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INTRODUCTION
Guru Nanak Dev Thermal Power Plant is a coal-based plant. The requirement of coal for
four units based on specific fuel consumption of 0.60 k ! k"h. The conve#in and crushin
s#stem will have the same capacit# as that of the unloadin s#stem. The coal comes in as lare
pieces. This coal is fed to primar# crushers$ which reduce the si%e of coal pieces from &00mm to
'(0mm. Then the coal is sent to secondar# crusher throuh forward conve#ors where it is
crushed from '(0mm to )00mm as required at the mills. Then the coal is sent to boilers with the
help of primar# fans. The coal is burnt in the boiler. *oiler includes the pipes carr#in water
throuh them+ heat produced from the combustion of coal is used to convert water in pipes into
steam. This steam enerated is used to run the turbine. "hen turbine rotates$ the shaft of
enerator$ which is mechanicall# coupled to the shaft of turbine$ ets rotated so$ three phase
electric suppl# is produced.
The basic requirements are,-
uel /coal
*oiler
1team turbine
Generator
2sh handlin s#stem
3nit au4iliaries
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*57 81T95: 9 T87 P;2NT
Due to hih rate of increasin population da# b# da#$ widenin ap between power demand and
its availabilit# was one the basic reason for envisain the G.N.D.T.P. for the state of Puni.
The historic town of bathinda was selected for this first and prestiious thermal pro
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2vailabilit# of fuel
2sh disposal facilities
1pace requirement
Nature of land
2vailabilit# of labour
Transport facilities
Public societ# problems
Development of *ackward 2rea
P;2NT 12;7NT 72T3571
PROJECT AREA:-
Power plant )CA acres
2sh disposal A&(
;ake 'A0
5esidential colon# )A(
?arshallin #ard )(6
Total area 'A0&
T9T2; B91T, - 5s. ''( crores
1T2T9N B2P2BT:, - four units of ''0?".each
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BOILER:-
?anufacturers *.8.7.;.
?a4imum continuous ratin /?.B.5. C@( T!hr.
1uperheater outlet pressure 'C= k!cm
5eheater outlet pressure CC.A k!cm
inal superheater!reheater temperature (&0°B
eed water temperature )&0°B
7fficienc# A6E
Boal consumption per da# per unit '&00 tones /2ppro4imate
STEAM TURBINE:-
?anufacturers *.8.7.;.
5ated output ''0 ?".
5ated speed C000 r.p.m.
Number of c#linders three
5ated pressure 'C0 k!cm
5ated temperature (C(°B
Bondenser vacuum 0.= k!cm
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GENERATOR:-
?anufacturers *.8.7.;.
5ated output
/3nit- ' F ) ')(000H2
/3nit -C F & 'C@000H2
Generator voltae ''000 volts
5ated phase current
/unit I' F ) 6(60 2mps.
/unit IC F & @))0 2mps.
Generator coolin h#droen
BOILER FEED PUMPS:-
Number per unit two of '00E dut# each
T#pe centrifual
5ated dischare &&( T!hr.
Dischare head '=60 ?"B.
1peed &(00 r.p.m.
CIRCULATING WATER PUMPS:-
Numbers for two units five of (0E dut# each
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T#pe mi4ed flow
5ated dischare A600 T!hr.
Dischare head )& ?"B.
COOLING TOWERS:-
Numbers four
"ater cooled 'A000 T!hr.
Boolin rane '0°B
8eiht ')0!') metres
COAL PULVERISING MILLS:-
Numbers three per unit
T#pe drum-ball
5ated output )@ T!hr.
Boal bunkers '6 per unit
RATING OF 6.6 KV AUXILLIARY MOTORS:-
Boal mill 6C0 "
Hapour fan C)0 "
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B.". an A00!@&6 "
Boal crusher ()0 "
Primar# air fan C)0 "
orced drauht fan C)0 "
*oiler feed pump C(00 "
nduced drauht fan =00!'000 "
Bondensate pump '@( "
"95NG 9 T87 T875?2; 57P95T
Coal received from collieries in the rail wagon is mechanically unloaded by
Wagon Tippler and carried by belt Conveyor ystem !oiler Raw Coal !un"ers after
crushing in the coal crusher# The crushed coal when not re$uired for Raw Coal
!un"er is carried to the coal storage area through belt conveyor# The raw coal
feeder regulates the $uantity of coal from coal bun"er to the coal mill% where the
coal is pulveri&ed to a 'ne powder# The pulveri&ed coal is then suc"ed by the vapour
fan and 'nally stored in pulveri&ed coal bun"ers# The pulveri&ed coal is then pushed
to boiler furnace with the help of hot air steam supplied by primary air fan# The coal
being in pulveri&ed state gets burnt immediately in the boiler furnace% which is
comprised of water tube wall all around through which water circulates# The water
gets converted into steam by heat released by the combustion of fuel in the
furnace# The air re$uired for the combustion if coal is supplied by forced draught
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fan# This air is however heated by the outgoing (ue gases in the air heaters before
entering the furnace#
The products of combustion in the furnace are the flue ases and the ash. 2bout )0E of
the ash falls in the bottom ash hopper of the boiler and is periodicall# removed mechanicall#.
