(c)  
Only one channel is necessary for FQIS operation.

 (d)  
Only one channel is selected to transmit data.

 (e)  
Both channels measure fuel in all fuel tanks but not in the same fuel tank at the same time.

 (f)  
If a fault is found in one channel, then the FQPU automatically switches over to the other channel.

 (g)  
Within the FQPU, each channel has its own power supply. If one channel loses its power supply, then the FQPU automatically switches over to the other channel.

 (h)  
A cross-channel comparison is done continuously during FQPU operation. If the cross-channel comparison encounters fuel quantity values outside of preset limits, then the channel with the lowest fuel quantity value is selected to transmit data. As a result of this, the EICAS status message, FUEL QTY CHANNEL, will show on the bottom display.

 (i)  
At FQPU power-up, one channel is randomly selected (enabled) to transmit data.

 (j)  
Upon landing of the airplane, the channel presently transmitting data is disabled and the other channel is enabled.

 (k)  
Upon operation of the VERIFY switch on the FQPU, the channel presently transmitting data is disabled and the other channel is enabled.

 (l)  
Upon operation of the FUEL QTY test switch on the right side panel P61, the channel presently transmitting data is disabled and the other channel is enabled.

 (m)  
Each channel has its own nonvolatile memory.

 (n)  
Whenever a fault is detected or fault data is received from the other channel, it is recorded into the nonvolatile memory (NVM). Whenever a fault detected by a channel is recorded into its NVM, data on the fault is transmitted to the other channel. Neglecting transport delay, each channels NVM will contain identical fault data. Therefore, either channel may do the BIT operation. It is not necessary to do the BIT on both channels since they should both contain the same fault data.

PRESS/TEST switch

 (a)  
Use of the PRESS TEST switch will check whether the selected channel of the FQPU is powered and whether all segments of the light emitting diode in the FQPU display are properly functioning. A successful test occurs when 88 appears on the FQPU display. The PRESS TEST switch can be used at any time. If the PRESS TEST switch is held down for more than 7 seconds, the FQPU display will gp off.

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 28-41-00
 ú CONFIG ú 08 Page 20 ú Sep 20/95

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MAINTENANCE MANUAL
　
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