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Module 13 > Instruments > Flashcards

Instruments Flashcards

1
Q

What is the difference between a Potentiometer and a rheostat?

A

In a potentiometer current flows both ends of the coil and in a rheostat only one

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2
Q

Explain a control transformer?

A

A primary coil that produces a continuously charging magnetic flux in the iron core and a secondary coil where the flux induces an AC voltage

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3
Q

How is a synchro built up?

A

A rotor and 3 stator coils. The coils are at 120 degrees to each other and act like 3 transformers contained in one unit.

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4
Q

What voltages do synchros use for excitation of the rotor and what does this do in the rotor coil?

A

26Vac or 115 Vac and it will create a magnetic field in the rotor.

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5
Q

When would you use a synchro with a servo loop?

A

When the torque or a synchro receiver is not high enough.

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6
Q

What is a differential synchro?

A

A synchro that has 3 coils in the rotor and 3 coils in the stator and is possible to add or subtract angles.

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7
Q

What is the build-up of a resolver?

A

It has 2 stator coils and a rotor coil at 90 degrees with respect to each other. From the signals in the stator coils it makes sine and cosine signals.

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8
Q

Name two possible applications for the resolver?

A

Angular transmitter (Thrust leavers) and Phase Angle Shifter (0 - 360 degree selector)

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9
Q

What is the build-up of a Linear Variable Differential Transformer?

A

A Primary Coil with a linear moveable iron core then 2 secondary coils connected in series.

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10
Q

How does a LVDT work?

A

The iron core moves in one direction, one of the secondary coils receives more of a magnetic flux and induces a higher coil voltage, the secondary coil receives less magnetic flux, therefore a lower voltage. The difference between the voltage in the secondary stator coil is proportional to mechanical position.

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11
Q

What type of demodulation is necessary for position reading with LVDT/RVDT?

A

Phase-dependant-demodulation

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12
Q

Explain the build-up of a DC servo loop?

A

A DC source connected to a variable control potentiometer and a follow up potentiometer. An amplifier amplifies the ratio signal and drives a motor with it.

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13
Q

How do you drive an AC motor in a DC servo Loop?

A

You must add a chopper circuit to make AC from the DC signal and to drive the AC motor from this signal we need an extra amplifier.

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14
Q

Why would you want to use an AC motor in a DC servo loop?

A

When we need even more torque.

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15
Q

Absolute pressure is measured from what reference?

A

zero pressure or vacuum

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16
Q

Gauge pressure is measured from what reference?

A

Existing atmospheric pressure

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17
Q

What pressure sensing devices work electrically?

A

Strain Gauges and Piezo-resistive sensors (Piezo-resistive is more accurate)

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18
Q

Name some quantity sensing systems?

A

Variable resistance, Mechanical Float Type, Float and Reed switches, Capacitance and Direct Read.

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19
Q

What is the dielectric constant of Air and Fuel?

A

Air = 1 and Fuel = 2 (but varies due to temp)

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20
Q

What does the capacitance of a capacitor depend on?

A
  • Area of the plates
  • Separation between the plates
  • Dielectric Constant
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21
Q

Why is compensator in a FQIS?

A

The dielectric constant of the fuel will change with rep so it is placed in parallel with the probes and cancels changes in the dielectric constant.

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22
Q

How does the capacitance bridge read fuel quantity?

A

It compares the impedance of the probe to a reference probe, when the 2 are equal there is no flow through the indicator. When the capacity of the tank changes the bridge unbalances and the indicator shows the amount of charge.

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23
Q

In which units is fuel quantity indication represented?

A

Number of pounds or kilograms on board.

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24
Q

Explain a Negative Temperature Coefficient Resistor?

A

Its resistance decreases at increasing temperatures. So it is called a High Temperature Conductor.

25
Q

Explain a Positive Temperature Coefficient Resistor?

A

Its resistance increases at increasing temperatures. So it is called a Low Temperature Conductor.