The remainin ash carried b# the flue ases$ is separated in the electrostatic precipitators and
further disposed off in the ash dampin area. The cleaner flue ases are let off to atmosphere
throuh the chimne# b# induced drauht fan.
The chemicall# treated water runnin throuh the water walls of boiler furnace ets
evaporated at hih temperature into steam b# absorption of furnace heat. The steam is further
heated in the super heater. The dr# steam at hih temperature is then led to the turbine
comprisin of three c#linders. The thermal ener# of this steam is utili%ed in turbine for rotatin
its shaft at hih speed. The steam dischared from hih pressure /8.P. turbine is returned to
boiler reheater for heatin it once aain before passin it into the medium pressure /?.P.
turbine. The steam is then let to the coupled to turbine shaft is the rotor of the enerator$ which
produces electricit#. The power from the enerator is pumped into power rid s#stem throuh the
enerator transformer b# steppin up the voltae.
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The steam after doin the useful work in turbine is condensed to water in the condenser for
rec#clin in the boiler. The water is pumped to deaerator from the condenser b# the condensate
e4traction pumps after bein heated in the low pressure heater /;.P.8 from the deaerator$ a hot
water storae tank. The boiler feed pump dischare feed water to boiler at the economi%er b# the
hot flue ases leavin the boiler$ before enterin the boiler drum to which the water walls and
super heater of boiler are connected.
The condenser is havin a lare number of brass tubes throuh which the cold water is
circulated continuousl# for condensin the steam passin out sides the surface of the brass tubes$
which has dischared down b# circulatin it throuh the coolin tower shell. The natural drauht
of cold air is created in the coolin tower$ cools the water fall in the sump and is then recirculated
b# circulatin water pumps to the condenser.
G7N752; D71B5PT9N
BOILER FEED PUMP:-
2s the heart is to human bod#$ so is the boiler feed pump to the steam power plant. t is used
for rec#clin feed water into the boiler at a hih pressure for reconversion into steam. Two nos.
'00E dut#$ barrel desin$ hori%ontal$ centrifual multistae feed pumps with h#draulic couplin
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are provided for each unit. This is the larest au4iliar# of the power plant driven b# C(00 "
electric motor. The capacit# of each boiler at GURU NANAK DEV THERMAL PLANT is C@(
tones!hr. The pump which supplies feed water to the boiler is named as boiler feed pump. This is
the larest au4iliar# in the unit with '00E capacit# which takes suction of feed water from feed
water tank and supplies to the boiler drum after preheatin the same in 8P-'$ 8P-) and
economi%er. The deliver# capacit# of each boiler feed pump is &&( tones!hr. to meet better
requirements correspondin to the various loads$ to control steam temperature$ boiler make up
water etc. The detailed particulars checkin of protections and inter locks$ startin permission
etc. are as below,-
Particulars of BFP and its main motor :-
BOILER FEED PUMP: - The ''0 ?" turbo set is provided with two boiler feed pumps$ each of '00E of total quantit#. t is of barrel desin and is of hori%ontal
arranement$ driven b# an electric motor throuh a h#draulic couplin.
T#pe )00 8
No. of staes 6
Deliver# capacit# &&( t!hr.
eed water temperature '(A°
B
1peed &(00 rpm
Pressure at suction A.C0 k!cm
1tuffin bo4 mechanical seal
;ubrication of pump b# oil under pressure
2nd motor bearin supplied b# h#draulic couplin
Bonsumption of coolin water )C0 ;!min.
WATER TREATMENT PLANT:-
The water before it can be used in the boiler has to be chemicall# treated$ since untreated water
results in scale formation in the boiler tubes especiall# at hih pressure and temperatures. The
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water is demineralised b# on 74chane Process. The water treatment plant has production
capacit# of 'A00 Tonnes per da# for meetin the make-up water requirement of the power
station.
COAL MILL:-
Boal ?ill pulveri%es the raw coal into a fine powder before it is burnt in the boiler furnace. The
pulveri%in of coal is achieved with the impact of fallin steel balls$ weihin ().( tonnes$
contained in the mill drum rotatin at a slow speed of '@.( r.p.m. The raw coal is dried$ before
pulveri%in$ with inert hot flue ases tapped from the boiler. Three coal mills each with a
pulveri%in capacit# of )@ T!hr. are provided for one unit.
INDUC)D DR*U+,T -*N./
Two nos. a4ial flow nduced Drauht ans are provided for each unit to e4haust ash laden flue
ases from boiler furnace throuh dust e4traction equipment and to chimne#. The fan is driven
b# an electric motor throuh a fle4ible couplin and is equipped with remote controlled
reulatin vanes to balance drauht conditions in the furnace. The fan is desined to handle hot
flue ases with a small percentae of abrasive particles in suspension.
CONTRO0 ROO1./
The control room is the operational nerve center of the power plant. The performance of all the
equipments of the plant is constantl# monitored here with the help of sophisticated
instrumentation and controllers. 2n# adverse deviation in the parameters of various s#stems is
immediatel# indicated b# visual and audio warnin and suitable corrective action is taken$
accordinl#. The control room is air conditioned to maintain the desired temperature for proper
functionin of the instruments.
