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Q1.

a/d conventor:

An analog-to-digital converter(ADC, A/D, or A to D) is a device that converts a continuous physical quantity (usually

voltage) to a digital number that represents the quantity's amplitude. An ADC is defined by its bandwidth (the range of

frequencies it can measure) and its signal to noise ratio (how accurately it can measure a signal relative to the noise itintroduces). he actual bandwidth of an ADC is characteri!ed primarily by itssampling rate,and to a lesser e"tent by how it

handles errors such asaliasing. he dynamic rangeof an ADC is influenced by many factors, including the resolution (the

number of output levels it canquanti!ea signal to), linearity and accuracy (how well the quanti!ation levels match the true

analog signal) and#itter(small timing errors that introduce additional noise). he dynamic range of an ADC is often

summari!ed in terms of itseffective number of bits($%&), the number of bits of each measure it returns that are on

average not noise.

da conventor

nelectronics, a digital-to-analog converter(DAC, D/A, D2Aor D-to-A) is a function that converts digital data (usually

binary) into ananalog signal(current, voltage, or electric charge). An analog*to*digital converter(ADC) performs the reverse

function. +nlie analog signals,digital datacan be transmitted, manipulated, and stored without degradation, albeit with

more comple" equipment. ut a DAC is needed to convert the digital signal to analog to drive an earphone or loudspeaer

amplifier in order to produce sound (analog air pressure waves).

application of ad conventor

Music recording-edit

Analog*to*digital converters are integral to current music reproduction technology. /eople produce much music on

computers using an analog recording and therefore need analog*to*digital converters to create the pulse*code

modulation(/C0) data streams that go ontocompact discsand digital music files.

he current crop of analog*to*digital converters utili!ed in music can sample at rates up to 123 ilohert!.Considerable

literature e"ists on these matters, but commercial considerations often play a significant role. 0ost -citation neededhigh*profile

recording studios record in 34*bit123*156.4 7! pulse*code modulation (/C0) or inDirect 8tream Digital(D8D) formats,

and then downsample or decimate the signal for 9ed*oo CD production (44.1 7!) or to 4: 7! for commonly used radio

and television broadcast applications.

Digital signal processing-edit

/eople must use ADCs to process, store, or transport virtually any analog signal in digital form. ; tuner cards, for e"ample,

use fast video analog*to*digital converters. 8low on*chip :, 1

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0anysensorsproduce an analog signal= temperature,pressure,p7, light intensityetc. All these signals can be amplified

and fed to an ADC to produce a digital numberproportionalto the input signal.

application of da conventor

Audio-edit

0ost modern audio signals are stored in digital form (for e"ample 0/>sandCDs) and in order to be heard through

speaers they must be converted into an analog signal. DACs are therefore found inCD players,digital music players,and

/Csound cards.

8pecialist standalone DACs can also be found in high*end hi*fisystems. hese normally tae the digital output of a

compatibleCD playeror dedicated transport(which is basically a CD player with no internal DAC) and convert the signal

into an analog line*leveloutput that can then be fed into an amplifierto drive speaers.

8imilar digital*to*analog converters can be found in digital speaerssuch as +8speaers, and insound cards.

n;o/(;oice over /) applications, the source must first be digiti!ed for transmission, so it undergoes conversion via

an analog*to*digital converter, and is then reconstructed into analog using a DAC on the receiving party's end.

op*loading CD player and e"ternal digital*to*analog converter.

Video-edit

;ideo sampling tends to wor on a completely different scale altogether thans to the highly nonlinear response both of

cathode ray tubes (for which the vast ma#ority of digital video foundation wor was targeted) and the human eye, using a

?gamma curve? to provide an appearance of evenly distributed brightness steps across the display's full dynamic range *

hence the need to use9A0DACsin computer video applications with deep enough colour resolution to mae engineering a

hardcoded value into the DAC for each output level of each channel impractical (e.g. an Atari 8 or 8ega @enesis would

require 34 such values= a 34*bit video card would need 56:...). @iven this inherent distortion, it is not unusual for a television

or video pro#ector to truthfully claim a linear contrast ratio (difference between darest and brightest output levels) of 1

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Mechanical-edit

An unusual application of digital*to*analog conversion was thewhiffletreeelectromechanical digital*to*analog converter

linage in the0 8electrictypewriter.