26
Q

What materials does a thermocouple consist of?

A

Chromel and Alumel

27
Q

How long is the recording capacity of a FDR?

A

25 - 50 hours

28
Q

What is the purpose of the FDAU?

A

Provides the FDR with converted information from the aircraft systems

29
Q

When is the FDR recording?

A

When one engine is started and will stop 5 minutes after last engine shutdown

30
Q

What is the purpose of the EVENT pushbutton in relation to the FDR?

A

It will record an event mark in the FDR memory

31
Q

What does a FDR ULB do?

A

Sends a 37Khz pulse 2 miles in any direction for about 30 days

32
Q

Where would you find the Three Axis Accelerometer of a FDR?

A

At the centre of gravity of the aircraft

33
Q

What does ADAS stand for?

A

Air Data Acquisition System

34
Q

What is the purpose of the ADAS system?

A

To accept large amounts of engine and aircraft system data for the analysis of troubleshooting.

35
Q

In the ADAS system where is the data stored?

A

On magnetic tapes or optical disks, and a printer prints the aircraft data.

36
Q

How can you read the data stored in ADAS?

A

It can be printed, sent via ACARS or read on the MCDU

37
Q

What is the standard air pressure and Temp at sea-level?

A

1013.2 MB 29.92 Hg and 15 Degrees

38
Q

Does a leak check have to be carried out when a pitot static system is disturbed?

A

Yes

39
Q

What is the reason for a left and right static port?

A

To eliminate instrument errors when aircraft yaws

40
Q

What energy does a pitot tube measure?

A

Kinetic energy of the airflow due to the motion of the aircraft.

41
Q

What temperature measuring device does a TAT probe use?

A

A temperature dependant resistor (platinum)

42
Q

Explain a pressure altimeter?

A

Static pressure is directed into an aneroid chamber that is connected to a gear??

43
Q

QNH is set what will your pressure altimeter read when landing at an airfield?

A

Airfield elevation

44
Q

QFE is set, when landing the altimeter will show?

A

0 feet

45
Q

During cruise the altimeter setting is …………. and shows the ………. ?

A

QNE, Flight Level

46
Q

The pneumatic vertical speed indicator uses the ………. Pressure?

A

Static

47
Q

What is incorporated in a Instantaneous VSI?

A

An accelerometer-operated air pump across the capsule.

48
Q

What does an airspeed indicator measure?

A

The difference between pitot and static pressure

49
Q

Ram air pressure is the difference between?

A

Total pressure and static pressure. If the aircraft is on the ground total pressure an static pressure would be equal.

50
Q

What is IAS?

A

Indicated airspeed is the uncorrected reading of an air speed indicator. Little use to navigation purposes

51
Q

What is CAS?

A

Calibrated airspeed (CAS) is the speed shown by a conventional airspeed indicator after correction for instrument error and position error

52
Q

What is TAS?

A

True Airspeed is CAS but with a correction applied for temperature and altitude. (Atmospheric conditions)

53
Q

What is GS?

A

Groundspeed represents the actual speed of an aeroplane over the ground. It is TAS adjusted for wind.

54
Q

What is TAT and Static Air Temperature used for?

A

TAT - Power settings of the engines

SAT - Navigational purposes and to inform passengers of OAT

55
Q

Mach number is?

A

Velocity / Local Speed Of Sound

56
Q

What do Vmo / Mmo mean?

A

The maximum operating limit speeds, and warning will alert the pilots if the limit is exceeded.

57
Q

An aircraft climbs with a constant TAS, its mach number?

A

Increases

58
Q

What are the inputs for an air data computer?

A

Discretes, TAT, Total pitot and static pressures, Baro settings, AOA.

59
Q

How does a ADC convert pneumatic pressure to electrical data?

A

It goes through a pressure transducer/oscillator the to an A to D converter.

Module 13 (22 decks)

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