W*+ON TI220)R./
The coal received from the collieries$ in more than '00 rail waons a da#$ is unloaded
mechanicall# b# two nos. waon tipplers out of which one serves as a standb#. 7ach loaded
waon is emptied b# tipplin it in the underround coal hopper from where the coal is carried b#
conve#or to the crusher house. 2rranements have been provided for weihin each rail waon
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before and after tipplin. 7ach tippler is capable of unloadin 6-A rail waons of (( tonnes
capacit# in an hour.
CRU,)R ,OU)./
Boal unloaded b# the waon tippler is carried to crusher house throuh conve#ors for crushin.
Two nos. hammer t#pe coal crushers are provided$ which can crush coal to a si%e of '0 mm. The
crushed coal is then supplied to *oiler 5aw Boal *unkers. The surplus coal is carried to coal
storae area b# series of conve#ors. Brushin of coal is an essential requirement for its optimum
pulveri%in and safe storae.
COOLING TOWERS:-
Boolin Towers of the power plant are the land mark of the *athindaBit# even for a far distance
of A-'0 kilometers. 9ne coolin tower is provided for each unit for coolin 'A000 tones of water
per hour b# '0°B. coolin towers are massive erro-concrete structure havin h#perbolic profile
creatin natural drauht of air responsible for achievin the coolin effect. Boolin tower is as
hih as &0 store# buildin.
BOILER:-
t is a sinle drum$ balanced drauht$ natural circulation$ reheat t#pe$ vertical combustion
chamber consists of seamless steel tubes on all its sides throuh which water circulates and is
converted into steam with the combustion of fuel. The temperature inside the furnace where the
fuel is burnt is of the order of '(00°B. The entire boiler structure is of &)meter heiht.
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BOILER CHIMNEY:-
The flue from the boiler$ after removal of ash in the precipitators$ are let off to atmosphere
throuh boiler chimne#$ a tall ferro-concrete structure standin as hih as the historic
Jutab?inar. our chimne#s$ one for each unit$ are installed. The chimne# is lined with fire
bricks for protection of ferro-concrete aainst hot flue ases. 2 protective coatin of acid
resistant paint is applied outside on its top '0 meters.
CIRCULATING WATER PUMP:-
Two nos. of circulatin water pumps provided for each unit$ circulate water at the rate of '@)00
T!hr. in a closed c#cle comprisin of Turbine Bondenser and BoolinTower. 2n additional
Birculatin "ater Pump provided serves b# for two units. The water requirement for bearin
coolin of all the plant au4iliaries is also catered b# these pumps.
B92; ?;NG P;2NT
1ince G.N.D.T.P. units are primaril# coal fired units so each boiler is provided with closed
millin circuits to pulveri%e the raw coal which is received from coal conve#in s#stem after
coal crushes before it is fired in the furnace. The necessit# of pulveri%in the coal is to be
ensurin its ma4imum possible combustion in the furnace. The coal data for units are, -
COAL DATA UNITS 1 & 2 UNITS 3 & 4
T#pe of Boal
Net Balorific Halue
?oisture
*ituminous
&C00 cal!k
'0 E
*ituminous
&@)@ cal!
@.( E
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2sh Bontent
Holatile ?atter ncombustible
nlet of Boal
C0 E
)& E
'0 mm
C) E
)@ E
)0 mm
5aw coal of pulveri%ed in the millin circuit and the output fromthe mill is fine coal. ma4imum
si%e '0 mm I )0 mm is
COAL MILL:-
These are mainl# of two t#pes,-
i *all ?ills
ii *owl ?ills
Ball Mll!: -n *all ?ills there are steel balls which are revolvin in hori%ontal c#lindrical
drum. These balls are free from an# shaft and balls are touchin with each other and with internal
bod# of drum. These t#pes of mills are at *athinda Thermal Plant. 9n the other hand$ bowl mills
part of the mill contain drive s#stem i.e. it contains 6.6 kH electric motor and ear s#stem whichtranslates the revolution about hori%ontal a4is to revolve about vertical a4is. The revolvin
vertical a4is contains a bowl about the drivin s#stem. This bowl is fi4ed with drivin and
revolvin with shaft. There are also three rollers which are suspended at some inclination$ so that
there is a ap of few mm between roller surface. These rollers are free to rotate about the a4is.
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Bowl Mills: The coal is rinded and then fed into the mill at the center or near of revolvin
bowl. t passes between the rindin rin in revolvin bowl and rolls as centrifual force causes
the material to travel towards the out perimeter of bowl. The sprins$ which load the rolls$ impart
the necessar# force for rindin. The partiall# pulveri%ed coal continue oin up and down and
over the ede of bowl.
!AGON TIPPLER
The tippler is desined to work on the followin c#cle of operation,-
Tippin =0 seconds
Pause (-') seconds
5eturn =0 second1
"eihin C0 seconds
Total )'(-))) seconds
2llowin A( seconds for waon chanin it will be seen that ') eiht-wheel waons or )& four-wheel waons per hours can be tipped. 8owever since the coal carr#in capacit# is (00 tones per
hour load of ') waons comes to A to = per hour.
