Malaysian Institute of Aviation Technology
Assignment 1
AAB31502 (Electronic Instrument System)
Answer all the questions
1. Describe the purposes, functions and operations of Build-in Test Equipment
(BITE).
(I)
Purposes of BITE

To assist the user to properly maintaining the aircraft systems in both fault
isolation and verification of system operation in the most ‘cost effective
manner’.

Isolate failing LRUs, then removed and repaired elsewhere.

This information may also be accessed to assist with the investigation of an
accident or incident.
(II)
Functions of BITE

Fault detection - Performed continuously during system operation.

Fault Isolation - BITE initiate signals to isolate defective components once
defect is sensed. Technician may access the BITE and identify the faulty
components.

Verifications - Operational check run through by the system after the
repair. Then, monitor and verify correct operation after properly repaired.
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(III)
Operations of BITE
BITE checks generally occur at three levels:

Firstly, when power is applied to the system, system’s integrity will be
checked.

Secondly, BITE checks are carried out continuously during operation of the
equipment sometimes called background bite.

Thirdly, BITE checks may be initiated by maintenance personnel for faultfinding or other maintenance purposes.
Operational Test (LAE)

Operational checks the systems upon initialization of the systems which is
power up.

BITE programs performed check of input signals, protection and control
circuitry.

In normal operation, BITE monitors and detects hardware faults or
excessive signal distortion which may cause faults.

Once failure detected, BITE perform isolation of the components, and
initiates warning, caution or advisory.

