Chapter 6 - Data Presentation

8/18/2019 Chapter 6 - Data Presentation

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Chapter 6

Data Presentation


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2BETR 3423 Instrumentation System

Objectives

At the end of the chapter, student should be able

to:

understand how data is presented eitherthrough display or recorder.

understand that data can be presented in

analog or in digital for.

understand soe of the basic operations of the

data presentation eleents.


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!. "ntroduction

#. Digital Display Principles

$. %&D Display

'. C() Display

*. %CD Display

6.

&% Display+. Chart (ecorders

. Paperless (ecorders

Content


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!. "ntroduction

)he data presentation eleent is the final eleent in

the easureent syste - instruentation syste -

data acuisition syste.

"ts function being to counicate the easuredvalue of the variable to a huan observer .

"t is iportant that the easured value is presented

as clearly and easily as possible, otherwise the

value registered by the observer ay be different.

Process,

/achine or

syste being

easured

"nstruentation 0yste"nput Output

)rue 1alue /easured 1alue


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"ntroduction

"f the data is represented for instant observation, the

device is called 2display device3 and when it is

represented for recording, in that case it is called as a

2recorder 3. )hese are also called as output devices for presentation

of inforation in visual .

Data

Presentation&leent


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"ntroduction Consider an accurate flow easureent syste where

true value of flow rate is !!.$$h4! and the easured value

!!.*$h4! with a easureent syste error of 5.#$h4!.

"f the observed value is !#.5$h4!, then the observation

error is 5.*$h4!. )his is greater than the easureenterror and eans that the high syste accuracy is wasted.

Observation error depends on any factors:

Distance of the eleent fro the observer.

Abient %ighting &yesight, patience and sill of the observer.

A clear presentation is of ajor iportance.


7/507BETR 3423 Instrumentation System

)ype of Data Presentations

DataPresentation

Elements

Displays

Digital

Light EmittingDiode (LED)

Cathode RayTube (CRT)

Liquid CrystalDisplay (LCD)

Electro

Luminescence(EL)

AnaloguePointer Scale

ndicator

Recorders !Printers

ChartRecorder

Laser Printer

PaperlessRecorder



)ype of Data Presentations



Data Display"f no peranent record of easured variables

is reuired, then displays can be used. A choice

ust be ade between analogue pointer and

digital displays.


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BETR 3423 Instrumentation System

Pointer40cale "ndicator

7ith the pointer4scale indicator, the observer ustinterpolate if the pointer lies between two scale ars: thus

if the pointer lies between 8 and !5 the observer ust

decide whether the easured value is 8.', 8.* or 8.6. )hus

an observation error of up to 95.* units is possible.


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#. Digital Display Principles

Digital display 4 a display that gives the

inforation in the for of characters nubers

or letters;.

)here are four types of digital display technology

widely used nowadays:

%ight &itting Diode %&D;

Cathode (ay )ube C(); %iuid Crystal Display %CD;

&lectroluinescent Display &%;


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a; 0even4segent character forat

=or an e>aple, to display

nuber 548 using seven4

segent display. &ach of the

segents abcdefg can beswitched individually on or off

using a seven digit parallel

binary code.


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b; +>* dot4atri> character display

&ach character forat is

an array of segents or

dots? these eleents are

referred to as pi>els. )o

display a character each

pi>el ust be separately

switched 2on3 and 2off3

independently of the other

pi>els.


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#.# @raphic Displays @raphic displays are used to show line diagras,

graphs, wavefors, bar charts, etc and consists of a

large nuber of pi>els arranged in rows along the y4

a>is; and coluns along the >4a>is;. A typical graphic display consists of $#5 > #'5 +6,55

pi>els, each of an area 5.$$ > 5.$$, giving a total

viewing area of !#5 > 8#. )o ae electrical

contact with each individual pi>el would reuired +655electrical connections occupying an area of a few suare

etersB

Connections done through ethod of ultiple>ing.


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/ethod of /ultiple>ing

)he principle of pi>el atri> ultiple>ing is based

on tie division ultiple>ing, where one pair of

conductors can serve any pi>els by suitabletiing of the voltage across the conductors. )he

pi>els are arranged in a atri> of coluns x ; and

rows y ;.

&ach colun >; and each row y; has an electricalconductor giving a corresponding atri> of

conductor.