CRUSHER HOUSE:
The crusher house accommodates the dischare ends of the conve#or &2$ &* receivin ends of
conve#or (2$ (* and conve#or @2 and @*$ two crushers$ vibratin feeders and necessar# chute
work. There are two crushers each driven b# @008.P. electric motor$ C phase$ (0 c#cles and 6.6
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kH suppl#. The ma4imum si%e of the crushed coal is '0mm. The capacit# of each crusher is (00
tones!hr. one crusher works at a time and the other is standb#. rom the crusher the coal can be
fed either to the conve#ors (2$ (* or @2$ @* b# ad
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t is main part of 1T72? G7N52T95K it is an assembl# of a lare no. of vertical riser tubes
embedded in refractor# walls. There are two boilers one for each unit. The t#pe of the boiler is
N2T352; B5B3;2T9N 52D7NT 1NG;7 57872T boiler. The four refector# walls
make a closed bo4 called 352NB7 .The walls are iven special names. These are+
' 5G8T "2;; consistin 'C0 T3*71.
) ;7T "2;; consistin 'C0 T3*71.
C 59NT "2;; consistin 'A' T3*71.& 5725 "2;; consistin 'A' T3*71.
9n the riht and left wall$ the "ND *9L71 are installed. Thus there are our urnace
Boroners.
The water tubes cool the walls b# absorbin the heat and transferrin it to the water runnin in
them. The tubes are embedded in refector# walls ver# close /the Gap between two tubes is '0
mm. The inner diameter of the tubes is 6C.(mm.
>31TB2T9N 9 T87 *9;75 T:P7+
The t#pe of boiler is "2T75 T3*7$ N2T352; B5B3;2T9N$ 52D7NT 1NG;7
57872T boiler. The meanin of each word has been e4plained below+
"2T75 T3*7+ t mean the water runs in the tubes and the fire is outside the tubes.
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N2T352; B5B3;2T9N+ The B5B3;2T9N word mean how the water is raised in the
walls. "e know that the water upwards we have to suppl# some e4ternal power e..$ some pump
s#stemK *ut here a law dose this work naturall#. The saturated water collected at the bottom
known as 5NG 872D75. The water rises from it in riser pipes naturall#. There is a T"9
P8217 ?LT357 of "2T75 and 1T72? in risers. There is a D757NB7 *7T"77N the
D7N1T71 of the ?LT357 and 12T352T7D "2T75 in 5in 8eader. 2lso there is a
1T2TB 872D. Due to the result of both factors there is N2T352; B5B3;2T9N operates
in boiler.
52D7NT T:P7, 2s the name implies$ the heat is transferred from combustion as to the water
b# 52D2T9N. The heat is then B9D3BT7D to water tubes and throuh the thickness of tubes. There is B9NH7BT7D to the T"9 P8217D ?LT357.
1NG;7 57872T+ t implies that the s#stem is reheated onl# once . "hen the steam oes to 8
Turbine its temperature decreases from (&0 de to C&C de. t is then send to reheater to increase
the temp to aain (&0 de.
' t should be absolutel# reliable and capable of raisin ma4imum amount of steam for
minimum fuel consumption$ attention$ initial cost and maintenance chares.
) t should be liht in weiht and should occup# small space
C The refractor# s#stem should be as little as possible$ but sufficient to secure eas# inition
and smokeless combustion of fuel on reduced load.
?anufacturers *.8.7.;
?a4imum continuous ratin C@( T! hr
1uperheater outlet Pressure 'C= !cm)
inal 1uperheater Temp. (&00B
eed "ater Temp. )&00B7fficienc# A6E
Boal Bonsumption Per da# '&00 tones /appro4.
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;2?7 1B2NN75
2 "l#$% %'%('o) is a sensor desined to detect and respond to the presence of a flame or fire.
5esponses to a detected flame depend on the installation$ but can include soundin an alarm$
deactivatin a fuel line /such as a propane or a natural as line$ and activatin a fire suppression
s#stem. "hen used in applications such as industrial furnaces$ their role is to provide
confirmation that the furnace is properl# lit+ in these cases the# take no direct action be#ond
notif#in the operator or control s#stem. 2 flame detector can often respond faster and more
accuratel# than a smoke or heat detector due to the mechanisms it uses to detect the flame.
https://en.wikipedia.org/wiki/Sensorhttps://en.wikipedia.org/wiki/Sensorhttps://en.wikipedia.org/wiki/Flamehttps://en.wikipedia.org/wiki/Firehttps://en.wikipedia.org/wiki/Firehttps://en.wikipedia.org/wiki/Propanehttps://en.wikipedia.org/wiki/Propanehttps://en.wikipedia.org/wiki/Propanehttps://en.wikipedia.org/wiki/Natural_gashttps://en.wikipedia.org/wiki/Flamehttps://en.wikipedia.org/wiki/Firehttps://en.wikipedia.org/wiki/Propanehttps://en.wikipedia.org/wiki/Natural_gashttps://en.wikipedia.org/wiki/Sensor
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9PTB2; ;2?7 D7T7BT951
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lame detector t#pe reions
Ul')#*iol%'3ltraviolet /3H detectors work b# detectin the 3H radiation emitted at the instant of inition.
