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Chapter: Measurements and Instrumentation : Storage and Display Devices

Important Short Questions and Answers:Storage and Display Devices

Measurements and Instrumentation - Storage and Display Devices - Important Short Questions and Answers:Storage and Display Devices



1. List the components of a magnetic tape recorder.


The components of a magnetic tape recorder are :

i. Recording head

ii. Magnetic head

iii.  Reproducing head

iv.  Tape transport mechanism

v.   Conditioning devices.


2.   What are the advantages of magnetic tape recorders?

The advantages of magnetic tape recorders are :

i.    They have a wide frequency range from D.C. to several MHz.

ii. They have low distortion,

iii.  They have a wide dynamic range which exceeds 50dB. This permits the linear recording from full scale signal level to approximately 0.3% of full scale.

iv.  The magnitude of the electrical input signal is stored in magnetic memory and this signal can be reproduced whenever desired. The reproduced signal can be analyzed by automatic data reduction methods.


3. Mention the different methods of magnetic tape recording.

The different methods of magnetic tape recording are :

i.    Direct recording

ii.   Frequency modulation (FM) recording and

iii.  Pulse duration modulation (PM) recording


4. Mention is the purpose of erase head.


The purpose of erase head is to erase the content of magnetic tae. It consists of a signal of high frequency and level sweeps the magnetic tape thereby completely wiping out the information contained there. This renders the magnetic tape to be used fresh for another signal.


5. List the advantages of direct recording.

The advantages of direct recording are:

i.    This recording process has a wide frequency response ranging from 50 Hz to about 2 MHz for a tape speed of 3.05 m/s. It provides the greatest bahdwidtn obtainable from a given recorder.


ii.   It requires only simple, modulately priced electronic circuitry.


iii.    It   is   used   to   record  signals  where  information  is contained  in         the relation between frequency and amplitude, such as spectrum analysis of noise.


iv.  It can be used for recording voice and in multiplexing a number of channels of information into one channel of tape recording.


6.   Mention the disadvantages of direct recording.


The disadvantages of direct recording are:


i.    Direct recording is used only when maximum bandwidth is required and when variations in amplitude are acceptable.


ii.   Direct recording can be used for instrumentation purposes but it is mainly used for recording of speech and music.


7.   What is drop out ?


In direct recording, some portions of the tape may not be perfectly recorded owing to dirt or poor manufacture and this is called drop out.


8. Mention the two factors in frequency modulation recording.

The two factors in frequency modulation recording are:

i.    Percentage deviation and

ii. Deviation ratio.


9. Define: percentage deviation


Percentage deviation is defined as the carrier deviation to centre frequency. i.e. Percentage deviation or modulation index, m


=(∆f/fc) x 100, where ∆f = carrier deviation from centre frequency

fc = centre or carrier frequency


10. Define: Deviation ratio


Deviation ratio is defined as the ratio of carrier deviation from centre frequency to signal or modulating frequency. Deviation ratio, ♪ = (∆f/fm) where, fm = data signal


11. Give few advantages of frequency modulation recording.

The advantages of frequency modulation recording are :


i.    It is useful when the D.C. component of the input signal is to be preserved or when the amplitude variations of the direct recording process cannot be tolerated.


ii.   This system has wide frequency range can record from D.C. voltages to several kHz.


iii.  It is free from dropout effect.


iv.  It is independent of amplitude variations and accurately reproduces the waveform of the input signal.


v.   It is used extensively for recording the voltages from the force, pressure and acceleration transducers.


vi.  It is extremely used for multiplexing in instrumentation systems.


12. List few disadvantages of frequency modulation recording.


The disadvantages of frequency modulation recording are :


i.    The circuitry of an FM recording system is more complicated than that of a direct recording system. This complexity of circuitry is an account of separate modulation systems.


ii.   It has a limited high frequency of about 80 kHz.


iii.  It requires a high tape speed.


iv.  It requires a high quality of tape transport and speed control and therefore expensive than the direct recording system.


13. Enumerate the merits and demerits of pulse width modulation recording.


The merits of pulse width modulation recording are :


It has the ability to simultaneously record information from a large number of channels.


It has a high accuracy due to the fact that it can be self-calibrated.


It has a high 3/N ratio.


The demerits of pulse width modulation recording are : It has the limited frequency response


It has a highly complex electronic circuitry and therefore, the reliability of such systems are low.


It is used only for special applications such as flight recorders, where a large number of slowly changing variables are involved.


14. What is the operation of a serial printer ?


The operating of serial printer is to produces a single character at a time, usually moving from left to right across a page. It prints 200 characters per second.


15. Mention the purpose of line printers.


The line printers are used to print line by line instead of characters. It prints 4000 lines per minute.


16. Give the operation of page printer.


The purpose page printer prints a line at time mode, but can be stopped and restarted

only on the page basis. The top Speed is 45,000 lines per minute.


17. List the classification of printer.

Printers are classified into three brad categories. They are


i.    Impact and non-impact printers.


ii.   Fully formed character and dot matrix character printer


iii.  Character at a time and a line at time.


19. What is impact and non-impact printers ?


Impact printers form characters on a paper by striking the paper with a print head and squeezing an inked ribbeia between the print head and paper.


Non-impact printers form characters without engaging the print mechanism with the print surface i.e. by heating sensitised paper or by spraying ink from a jet.


20. Write short notes on printer character set.


Mini and micro computers use ASCII codes for the printers. They are specified using the 48 character set, the 64 character set, the 96 character set or the 128 character set. The entire 128 character ASCII set contains 32 characters normally used for communication and control.


