Lecture Slides for the course Electronic Instrumentation-II delivered by me to Diploma in Electronics/Instrumentation Engineering.

1. BIE-601
Electronic Instrumentation-II
Unit-4
Display Devices & Recorders
Lecture-1
Mohd. Umar Rehman
umar.ee.amu@gmail.com
15. 4. 2020
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2. Contents
LEDs, LCDs, seven segment and dot matrix displays, Electro lumines-
cent, electrophoretic image and liquid vapour displays, printers- dot
matrix, inkjet, laser jet printer, recorders-Potentiometric, X-Y recorders.
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3. Introduction
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4. Introduction
Due to the rapid growth of electronic handling of numerical data, there
is a great demand for the measurements systems to display the data in
readily understandable form.
Display devices provide a visual display of numbers, letters, and sym-
bols in response to electrical/electronic input and serve as a constituent
part of an instrumentation system.
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5. Introduction
Due to the rapid growth of electronic handling of numerical data, there
is a great demand for the measurements systems to display the data in
readily understandable form.
Display devices provide a visual display of numbers, letters, and sym-
bols in response to electrical/electronic input and serve as a constituent
part of an instrumentation system.
Attributes of a digital display
Accurate
Long life
No ageing effect
Compact size
Easy to read out
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6. Classification of Displays
In general, displays are classified in a number of ways as follows:
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7. Classification of Displays
In general, displays are classified in a number of ways as follows:
1. On the basis of processing of light energy
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8. Classification of Displays
In general, displays are classified in a number of ways as follows:
1. On the basis of processing of light energy
(a) Active Displays: Light emitters –incandescent bulb, LED, CRT,
plasma tubes
(b) Passive Displays: Light controllers –LCD, EPID etc.
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9. Classification of Displays
In general, displays are classified in a number of ways as follows:
1. On the basis of processing of light energy
(a) Active Displays: Light emitters –incandescent bulb, LED, CRT,
plasma tubes
(b) Passive Displays: Light controllers –LCD, EPID etc.
2. On the basis of application
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10. Classification of Displays
In general, displays are classified in a number of ways as follows:
1. On the basis of processing of light energy
(a) Active Displays: Light emitters –incandescent bulb, LED, CRT,
plasma tubes
(b) Passive Displays: Light controllers –LCD, EPID etc.
2. On the basis of application
(a) Analog Displays: CRT, CRO
(b) Digital Displays: LED, LCD, Nixie Tube
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11. Classification of Displays
In general, displays are classified in a number of ways as follows:
1. On the basis of processing of light energy
(a) Active Displays: Light emitters –incandescent bulb, LED, CRT,
plasma tubes
(b) Passive Displays: Light controllers –LCD, EPID etc.
2. On the basis of application
(a) Analog Displays: CRT, CRO
(b) Digital Displays: LED, LCD, Nixie Tube
3. On the basis of physical dimensions & size
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12. Classification of Displays
In general, displays are classified in a number of ways as follows:
1. On the basis of processing of light energy
(a) Active Displays: Light emitters –incandescent bulb, LED, CRT,
plasma tubes
(b) Passive Displays: Light controllers –LCD, EPID etc.
2. On the basis of application
(a) Analog Displays: CRT, CRO
(b) Digital Displays: LED, LCD, Nixie Tube
3. On the basis of physical dimensions & size
(a) Symbol Displays: Nixie tubes, alphanumeric displays
(b) Console Displays: LED, CRT
(c) Large Screen Displays: Enlarged projection system
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13. Classification...Contd
4. On the basis of display format
(a) Flat panel/direct view type displays: Segmental & dot-matrix
displays
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14. Classification...Contd
4. On the basis of display format
(a) Flat panel/direct view type displays: Segmental & dot-matrix
displays
(b) Stacked/Non-planar: Nixie tube
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15. Classification...Contd
4. On the basis of display format
(a) Flat panel/direct view type displays: Segmental & dot-matrix
displays
(b) Stacked/Non-planar: Nixie tube
5. On the basis of resolution
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16. Classification...Contd
4. On the basis of display format
(a) Flat panel/direct view type displays: Segmental & dot-matrix
displays
(b) Stacked/Non-planar: Nixie tube
5. On the basis of resolution
(a) Simple single element indicator: Analog instruments
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17. Classification...Contd
4. On the basis of display format
(a) Flat panel/direct view type displays: Segmental & dot-matrix
displays
(b) Stacked/Non-planar: Nixie tube
5. On the basis of resolution
(a) Simple single element indicator: Analog instruments
(b) Multi-element displays: Nixie tubes/LCDs
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18. Light Emitting Diode (LED)
A PN junction diode which emits light when forward biased is known
as LED.
