The FQPU uses separate and independent tank circuits for each tank. Each tank circuit has a data concentrator card and a tank circuit card.
FQIS Channels
The I/O circuit cards calculate total fuel weight and send the individual tank weights and the total weight to the AIMS and the IRP.
The ARINC 629/429 card transmits and receives ARINC 629 and ARINC 429 data.
FQIS Tank Circuits
The data concentrator cards supply excitation to, and get data from, the fuel tank sensors. The tank circuit cards calculate fuel volume and weight. The calculations for each tank are independent. A fault that causes loss of indication for one tank does not affect indication for the other tanks.
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FUEL INDICATING -FQIS -FUNCTIONAL DESCRIPTION

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FUEL INDICATING -FQIS -INDICATIONS

General
The EICAS display shows total fuel quantity and fuel temperature in the lower right corner of the EICAS display.
The fuel synoptic display shows individual tank quantities and the total fuel quantity. It also shows the fuel temperature and the minimum fuel temperature. The minimum temperature is 3C more than the freeze temperature.
Non-Normal EICAS Displays
The EICAS display also shows the fuel quantity for each tank for these non-normal conditions:
*
Low fuel in the main tanks

*
Fuel is in the center tank and the center tank pumps are off

*
Forward or aft crossfeed valve is open

*
You select the fuel synoptic display and the MFD does not work

*
Fuel imbalance between the left and right main tanks.

BEJ 001-007
When a fuel imbalance larger than 2000 lb (909 kg) exists, the EICAS display also shows a fuel imbalance pointer. The pointer points to the main tank that has the least fuel. The pointer stays until the imbalance is less than 200 lb (91 kg). If a crossfeed valve is open, a fuel imbalance larger than 200 lb (91 kg) will cause the pointer to show.
BEJ 008-999
When there is a fuel imbalance more than 3000 lb (1361 kg), the EICAS display also shows a fuel imbalance pointer. The pointer points to the main tank that has the least fuel. The pointer stays until the imbalance is less than 200 lb (91 kg). If a crossfeed valve is open, a fuel imbalance more than 200 lb (91 kg) causes the pointer to show.
BEJ ALL
The pointer is usually white. When the FUEL IMBALANCE EICAS advisory message shows, the color of the pointer changes to amber.
The fuel temperature data on the EICAS display and the fuel synoptic display can change from white to amber. This occurs when the fuel temperature equals or becomes less than the minimum fuel temperature.
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777 AIRCRAFT MAINTENANCE MANUAL

FUEL INDICATING -FQIS -INDICATIONS

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FUEL INDICATING -FQIS -MAINTENANCE PAGES

General
Fuel quantity data shows on the fuel quantity maintenance pages 1 and 2. Page 1 shows data for the left and right main tanks. Page 2 shows similar data for the center tank.
The maintenance page shows this data:
*
Fuel quantities

*
Fuel temperature

*
Fuel densities

*
Height of fuel at each tank unit

*
Velocity of sound (VOS) at each tank unit

*
Volumetric top-off (VTO) values

*
Water detection status.

Uplift Quantity
The uplift quantity is the change in the total quantity from the time that the refuel station door opens to the time that the last refuel valve closes.
Uplift Density
The uplift density is the average density of the fuel added from the time that the refuel station door opens to the time that the last refuel valve closes.
Volumetric Top-Off
The VTO for a tank is the volume of fuel the tank can hold. The FQPU uses VTO values to calculate the load select set values for the main tanks when you do a total load select set for automatic refueling. The FQPU also uses the VTO value to close the refuel valves when the tank is full.
Water Detection Status
If a water detector finds water in a tank, the FQPU causes the water detection message for that tank to show. The main tank water detection messages show at the bottom of maintenance page 1. The center tank water detection messages show at the bottom of maintenance page 2. The amount of water required to set the L MAIN WATER or R MAIN WATER message is approximately 7 gallons (31.8 liters). The amount of water for the center tank water message is approximately 14.5 gallons
　
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