Q2. A)

An LVDT, or Linear Variable Differential Transformer, is a transducer that converts a linear

displacement or position from a mechanical reference (or zero) into a proportional electrical

sinal containin phase (for direction) and amplitude information (for distance). The LVDT

operation does not re!uire electrical contact bet"een the movin part (probe or core rod

assembl#) and the transformer, but rather relies on electromanetic couplin$ this and the fact

that the# operate "ithout an# built%in electronic circuitr# are the primar# reasons "h# LVDTs

have been "idel# used in applications "here lon life and hih reliabilit# under severeenvironments are a re!uired, such &ilitar#'Aerospace applications.

LVDT cross%section, short stroe LVDT cross%section, lon stroe

The LVDT consists of a primar# coil (of manet "ire) "ound over the "hole lenth of a non%

ferromanetic bore liner (or spool tube) or a c#lindrical coil form. T"o secondar# coils are

"ound on top of the primar# coil for lon stroe* LVDTs (i.e. for actuator main +A&) or each

side of the primar# coil for hort stroe* LVDTs (i.e. for electro%h#draulic servo%valve or

-V). The t"o secondar# "indins are t#picall# connected in opposite series* (or "ound in

opposite rotational directions). A ferromanetic core, "hich lenth is a fraction of the bore linerlenth, maneticall# couples the primar# to the secondar# "indin turns that are located above

the lenth of the core. -ven thouh the secondar# "indins of the lon stroe LVDT are sho"n

on top of each other "ith insulation bet"een them, on the above cross section, &easurement

pecialties actuall# "inds them both at the same time usin dual carriae, computerized "indin

machines. This method saves manufacturin time and also creates secondar# "indins "ith

http://en.wikipedia.org/w/index.php?title=Digital-to-analog_converter&action=edit&section=6http://en.wikipedia.org/w/index.php?title=Digital-to-analog_converter&action=edit&section=6http://en.wikipedia.org/wiki/Whippletree_(mechanism)http://en.wikipedia.org/wiki/Whippletree_(mechanism)http://en.wikipedia.org/wiki/IBM_Selectrichttp://en.wikipedia.org/wiki/IBM_Selectrichttp://en.wikipedia.org/wiki/IBM_Selectrichttp://en.wikipedia.org/w/index.php?title=Digital-to-analog_converter&action=edit&section=6http://en.wikipedia.org/wiki/Whippletree_(mechanism)http://en.wikipedia.org/wiki/IBM_Selectric

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s#mmetrical capacitance distribution and therefore allo"s meetin customer specifications more

easil#.

LVDT chematic

/hen the primar# coil is e0cited "ith a sine "ave voltae (Vin), it enerate a variable manetic

field "hich, concentrated b# the core, induces the secondar# voltaes (also sine "aves). /hile

the secondar# "indins are desined so that the differential output voltae (Va%Vb) is

proportional to the core position from null, the phase anle (close to 1 deree or close to 31

derees dependin of direction) determines the direction a"a# from the mechanical zero. The

zero is defined as the core position "here the phase anle of the (Va%Vb) differential output is 41

derees.

The differential output bet"een the t"o secondar# outputs (Va%Vb) "hen the core is at the

mechanical zero (or 5ull 6osition*) is called the 5ull Voltae$ as the phase anle at null

position is 41 derees, the 5ull Voltae is a !uadrature* voltae. This residual voltae is due to

the comple0 nature of the LVDT electrical model, "hich includes the parasitic capacitances of

the "indins. This comple0 nature also e0plains "h# the phase anle of (Va%Vb) is not e0actl# 1

deree or 31 derees "hen the core is a"a# from the 5ull 6osition.