"hile capable of detectin fires and e4plosions within CI& milliseconds$ a time dela# of )IC
seconds is often included to minimi%e false alarms which can be triered b# other 3H sources
such as lihtnin$ arc weldin$ radiation$ and sunliht. 3H detectors t#picall# operate
with wavelenths shorter than C00 nm. The solar blind 3H wavelenth band is also easil#
blinded b# oil# contaminants.
N%#) IR #))#+ Near infrared /5 arra# flame detectors$ also known as visual flame detectors$
emplo# flame reconition technolo# to confirm fire b# anal#%in near 5 radiation usina chare-coupled device
I,")#)%nfrared /5 flame detectors monitor the infrared spectral band for specific patterns iven off b#
hot ases. These are sensed usin a speciali%ed fire-fihtin thermal imain camera /TB$ a
t#pe of thermo raphic camera. alse alarms can be caused b# other hot surfaces and
backround thermal radiation in the area. "ater on the detectorMs lens will reatl# reduce the
accurac# of the detector$ as will e4posure to direct sunliht. 2 sinle-frequenc# 5 flame detector
is t#picall# sensitive to wavelenths around &.& micrometers$ which is a spectral characteristic
peak of hot carbon dio4ide as is produced in a fire. The usual response time of an 5 detector is
CI( seconds.
UV-IR
https://en.wikipedia.org/wiki/Ultraviolethttps://en.wikipedia.org/wiki/Lightninghttps://en.wikipedia.org/wiki/Arc_weldinghttps://en.wikipedia.org/wiki/Arc_weldinghttps://en.wikipedia.org/wiki/Radiationhttps://en.wikipedia.org/wiki/Sunlighthttps://en.wikipedia.org/wiki/Sunlighthttps://en.wikipedia.org/wiki/Wavelengthhttps://en.wikipedia.org/wiki/Wavelengthhttps://en.wikipedia.org/wiki/Nanometrehttps://en.wikipedia.org/wiki/Infraredhttps://en.wikipedia.org/wiki/Infraredhttps://en.wikipedia.org/wiki/Charge-coupled_devicehttps://en.wikipedia.org/wiki/Charge-coupled_devicehttps://en.wikipedia.org/wiki/Infraredhttps://en.wikipedia.org/wiki/Thermal_imaging_camera_(firefighting)https://en.wikipedia.org/wiki/Thermographic_camerahttps://en.wikipedia.org/wiki/Thermographic_camerahttps://en.wikipedia.org/wiki/Thermal_radiationhttps://en.wikipedia.org/wiki/Carbon_dioxidehttps://en.wikipedia.org/wiki/Ultraviolethttps://en.wikipedia.org/wiki/Lightninghttps://en.wikipedia.org/wiki/Arc_weldinghttps://en.wikipedia.org/wiki/Radiationhttps://en.wikipedia.org/wiki/Sunlighthttps://en.wikipedia.org/wiki/Wavelengthhttps://en.wikipedia.org/wiki/Nanometrehttps://en.wikipedia.org/wiki/Infraredhttps://en.wikipedia.org/wiki/Charge-coupled_devicehttps://en.wikipedia.org/wiki/Infraredhttps://en.wikipedia.org/wiki/Thermal_imaging_camera_(firefighting)https://en.wikipedia.org/wiki/Thermographic_camerahttps://en.wikipedia.org/wiki/Thermal_radiationhttps://en.wikipedia.org/wiki/Carbon_dioxide
8/19/2019 Garry Gill
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These detectors are sensitive to both 3H and 5 wavelenths$ and detect flame b# comparin the
threshhold sinal of both ranes. This helps minimi%e false alarms.
IR-IR "l#$% %'%('io,
Dual 5 /5!5 flame detectors compare the threshold sinal in two infrared ranes. 9ften one
sensor looks at the &.& micrometer carbon dio4ide /B9) emission$ while the other sensor looks
at a reference frequenc#. 1ensin is B9) emission is appropriate for h#drocarbon fuels+ for
non-carbon based fuels$ e..$ h#droen$ the broadband water bands are sensed.
IR3 "l#$% %'%('io,
Triple-5 flame detectors compare three specific wavelenth bands within the 5 spectral reion
and their ratio to each other. n this case one sensor looks at the &.& micrometer rane while the
other sensors look at reference wavelenths both above and below &.&. This allows the detector
to distinuish between non-flame 5 sources and actual flames which emit hot B9) in the
combustion process. 2s a result$ both detection rane and immunit# to false alarms can be
sinificantl# increased. 5C detectors can detect a 0.'m)/' ft) asoline pan fire at up to 6( m
/)'( ft in less than ( seconds. Triple 5s$ like other 5 detector t#pes$ are susceptible to blindin
b# a la#er of water on the detectorMs .?ost 5 detectors are desined to inore constant
backround 5 radiation$ which is present in all environments. nstead the# are desined to
detect suddenl# chanin or increasin sources of the radiation. "hen e4posed to chanin
patterns of non-flame 5 radiation$ 5 and 3H!5 detectors become more prone to false alarms$
while 5C detectors become somewhat less sensitive but are more immune to false alarms.
Visi.l% s%,so)s
n some detectors$ a sensor for visible radiation /liht is added to the desin in order to better
discriminate aainst false alarms or to improve the detection rane.
