IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 71, 2022 7005711
An Op ical-Based Senso o Au omo i e Exhaus
Gas Tempe a u e Measu emen
Michal P auzek ,Membe , IEEE,RadimHe cik , Ja omi Konecny , Ma in Mikolajek , Ma in S ankus ,
Ji i Kozio ek , and Radek Ma inek ,Senio Membe , IEEE
Abs ac — The a icle in oduces he design o an op ical-based
senso ha measu es au omo i e exhaus gas empe a-
u es (EGTs) o e a wide empe a u e ange. To measu e
empe a u e, we combined he luminescence me hod and he
blackbody adia ion (BBR) p inciple. We also de eloped ou
own measu emen ha dwa e ha includes he means o p ocess
and e alua e he signals ob ained o empe a u e con e sion
using op ical me hods o applica ion in he a ge empe a u e
ange (−40 ◦C o 820 ◦C). This empe a u e ange is speci ied by
he au omo i e indus y acco ding o cu en combus ion engine
designs and emission equi emen s, which s ipula e accu a e
measu emen o ope a ing empe a u e o op imal unc ioning.
Cu en measu emen solu ions a e based on he he mocouple
p inciple. This app oach is p oblema ic, especially wi h ega d o
elec omagne ic in e e ence and sel -diagnos ics, and p oblems
also exis wi h he g adual pene a ion o mois u e in o he
empe a u e p obe unde ex eme he mal s ess. The case s udy
con i med he ull unc ionali y o he new op ical senso concep .
The bene i o he p oposed concep is ull compa ibili y wi h
exis ing concep ual solu ions while main aining he ad an ages o
op ical-based senso s. The esul s indica ed ha a combina ion
o he BBR and luminescence me hods wi h a uby c ys al in he
p oposed solu ion p oduced an a e age absolu e e o o 2.32 ◦C
in he empe a u e ange −40 ◦C o 820 ◦C o e a measu emen
cycle ime o 0.25 s.
Index Te ms— Au omo i e applica ion, blackbody adia ion
(BBR), hyb id senso , luminescence, op ical-based senso , op ical
ibe , op ical signal analysis, empe a u e measu emen .
I. INTRODUCTION
THE au omo i e indus y is an e e -g owing a ea ac-
ing many esea ch challenges. The numbe o ehi-
cles ope a ing on oads is inc easing, and au ho i ies a e
con inually pushing ha de o dec eases in emissions [1].
Manusc ip ecei ed 4 Ap il 2022; e ised 28 June 2022; accep ed 6 July
2022. Da e o publica ion 28 July 2022; da e o cu en e sion 2 Augus
2022. This wo k was suppo ed in pa by he P ojec “De elopmen
o Algo i hms and Sys ems o Con ol, Measu emen and Sa e y Appli-
ca ions VIII” o he S uden G an Sys em, VSB-TU Os a a, unde
P ojec SP2022/11; in pa by he Eu opean Regional De elopmen
Fund o he Resea ch Cen e o Ad anced Mecha onic Sys ems P ojec
h ough he Ope a ional P og am Resea ch, De elopmen and Educa ion
unde P ojec CZ.02.1.01/0.0/0.0/16_019/0000867; and in pa by he
Eu opean Union’s Ho izon 2020 Resea ch and Inno a ion P og am unde
G an 856670. The Associa e Edi o coo dina ing he e iew p ocess was
D . Jagadeesh Va ada ajan Kuma . (Co esponding au ho : Michal P auzek.)
The au ho s a e wi h he Depa men o Cybe ne ics and Biomedical
Enginee ing, VSB—Technical Uni e si y o Os a a, 708 00 Os a a-Po uba,
Czech Republic (e-mail: michal.p auzek@ sb.cz; adim.he cik@ sb.cz;
ja omi .konecny@ sb.cz; ma in.mikolajek@ sb.cz; ma in.s ankus@ sb.cz;
ji i.kozio ek@ sb.cz; adek.ma inek@ sb.cz).
Digi al Objec Iden i ie 10.1109/TIM.2022.3192274
Fig. 1. Tempe a u e senso p inciple and applica ion: a ge ed measu emen
poin s in ehicles, he p inciple o op ical sensing (op ical ibe s), and
communica ion wi h a cen al uni .
Al hough elec ic ehicles d aw signi ican esea ch in e -
es [2], much esea ch s ill a ge s he imp o emen o com-
bus ion engines [3] o mo e ecological ope a ion. Op imal
unc ionali y in a combus ion engine equi es nume ous sen-
so s [4] ha measu e se e al p ope ies o in e es .
