2. I. Engine Pressure Ratio System
The engine pressure ratio system is comprised of two engine pressure
ratio transmitters.
The engine pressure ratio transmitter (EPRT) is a solid-state,
microprocessor-controlleddevice.
Its primary function is to calculate
and output the ratio of engine fan duct pressure divided by engine inlet
total pressure. The EPRT receives fan duct pressure from the on-side
aircraft engine and total pressure (Pt) and calibrated airspeed (CAS)
from the on-side AZ-81O Digital Air Data Computer (DADC) over ARINC 429.
Data from the cross-side DADC is used when the on-side is invalid. To
compensate for variations in the actual thrust versus EPR of different
Rolls Royce Tay engines, a seven-wire trim plug discrete input is
provided.
This allows the engine test people to select a trim
appropriate for each engine.
The trim plug input is read by the EPRT
during power-up initialization and is used by its software to trim the
computed EPR. The computed engine pressure ratio is then transmitted to
the DA-884 Data Acquisition Unit (DAU) and to the standby engine
instrument signal conditioner via the two redundant low speed ARINC 429
buses. The DAU transmits the EPR data to the SG-884 Symbol Generator
over the ASCB. Calibrated airspeed is used for built-in test only and
does not affect calculation of EPR.
J. VLF/Omega
The Omega
Processor
● AT-800
● AT-801
● AT-803
System (Optional)
Sensor System (0SS) is comprised of the OZ-800 Receiver
Unit and one of the following antennas:
Antenna Coupler Unit, Teardrop H-Field
Antenna Coupler Unit, Brick H-Field
Antenna Coupler Unit, Blade E-Field
The antenna coupler units receive the OMEGA/VLF signals and convert them
for processing by the OZ-800 Receiver Processor Unit (RPU). The RPU
receives the amplified antenna signals and processes them to provide
updated position and velocity information to the navigation computer of
the FMS. In addition to the antenna signals, the NZ-920 Navigation
Computer provides the following input data over an ARINC 429 bus to the
RPU:
. Heading and true airspeed
. Initializationdata comprised of LAT/LON, GMT, and the date.
The RPU provides the following output data over an ARINC 429 bus to the
navigation computer.
● Latitude
. Longitude
. N-S Velocity
● E-W Velocity
● OMEGA/VLF Station Quality
. Estimated Position Error
● Status Information
● Stations Used
● Failure Detection Messages
22-14-00
Page 18
Apr 15/93
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