The value displayed would be the number 5. In a common anode seven-segment display, applying voltage (turning on) the segments labeled a and b would light up the top part of the number 5, and applying voltage to the segments labeled c, d, and e would light up the bottom part, creating the full number 5 pattern.

1. 1

2. Outline
• Introduction (analog and digital displays)
• Types of displays
a. Cathode ray tube CRT
b. Liquid crystal display LCD
c. Light emitting diode display LED
e. Plasma display PD
• Applications of displays in measurement
2

3. Displays
3

4. Introduction
• The display system is the final link between
the measuring process and the user.
• Display devices are used in instrumentation
systems to provide instantaneous but non-
permanent communication of information
between a process or system and a human
observer.
• Data can be presented to the observer in
either an analog or a digital form
4

5. Continue
• In measurement there are two types of
Displays–analogue and digital.
• Analogue displays use a needle and calibrated
scale to indicate values.
• Analogue displays have a pointer which moves
over a graduated scale. They can be difficult to
read because of the need to work out the value
of the smallest scale division.
5

6. Continue
• For example the scale in the picture has 10
small divisions between 0 and 1 so each small
division represents 0.1. The reading is
therefore 1.25V (the pointer is estimated to be
half way between 1.2 and 1.3)
• The analogue meter can show any value
between 1.2 and 1.3 but we are unable to
read the scale more precisely than about half
a division.
6

7. Continue
• Digital displays show the measured value as
digits and they are more accurate than
analogue.
• They are easier to use because they give
specific value.
• Digital displays are often capable of displaying
smaller values in easy understandable way.
7

8. Types of displays
• Generally there are different types of displays
but the most commonly used are:
1.Cathode ray tube (CRT)
2.LED displays
3. Liquid crystal displays(LCD)
4.Plasma displays (PD)
8

9. Cathode ray tube
• The Cathode Ray Tube or Braun’s Tube was
invented by the German physicist Karl
Ferdinand Braun in 1897.
• Today its used in computer monitors, TV sets and
oscilloscope tubes.
• CRTs have advanced employing many different
techniques to increase image precision and
quality
• Today's CRT displays are much more advanced
than those of a decade ago, they are much
simpler than other display technologies.
9

10. Main components of CRT
• The CRT consists of three main components:
the electron gun, the electron beam deflector,
and the screen and phosphors
10

11. Electron gun
• The electron gun fires electrons.
• A strong electric field between cathode and anode
accelerates the electrons, before they leave the
electron gun through a small hole in the anode
• The electron gun consists of two main components, the
cathode and the electron beam focuser
• These two parts work together to fire an electron and
help determine where it will go
11

12. The Electron Beam Deflector
• The electron deflector is positioned at the base
of the vacuum tube and controls what part of
the screen the electron strikes.
• The electron beam deflector, like the focuser,
can rely on either an electromagnetic or
electrostatic mechanism
12

13. Continue
• The electrostatic mechanism changes the path
of the electron rather than focus it.
• Most television and computer displays use an
electromagnetic coil to control the path of the
electron
Electrostaticelectromagnetic
13

14. Continue
• The deflector determines the path of the
electron
• There are really two deflectors, one that
controls the position in the x, or horizontal
direction and one in the y, or vertical direction
• The electromagnetic force causes the electron
to move towards either the left or the right in
the case of the horizontal deflector.
14

15. Continue
• The deflector uses the force to change the
path of the electron to determine what part of
the screen the electron hits, but not which
phosphor.
15

16. The Screen
• The screen, which is at the front of the CRT, is
what actually displays the images.
• In color CRTs, the screen contains light-
emitting phosphors with three different
colors.
• When the electron fired from the gun strikes
the screen and hits an atom in the phosphor,
it transfers its energy to an electron in the
phosphor 16

17. Advantages of CRT
• Wide viewing angle
• Very simple implementation
• High resolution technology
• Excellent color fidelity
• Long life and reliability
17

18. Disadvantages of CRT
• High power consumption
• So Big and Bulky
• Needs cooling system
• Interference
• Less bright than CRT
18