The aim o his s udy is o apply and examine an exhaus
gas empe a u e (EGT) measu emen me hod which is c i ical
o op imal ehicle ope a ion and e ec i e emissions educ-
ion [5]. Fig. 1 illus a es he p inciple and applica ion o he
empe a u e senso desc ibed in his a icle. The p oposed solu-
ion is designed o ehicles (ca s, ucks, e c.) equipped wi h
diesel combus ion engines. Exhaus pipes ha e h ee loca ions
whe e empe a u e mus be measu ed: nea he engine, in on
o he diesel pa icula e il e (DPF), and behind he DPF.
Reliable and p ecise empe a u e measu emen is a majo
challenge o he au omo i e indus y. Combus ion engines
mus be ope a ed in a speci ic empe a u e ange o achie e
op imal ope a ion, minimal emissions, and low uel consump-
ion. The mocouples a e commonly used in he au omo i e
indus y o measu e empe a u es, bu hei maximum mea-
su able empe a u e, ime esponse, accu acy, s abili y, and
se ice li e ha e limi a ions [6].
Op ical-based he mome e s a e eliable, ha e an excel-
len measu able ange, and a e esis an o elec omagne ic
dis o ion [7].
Table I summa izes he s a e-o - he-a and ad an ages
and disad an ages o cu en op ical me hods de eloped o
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7005711 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 71, 2022
TABLE I
ADVANTAGES AND DISADVANTAGES OF CURRENT METHODS OF OPTICAL TEMPERATURE MEASUREMENT
empe a u e measu emen . Op ical he mome e s employ se -
e al physical p inciples, o example, blackbody adia ion
(BBR) [13], which is based on Plank’s law and used in
high- empe a u e measu emen [8]. The BBR me hod has
applica ions in ields such as ae ospace [15], medicine [17],
and manu ac u ing [14].
Luminescence ibe -op ic empe a u e senso s based on he
p inciple o measu ing luminous in ensi y can be used as
an al e na i e empe a u e measu emen me hod. In his case,
a pulse exci a ion ligh is emi ed by a ligh sou ce in o
luo escen ma e ial and he subsequen ly emi ed luo escen
signal is ansmi ed o a pho oelec ic de ec o . The luo-
escen signal is hen con e ed in o elec ical signals, and
empe a u e is calcula ed acco ding o he ime esponse o
de ec ed ampli ude [27]. The empe a u e senso ’s ange is
signi ican ly dependen on he luminescence ma e ial [18],
[20], [21]. Zhang e al. [19] p o ide an o e iew o he s a e-
o - he-a co-doped ma e ials used o pu poses based on
luminescence p inciples. High- empe a u e op ical p obes ha
apply he luminescence p inciple ha e also been cons uc ed
and p o ed e ec i e [28].
Ad ances om esea ch in lase echnology and ibe B agg
g a ing (FBG) senso s now allow g ea e possibili ies in he
de elopmen o op ical he mome e s. The p inciple in ol es
he ansmission o b oadband ligh in o an FBG, whe e a
ligh wa e ha con o ms wi h he B agg condi ion is e lec ed
o gene a e a e lec ion spec um. A change in a sapphi e
ibe g a ing empe a u e esul s in a a ia ion in he e ec i e
e ac i e index, and he e o e he e lec ed ligh ’s wa eleng h
will change. The e lec ed ligh is cap u ed by a spec al ana-
lyze , and he empe a u e is ob ained h ough demodula ion
o he e lec ed spec um [8]. FBGs a e also c oss-sensi i e
o s ains [29]. A s ain caused by a misma ch in he mal
expansion o he ibe g a ing ma e ial and he hos specimen
leads o an ex a shi in he B agg wa eleng h in he FBG [30].
The c oss-sensi i i y be ween empe a u e and s ain in he
sapphi e FBG mus he e o e be e alua ed accu a ely [31].
Resen e al. [9] p oposed a new, e icien op ical he e odyne
in e oga ion sys em o op ical senso s. FBG can also be used
o moni o a ious pa ame e s, such as soil mois u e [12] o
ai humidi y [10].
The p esen ed solu ion in oduces a new ype o au omo i e
senso ha combines he luminescence me hod om a uby
c ys al and BBR o eplace he widely used he mocouple
senso ype [32], which has many disad an ages and is espe-
cially suscep ible o elec omagne ic noise. Op ical senso s
PRAUZEK e al.: OPTICAL-BASED SENSOR FOR AUTOMOTIVE EXHAUST GAS TEMPERATURE MEASUREMENT 7005711
sol e hese disad an ages, bu manu ac u ing and o al cos s
a e p incipally highe han he mocouple solu ions. The aim o
de eloping a new senso is o ind an op imal adeo be ween
highe cos and supe io p ope ies. The a icle con ibu es
wi h he no el use o wo op ical p inciples o de elop a
cos -e ec i e senso ha is esis an o elec omagne ic in e -
e ence, possesses sel -diagnos ic abili ies, and is immune
o he g adual pene a ion o mois u e in o he empe a u e
p obe unde ex eme he mal s ess. Wi h espec o au omo i e
equi emen s, he inal cos should be as low as possible. FBGs
p o ide su icien echnical pa ame e s; howe e , he cos o
a p ocessing uni is ela i ely high due o he equi emen s
o signal acquisi ion, da a p ocessing, and spec al analysis.
