15.14 - Engine Indication Systems Flashcards
What does CRT stand for?
Cathode ray tube
What effect is the thermocouple relying on?
The Seebeck effect.
What metals are commonly used in a thermocouple?
Copper and Constantan
Chromel and Alumel (aircraft engines)
What metals make up the Constantan alloy?
Copper and nickel
What is the electric voltage generated in a thermocouple per 100°C?
5 mill volts
What makes up Chromel and Alumel?
Chromel - Nickel chromium
Alumel - Nickel aluminium
What colour codes are Chromel and Alumel?
Chromel is colour coded white
Alumel is colour coded green
Why are Chromel and Alumel used in jet engines?
Most resistive to oxidisation. They are durable in high temperature environments.
What is the purpose of an amplifier for an indication thermocouple system?
It increases the sensitivity of the instrument.
Which lead out of Chromel and Alumel contains excess free electrons?
Alumel
What is used to correct the instrument reading in the cockpit?
A bimetal hairspring
What type of resistor is fitted to an EGT indicator?
A carbon resistor - Negative Temperature Coefficient (NTC)
If you get a false low EGT when testing a thermocouple, what is the diagnosis?
The resistance is high, meaning corroded terminals or leads are too long after a repair
If you get a false high EGT when testing a thermocouple, what is the diagnosis?
Resistance is low, meaning loose terminals or a gauge fault
What is engine EPR?
The ratio between the exhaust pressure and the intake pressure
What happens to the ability to compress air if the compressor inlet temperature decreases?
It increases.
What are the EPR probes reference numbers on a large turbo fan engine?
Pt2, and Pt5 or Pt7
For newer engines with FADEC systems, where is the P20/T20 line connected?
To the EEC/ECU where it is converted to an electronic signal
How does a vibrating transducer type EPR probe work?
With an electrical signal, a vibrating transducer vibrates at a natural frequency in a vacuum. When the inlet pressure changes, the frequency changes and is sent to the EEC
What is the maximum EPR?
The maximum certified thrust limit for all phases of flight.
What are the two types of oil quantity indication systems?
Capacitance type transmitter
Reed switch type transmitter
What is a Wheatstone bridge?
A capacitance probe with 3 other fixed capacitors
What is a direct-reading quantity indication system?
A dipstick
How does the Reed switch indicator work?
It’s a metal tube with a float inside. The side has a ladder of Reed switches connected with resistors. The float closes the switch nearest to it, giving the indication.
How does a strain gauge oil sensor work?
The normal pressure gives straight wires. This is the reference pressure. Pressure on the bellows changes the wire lengths and areas because it pushes against them. The resistance is measured.
What type of indicator is used for oil in older aircraft cockpits?
Bourdon tube type transmitter
What are the two types of oil temperature sensors?
Thermocouple
Thermistor
What are the two types of thermistor?
Positive temperature coefficient (PTC)
Negative temperature coefficient (NTC)
True or false, the oil output flow always in excess of lubrication requirements.
True.
What law of physics does a fuel flow transmitter use?
Force = mass x acceleration
How does a modern fuel flow transmitter work?
The fuel flows turning a turbine which is connected to an impeller via a spring. The fuel flow hits the impeller causing a brake on the action.
This force is measured with magnets and is directly proportional to the fuel flow.
How is fuel used calculated for an engine?
Fuel flow
—————— = fuel used
Hour x time
What is an ultrasonic flow sensor?
It beams two pulses through the flowing fluid & both are measured. One against the flow, and one with the flow, the one against is slower and the flow rate can be defined.
What are the three methods of measuring rotational speeds of an engine?
Mechanical (magnetic) tachometer
Electrical generator system
Inductive probe system
What is the advantage of a tachometer on a older generation of aircraft or turbo prop engines?
It generates its own voltage and therefore is independent of the aircrafts electrical circuit.
How does an inductive probe type RPM system work?
It contains a phonic wheel made from ferrite material next to a magnet. It can be placed near the fan blade tips or near a gear rotating on a shaft. The rotation crates pulses of magnetic flux which generates a voltage in the coil winding.
What are the two different ways of measuring torque in a turboprop and turboshaft engine?
Oil pressure method
Electric pick-up sensor (laser sensor type is the most modern type)
What methods are used to measure vibration?
Piezoelectric crystal sensor
Trim balance probe
Electromagnetic vibration sensor
What is the purpose of a remote charge converter with a piezoelectric sensor?
The sensor is insensitive to electromagnetic fields, large temperatures and radiation, whereas the small signals through the wires are not. The RCC is located near the sensor and converts it into voltage signals.
What is the purpose of a trim balance probe?
In the MCDU it will show you where the fan imbalance is as a vector in degrees.
What is a CIT sensor made up of?
Platinum-Rhodium
Which is positive/negative of Alumel & Chromel?
Chromel is Positive
Alumel is Negative
What is the P7 gauge indicating?
Jet pipe pressure (older engine indication)
What are the two main methods of measuring torque in a turboprop engine?
Oil pressure and electronic torque sensor
Which indication shows an “off scale” position when experiencing a power supply failure or a signal failure.
RPM electric speed probe
How are turbine temperature probes connected electrically?
In parallel, so that if one fails, it can still use the rest of the probes (Chromel +ve/Alumel -ve)
What units is engine vibration measured in?
Relative amplitude
In a fuel capacitor sensor; what does a 0 reading mean?
A failure has occurred or test button has been pressed
In a fuel capacitor sensor; what does an off the scale reading mean?
Too much water is in the tanks, altering the reading
