and airspeed data, which when processed and combined with the engine parameters enables an abnormal start condition to be detected. An abnormal start condition is indicated on the EGT display of the appropriate engine by means of a discrete signal to the EGT module.
(11)
Engine Idents
(a) Engine variants having different limits for N1, N2 and EGT are identified by means of program pins which enable engines with four different red-line limit options to be selected. The program pins are located on the display unit rear connectors. The microprocessor system decodes the program pin data and provides the necessary scaling to fit the presentation limit bands.
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