PrimaryExcitation

Diferential output Va-VbDirection 1: In-phase withexcitation (0 deree!

Diferential output Va-VbDirection ": #ut-o$-phasewith excitation (1%0 deree!

LVDT waveforms

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Temperature effects:

While the temperature coefficient of sensitivity (output per unit of displacement) is determined by the

number of winding turns, the resistance of the windings, the geometry of the armature, and the resistivity

& permeability of the metals used in the LVDT construction, the null shift with temperature is solelyaffected by the expansion coefficients and lengths of the materials used in the construction of the

transducer.

Ratiometric operation:

For the lowest temperature coefficient of sensitivity, the LVDT can be designed so that the sum of the

secondary voltages (Va+Vb) remains constant over the displacement measuring range. By designing the

signal conditioning electronic circuitry to measure the difference over sum ratio (Va-Vb)/(Va+Vb), one can

see that the first order of the temperature coefficient of sensitivity is eliminated, as demonstrated below:

Va(t)=Va(70F)*Ca Vb(t)=Vb(70F)*Cb

The variable t is the temperature; 70F is the temperature reference (70 degrees F); Ca and Cb are the

temperature coefficients of sensitivity. If Ca and Cb are assumed equal (first order approximation), then

the ratio is independent of temperature:

[Va(t)-Vb(t)]/[Va(t)+Vb(t)] = [Va(70F)-Vb(70F)]/[Va(70F)+Vb(70F)]

7)

X-Y recorder

A strip chart recorder records the variations of a quantity with respect to time while a X-Y recorder is an instrument which

gives a graphic record of the relationship between two variables.

In strip recorders, usually self-balancing potentiometers are used. These self-balancing potentiometers plot the emf as a

function of time. In X-Y recorders, an emf is plotted as a function of another emf. This is done by having one self-balancing

potentiometer control the position of the rolls. while another self-balancing potentiometer controls the position of the

recording pen.

In some X-Y recorders, one self-balancing potentiometer circuit moves a recording pen in the X direction while another

self-balancing potentiometer circuit moves the recording pen in the Y direction at right angles to the X direction, while the

paper remains stationary.

There are many variations of X-Y recorders. The emf, used for operation of X-Y recorders, may not necessarily measure

only voltages. The measured emf may be the output of a transducer that may measure displacement force, pressure,

strain , light intensity or any other physical quantity. Thus with the help of X-Y recorders and appropriate transducers, a

physical quantity may be plotted against another physical quantity.

ence an X-Y recorder consists of a pair of servo-systems, driving a recording pen in two a!es through a proper sliding pen

and moving arm arrangement, with reference to a stationary paper chart. Attenuators are used to bring the input signals

to the levels acceptable by the recorder.

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This figure shows a bloc" diagram of a typical X-Y recorder. A signal enters each of the two channels. The signals are

attenuated to the inherent full scale range of the recorder, the signal then passes to a balance circuit where it is comparedwith an internal reference voltage. The error signal the difference between the input signal voltage and the reference

voltage is fed to a chopper which converts d.c signal to an a.c signal. The signal is then amplified in order to actuate a

servometer which is used to balance the system and hold it in balance as the value of the quantity being recorder changes.

The action described above ta"es place in both a!ed simultaneously. thus we get a record of one variable with respect to

another.