Vi%o
Blosed-circuit television or a web camera can be used for visual detection of
/wavelenths between 0.& and 0.@ m. 1moke or fo can limit the effective rane of these$ since
the# operate solel# in the visible spectrum.
Io,i/#'io, (0))%,' "l#$% %'%('io,
The intense ioni%ation within the bod# of a flame can be measured b# means of a current that
flows when a voltae is applied b# the phenomena of lame 5ectification. This current can be
https://en.wikipedia.org/wiki/Closed-circuit_televisionhttps://en.wikipedia.org/wiki/Web_camerahttps://en.wikipedia.org/wiki/Web_camerahttps://en.wikipedia.org/wiki/Web_camerahttps://en.wikipedia.org/wiki/Wavelengthhttps://en.wikipedia.org/wiki/Smokehttps://en.wikipedia.org/wiki/Smokehttps://en.wikipedia.org/wiki/Foghttps://en.wikipedia.org/wiki/Foghttps://en.wikipedia.org/wiki/Flame_rectificationhttps://en.wikipedia.org/wiki/Flame_rectificationhttps://en.wikipedia.org/wiki/Closed-circuit_televisionhttps://en.wikipedia.org/wiki/Web_camerahttps://en.wikipedia.org/wiki/Wavelengthhttps://en.wikipedia.org/wiki/Smokehttps://en.wikipedia.org/wiki/Foghttps://en.wikipedia.org/wiki/Flame_rectification
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used to verif# flame presence and qualit#. 1uch detectors are used in lare industrial process as
heaters and are connected to the flame control s#stem. The# usuall# act as both flame qualit#
monitors and for flame failure detection.
These t#pes of sensors are also common in a variet# of household as furnaces.
T%)$o(o0l% "l#$% %'%('io,
Thermocouples are used e4tensivel# for monitorin flame presence in combustion heatin
s#stems and as cookers. 2 common use in these installations is to cut off the suppl# of fuel if
the flame fails$ in order to prevent unburned fuel from accumulatin. These sensors measure heat
and therefore are commonl# used to determine the absence of a flame. This can be used to verif#
the presence of a Pilot flame.
Types of pressure measurements
1ilicon resistive pressure sensors
Pressure sensors can be classified in terms of pressure ranes the# measure$ temperature ranes
of operation$ and most importantl# the t#pe of pressure the# measure. Pressure sensors are
variousl# named accordin to their purpose$ but the same technolo# ma# be used under
different names.
• A.sol0'% )%ss0)% s%,so)
This sensor measures the pressure relative to perfect vacuum.
• G#0% )%ss0)% s%,so)
This sensor measures the pressure relative to atmospheric pressure. 2 tire pressure aue is an
e4ample of aue pressure measurement+ when it indicates %ero$ then the pressure it is measurin
is the same as the ambient pressure.
• V#(00$ )%ss0)% s%,so)
This term can cause confusion. t ma# be used to describe a sensor that measures pressures
below atmospheric pressure$ showin the difference between that low pressure and atmospheric
pressure /i.e. neative aue pressure$ but it ma# also be used to describe a sensor that measures
low pressure relative to perfect vacuum /i.e. absolute pressure.
• Di""%)%,'i#l )%ss0)% s%,so)
https://en.wikipedia.org/wiki/Furnacehttps://en.wikipedia.org/wiki/Furnacehttps://en.wikipedia.org/wiki/Furnacehttps://en.wikipedia.org/wiki/Thermocouplehttps://en.wikipedia.org/wiki/Pilot_lighthttps://en.wikipedia.org/wiki/Vacuumhttps://en.wikipedia.org/wiki/Vacuumhttps://en.wikipedia.org/wiki/Atmospheric_pressurehttps://en.wikipedia.org/wiki/Furnacehttps://en.wikipedia.org/wiki/Thermocouplehttps://en.wikipedia.org/wiki/Pilot_lighthttps://en.wikipedia.org/wiki/Vacuumhttps://en.wikipedia.org/wiki/Atmospheric_pressure
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This sensor measures the difference between two pressures$ one connected to each side of the
sensor. Differential pressure sensors are used to measure man# properties$ such as pressure drops
across oil filters or air filters$ fluid levels /b# comparin the pressure above and below the liquid
or flow rates /b# measurin the chane in pressure across a restriction. Technicall# speakin$
most pressure sensors are reall# differential pressure sensors+ for e4ample a aue pressure
sensor is merel# a differential pressure sensor in which one side is open to the ambientatmosphere.
• S%#l% )%ss0)% s%,so)
This sensor is similar to a aue pressure sensor e4cept that it measures pressure relative to some
fi4ed pressure rather than the ambient atmospheric pressure /which varies accordin to the
location and the weather.
a Gaue Pressure b 2bsolute Pressure
c Differential Pressure
*ut the# are all related to each other
# G#0% P)%ss0)% is $%#s0)% wi' )%"%)%,(% 'o #'$os%)i( )%ss0)% 5l%#s% s%% 6737
n our e4ample above we e4plained that we had to remove atmospheric pressure to measure the
weiht of the fi%%# drink and because it was on the outside of the bottle we could measure it. n
da# to da# practice$ pressure measurement that uses atmospheric pressure as its referece iscalled G#0% P)%ss0)%. To indicate that this is what has been done$ 3nits of measurement are
noted with the OO Pascals Gaue /Pa or Pound per 1quare nch Gaue /Psi abbreviationsare used.