The light emitted may be in the visible or infrared (invisible) spectrum.
The amount of light emitted is directly proportional to the current.
Thus, higher the amount of forward current, higher is the light out-
put.
The figure shows the symbol and the basic structure of LED.
The light is emitted due to re-combinations of of holes and electrons.
The light output is obtained through a window provided at the top
of the surface. The semiconductor materials used for manufacturing
LEDs are: GaAs (Gallium-Arsenide), GaAsP (Gallium Arsenide Phos-
phide)
Si/Ge are not used for manufacturing LEDs as they produce heat and
have low light output
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19. LED...Contd
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20. Advantages of LED I
1. Efficiency: LED emits more light per watt than incandescent bulb.
Efficiency is not affected by shape and size unlike bulb/tubes.
2. Color: LEDs can emit light of an intended color withour using any
color filters as other traditional lighting methods.
3. Size: LEDs can be very small (< 2 mm) and can be easily used with
solid-state electronics and PCBs.
4. Response time: LEDs can light up very quickly. The response time
is of the order of µs or ns. LEDs used in communication systems
have even faster response time.
5. Age: LEDs can have a relatively long useful life. Their estimated
lifetime ranges from 35,000 to 50,000 hours. This is sufficiently
longer that that for fluorescent tube (15,000 hours) or bulbs (2000
hours)
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21. Advantages of LED II
6. Shock resistant: LEDs do not have much effect of external me-
chanical shock unlike tube or bulbs.
7. Focus: LED package can be designed to focus its light for greater
visibility.
8. Low toxicity: Unlike fluorescent lamp they do not contain mercury
and are less hazardous to the environment.
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22. Disdvantages of LED
1. Higher initial cost: They are more expensive than other display
devices.
2. Temperature dependence: The performance of LED depends upon
the operating conditions such as ambient temperature.
3. Voltage sensitivity: LEDs must be supplied with the voltage above
the threshold and current below the rating. This may require use
of external resistors or regulated power supplies.
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23. Applications of LED
Following are the important applications of LEDs
1. For 7-segment, 16-segment and dot-matrix displays. Such displays
are used in digital instruments like power supplies, multi-meters,
digital clocks etc.
2. For indicating power on/off for various lab instruments.
3. Optical switching applications and optical communication systems
employing fibre optic cables.
4. In security systems. However, infra-red LEDs are preferred in such
systems.
5. Nowadays, CRTs are being replaced by LEDs for solid-state video
displays.
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24. Liquid Crystal Displays (LCDs)
Figure: (a) Ordinary Liquid (b) Nematic Liquid Crystal
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25. Liquid Crystal Displays (LCDs)
Figure: A Liquid Crystal Cell
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26. LCDs...Contd
Liquid crystal is a material (usually an organic compound) which
flows like a liquid at room temperature, whose molecular structure
has some properties normally associated with solids.
The molecules in ordinary liquids have random orientation but in
a liquid crystal they are oriented in a definite pattern.
Normally , a thin layer of liquid crystal is transparent to incident
light but when an electric field is applied across it, its molecular ar-
rangement is disturbed causing the light to be absorbed or scat-
tered. In other words, the liquid crystal turns opaque.
As shown in figure, a liquid crystal cell consists of a thin layer.
About 10 mm of a liquid crystal sandwiched between two glass
sheets with transparent electrods on their inside faces with both
glasses transparent is known as transmittive type.
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27. LCDs...Contd
When only one glass sheet is transparent, and the other has reflec-
tive coating, then the cell is called reflective type.
The LCD does not produce any illumination of its own. In fact, its
working entirely depends upon illumination falling on it from an
external source for its visual effect.
The most popular liquid crystal is the nematic liquid crystal. It works
in the same way as described above and regains transparency upon
removal of electric field.
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28. Advantages of LCD
1. One of the most important advantages of LCD is its extremely low
power requirement ( ~ 10-15 µW) per 7-segment display as
compared to few mW for LED.
It is due to the fact that LCD does not generate any illumination
but depends on the external source of light.
2. NLC materials have very high resistance (> 1010 Ω) therefore, the
current reqirement is also very small (0.1 µA/cm2)
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29. Disadvantages of LCD
1. LCDs are slow devices as compared to LEDs. Turn ON time is
few ms and turn OFF time is few tens of ms.
2. They have limited life because the liquid crystal loses its properties
due to chemical degeneration.
3. Cannot operate over a wide temperature range.
4. For better resolution, LCDs require a large area.
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30. Applications of LCD
1. Field-effect LCDs: normally used in watches and portable instru-
ments such as digital thermometers, BP instruments, DMM etc.
2. Desktop monitors: almost obsolete now a days.
3. Cellphones: older models and some low cost models.
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