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Module 5 > 5.11 Electronic Displays > Flashcards

5.11 Electronic Displays Flashcards

1
Q

What component when forward biased produces light?

A

LED

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2
Q

What determines the color of the LED

A

The material of which it is made of.

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3
Q

LED’s are designed to work at very?

A

Low voltages (-2V) and low currents

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4
Q

Peak wavelength of a diode is measured in nanometers what is the order of colors?

A

Top - Red (950nm)
Bottom - Blue (450nm)

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5
Q

How is yellow produced on a Bi-Coloured LED?

A

By mixing the 2 colors red and green together by operating at the same time.

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6
Q

How are tri coloured LED’s produced?

A

By having a common cathode or common anode.

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7
Q

What is this image? and what are the 2 types? Which type is illustrated?

A
  1. 7 Segment LED
  2. Common Anode and Common Cathode
  3. Common Anode (illustrated)
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8
Q

What are the 7 segment and 16 segment displays?

A

7 = Numerical
16 = Alpha Numerical

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9
Q

What is the more flexible/common display used to produce the full alphanumeric range?

A

35 Dot Matrix

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10
Q

What allows the travel of light in one position to pass through (LCD)

A

Polarized filter, made of parallel micro sized slits that block out all but one direction of wave.

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11
Q

What will happen if you cross polarize lenses?(LCD)

A

Stop light altogether.

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12
Q

In order to stop the path of light through an LCD resulting in a dark spot what conditions must be met?

A

Power applied to the liquid crystals which will align the wave either vertically or horizontally, the last polarized filter will completely block out the light.

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13
Q

What would happen to your display if the frequency dropped below <25 Hz?

A

Produce visible flicker.

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14
Q

The backplane is common to all segments. what does this form? (LCD)

A

A Capacitor

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15
Q

What are the advantages and disadvantages of an LCD?

A

Advantages = Draws very little current
Disadvantages = Requires its own light source.

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16
Q

What will turn on the LCD segment?

A

When an AC voltage is applied between the segment and the backplane.

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17
Q

Most LCD’s can create a grayscale, how many levels of brightness can be achieved?

A

256 levels of brightness

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18
Q

What type of colour mixing does an LCD use?

A

Additive color mixing.

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19
Q

What are the 3 additive primary colors of an LCD?

A

Red, Green, Blue

20
Q

What has failed to create a “bad” pixel?

A

a transistor has failed, producing a black pixel or a bright pixel.

21
Q

What 2 effects do Cathay Ray Tubes use?

A

Thermionic emission and Deflection

22
Q

What is the purpose of the cathode in the electron gun of a CRT?

A

Emit electrons, but also to concentrate emitted electrons into a tight beam using a special grid.

23
Q

The electron gun of a CRT utilises?

A

Thermionic emissions

24
Q

What method is used to control secondary emissions inside a CRT?

A

Aquadag Coating - positively charged, aids in acceleration of electrons toward screen.

25
Q

Define Persistence in relation to a CRT

A

Duration of display, how long the phosphor continues to emit light after the electron beam is removed.

26
Q

What determines the number of electrons leaving the area of the cathode?

A

Potential on the grid (Brightness control)

27
Q

What concentrates the emitted electrons into a beam?

A

The grid.

28
Q

How is the electron beam focused and accelerated in a CRT?

A

Focusing anode (1200V) and a Accelerating Anode (+2000V)

29
Q

What causes a bright spot to appear at the point of electron beam impact with the screen?

A

Phosphor coating

30
Q

What are the 2 methods of deflection for a CRT?

A

Deflection plates or Deflection Coils.

31
Q

Which principle of deflection do the plates use? and its Disadvantages

A

Electrostatic, Less Accurate

32
Q

What principle of deflection do the Coils use? Advantages?

A

Electromagnetic. - More Reliable and Accurate

33
Q

How do you establish the deflection of an electron beam within a coil deflection system?

A
  1. Draw your flux lines going from North pole to South Pole
  2. Establish electrons field rotation using the left hand grasp rule.
  3. establish direction of deflection using repel, opposites attract, likes repel.
34
Q

Describe the function of the focusing anode.

A

Attracts electrons from grid and focuses into beam.

35
Q

What are some precautions when handling CRT’s?

A

Scratches, excessive force, never hold by neck, always set CRT face down on piece of rubber, wear safety glasses and protective gloves.

36
Q

Describe the process of disposal for a CRT.

A
  1. Break off plastic locating pin from base br crushing with pliers
  2. Grasp the vacuum seal near the end with pliers and crush it.
37
Q

What is the difference between a normal CRT and a coloured CRT?

A

3 Electron guns and incorporates a shadow mask.

38
Q

What is the purpose of the shadow mask?

A

Has one hole for each triad and is arranged so that each beam can only “see” the phosphor dots for its colour.

39
Q

How many Hz is the Scanning Raster method?

A

50 Hz, 50 sets of line scans per second.

40
Q

How does Scanning raster read lines of light.

A

Starting top left, scanning left to right then quickly dropping down and starting again on the next line, It scans EVERY line.

41
Q

What frequency does Interlace scanning operate at?

A

25 Hz

42
Q

What allows interlace scanning to drop its frequency down to 25 Hz?

A

It does not scan every line, it scans all the odd number of lines first followed by the even number of lines.

43
Q

Interlace scanning relies more on?

A

Persistence of the phosphor.

44
Q

In an aircraft CRT what controls the picture painted on the screen?

A

Symbol generators.

45
Q

Aircraft CRT screens are refreshed every?

A

50 Second (50 Hz - Raster)

46
Q

What can be done to prolong the life of Electronic displays?

A

Where ever possible be turned down from full brightness.

47
Q

How are electronic instrument displays cleaned?

A

Side to side action using only a soft lint free cloth and approved cleaning detergent.

Module 5 (10 decks)

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