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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.
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)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
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)ype of Data Presentations
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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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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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