19. LCD (Liquid Crystal Displays)
• The most output device Like a TV mobiles &
computer makes (display) .
• Most computers use a (LCD) , light-emitting
diode (LED), and gas plasma or other image
projection technology.
• Monitors using LCD technologies are
beginning to replace CRT
19

20. LCD History
• LCD were first discovered in 1888 by
Austrian botanist Friedrich Reinitzer.
• Liquid Crystals will play an important role in
modern technology .
• RCA made the first experimental LCD in
(1968).
• Manufacturers have been developing creative
variations and improvements on LCDs.
20

21. THE Main Categories of LDC
• The passive matrix of LCD
• The active matrix of LCD
21

22. THE Main Categories of LDC
• The Passive Matrix LCD
• Relies on Transistors for each Row and each
Column of pixels, the color displayed by a
pixel is determined by the electricity coming
from the transistors at the end of the row and
the top of the column .
• The most passive matrix LCD technology
screens now use dual-scan LCD Technology,
which scans the pixels twice as often.
22

23. THE active matrix of LCD
• Technology Assigns A Transistor to each
pixel, and each pixel is turned on and off
individually.
• Active matrix screens have a wider viewing
angle than passive matrix screens.
• Active matrix displays use Thin-Film
Transistor(TFT) Technology which employs as
many as four Transistors per pixel.
23

24. LCD Classifications of Color
• Monochrome
• Gray-Scale
• Color
24

25. LCD Classifications of Color
• Monochrome: Display only one color(such
as green, amber, or white) against a
contrasting back-ground , which is usually
black .
• These are displays used for text only displays
where the user does not need to see color
graphics.
25

26. LCD Classifications of Color
• Gray-Scale: A special type of monochrome
display varying intensities of gray(from a very
light gray to black) against a white or off-
chrome display.
• Gray scale flat-panel display are used in low –
end portable system-especially handheld
computers.
26

27. LCD Classifications of Color
• Color: Can display any where from 16 color
to over 16 million color and different colors.
Sometimes called RGB(Red , Green, Blue)
monitors .
• Today, most new display can be set to work in
monochrome or grayscale
27

28. Advantages of LCDs
• Physical Size
• Compact and Lightweight
• Space saving
• Can be mounted on a wall or panel
• Until recently, was only used on notebook
computers and other portable devices
28

29. Advantages of LCDs
• Less Power Consumption and Radiation
Emission
• LCD consumes fewer watts than a CRT. LCD
will use an average 30 watts compared to 120
watts for the CRT.
• Can reduce electric bill by 40-85%.
• Doest not emit Radiation
• Not subject to Electromagnetic Interference
29

30. Advantages of LCDs
• Viewing
– Cause less eyestrain
– Does not flicker or glare
• Color
– Most are capable of displaying unlimited colors.
• Resolution
– Multiple video Resolutions.
30

31. Disadvantages of LCDs
• It has Narrow viewing angle
• Do not Refresh the pixels very QUICKLY
• LCD Display is that their images can be
difficult To see in bright light.
31

32. Light-Emitting Diode Displays
• Light-emitting diode (LED) displays involve single-
crystal phosphor materials.
• LED displays are highly versatile and well suited to a
variety of measurement applications.
• Advantages of LED displays include high reliability
and graceful degrades; individual LED elements can
fail without affecting overall display performance.
32

33. Continue
• LEDs are rugged, for operation in harsh
environments, and they are more tolerant of
temperature extremes than other technologies.
• LEDs demonstrate better viewing angles than
LCDs, and excellent brightness for visibility in
sunlight.
33

34. LED Display Performance
• LED devices have excellent brightness, but because
display brightness is also a function of the filter or
magnification lenses used over the LED elements.
• Device luminance is not, by itself, a reliable measure
of overall system performance.
• LED displays also show very good luminance contrast.
34

35. Seven Segment Displays
• A seven-segment display can be used to display
the decimal numbers 0-9 and some alpha
characters.
• A common anode seven-segment display works.
• A common cathode seven-segment display works.
• To select the resistor value for a seven-segment
display.
35