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&ach pi>el, with position coordinates

>,y; is connected across the

corresponding > and y conductors at

their point of intersection.!. )he voltage applied to a colun

conductor will present at all of the

pi>els in that colun? the voltage

applied to a row conductor will

present at all of the pi>els in that row.

#. )he iniu voltage reuired to

turn on a pi>el is 1s.

$. )he colun voltages 1> switch

between 5 and 1s-#.

'. )he row voltages 1y switch between

5 and 1s-#.*. A pi>el at position >,y; is switched

on during a tie interval when the

colun voltage is 1s-# and the row

voltage is 1s-#.


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)he pi>el #,!; is switched on during

tie interval 5 to )-$.

)he pi>el !,!;, #,!;, !,$;, and #,$;

are switched on during tie interval)-$ to #)-$.

Pi>el $,#; is switched on during tie

interval #)-$ to ).

"n this e>aple there are si> electrical

conductors for nine pi>els so that thesaving in e>ternal connections is

sall.

Eowever, in the above e>aple of a

$#5>#'5 atri>, $#5#'5 *65

e>ternal connections are reuired to

address +655 pi>els. All waveforsare repeated every repetition period )?

this is to refresh the display.

Provided ) is sufficiently short, the

brightness of the screen reains

reasonably constant without flicer.


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$. %&D Display

%&Ds have high power consuption, which aes

the only suitable for sall4scale character

displays? they are not used in graphic displays.

%&D have the special property that when forward

biased they emit electromagnetic radiation o"er

a certain band o# $a"elengths. )wo coonly

used %&D aterials are galliu arsenidephosphide @aAsP;, which eits red light, and

@allui Phosphide @aP;, which eits green or

yellow light.


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"n both cases the luinous intensity "v of the diode light

source increases with current i=

, for diode the

relationship is appro>iately linear. =igure c;;

=igure d; shows the relationship between relative

luinous intensity and wavelength F.

)he light eitted by a @aAsP red; diode is distributed

over a narrow band of wavelengths centered on

5.6**G.

)he light eitted by a @aP green; diode is distributed

over a narrow band of wavelengths centered on

5.*65G. )he huan eye is far ore sensitive to green light than

red, so a green %&D of low radiant power ay appear as

bright as a red %&D of uch higher radiant power.


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)he response of %&Ds to step changes in i= is e>treely

fast? turn4on and turn off ties of !5ns are typical. 7hen switched HOIJ, a typical @aAsP diode reuires a

forward current i= of around #5A corresponding to a

luinous intensity "v of '.5cd illicandela;, and a

forward voltage 1= of #.#1.

=igure e; shows a siple circuit for achieving this, using

a series resistor ( of !'5K.

=or a H!J input, 1s *1, i= *4#.#;-!'5 #5A and thediode is OI.


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a; =orward biased %&D

b; Current-voltage @aAsP;

c; %uinous intensity-current @aAsP;

d; (elative intensity wavelength @aAsP;

e; 0eries (esistor


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A seven segent %&D display device consists of eight

individuals %&Ds, one for each segent and one for the

decial point. )here are two possible ethods ofinterconnection, coon anode or coon cathode figure

f;;.

Lsing the above data, the power consuption of an individual

pi>el is #.#1 > #5A ''7? the total power consuption of

the seven segent display is therefore $#57. )his high power consuption eans that %&Ds are only

suitable for character displays and are unsuitable for graphic

displays.

f; "nterconnection /ethods


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'. C() Display

C()s are used for character and graphics displays,

onochroe and colour, but have the disadvantage of

high operating voltages and are high volue bulydevices.

C() are used to create large4scale displays. )hese

devices are often referred to as onitors.

A visual display unit 1DL; isa cobination of a C() display

and a eyboard.


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&lectrons are eitted at the cathode and

accelerated towards the anode.

A third electrode, called a grid or odulator, is

placed between cathode and anode: by altering thepotential of the odulator the nuber of electrons in

the bea, the bea current can be adjusted.

)he bea then passes through a focusing syste

followed by M and N deflection syste: the focusing

syste can be electroagnetic or electrostatic.

asic C() Operation


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)he electron bea is brought to a focus on the

inside surface of the screen, which is coated with a

large nuber of phosphor dots. )hese dots for thepi>els.