21. What is daisy wheel printer?


Daisy wheel printer is a fully formed character printer, designed for computer usage and has characters mounted on the periphery of a spinning print head similar to a daisy flow. They are capable of bidirectional printing.


22. Give short notes on dot-matrix printers.


In dot-matrix printers, the characters are formed by printing a group of dots to form a letter, number or other symbol. It can print any combination of dots with all availble print position in the matrix.


23. List the important features of CRTs.

The important features of CRTs are :

i.    Size

ii.   Phophor

iii.  Operating voltages

iv.  Deflection voltages

v.   Viewing screen


24. What is meant by deflection sensitivity in cathode ray tube ?


The deflection sensitivity of the cathode ray tube is usually stated as the D.C. voltage

required for each cm of deflection of the spot on the screen,


25. List the requirements of a sweep generator.

The requirements of a sweep generator are :

i.    The sweep must be linear.

ii.   The spot must move in one direction only, i.e. from left to right only, else  the signal  will  be  traced    backwards  during  the  return  sweep.

This  means  that  the  sweep  voltage   must   drop   suddenly  after reaching  its   maximum  value.          These requirements call for a sweep voltage having a linear sawtooth waveform.


26. What is meant by recurrent sweep in cathode ray tube ?


When the sawtooth, being an A.C. voltage alternates rapidly, the display occurs respectively, so that a lasting image is seen by the eye. This repeated operation is known as recurrent sweep.


27. What is intensity modulation in CRT?


In some applications, an A.C. signal is applied to the control electrode of the CRT. This causes the intensity of the beam to vary in step with signal alterations. As a result, the trace is brightened during the positive half cycle and diminished or darkened during negative half cycle. This process is called intensity modulation or z-axis modulation. It produces bright segments or dots on the trace in response to positive peak or dim segments or holes in response to negative peaks.


28. Mention the methods that are used for generating the two electron beams within the CRT.


The methods that are used for generating the two electron beams within the CRT are the double gun tube and split beam method.


29. Mention  the  two  storage  techniques  used  in oscilloscope CRTs.




The two storage techniques used in oscilloscope CRTs are mesh storage and phosphor storage.


30. CRO has become an universal tool in all kinds of electrical and electronic investigation. Why ?


CRO has become an universal tool in all kinds of electrical and electronic investigations because in CRO, the vertical input voltage is the voltage under investigation and it moves the luminous spot up and down in accordance with the instantaneous value of the voltage. When the input voltage repeats itself at a fast rate, the trace (display) on the screen, appears stationary on the screen.


31. Name the components of a CRO.


The Components of CRO are:

i.    cathode ray tube (CRT) along with electron gun ssembly

ii.   deflection plate assembly

iii.  fluorescent screen

iv.  glass envelope and

v.   base.


32. What is an electon gun ?

An electon gun is the source of focussed and accelerated electron beam is the electron gun. The electron gun which emits electrons and forms them into a beam consists of a heater, a cathode, a grid a pre-accelerating anode, a focussing anode and an accelerating anode.


33. Name the basic circuitry of CRO.

The basic circuitry of CRO are named as :


i.Vertical (Y) deflection system

ii.   Horizontal (X) deflection system

iii.  Synchronization

iv. Blanking circuit

iv.  Intensity (z-axis) modulation

v.   Positioning controls

vi.  Focus control

vii. Intensity control

vii. Calibration control

viii.    Astigmatism.


34. Write  notes  on  dual  trace  cathode  ray oscilloscopes.


In a dual trace CRQ, there are two separate vertical input channels A and B and these use separate attenuator and preamplifier stages. Hence the amplitude of each input as viewed on the oscilloscope can be individually controlled, after preamplification, the two channels meet at an electronic switch and this has the ability to pass one channel at a time into the vertical amplifier via the delay line.


35. State the purpose of a lissajous pattern in CRO.


The lissajous pattern is used for determining the frequency. The particular pattern results when sine waves are applied simultaneously to both pairs of the deflection plates.


36. What is a LED ?


The LED is basically a semiconductor PN junction diode capable of emitting electromagnetic radiation under forward conductions.


37. List the different materials used in manufacturing LED’s

The different materials used in manufacturing LEDs are

i.    Gallium Arsenide (GaAs) - red

ii.   Gallium Arsenide Phosphide (GaAsP) - red or yellow

iii.  Gallium Phosphide (GaP) - red or green.


38. How are LCDs created ?


LCDs are created by sandwitching a thin (10 to 12um) layer of a liquid-crystal fluid between two glass plates. A transparent, electrically conductive film or backplane is put on the rear glass sheet. Transparent sections of conductive film in the shape of the deviced character are coated on the front glass plate. When a voltage is applied between a segment and the backplane, an electric field is created in the region under the segment. This electric field change the transmission of light through the region under the segment film.


39. List the characteristics of LCD.

The characteristics of LCD are :

i.    They are light scattering.

ii.   They can operate in a reflective or transmissive configuration.

iii.  They do not actively generate light and depend for their operation on ambient or back lighting.


40. Name the two commonly available types of LCDs.


The two commonly available types of LCDs are :

i.    Dynamic scattering and ii.  Field effect type


41.State the purpose of dot matrix displays.

 Excellent alphanumeric characters can be displayed by using dot matrix LEDs with an LED at each dot location.


42. Write the two writing patterns of dot matrix displays.

The two wirting patterns of dot matrix displays are :

i.    Common anode or common cathode connection (uneconomical).

ii.   X-Y array connection (economical and can be extended vertically or horizontally using a minimum number of wires).


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