Sapphi e ibe also has an excellen empe a u e ange (up o
2000 ◦C). Sapphi e ibe signi ican ly inc eases p oduc p ice,
howe e [8]. We, he e o e, employed a low-cos glass op ical
ibe wi h a simple pho odiode as a pho ode ec o .
The a icle con ains six sec ions. Sec ion I p o ides a gen-
e al desc ip ion o he a ge and applica ion a ea and a b ie
o e iew o he s a e-o - he-a . Sec ion II de ails he senso ’s
design, including au omo i e equi emen s, p obe cons uc ion,
elec onic design, measu emen cycle, and empe a u e cal-
cula ion. Sec ion III desc ibes he i ual ins umen a ion
measu emen sys em and expe imen al se up. Sec ion IV
p esen s he inal esul s. Sec ion V con ains a discussion, and
Sec ion VI concludes he a icle wi h ou lines o u u e wo k.
II. SENSOR DESIGN
High- empe a u e senso s in he au omo i e indus y a e
mainly used o measu e empe a u es in he exhaus subsys em,
especially in on o and behind he DPF. Measu emen is
pe o med di ec ly in he exhaus pa h om he engine o
ensu e op imal engine ope a ion wi h sa e ope a ing condi ions
and low emissions [33].
The mocouples consis o wo me al wi es made o di e en
ma e ials/alloys connec ed a one end. The mos impo an
aspec o conside in selec ing wo sui able ma e ials is he
he moelec ic di e ence ha exis s be ween hem. The au o-
mo i e indus y uses K- ype and N- ype he mocouples. The
N- ype is a newe al e na i e o he K- ype, pe mi ing highe
empe a u es and being mo e esis an o oxida ion [34]. The
N- ype he mocouple allows he measu emen o empe a u es
in he ange −270 ◦C o 1300 ◦C. The aim o de eloping an
op ical senso is o sa is y he a ge empe a u e measu emen
ange accu acy in acco dance wi h he equi emen s o he
applica ion a ea. The main bene i o an op ical senso solu ion
is esis ance o elec omagne ic in e e ence and mois u e.
A. Au omo i e Requi emen s
The p oposed empe a u e senso has ou zones wi h di e -
en he mal load equi emen s (see Fig. 2). Zone A is exposed
o empe a u es o −40 ◦C o 800 ◦C and loca ed di ec ly
in he exhaus pipe. Zone B is whe e he empe a u e p obe
is i mly a ached o he lue gas pa h and mus wi hs and
empe a u es o −40 ◦C o 300 ◦C. Zone C is he cable ha
connec s he p obe o he senso ’s e alua ion elec onics and
Fig. 2. De ailed composi ion o he empe a u e senso (p obe, cable, and
elec onics used o analysis). The zones a e di ided acco ding o empe a u e
esis ance equi emen s.
TABLE II
REQUIRED ACCURACY FOR SENSOR TEMPERATURE RANGES
is exposed o empe a u es o −40 ◦C o 200 ◦C. Zone D con-
ains he senso ’s elec onics and mus wi hs and empe a u es
o −40 ◦C o 155 ◦C.
Table II shows he a ge accu acy o he inal senso
solu ion. The usual wo king ange o he EGT p obe is
150 ◦C–820 ◦C and equi es a high measu emen accu acy
o ±5◦C. The low- empe a u e ange o −40 ◦C o20◦C
is impo an du ing engine cold s a s and also equi es
high accu acy [35]. Measu emen accu acy in he ange
20 ◦C–150 ◦C is no c i ical, mainly because ho lue gases
which all in o his empe a u e ange pass h ough he exhaus
sys em quickly and a e p esen only o se e al seconds [36].
Measu emen accu acy acco ding o hese equi emen s
mus be gua an eed o he li e ime o he EGT senso ,
al hough 1000 h o ope a ion is conside ed a minimum
in he au omo i e indus y. This igu e co esponds o he
planned se ice li e o he ehicle. Since he comple e solu ion
should be cos -e ec i e, we selec ed glass ibe as a sui able
componen .