Phosphors are seiconductor aterials which

eit visible radiation in response to the ipact

of electrons: a spot of light therefore appears onthe screen.


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A colour display produces iages containing a wide

range of colours. )he screen of a colour C() is coated

with dots of three di##erent types o# phosphor : oneeits red light, the second green light and the third

blue light (@ colours;. Dots of each type are arrange in euilateral triangles

called triads.


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)he onitor has three electron

guns, one for each type of phosphor.

)he corresponding electron beasare deflected horiQontally and

vertically to produce a raster display

as in onochroe onitor. As the bea traverse the screens,

the intensity of each bea is variedaccording to the voltage applied to

the corresponding odulator

electrode.

)his creates varying colourintensities at the triads and colour

iages on the screen. )he colour display syste can be

used to create graphic displays.


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"n a fi>ed forat alphanueric display character occupy

fi>ed position in a display and each character is built up

using a fi>ed +>* or 8>+ dot atri> forat. "n a graphic display the screen contains a full atri> of

pi>els, each of which can be turned on or off to produce

graphical iages or pictures, alphanueric characters at

any position on the screen or a cobination of both. C() displays have the disadvantages

!. not Hflat screenJ technology

#. occupy ore volue

$. have uch higher operating voltages around !61;than %CD around !*1;

'. power consuption is also higher in C() than in %CD

display.


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*. %CD Display

%CDs are used for both character and graphics

displays. %CD character displays, usually

onochroe, have uch lower power consuption

than euivalent %&D displays. %CD graphics

displays, onochroe and colour, are flat screen

panels and have lower operating voltages and

power consuption than euivalent C() devices.


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=igures below show the construction of a reflective onochroe

display using field effect or twisted neatic )I; liuid crystal

aterial.

)he %C aterial is in contact with a pair of conducting

electrodes which are transparent to light? a voltage is applied

across these to create an electric field. )here are glass plates

above and below the electrodes. An >4polarising filter is situatedabove the upper glass plate? this transit only >4polarised light.

0iilarly a y4polarising filter below the lower glass plate transit

only y4polarised light.


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=igure a; shows the situation when the

applied voltage 15. )he olecules

near the top are lined up along >4

direction. /oving downwards through

the liuid, their orientation gradually

changes so that the olecules at the

botto are lined up along the y4

direction. )he light is therefore able to

pass through the y4polarised filter andis reflected bac to the observer, the

surface appearing pale grey or green.

=igure b; shows the situation when the

applied voltage 1R5. "n this case the

olecules reain aligned along the >4

direction throughout the liuid crystal:

this eans that the light reains >4

polarised as it oves downward. )he

light cannot pass through the lower y4

polarised filter and is absorbed? the

surface appears blac to an observer.

y controlling the voltage applied across the liuid crystal layer in each pi>el, light

can be allowed to pass through in varying aounts thus constituting different

levels of gray.


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"lluination

As %CD panels produce no light of their own, they reuire an e>ternallighting echanis to be easily visible. On ost displays, this consists of

a cold cathode fluorescent lap that is situated behind the %CD panel.

Passive4atri> displays are usually not baclit, but active4atri> displays

alost always are, with a few e>ceptions such as the display in the

original @aeboy Advance.

(ecently, two types of %&D baclit displays have appeared in soe

televisions as an alternative to conventional baclit %CDs. "n one schee,

the %&Ds are used to baclight the entire %CD panel. "n another schee,

a set of red, green and blue %&Ds is used to illuinate a sall cluster of

pi>els, which can iprove contrast and blac level in soe situations. =or

e>aple, the %&Ds in one section of the screen can be died to

produce a dar section of the iage while the %&Ds in another section are

ept bright. oth schees also allows for a slier panel than on

conventional displays.


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6. &% Display &lectroluinescent displays are also flat screen and are

used for both character and graphics onochroe

displays. )hey have higher operating voltages and power

consuption than euivalent %CD devices but greater

contrast ratio and viewing angle. 7hen a voltage is applied across a phosphor aterial, light

is eitted. )his effect is called electroluinescence.


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=igure a; above shows the construction of an &% displaywhich consists of a nubers of layers deposited on a glass

substrate.

4 )he first layer is a nuber of >4a>is or colun electrodes

which are electrically conductive and transparent to light.

