FQI System - Interfaces
 Figure 006A 
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 Usually, the two channels operate continuously, with each channel monitoring the status of the other channel. The primary power supply is 28VDC connected to the power supply module in the computer. The 28VDC input is filtered to decrease noise and is connected to a DC-DC converter. The converter generates and regulates the different voltages for each channel. All the outputs from the computer are current-limited to be safe.
 If an input power supply fails, the related power supply unit and CPU board will fail. This will not decrease the satisfactory operation of the FQI system, as its operation will be changed to the other channel. If one Power Supply Module (PSM) fails, the PSM that remains will supply all the fuel probe excitation oscillators and signal conditioning. Thus the fuel quantity indications are not affected because of diode cross-coupling of the fuel probe excitation oscillators and signal conditioning circuits.
 B. On-Board Replaceable Memory (OBRM) Module (3QT1)
 A multi-pin connector plug attaches the OBRM to the FQIC. Two clips keep the OBRM in position. The connector is polarised to prevent damage caused during incorrect installation. The power supply to the module goes through two long centering pins in the plug, which will switch on the supply during installation, and switch off the supply during removal.
 Inside the OBRM are 2, 4 or 6 memory packs. The printed circuit boards (PCBs) installed with the memory packs are in sealed cases, that give good protection against mechanical shocks and electrostatic charges.
 When attached to the FQIC, the OBRM connects with the FQIC computer processor unit (CPU) card, and gives the microprocessor an Erasable Programable Read Only Memory (EPROM). The EPROM includes a program that identifies the module and supplies the data necessary to program the OBRM.
 **ON A/C 301-399,
 A. FQI Computer (FQIC) 3QT The FQIC is contained in a 4MCU case. When the OBRMs and the FQIC front panel are removed, access is made to the FQIC circuit cards. The circuit cards can be installed or removed, through the front of the computer.
 Each circuit card is installed on a mother board assembly. The guide rails at the top and bottom of the case help to locate the circuit cards. The mother board assembly controls the complete computer interconnection. The electrical connection to the computer is made through an electrical connector.
 The primary components of the computer are:
 -a signal conditioning board
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R  - an input/output board 
R  - a Central Processing Unit (CPU) board. 
R 
R  The two sets of these components gives two processing channels that are 
R  almost the same. The channels are identified as Channel 1 and Channel 2. 
R  Each channel does these operations: 
R  - computation of the fuel mass held in each wing and in the center tank 
R  - computation of the ACTUAL total fuel mass 
R  - computation of the PRESELECTED fuel mass 
R  - computation of the automatic refuel control 
R  - discrete outputs to the refuel valves, and flight warning system (FWS) 
R  (Ref. 31-50-00) 
R  - system failures 
R  - continuous automatic tests for faults (BITE) 
R  - Fuel Level Sense System (FLSS) BITE (Ref. 28-46-00) 
R  - continuously monitors the status of the other channel 
R  - ARINC 429 digital output to the interfaces. 
R 
R  Usually, the two channels operate continuously, with each channel 
R  monitoring the status of the other channel. The primary power supply is 
R  28VDC connected to each power supply module in the computer. The 28VDC 
R  input is filtered to decrease noise and is connected to a DC-DC 
R  converter. The converter generates and regulates the different voltages 
R  required for each channel. All the outputs from the computer are 
R  current-limited to be safe. 
R 
R  If an input power supply fails, the related power supply module and CPU 
R  board will fail. This will not decrease the satisfactory operation of 
R  the FQI system, as its operation will be changed to the other channel. 
R  If one of the power supply modules fails, half the number of the probes 
　
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