36. Segment Identification
• A Seven-Segment Display (SSD) is simply a figure eight
grouping of LEDs {some include a decimal point (DP)}.
• Each Segment is labeled (a) thru (g).
• SSDs are available in two configurations
– Common Cathode (all LED cathodes are connected)
– Common Anode (all LED anodes are connected)
a
b
c
d
e
g
dp
f
36

37. SSD Display Possibilities
Decimal Digits 0-9
Simple Messages
Select Alpha Characters
37

38. Basic LED Operations
• To understand how a seven-segment
display works, we must review how an
LED works.
To Turn an LED ON . . .
• The ANODE must be at a higher
voltage potential (1.5v) than the
CATHODE.
• The amount of current flowing
through the LED will determine the
brightness of the LED.
• The amount of current is controlled by
a series resistor. (not shown)
CATHODE (‒) (+) ANODE
← Current Flow
38

39. LED Configuration – Anode @ 5 Volts
Switch @ 5v
• Top Circuit
• LED Off
Switch @ 0v
• Bottom Circuit
• LED On
• ANODE @ 5v
• CATHODE @ 0v (nearly)
• The 220  resistor controls the
current.
• A larger resistor . . . less current .
. . dimmer LED
• A smaller resistor . . . more
current . . . brighter LED
Common Anode
Configuration
(5v=Off / 0v=On)
39

40. Example #1: Common Anode SSD
Example
What value would be displayed in the common
anode seven-segment display shown?
40

41. Example #1: Common Anode SSD
Example
What value would be displayed in the common
anode seven-segment display shown?
Solution
Common Anode:
• 0 volts = Segment On
• b, c, f, & g
• 5 volts = Segment Off
• a, d, & e
a
b
c
d
e
gf
41

42. LED Configuration – Cathode @ Ground
Switch @ 5v
• Top Circuit
• LED On
• ANODE @ 5v (nearly)
• CATHODE @ 0v
• The 220  resistor controls the
current.
• A larger resistor . . . less current . . .
dimmer LED
• A smaller resistor . . . more current . .
. brighter LED
Switch @ 0v
• Bottom Circuit
• LED Off
Common Cathode
SSD Configuration
(5v=On / 0v=Off)
42

43. Example #2: Common Cathode SSD
Example
What value would be displayed in the common
cathode seven-segment display shown?
43

44. Example #2: Common Cathode SSD
Example
What value would be displayed in the common
cathode seven-segment display shown?
Solution
Common Cathode:
• 5 volts = Segment On
• a, b, d, e, & g
• 0 volts = Segment Off
• c & f
a
b
c
d
e
gf
44

45. Resistor Values for SSD
• The resistor value determines the amount of current that is flowing
through the LED in the SSD.
• This is why they are sometimes called current limiting resistors.
• The amount of current determines how luminous the LED will be.
• If the resistor is too large, the current will be too small and the LED
will not be visible.
• If the resistor is too small, the current will be too large and the LED
will be damaged.
• So, how do you select the correct value? You must read the data
sheet for the SSD that you are using.
45

46. Merits of LED displays
• Energy efficient - LED’s are now capable of
outputting 135 lumens/watt
• Long Lifetime - 50,000 hours or more if properly
engineered
• Not affected by cold temperatures - LED’s “like”
low temperatures and will startup even in
subzero weather
•
Controllable - LED’s can be controlled for
brightness and color 46

47. Disadvantage of LED
• LEDs are currently more expensive.
• LED performance largely depends on
correctly engineering the fixture to manage
the heat generated by the LED, which causes
deterioration of the LED chip itself.
• LEDs must be supplied with the correct
voltage and current at a constant flow. This
requires some electronics expertise to design
the electronic drivers.
47

48. Plasma display
• Plasma display panel is a type of flat panel display
common to large TV displays 30 inches(76 cm) or
larger.
• They are called ‘’plasma’’ displays because the
technology utilizes small cells containing
electrically charged ionized gases or what are in
essence chambers more commonly known as
fluorescent lamps .
• The plasma flat panel display. These televisions have
wide screens, comparable to the largest CRT sets, but
they are only about 6 inches (15 cm) thick.
48