B. P obe Cons uc ion
The sensing componen is depic ed in Fig. 3 and consis s
o a s ainless s eel ube ha con ains a pai o op ical ibe s
ouching he uby c ys al. The op ical ibe s ha e a diame e
o 660 μm. Ins ead o a hea - esis an polyamide, he ibe is
p o ec ed by a ce amic inse which simul aneously a ixes he
uby c ys al and ibe s in o place.
The uby c ys al is he co e o he sensing elemen . I is
cylind ical in shape wi h a leng h o 2.5 mm and a diame e
o 1.8 mm. The op ical ibe s a e placed on one side o he
c ys al, which is polished o inc ease op ical ansmission. The
o he side o he empe a u e p obe consis s o a e minal wi h
a me ic h ead, which con ains he special op ical connec o
7005711 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 71, 2022
Fig. 3. Design o he sensing elemen in he p obe and de ail o he ho end
( uby c ys al, op ical ibe s, and ce amic ube wi h wo holes).
TABLE III
THERMAL EXPANSION COEFFICIENTS OF THE
MATERIALS USED IN THE SENSOR
o connec ing he op ical cable. The p obe assembly is sealed
wi h a high- empe a u e epoxy sealan .
The p obe’s design main ains a igh seal which minimizes
he e ec o ib a ions (see de ail in Fig. 3). Di ec con ac
is p o ided by he polished end o he op ical ibe and
c ys al. I an expansion gap occu s because o ib a ions o
he mal expansion, he op ical signal should s ill be able o
pass h ough he expansion gap wi hou signi ican ly a ec ing
he ou pu signal’s quali y. This is mainly because he size o
he expansion gap is insigni ican , and he polished su aces
o he op ical ibe s and a c ys al a e ixed in he ce amic ube
and emain pe pendicula .
The mal expansion was educed by using he selec ed
ma e ials. The uby c ys al, which is he co e o he p obe,
is inse ed in o a ce amic ube con aining wo d illed holes o
he silicon op ical ibe s. A high- empe a u e sealan is applied
a he coole end o he p obe. The main ea u e hese ma e ials
ha e in common is simila coe icien s o he mal expansion
(CTE) (see Table III), he eby minimizing any changes in
coupling e iciency. The only ma e ial which has a g ea e
CTE is he s ainless-s eel p obe sh oud. Howe e , he mal
expansion in he sh oud no only occu s along i s leng h bu
also i s olume, esul ing in an in e nal p essu e ha s abilizes
he c ys al, ce amic illing, and op ical ibe s.
An expansion gap educes he coupling e iciency be ween
he ligh signal and he op ical ibe . Tes ing showed ha he
exci a ion ligh and luminescence ligh powe educed signi -
ican ly as he empe a u e inc eased, indica ing a dec ease in
he op ical coupling e iciency. This is con i med in he spec-
um gi en in Fig. 5. The he mal expansion e ec ep esen s
Fig. 4. Simpli ied block diag am o he elec onics: MCU wi h pe iphe als,
communica ions in e ace, he exci a ion LED, and analog on -end wi h
ecei ing pho odiode.
he ime-in a ian o a gi en empe a u e and could he e o e
be compensa ed o wi h calib a ion. Calib a ion could also
compensa e o he manu ac u ing ole ances which occu
du ing he p oduc ion o he c ys al- ibe coupling.
C. Senso E alua ion Elec onics
This sec ion desc ibes he senso elec onics e alua ion
uni . Fig. 4 p esen s a simpli ied block diag am o he uni .
The senso elec onics con ain an exci a ion ligh -emi ing
diode (LED) and ecei ing pho odiode. The LED is d i en
by a mic ocon olle uni (MCU) and is used o exci e he
luminescen e ec o he uby c ys al. The ecei ing pho odi-
ode measu es he op ical esponse o he uby c ys al, and
he esul ing ou pu om he pho odiode is deli e ed o a
da k cu en compensa o and signal p ocessing ci cui . The
signal is hen p ocessed by he MCU, which uses an analog
compa a o and inpu cap u e ci cui . A 16-b analog- o-digi al
con e e (ADC) block is hen used o measu e he BBR signal
and ampli udes du ing low empe a u es.
Da k cu en compensa ion is based on measu ing he
ecei ing pho odiode ansi ion empe a u e om he ol age
d op which occu s ac oss he pho odiode by using he ci cui
o moni o ing he e e ence ol age and connec ing he anode
and ca hode ol ages o he pho ocell o a ca hode wi h a
e e ence ol age ia a calib a ion esis o . The amoun o
compensa ion can hen be calib a ed by he magni ude o he
esis ance o he calib a ion esis o . I s size depends on he
in e nal esis ance o he pho odiode.