The use of X-Y recorders in laboratories greatly simplifies and e!pedites many measurements and tests. A few e!amples

are being given below

#. $peed torque characteristics of motors

%. lift &rag wind tunnel tests

'. (lotting of characteristics of vaccum tubes, )ener diodes rectifiers and transistors etc

*. +egulation curves of power supplies

. (lottering stress-strain curves, hysteresis curves and vibrations amplitude against swept frequency

. lectrical characteristics of materials such as resistance versus and temperature plotting the output from

/. electronic calculators and computers

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Q8. A)

Thecathode ray oscilloscopeis an extremely useful and versatile laboratory instrument used for studying wave

shapes of alternating currents and voltages as well as for measurement of voltage, current, power and frequency, in

fact, almost any quantity that involves amplitude and waveform. It allows the user to see the amplitude of electrical

signals as a function of time on the screen. It is widely used for trouble shooting radio and TV receivers as well as

laboratory work involving research and design. It can also be employed for studying the wave shape of a signal with

respect to amplitude distortion and deviation from the normal. In true sense the cathode ray oscilloscope has been

one of the most important tools in the design and development of modern electronic circuits.

Block Diagram of a CR

!" #lock $iagram

The instrument employs a cathode ray tube%!T&, which is the heart of the oscilloscope. It generates the electron

beam, accelerates the beam to a high velocity, deflects the beam to create the image, and contains a phosphor screen

where the electron beam eventually becomes visible. 'or accomplishing these tasks various electrical signals and

voltages are required, which are provided by the power supply circuit of the oscilloscope. (ow voltage supply is

required for the heater of the electron gun for generation of electron beam and high voltage, of the order of few

thousand volts, is required for cathode ray tube to accelerate the beam. )ormal voltage supply, say a few hundred

volts, is required for other control circuits of the oscilloscope.

*ori+ontal and vertical deflection plates are fitted between electron gun and screen to deflect the beam according toinput signal. lectron beam strikes the screen and creates a visible spot. This spot is deflected on the screen in

hori+ontal direction %-axis& with constant time dependent rate. This is accomplished by a time base circuit

provided in the oscilloscope. The signal to be viewed is supplied to the vertical deflection plates through the vertical

amplifier, which raises the potential of the input signal to a level that will provide usable deflection of the electron

beam. )ow electron beam deflects in two directions, hori+ontal on -axis and vertical on /axis. 0 triggering circuit is

provided for synchroni+ing two types of deflections so that hori+ontal deflection starts at the same point of the input

vertical signal each time it sweeps. 0 basic block diagram of a general purpose oscilloscope is shown in figure.

athode ray tube and its various components will be discussed in the following 0rts.

7)

AF Sine and Square Wave Generator

A "ien bride oscillator (suitable for A9 rane) is used in this enerator (refer

9i. 8). The fre!uenc# of the oscillations can be chaned b# var#in the

capacitance in the oscillator or in steps b# s"itchin in resistors of different

values. The output of the oscillator oes to a function s"itch "hich directs the

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oscillator output to either sine "ave amplifier or to the s!uare "ave shaper. The

attenuator varies the amplitude of the output "hich is taen throuh a push%pull

amplifier.

The front panel of the sinal enerator consists of the follo"in:

9re!uenc# selector :;t selects the fre!uenc# in different ranes and varies it

continuousl# in a ratio of : 1. The scale is non%linear.

9re!uenc# multiplier :;t selects the fre!uenc# rane over < decades, from 1 z to

&z.

Amplitude multiplier: ;t attenuates the sine "ave in 8 decades, 0 , 0 1. and 0

1.1.

Variable amplitude : ;t attenuates the sine "ave amplitude continuousl#.

#mmetr# control: ;t varies the s#mmetr# of the s!uare "ave from 81= to >1=.Amplitude: ;t attenuates the s!uare "ave output continuousl#.

9unction s"itch: ;t selects either sine "ave or s!uare "ave output.

?utput available: This provides sine "ave or s!uare "ave output.

#nc: This terminal is used to provide s#nchronization of the internal sinal "ith

an e0ternal sinal.

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Q@. A)

STANDARD SIGNAL GENERATOR

A standard sinal enerator produces no"n and controllable voltaes. ;t is

used as po"er source for the measurement of ain, sinal to noise ratio ('5),band"idth, standin "ave ratio and other properties. ;t is e0tensivel# used in the

testin of radio receivers and transmitters. The instrument is provided "ith a

means of modulatin the carrier fre!uenc#, "hich is indicated b# the dial

settin on the front panel (see 9i. ). The modulation is indicated b# a

meter. The output sinal can be Amplitude&odulated (A&) or 9re!uenc#

&odulated 9&. &odulation ma# be done b# a sine "ave, s!uare "ave,

trianular "ave or a pulse.