2ll pressure aues$ sensors$ transducers and transmitters that measure aue pressure actuall#measure the difference between atmospheric pressure and the pressure to be measured as shown
in fiC.
. A.sol0'% P)%ss0)% is $%#s0)% wi' )%"%)%,(% 'o V#(00$7
n some applications the variation in atmospheric pressure ma# affect our calculation. 2s ane4ample the as in our fi%%# drink chanes in si%e with atmospheric pressure$ so to ensure we are
consistant with the riht amount of as$ we in
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To measure absolute pressure it is possible to meaure both aue pressure and atmospheric
pressure. *ut in realit# most absolute pressure aues$ sensors$ transducers and transmitters that
measure absolute pressure do so b# measurin the difference between a reference vacuum andthe pressure to be measured as shown in fi).
( Di""%)%,'i#l P)%ss0)% is ,o' $%#s0)% wi' )%"%)%,(% 'o # s%(i"i( )%"%)%,(% )%ss0)% 5s%%
6747
3nlike Gaue or 2bsolute pressure transmitters$ Differential Pressure Transmitters do not
attempt to fi4 the reference. mportantl# an increase in differential can be the result of increasinone of the pressures or decreasin the other.
2n increase in differential pressure would occur if P' became smaller OR if P) became larer. na similare wa#$ a decrease in differential pressure would occur if P' became larer 95 if P)
became smaller. The differential pressure measurement is not concerned whether the lower of the
two pressures is at a vacuum$ atmospheric or some other pressure. t is onl# interested in thedifference between the two pressures bein measured.
The fundamental of differential pressure measurement is established.
Not all aues$ sensors$ transducers and transmitters that measure differential pressure actuall#measure the difference between two pressure as shown in fi&. 1ome devices attempt to measure
two atmospheric or aue pressures and then mathematicall# calculate the difference. Thismethod in our opinion is flawed$ as it multiplies uncertainl# with the number of measurements
made. f #ou would like to know more about this sub
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R)IT*NC) T)12)R*TUR) D)T)CTOR 3RTD4 / 2RINCI20) O- O2)R*TION
2n 5TD /resistance temperature detector is a temperature sensor that operates on the
measurement principle that a materialKs electrical resistance chanes with temperature. The
relationship between an 5TDKs resistance and the surroundin temperature is hihl# predictable$allowin for accurate and consistent temperature measurement. *# suppl#in an 5TD with a
constant current and measurin the resultin voltae drop across the resistor$ the
5TDKs resistance can be calculated$ and the temperature can be determined.
RTD 1aterials
Different materials used in the construction of 5TDs offer a different relationship between
resistance and temperature. Temperature sensitive materials used in the construction of 5TDinclude platinum$ nickel$ and copper+ platinum bein the most commonl# used. mportantcharacteristics of an 5TD include the temperature coefficient of resistance /TB5$ the nominal
resistance at 0 derees Belsius$ and the tolerance classes. The TB5 determines the relationship
between the resistance and the temperature. There are no limits to the TB5 that is achievable$ but
the most common industr# standard is the platinum CA(0 ppm!. This means that the resistanceof the sensor will increase 0.CA( ohms per one deree Belsius increase in temperature. The
nominal resistance of the sensor is the resistance that the sensor will have at 0 derees Belsius.
2lthouh almost an# value can be achieved for nominal resistance$ the most common is the platinum '00 ohm /pt'00. inall#$ the tolerance class determines the accurac# of the sensor$
usuall# specified at the nominal point of 0 derees Belsius. There are different industr# standards
that have been set for accurac# includin the 21T? and the 7uropean DN. 3sin the values of TB5$ nominal resistance$ and tolerance$ the functional characteristics of the sensor are defined.
RTD Con'gurations
n addition to different materials$ 5TDs are also offered in two ma
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dimensions that lead to better response times and packain capabilities. or a lon time wire
wound sensors featured much better accurac#. Thanks to recent developments$ however$ there is
now thin film technolo# capable of achievin the same level of accurac#.
Operations of RTD
2n 5TD takes a measurement when a small DB current is supplied to the sensor. The current
e4periences the impedance of the resistor$ and a voltae drop is e4perienced over the resistor.Dependin on the nominal resistance of the 5TD$ different suppl# currents can be used. To
reduce self-heatin on the sensor the suppl# current should be kept low. n eneral$ around 'm2
or less of current is used.
2n 5TD can be connected in a two$ three$ or four-wire confiuration. The two-wireconfiuration is the simplest and also the most error prone. n this setup$ the 5TD is connected
b# two wires to a "heatstone bride circuit and the output voltae is measured. Thedisadvantae of this circuit is that the two connectin lead wire resistances add directl# twothe 5TDKs resistance and an error is incurred.
5/Wire Con'guration
The four-wire confiuration consists of two current leads and two potential leads that measurethe voltae drop across the 5TD. The two potential leads are hih resistance to neate the effect
of the voltae drop due to current flowin durin the measurement. This confiuration is ideal
for cancelin the lead wire resistances in the circuit as well as eliminatin the effects of different
lead resistances$ which was a possible problem with the three-wire confiuration. The four-wireconfiuration is commonl# used when a hihl# accurate measurement is required for the
application.