Accu a e measu emen o luminescence ime is ensu ed by
using a compa a o , which de ines he h eshold ampli ude o
he signal a he end o he limi a ion e ec , in combina ion
wi h an inpu cap u e ci cui and subsequen use o a di ec
memo y access module.
An LED wi h a nominal 465-nm wa eleng h is used as
an exci a ion sou ce. Luminescence is p oduced in he uby
c ys al, and he exci ed ligh is emi ed a a wa eleng h o
PRAUZEK e al.: OPTICAL-BASED SENSOR FOR AUTOMOTIVE EXHAUST GAS TEMPERATURE MEASUREMENT 7005711
Fig. 5. Op ical powe spec um o he uby c ys al exci ed a λ=465 nm.
Fig. 6. Single measu emen cycle: Luminescence (VLUM)—BBR (VBBR),
ol age le el measu emen , and ime measu emen (TMEAS ).
a ound 695 nm (see Fig. 5). A pho odiode wi h high sensi i i y
a 695 nm is he e o e posi ioned on he ecei ing side.
A pola izing il e is also inse ed be ween he pho odiode and
ibe o elimina e any in e e ing wa eleng hs.
D. Measu emen Cycle
To compu e he empe a u e alue, wo ol ages and a
single ime alue a e measu ed. The measu emen s mus be
synch onized wi h he exci a ion ligh sou ce cycle, as depic ed
in Fig. 6.
The wa e o m deno es he LED s a e. The LED is swi ched
ON and OFF du ing each measu emen cycle; espec i e imes
a e deno ed T1( he LED is ON)andT2( he LED is OFF).
Be o e any change in he LED’s s a e, he ol age adjus ed
by he signal condi ioning block (see Fig. 4) is measu ed
using he MCU’s buil -in ADC. Measu emen s a e aken only
a e he ol age alue has se led. This is accomplished
by s a ing he espec i e ADC measu emen in ad ance
Fig. 7. P inciple o swi ching be ween luminescence ime, luminescence
ampli ude, and BBR me hods.
immedia ely be o e he LED changes s a e. Du ing his ime,
deno ed THOLD, he ol age should be cons an . Two ol age
alues a e acqui ed in each measu emen cycle: VLUM o he
luminescence phase and VBBR o he blackbody phase.
The VLUM alue is used o compu e VTHRESH acco ding o
he ollowing equa ion:
VTHRESH =VLUM −VDIFF (V)(1)
whe e VDIFF is a ixed pa ame e ha a ec s he possible em-
pe a u e ange, which can be es ima ed using he luminescence
ime me hod and maximal TMEAS.
In he nex s ep, TMEAS is measu ed. The ob ained VTHRESH
alue is swi ched o he ou pu o he digi al- o-analog con-
e e (DAC). As depic ed by Fig. 6, he MCU has an
in eg a ed analog compa a o . The compa a o ’s nonin e ing
inpu is connec ed o he ol age gene a ed by he signal con-
di ioning block. The in e ing inpu is connec ed o VTHRESH.
The ou pu signal o he compa a o is he e o e asse ed
whene e he inpu ol age is less han VTHRESH. The ou pu o
he compa a o is used o igge he inpu cap u e module. The
inpu cap u e module in eg a es a 32-b ime wi h a 1-MHz
clock inpu ; he ime is ac i a ed when he LED is swi ched
o (LEDo e en ) and s opped when he compa a o ou pu is
asse ed.
E. Tempe a u e Calcula ion
When he senso has measu ed all pa ame e s in one cycle
(VBBR,VLUM,TMEAS), he cu en empe a u e is calcula ed.
The senso uses wo op ical me hods (BBR and luminescence),
al hough h ee p inciples a e applied o es ima e empe a u e.
Using he BBR me hod, he senso calcula es empe a u e
based on he ampli ude ou side exci a ion. Using he lumi-
nescence me hod, he senso swi ches be ween es ima ions
de i ed om measu ed ime and ampli ude.
Fig. 7 illus a es he p inciple o swi ching me hods. Fi s ,
he e alua ion algo i hm checks whe he a su icien le el
(VREF) o BBR exis s ou side he exci a ion phase. I ue,
he p obe empe a u e is calcula ed using he VBBR pa ame e .
When he VBBR pa ame e does no each a su icien le el, he
luminescence me hod is used. I TMEAS is less han e e ence
TREF, he algo i hm calcula es acco ding o he ime me hod;

7005711 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 71, 2022
in he o he case, he empe a u e is calcula ed using he
ampli ude me hod.