The carrier fre!uenc# is enerated b# a ver# stable +9 oscillator usin an L

tan circuit, havin a constant output over an# fre!uenc# rane. The output

voltae is read b# an output meter. 7uffer amplifiers provided in hih fre!

oscillators to isolate the oscillator circuit from the output circuit.

7)

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Dual Trace Oscilloscopes

9i. > illustrates the construction of a t#pical dual trace oscilloscope. There are t"o separate vertical input channels,

A and 7, and these use separate attenuator and preamplifier staes. Therefore the amplitude of each input, as vie"ed

on the oscilloscope, can be individuall# controlled.

After pre%amplification the t"o channels meet at an electronic s"itch. This has the abilit# to pass one channel at atime into the vertical amplifier, via the dela# line. There are t"o common operatin modes for the electronic s"itch,

called alternate and chop, and these are selected from the instrumentBs front panel.

The alternate mode is illustrated in 9i.3. ;n this the electronic s"itch alternates bet"een channels A and 7, lettin

each throuh for one c#cle of the horizontal s"eep. The displa# is blaned durin the fl#bac and hold%off periods,

as in a conventional oscilloscope. 6rovided the s"eep speed is much reater than the deca# time of the +Tphosphor, the screen "ill sho" a stable displa# of both the "aveform at channels A and 7. The alternate mode

cannot be used for displa#in ver# lo" fre!uenc# sinals.

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Chopped Operatin !ode

;n this mode the electronic s"itch free runs at a hih fre!uenc# of the order of 11 z to

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nside the housing, the tubes are vibrated in their natural freuencies using drive coils and afeedbac0circuit. This resonant freuency of the assembly is a function of the geometry of the element,materialof construction, and mass of the tube assembly. The tube mass comprises two parts: the mass ofthe tubeitself and the mass of the !uid inside the tube. The mass of the tube is 2ed for a given sensor.

The massof !uid in the tube is eual to the !uid density multiplied by volume. 3ecause the tube volume isconstant,the freuency of oscillation can be related directly to the !uid density. Therefore, for a given

geometry

'I)*E "1+1,nde2 of refraction-type densitometer. The angle of refraction of the beam depends on the shape,si"e, and thic0ness of the container, and the density of !uid in the container. 3ecause the container has the2edcharacteristics, the position of the beam can be related to density of the !uid. 4ccurate measurement of thepositionof the beam is necessary.

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Coriolis densitometer. 5ibration of the tube is detected and related to the mass and !ow rate of the!uid. &urther calibrations and calculations must be made to determine the densities.

of tube and the material of the construction, the density of the !uid can be determined bymeasuringthe resonant freuency of vibration. Temperature sensors are used for overcoming the e6ects ofchangesin modulus of elasticity of the tube. The !uid density is calculated using a linear relationshipbetweenthe density and the tube period and calibration constants.7pecial peripherals, based on microprocessors, are o6ered by various manufacturers for a varietyofmeasurements. 8owever, all density peripherals employ the natural freuency of the sensorcoupled withthe sensor temperature to calculate on-line density of process !uid. 9ptional communication,interfacing

facilities, and appropriate software are also o6ered.

;77)7T9?T;

6ressure head t#pe densitometers:The pressure at the bottom of the tan of the constant li!uid

column is proportional to densit# and the "eiht of the iven volume of the fluid is proportional

to densit#. ;t compares h#drostatic pressures due to the heiht of the li!uids in t"o tans. one is

the reference tan, consistin of a li!uid of constant heiht and densit#. The other tan maintains

the heiht constant b# overflo", so that the manometer can be directl# in terms of densit#

measurement.

7)