49. Plasma display
• Plasma is referred to be the main element of a
fluorescent light. It is actually a gas including
ions and electrons.
• Under normal conditions, the gas has only
uncharged particles. That is, the number o f
positive charged particles [protons] will be
equal to the number of negative charged
particles [electrons].
• This gives the gas a balanced position.
49

50. Plasma display
• Suppose you apply a voltage onto the gas, the number
of electrons increases and causes an unbalance.
• These free electrons hit the atoms, knocking loose
other electrons.
• Thus, with the missing electron, the component gets a
more positive charge and so becomes an ion.
• In plasma, photons of energy are released, if an
electrical current is allowed to pass through it. Both
the electrons and ions get attracted to each other
causing inter collision.
• This collision causes the energy to be produced. Take a
look at the figure illustrated below
50

51. Plasma display
51

52. Plasma display
• The basic idea of a plasma display is to
illuminate tiny, collared fluorescent lights to
form an image.
• Each pixel is made up of three fluorescent
lights -- a red light, a green light and a blue
light. Just like a CRT television, the plasma
display varies the intensities of the different
lights to produce a full range of colors.
52

53. working of Plasma Display
• Two plates of glass are taken between which
millions of tiny cells containing gases like
xenon and neon are filled.
• Electrodes are also placed inside the glass
plates in such a way that they are positioned in
front and behind each cell.
53

54. working of Plasma Display
• As told earlier when a voltage is applied, the
electrodes get charged and cause the
ionization of the gas resulting in plasma.
• This also includes the collision between the
ions and electrons resulting in the emission of
photon light.
54

55. working of Plasma Display
• When the photon light is emitted they are
ultraviolet in nature.
• These UV rays react with phosphor to give a
coloured light
• Take a look at the diagram given below.
55

56. working of Plasma Display
56

57. Advantages of Plasma display
• The slimmest of all displays
• Weighs less and is less bulky than CTR’s.
• Higher viewing angles compared to other
displays [178 degrees].
• Can be placed even on walls.
• Has a life span of about 100,000 hours.
57

58. Disadvantages of plasma display
• Cost is much higher compared to other
displays.
• Energy consumption is more.
• Produces glares due to reflection.
• These displays are not available in smaller
sizes than 32 inches..
• Cannot be used in high altitudes. The pressure
difference between the gas and the air may
cause a temporary damage or a buzzing noise.58

59. Applications of displays in
measurement
59

60. Voltmeters- analogue and digital
• Voltmeters measure voltage or
voltage drop in a circuit.
• Lack of voltage at a given point
may indicate an open circuit or
ground.
• Low or high voltage drop may
indicate a high resistance
problem like a poor connection
60

61. Voltmeters- analogue and digital
• Digital voltmeter has a fixed
impedance which does not
change from scale to
scale…..10M ohms or more
• Impedance is the biggest
difference between analog
and digital voltmeter.
61

62. AMMETERS-ANALOG AND DIGITAL
• There is not great difference between analogue and
digital ammeters.
• Digital meter are often capable of measuring smaller
currents, all the way down to micro amps.
• They are easier to use because they give specific value.
• Most digital ammeters are combined with a voltmeter.
62

63. oscilloscope
• Electronic test instrument that allows
observation of constantly varying
signal voltages, usually as a two-dimensional
graph
• Oscilloscopes are used to observe the change
of an electrical signal over time, such that
voltage and time describe a shape
• This shape is commonly referred to as
a waveform, and makes it easy to view
voltage changes.
• Oscilloscopes are used in the sciences,
medicine, engineering, and
telecommunications industry.
63

64. References ….
• Instrumentation reference book by Walt
Boyes
• Instrumentation Engineers HANDBOOK by
RCC
• Measurement & instrumentation principles by Alan
S. Morris
64

65. END
Any questions ????
65