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MAINTENANCE MANUAL

TERMINAL BLOCK
(TOP VIEW)

FQIS Tank Units
Figure 2 (Sheet 2)

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COMPENSATOR SEE A
COMPENSATOR SEE A
TERMINAL BLOCK  MOUNTING CLAMP 
SUPPORT TUBE 
MOUNTING CLAMP 
TUNING PLATE 
ELECTRODES LO-Z HI-Z 
Figure 3 FQIS Compensator A COMPENSATOR

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MAINTENANCE MANUAL

 (3)  
The compensator senses the dielectric constant of the fuel. It is a capacitance sensing device similar to the tank unit. The compensator is installed at the bottom of the fuel tank, completely covered by fuel until the tank is almost empty. As a result, the compensator capacitance is affected only by changes in the dielectric constant of the fuel.

 C.
Densitometer (Fig. 4)

____________
 (1)  
One densitometer is installed in each fuel tank. The densitometer measures the fuel density.

 (2)  
The densitometer consists of two parts, the densitometer emitter and the densitometer electronics unit. All densitometers are installed on the rear spar with the densitometer emitter in the fuel tank, and the densitometer electronics unit out of the tank. Removal of the densitometer electronics unit does not require defueling.

 D.
Densitometer Electronics Unit (Fig. 5)

_____________________________
 (1)  
The densitometer electronics unit is installed on the studs of the emitter mounting plate, on the aft surface of the rear spar. Removal takes place without defueling.

 (2)  
The electronics unit consists of a power supply circuit board, two detector tubes, a preamplifier assembly board, a processor assembly board, and an electrical connector. The unit requires 28 volts dc power.

 (3)  
The two detector tubes are filled with xenon gas. When a high voltage of 1400 volts from the power supply board is applied to the anode of the detector tubes, the interaction of the xenon gas, and the gama radiation from the emitter, produces a variation in voltage at the anodes. The variation in voltage, or pulse, passes to the signal processing electronics. The two pulse train output signals of the electronics unit goes to the FQPU for calculation of fuel density. Fuel density is proportional to the natural logarithmic value of the ratio of the two pulse output signals.
　
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