4 )hen there is the atri> of phosphor eleents, which is

sandwiched between two dielectric layers.

4 =inally there are a nuber of y4a>is or row electrodes

which absorbed light.


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&ach pi>el is located at an intersection of an > and a

y electrode and connected across the.

)he display is viewed through the glass substrate?

with no voltage across the electrodes the pi>el

appears blac.

"f a voltage pulse, typically of height of !551 and

duration of !5Gs, is applied across the electrodes,

the pi>el eits light.


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)he luinance of the pi>el decays fro an initialvalue, just after the pulse of around !555cd-#, with a

tie constant of typically *55Gs.

)his eans that the display ust be continuously

refreshed to avoid flicer. )he pulse is repeatedappro>iately every !555Gs? this enables a

continuous luinance of at least !55cd-# to be

obtained.

ecause the voltage is applied for only !S of thetie, the power reuired for each pi>el is considerably

reduced? around !55G7 per pi>el is typical.


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REC%RDERS

A record of the tie variation of the easured variables wouldbe essential, for e>aple:

Eigh 0peed events, eg. A huan heartbeat, which are too

fast to be followed by a huan observer. Changes in the

recorded blood pressure wavefor will then show clearly any

irregular or abnoral behaviour,

)he onitoring of a cople> process such as a gas

copressor which has a nuber of associated easured

variables. "f the copressor breas down, then the e>act

seuence of events drop in lubricating oil pressure rise in

bearing teperature drop in delivery pressure can be found

and the cause of failure established.


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+. Chart (ecorders

)he recorder ay use paper strips or polar

plots. )he paper oves one way and the arer

pen oves right angle to this.


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Chart 0peed is a ter used to

e>press the rate at which the

recording paper in a strip chartrecorder oves. "t is e>pressed in

inches-sec or -sec and is

deterined by echanical gear

trains. "f the chart speed is nown,

the period of the recorded signal

can be calculated as

Period

A typical chart recorder


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&>aple !

)he chart speed of a recording instruent is '5-s.

One cycle of the signal is recorded over * this

referred to soeties as the tie base;. Deterine

the freuency of the signal. Ans

Period T

)herefore, period *-'5 s-cycle 5.!#*s-cycle

=reuency, cycles-sec


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&>aple #

"f the freuency of a signal to be recorded with a strip4

chart recorder is #5EQ, what ust be the chart speed

used to record one coplete cycle on a * of

recording paperU Ans

@iven freuency #5EQ and tie base *

Period , therefore 5.5* Chart 0peed


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. Paperless (ecorders

Paperless recorders use %CD displays and

digital archive eory? these typically can

record four easured variables and have less

aintenance reuireents than chart recorders.

)hey also have a fast speed of response.


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=igure to the right shows a bloc

diagra of a typical paperless

recorder. )he input easureent

signals are input to a ultiple>erand the selected signal is converted

into parallel digital for by an

analogue4to4digital converter for

input to a icroprocessor. )he

icroprocessor generates the rowand colun address signals

reuired for pi>el atri> ultiple>ing

in graphic displays.

"nput data is stored initially in (A/and then transferred to archive

eory? past data can then be

retrieved fro archive eory and

displayed on the screen.


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8. %aser Printer =igure a; shows the basic layoutof a laser printer. )he printer

receives input data in parallel

digital for: for character this could

be in A0C"" forat? for graphics it

will be in vector forat, where

geoetrical shapes are encoded

into nuerical values.

)he operation of the printer is

controlled by a coputer acting as

a print controller. )he controllerconverts this incoing data into

bitap iage pages, each page

corresponding to an array of blac

and white or coloured dots.


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)he photoreceptor drum is an array of photoconductive eleents or pi>els

which correspond to the above bitap iage page. "nitially all of the eleents are

given a positive charge, this is done by passing an electric current through the

corona $ire.

)he dru rotates and the controller directs a laser bea to ove across the

entire photoreceptor array in a raster pattern. )he laser bea is oved by a

rotating polygonal irror and is switched on and off at high speed as it strieseach pi>el. "f light hits an eleent, its resistance falls sharply, causing the charge

to fall to a negative value. "f no light is incident, the pi>el retains its positive

charge.

)he result is that the dru is an array of positively and negatively charged pi>els.

an electrostatic image of the bitap page;.


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Chapter 6 - Data Presentation