Each me hod applies he same p inciple o es ima e p obe
empe a u e [37]. E alua ion is based on a qua ic unc ion
[see (2)], whe e pa ame e p ep esen s he measu ed alue
VBBR,VLUM o TMEAS acco ding o he me hod used
TEMP =ap4+bp3+cp2+dp+e.(2)
Each me hod (BBR, luminescence ime, and luminescence
ampli ude) has an indi idual se o pa ame e s (a,b,c,
d,ande). This se was es ima ed om he expe imen al
measu emen pe o med du ing senso p o o yping. This se
o pa ame e s is also s o ed in he non ola ile memo y con-
ained in he senso ’s elec onics and he e o e upda ed du ing
calib a ion. Fo his eason, each senso has h ee unique se s
o calib a ion alues.
III. EXPERIMENTAL INSTRUMENTATION
This sec ion desc ibes he i ual ins umen a ion and se up
o measu ing and e alua ing empe a u es and a desc ip ion
o he expe imen ’s p ocedu e.
A. Vi ual Ins umen a ion Measu emen Sys em
Accu a e and eliable es ing in he a ge EGT ange is an
impo an pa o he p oposed senso . Fo he pu poses o
he case s udy, we designed a modula measu emen sys em
based on i ual ins umen a ion. The aim o he design was
i s abili y o objec i ely e i y he ull unc ionali y, accu acy,
and s abili y o he p oposed op ical senso wi h he ele-
an e e ence acco ding o scena ios de ined by au omo i e
indus y speci ica ions ( empe a u e ange, humidi y, dynamic
empe a u e changes, e c.). Tes ing was pe o med unde p e-
cisely de ined labo a o y condi ions using a comme cially
a ailable calib a ed he mocouple (K- ype) as e e ence. Ha d-
wa e componen s (NI-9223) implemen ed wi h he Compac -
DAQ pla o m we e used o da a collec ion, p ocessing, and
analysis. Fig. 8 depic s a simpli ied scheme o he expe imen al
wo kplace. The measu emen sys em consis ed o h ee blocks:
1) op ical senso ; 2) e e ence he mocouple; and 3) i ual
ins umen a ion measu emen sys em.
The i ual ins umen measu emen sys em shown in Fig. 8
execu es a collec ion p ocedu e o analog signals om he
es ed senso loca ed in he expe imen al u nace. Measu e-
men is pe o med wi h wo NI-9223 measu ing ca ds, which
ha e a ou -channel simul aneous inpu (±10 V, 1 M/s, 16-bi ).
Synch oniza ion is p o ided by cDAQ-9158, which is con-
nec ed o he measu ing compu e ia E he ne . The i ual
senso ob ains da a in pa allel om he wo UART channels
o he elec onics.
B. Expe imen al P ocedu e
The aim o he expe imen al p ocedu e was o es he
senso s in he EGT measu emen ange (−40 ◦C o 820 ◦C).
The es ing p ocedu e was di ided in o wo s ages because
o he di e en equi emen s o cooling and hea ing (see
Table IV).
Fig. 8. Ins umen a ion diag am: measu emen using an op ical p obe,
elec onics, a e e ence he mocouple wi h NI modules, and he LabView
applica ion on a PC.
TABLE IV
HEATING AND COOLING PROCESS
Cooling was achie ed wi h liquid ni ogen placed inside he
u nace o cool he in e nal space o −45 ◦C. The u nace was
hen hea ed by ambien empe a u e o 20 ◦C. The second
s age was he hea ing p ocess. Gene ally, he BBR me hod
can be used wi hou any empe a u e limi s. In he p esen ed
solu ion, we used glass op ical ibe s wi h a so ening poin o
846 ◦C and a mel ing poin o 1121 ◦C. The maximum em-
pe a u e was he e o e se o 830 ◦C o a oid any mechanical
p oblems. To educe signi ican elec ical noise om hea ing
elemen s, he u nace was empe ed o 830 ◦C. When a ge he
empe a u e was eached, he cooling p ocess began and he
u nace was allowed o cool o a empe a u e o app oxima ely
25 ◦C o e 12 h. The p ocess o slowly cooling he u nace
minimized apid empe a u e di e ences in he space be ween
he p obe and he e e ence he mocouple. A slowe cooling
p ocess also allowed su icien ime o cap u e signals du ing
s able empe a u es. The expe imen al p ocedu e was epea ed
ou imes on one senso p o o ype.
IV. RESULTS
This sec ion con ains wo pa s: he i s pa shows he
dependence o he measu ed pa ame e s on a ious empe -
a u es h ough a ime-domain analysis o one o he es ed
senso s; he second pa includes an analysis o he o al
absolu e e o o he senso p o o ype in he EGT measu emen
ange.
A. Resul s o he Time-Domain Analysis
Tempe a u e es ima ion is dependen on he cha ac e o
he measu ed signal. The cha ac e o he ecei ed pho odiode
signal a a ious empe a u es is desc ibed below.