BITE shall records these faults in its non-volatile memory.
2. Describe the differences of these three types of display; CRT, LCD and LED in
term of its constructions, advantages and disadvantages.
 CRT (CATHODE RAY TUBE)
 Evacuated glass envelope (screen)
 Electron Gun
 Beam Focusing
 Beam Deflecting
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 Advantages of CRT
 Highest Resolutions
CRTs run at the highest pixel resolutions generally available.
 Black-Level and Contrast
Produce a very dark black and the highest contrast levels normally available.
Suitable for use even in dimly lit or dark environments.
 Color and Grey-Scale Accuracy
CRTs produce the very best color and grey-scale and are the reference standard
for all professional calibrations. They have a perfectly smooth grey-scale with
an infinite number of intensity levels. Other display technologies are expected
to reproduce the natural power-law Gamma curve of a CRT, but can only do so
approximately.
 Motion Artifacts
CRTs have fast response times and no motion artifacts. Best for rapidly moving
or changing images.
 Cost
CRTs are less expensive than comparable displays using other display
technologies.
 Disadvantages of CRT
 Sharpness
The CRT's Gaussian beam profile produces images with softer edges that are
not as sharp as an LCD at its native resolution. Imperfect focus and color
registration also reduce sharpness. Generally sharper than LCDs at other than
native resolutions.
 Interference
All color CRTs produce annoying Moiré patterns. Many monitors include
Moiré reduction, which normally doesn't eliminate the Moiré interference
patterns entirely.
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 Geometric Distortion
CRT Subject to geometric distortion and screen regulation problems. It is also
affected by magnetic fields from other equipment including other CRTs.
 Brightness
CRT is relatively bright but not as bright as LCDs. Not suitable for very brightly
lit environments.
 Screen Shape
Some CRTs have a rounded spherical or cylindrical shape screen and newer
CRTs are flat.
 Liquid Crystal Display (LCD)
 The construction of LCD panels used for aircraft is the same as those for LCDs
used in personal computers but subjected to severer environments as to
temperature, barometric pressure, vibration and impact.
 Advantage of LCD
 Unlike CRT monitors, LCD monitors are slim, occupy less space and consume
less energy.
 The large screen area makes it perfect for playing games, watching movies
while the size of the CRT monitor is always less than the specified size on the
paper as its frame around the glass screen covers more than one-inch space.
 The flat Screen displays the perfect image while it’s harmless for the eyes as it
emits very small part of the radiation.
 The feature of an auto button lets the user resize the screen size to make images
sharp and flexible.
 It’s free from the burn-in issue which is a major drawback of CRT and Plasma
monitors.
 Unlike LED monitors, LCD monitors are less expensive than CRT and LED.
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 Disadvantages of LCD
 The LCD is a slow device because their turning on and off times are quite large.
The turn-on time of the LCD is millisecond while there turn off time is ten
milliseconds.
 The LCD requires the large area.
 The direct current reduces the lifespan of LCD. Therefore, the LCD uses with
AC supply, having the frequency less than 500Hz.
 The LCD requires AC voltage for working.
 Light Emitting Diode
 The recombination of the charge carrier occurs in the P-type material, and hence
P-material is the surface of the LED.
 For the maximum emission of light, the anode is deposited at the edge of the Ptype material.
 The cathode is made of gold film, and it is usually placed at the bottom of the
N-region.
 This gold layer of cathode helps in reflecting the light to the surface.
 The gallium arsenide phosphide is used for the manufacturing of LED which
emits red or yellow light for emission.
 The LED are also available in green, yellow amber and red in colour.
 Advantages of LED
 The LED are smaller in sizes, and they can be stacked together to form numeric
and alphanumeric display in the high-density matrix.
 The intensity of the light output of the LED depends on the current flows
through it. The intensity of their light can be controlled smoothly.
 The LED are available which emits light in the different colours like red,
yellow, green and amber.
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 The on and off time or switching time of the LED is less than of 1 nanoseconds.
Because of this, the LED are used for the dynamic operation.
 The LEDs are very economical and giving the high degree of reliability because
they are manufactured with the same technology as that of the transistor.
 The LED are operated over a wide range of temperature say 0° – 70°. Also, it
is very durable and can withstand shock and variation.
 The LED have a high efficiency, but they require moderate power for operation.
Typically, the voltage of 1.2V and the current of 20mA is required for full
brightness. Therefore, it is used in a place where less power are available.
 Disadvantages of LED
 The LED consume more power as compared to LCD and CRT.
 LED is expensive compared to CRT and LCD.
 It is not used for making the large display.
 They also require more precise current and heat management than traditional
light sources.
3. Explain the differences between conductive and static dissipate materials for ESD
protection.
 For ESD control purposes, materials are classified by how quickly electricity moves
through the material.
 The speed is referred to as the “resistance” of the material which is how strongly
the material resists charge movement.
 Conductive Materials
 For conductive materials with a low electrical resistance, electrons flow easily
across the surface or through the bulk of these materials.
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 Charges go to ground or to another conductive object that the material contacts
or comes close to.
 Conductive materials have a surface resistivity less than 1 x 10^5 Ω/sq. or a
volume resistivity less than 1 x 10^4 Ω-cm.
 Conductive materials are classified “Antistatic”.
 Static Dissipative Materials
 Static dissipative materials, the charges flow through the material slowly and in
a somewhat more controlled manner than with conductive materials.
 Dissipative materials are classified “Antistatic” and are considered to be the
ideal range for ESD materials.
 Dissipative materials allow the charges to flow to ground more slowly in a more
controlled manner than with conductive materials.
4. Find the static voltage susceptibility range value for the type of devices given in
Table 1. Identify which is the most sensitive device to static voltage.
Table 1
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Types of Devices
Typical Static Voltage Susceptibility
CMOS logic
250V to 1kV
TTL logic
550V to 2.5kV
Bipolar Junction Transistors
150V to 5kV
Dynamic Memories
20V to 100V
VLSI Microprocessor
20V to 100V
MOSFET Transistors
50V to 350V
Thin-film Resistors
300V to 3kV
Silicon-Controlled Rectifiers
4kV to 15kV
 The Most sensitive device to static voltage will be Silicon-Controlled
Rectifiers with typical Static Voltage Susceptibility of 4kV to 15Kv.