I develop this document while studying for my EASA ATPL exams. To accomplish this I studied the Oxford Manual and did the Aviation Exam database. The information is brief and easy to read. I believe it contains all the information you will need to pass your exam. I hope you like it and can use it t...
InstrumentATION
ATPL
STUDENT
pilot
resume
all info you need to pass atpl exams
, INSTRUMENTS
Pressure
• Aneroid capsule/pressure diaphragm used for
- Low pressure fuel pump
- Intake pressure of gas turbine engine powerplant
- Manifold pressure gauge
• Bellows sensor used for
- Cabin differential pressure
- Fuel pressure gauge
- Manifold pressure
• Bourdon tube/transducer measures hydraulic pressure
• Manifold pressure is absolute pressure in intake near inlet valve
• 1 BAR = 15 psi = 1000hpa or 100000 PASCAL
Temperature
• SAT = TAT – (Ram rise x Kr)
SAT = RAT ÷ [1+ (0.2 x Kr x M2)]
SAT = TAT ÷ [1+ (0.2 x M2)]
• Ratiometer: Operates without SUPPLY VOLTAGE*
• Bimetallic thermometers
- Based on iron & brass having different coefficients of linear expansion
- - 50°c to 400°C
• Thermocouple
- Temperature increase voltage increase
- Uses thermoelectric effect to measure differential temperature
Fuel measurement
• Electric float: Simple, independence of power supply voltage if made of ratiometer
• Integrating fuel flow with respect to time
• Mechanical fuel flow meter: Spring loaded vane
Tachometer
• Measures angular speed
• Transmitter fitted with magnetic sensor connected to an RPM indicator: Permanent magnet rotating in a non-
magnetic cup, AC converted to square pulses
• Magnetic tachometer: Permanent magnet rotating inside a non-magnetic cup
• Mechanical: Shaft rotates magnet in drag cup
• Electronic: Inductive probe/notched wheel rotating in a magnetic field. Uses magnetic sensor, Disadvantage:
Needs power supply
• Electrical: Uses generator, magnet rotor, principle of measuring rotation speed of a synchronous motor
energized by an alternator
1. DC generator:
- Advantage: Easy transmission, independent of power supply
- Disadvantage: Spurious signals
2. Single phase:
- Advantage: Suppression of spurious signals due to D.C, independent of power supply, simple design, no
influence of temperature
- Disadvantage: Suffers line resistance, transmission problems
3. 3 Phase: Consists of generator, synchronous motor turning drag cup & magnetic tachometer. Frequency
varies with RPM. (Most common)
4. Electrical induction:
- Advantage: Not sensitive to line resistance, independent of power supply, can use several indicators
connected in parallel to a single transmitter
- Disadvantage: Affected by temperature variations
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