PRAUZEK e al.: OPTICAL-BASED SENSOR FOR AUTOMOTIVE EXHAUST GAS TEMPERATURE MEASUREMENT 7005711
Fig. 9. Measu ed ol age signals a he analog on -end ( ecei ing pho odiode) in he ange −40 ◦C o 820 ◦C.
TABLE V
OVERVIEW OF MEASURED PARAMETERS IN THE RANGE −40 ◦CTO 820 ◦C
Fig. 9 cha s he ecei ing pho odiode ol ages o empe -
a u es in he ange −40 ◦C o 820 ◦C, and Table V p o ides
a nume ical o e iew o he measu ed pa ame e s.
The measu emen pe iod (T) in he expe imen was se o
250 ms and di ided in o wo exci a ion phase in e als (T1,T2),
each wi h a du a ion o 125 ms. In u u e expe imen s, he
exci a ion phase in e als can be op imized. T2is di ec ly
dependen on he luminescence o he uby c ys al. This ime
can be dec eased only wi h he use o a uby c ys al wi h a
di e en ch ome concen a ion. Exci a ion ime is dependen
on se e al physical aspec s: he i s s age o exci a ion is
abso p ion by he uby c ys al, las ing app oxima ely 50 ms;
o he emaining ime (75 ms), he ampli ude is sampled. The
o al measu emen ime has ano he op ion o op imiza ion.
When he BBR me hod is used o high- empe a u e si ua ions
(>350 ◦C), exci a ion can be swi ched o un il VBBR becomes
insu icien . In his case, he senso ’s esponse ime is limi ed
only by he ADC’s sample equency.
Tempe a u e alues can be es ima ed acco ding o h ee
me hods, as desc ibed in Sec ion II-E. I VBBR is less han
he ol age e e ence (VREF =0.65 V), he empe a u e is less
han 350 ◦C and he luminescence me hod is used. Fo he
lowe empe a u e ange o −40 ◦C o60◦C, he empe a u e
is calcula ed om he exci a ion ampli ude le el (VLUM)since
exci a ion ime is no dependen on empe a u e. Fo he
empe a u e ange o 60 ◦C–350 ◦C, exci a ion ime is used o
ob ain empe a u es since he exci a ion ime (TMEAS) changes
mo e signi ican ly han VLUM.
7005711 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 71, 2022
TABLE VI
EFFECT OF VDIFF VALUES ON THE ABILITY TO MEASURE
USING THE LUMINESCENCE TIME METHOD
When he empe a u e exceeds 350 ◦C, VBBR is g ea e han
he ol age e e ence, and BBR is used (i.e., he empe a u e is
e alua ed om VBBR). I is in e es ing ha VBBR ises, whe eas
VLUM alls (app ox. empe a u e ange o 350 ◦C–520 ◦C). This
phenomenon esul s om a pa o a uby c ys al luminescence
powe spec um being shi ed o sho e wa eleng hs by highe
empe a u es occu ing beyond he pho ode ec o ’s a ea o
sensi i i y. The e o e, he de ec o in he elec onics o he
senso can cap u e only a po ion o he emi ed luminescence
ligh , esul ing in a lowe ol age a he ampli ie ’s ou pu .
F om a empe a u e o 420 ◦C, he exci a ion ime TMEAS is
cons an , bu om 480 ◦C, i is no possible o measu e TMEAS
canno because o sa u a ion caused by BBR.
Table VI shows he esul s o a case s udy o a ious VDIFF
se ings. The alue o VDIFF a ec s he maximum measu able
empe a u e. A lowe VDIFF pe mi s he measu emen o highe
empe a u es using he ime luminescence me hod, bu he
ime ange apidly diminishes. The p oposed solu ion used
VDIFF =0.2V.Alowe VDIFF inc eases he empe a u e ange
by 20 ◦C, bu MAX, which e lec s he accu acy o he ime
luminescence me hod, dec eases by mo e han 50%. A highe
VDIFF dec eases he empe a u e ange, and i is unnecessa y
o ob ain a longe MAX, 7.8 ms being su icien o accu a ely
measu e alling ime.
The pa ame e VREF mus ake in o accoun he p inciple
o BBR. This VREF alue should be g ea e han he BBR
noise caused by ambien empe a u e and he empe a u e o
he op ical cable. VREF mus also be less han VLUM, in ou
case alling in he ange 0.7–1 V. The pa ame e TREF mus
ake in o accoun he physical p inciple o luminescence. When
he empe a u e is low, he alue TMEAS does no su icien ly
change. The p oposed solu ion used TREF =7ms.
