Chapter 3 - Fuel Quantity Flashcards
What does a reed switch transmitter consist of?
Float-mounted magnet which moves vertically over the outside of a central tube
Central tube contains a chain of resistors and reed switches arranged on a printed circuit board
What are the inherent errors of a float-operated gauging system?
- Movement of the tank
- Unfavourable tank shape
- Differences in fluid characteristics
- Mechanical malfunctions
Why do different fluid characteristics affect fluid indication with a float switch?
If specific gravity is low, the float will settle deeper and cause an under reading
How does the relative permittivity of fuel compare to air?
Twice that of air
Capacitance of the tank unit increases as the fuel progressively takes the place of the air in the gap between the capacitor plates
What are the categories of tank unit (capacitor)?
- Tubular
- Channel
- Flexible
Describe the tubular tank unit construction?
Two coaxial cylinders
Inner electrode is a variable diameter nickel alloy tube connected to the amplifier
Outer electrode is an aluminium alloy tube of constant diameter connected to excitation voltage
Why must the cables and connectors all be of a known and fixed value?
The capacitance of the capacitive systems relies on the tank unit being the only variable
What do capacitance trimmers allow?
Replacement of fuel quantity indicators without the need to recalibrate the indicator itself
The refuel quantity indicators are … with the fuel quantity indicators?
Interchangeable
How is power interrupted to the refuelling quantity indicators?
Proximity switch turns indicators off when the access door is closed
What does a compensator unit allow?
Maintain a linear relationship between fuel dielectric properties and fuel density
What does a compensator unit consist of?
Low impedance plate and two high impedance plates, which are protected by a mechanical shield
In an unbalanced capacitive bridge, how is an empty condition calibrated?
Adjustment of the potentiometer in the bridge
In an unbalanced capacitive bridge, how is a ‘full’ adjustment achieved?
By adjustment of the amplifier gain
In the balanced capacitive bridge, how is an empty condition calibrated?
Adjusting the ‘empty’ potentiometer until zero is indicated