6/Wire Con'guration
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The four-wire confiuration consists of two current leads and two potential leads that measure
the voltae drop across the 5TD. The two potential leads are hih resistance to neate the effect
of the voltae drop due to current flowin durin the measurement. This confiuration is idealfor cancelin the lead wire resistances in the circuit as well as eliminatin the effects of different
lead resistances$ which was a possible problem with three-wire confiuration. The four-wire
confiuration is commonl# used when a hihl# accurate measurement is required for theapplication.
7/Wire Con'guration
n combination with the wirin diarams shown$ a more comple4 circuit is often emplo#ed.There are man# different options for circuits when workin with an 5TD. The two most
important features of this circuit are current eneration and sinal conditionin. or purposes of
linearit#$ it is important that the current eneration circuit supplies a stable e4citation to the 5TD.
9nce a stable e4citation current is applied to the 5TD$ the sinal conditionin path of the circuitcancels lead resistances$ ains the sinal and converts the sinal to diital usin an 2DB$ which
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can then be read b# a controller.
Temperature 1witch
Temperature switches /also called thermostats$ aquastats or free%estats dependin on application
are commonl# used in DDB control s#stems to provide a diital input when a process medium
temperature rises or falls to a set temperature. 1witches with a number of different operatin
principles are manufactured. 1ome of the common t#pes include bimetallic$ fluid thermal
e4pansion$ free%estat and electronic.
*imetallic temperature switches use a bonded ObimetalO strip consistin of two dissimilar metals
with different thermal coefficients of e4pansion. "hen the temperature chanes$ the metals
e4pand or contract at different rates causin the strip to bend. Harious confiurations such as
coiled elements are used to increase the thermal movement to cause two contacts to come
toether or separate. 1ome confiurations use the bimetallic principle to chane the orientation
of a bulb containin liquid mercur# so that the mercur# flows into contact with two electrodes$
completin the circuit.
luid thermal e4pansion temperature switches use the principle of thermal e4pansion of a fluid to
cause displacement of a bellows$ diaphram$ bourdon tube$ or piston to open or close a set of
contacts. luid s#stem based temperature switches can be connected to a remote fluid containin
bulb b# a capillar# tube$ allowin the switch element to be remote from the sensin bulb.
iure ).6- 5emote *ulb Thermostat
The free%estat is commonl# used to prevent water or steam coils in air handlin units from
free%in. ree%estats use a fluid that is a saturated vapor at the switch set point temperature. This
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P)%ss0)% swi'(
?urph# oil pressure aues with switches that activate on low pressure
2 )%ss0)% swi'( is a form of switch that closes an electrical contact when a certain
set pressure has been reached on its input. The switch ma# be desined to make contact either on
pressure rise or on pressure fall.
2nother t#pe of pressure switch detects mechanical force+ for e4ample$ a pressure-sensitive mat
is used to automaticall# open doors on commercial buildins.
2ressure switch
2 pressure switch for sensin fluid pressure contains a capsule$ bellows$ *ourdon tube$
diaphram or piston element that deforms or displaces proportionall# to the applied pressure.
The resultin motion is applied$ either directl# or throuh amplif#in levers$ to a set of switch
contacts. 1ince pressure ma# be chanin slowl# and contacts should operate quickl#$ some kind
of over-center mechanism such as a miniature snap-action switch is used to ensure quick
operation of the contacts. 9ne sensitive t#pe of pressure switch uses mercur# switches mounted
on a *ourdon tube+ the shiftin weiht of the mercur# provides a useful over-center
characteristic.
The pressure switch ma# be ad
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The pressure-sensin element of a pressure switch ma# be arraned to respond to the difference
of two pressures. 1uch switches are useful when the difference is sinificant$ for e4ample$ to
detect a cloed filter in a water suppl# s#stem. The switches must be desined to respond onl#
to the difference and not to false-operate for chanes in the common mode pressure.
The contacts of the pressure switch ma# be rated a few tenths of an ampere to around '(
amperes$ with smaller ratins found on more sensitive switches. 9ften a pressure switch will
operate a rela# or other control device$ but some t#pes can directl# control small electric motors
or other loads.
1ince the internal parts of the switch are e4posed to the process fluid$ the# must be chosen to
balance strenth and life e4pectanc# aainst compatibilit# with process fluids. or e4ample$
rubber diaphrams are commonl# used in contact with water$ but would quickl# derade if used
in a s#stem containin mineral oil.
1witches desined for use in ha%ardous areas with flammable as have enclosure to prevent
an arc at the contacts from initin the surroundin as. 1witch enclosures ma# also be required
to be weatherproof$ corrosion resistant$ or submersible.
2n electronic pressure switch incorporates some variet# of pressure transducer /strain aue$
capacitive element$ or other and an internal circuit to compare the measured pressure to a set
point. 1uch devices ma# provide improved repeatabilit#$ accurac# and precision over a
mechanical switch.
T%$%)#'0)% Swi'(%s
T%$%)#'0)% swi'(%s are the mechanisms used to measure temperature. The workin of a
temperature switch is based upon the temperature variations takin place in an enclosed space$ or
in an open area ad