B. Absolu e E o o he Senso P o o ype
The p oposed solu ion was es ed on a senso p o o ype. The
o al absolu e e o was calcula ed as an ex ended unce ain y
o k=3 (99.7% cen ile) and ep esen ed 2.32 ◦C. In e ms
o EGT measu emen , he mos signi ican empe a u e anges
a e du ing engine cold s a (−40 ◦C o20◦C) and when
exhaus gases each empe a u es g ea e han 600 ◦C. The
empe a u e ange 20 ◦C–150 ◦C is no c i ical o p ope
engine unc ionali y since exhaus gases each his empe a u e
ange only du ing he i s ew seconds o engine ope a ion.
Table VII shows he o al absolu e e o s in he speci ied
anges o he senso p o o ype. A compa ison o he o al
TABLE VII
ERRORS IN THE TEMPERATURE INTERVALS FOR THE SENSOR PROTOTYPE
ACCORDING TO THE AUTOMOTIVE REQUIREMENTS
AND FOUR MEASUREMENTS
Fig. 10. Summa y boxplo s o absolu e e o s in he senso p o o ype in he
ange −40 ◦C o 820 ◦C o ou measu emen s.
TABLE VIII
SUMMARY OF ABSOLUTE ERRORS IN THE SENSOR PROTOTYPE FOR THE
SPECIFIED TEMPERATURE RANGES AND FOUR MEASUREMENTS
absolu e empe a u e e o s wi h he anges speci ied in he
au omo i e equi emen s sec ion (see Table II) indica es ha
he senso ul illed he speci ied equi emen s.
Fig. 10 plo s he absolu e e o s in he senso p o o ype o
he ange −40 ◦C o 820 ◦C.
The expe imen s con i med he hypo heses o using a hyb id
op ical senso o EGT measu emen s. The esul s p esen ed
in Table VIII and Fig. 10 show he absolu e e o s o speci ic
empe a u e anges. The main p oblem wi h cu en ly a ailable
op ical senso s is he measu emen o nega i e empe a u es
in he ange −40 ◦C o0◦C, whe e he p oposed solu ion
p oduced an absolu e e o o less han 2 ◦C: his ully e lec s
he au omo i e equi emen s o EGT measu emen . Posi i e
alues we e analyzed in 100 ◦C in e als, and acco ding
o engine speci ica ions, he wo king empe a u e o a ully
loaded and unloaded combus ion engine is om 400 ◦C o
700 ◦C. Ou solu ion achie ed an accu acy wi hin 0.5 ◦Cin
his ange. High accu acy in his a ea is he mos c i ical aspec
o he a ge applica ion. The absolu e e o was less han 2 ◦C
in he ange 100 ◦C–400 ◦C, and he la ges measu emen e o
was in he ange 0 ◦C–100 ◦C.
PRAUZEK e al.: OPTICAL-BASED SENSOR FOR AUTOMOTIVE EXHAUST GAS TEMPERATURE MEASUREMENT 7005711
TABLE IX
COMPARISON WITH STATE-OF-THE-ART OPTICAL SENSORS
V. DISCUSSION
The aim o he wo k was o de elop a eplacemen o an
exis ing EGT senso solu ion which is based on he he mo-
couple p inciple. F om a design poin o iew, he eplace-
men solu ion is inno a i e and deli e s se e al ad an ages.
The he mocouple measu ing p inciple was eplaced wi h an
op ical-based empe a u e measu emen me hod using a uby
c ys al and wo op ical ibe s in combina ion wi h e alua ion
elec onics. The senso applies he luminescen and BBR
measu emen p inciples. The ex e nal mechanical dimensions
o he senso a e compa ible wi h he exis ing solu ion, and
no u he modi ica ions a e equi ed in ehicle cons uc ion.
Based on ou mechanical esis ance es s, he newly de el-
oped senso demons a es simila mechanical p ope ies. The
se ice li e o he sensing componen o he senso is 1000 h.
Beyond his ime, exposu e o high empe a u es begins o
deg ade he op ical ibe co es and measu emen accu acy
educes. The undispu ed ad an age o he solu ion is he
absolu e esis ance o he sensing componen and he senso ’s
op ical cable o EMC and EMI. I is he e o e possible o place
he senso ’s sensing componen nea e y s ong sou ces o
elec omagne ic adia ion.
The senso ’s main ea u e is i s measu emen accu acy
speci ied by he equi emen s o he au omo i e indus y. Ou
analysis and e alua ion o long- e m measu emen s indica e
ha he p oposed senso mee s he accu acy equi emen s
ac oss he en i e ange. The absolu e e o a ies wi hin
he en i e ange, a esul ob ained by using h ee di e en
measu emen me hods. The BBR me hod a ains he highes
accu acy since he ligh is emi ed di ec ly by a uby c ys al
and ibe . The luminescence me hod p oduces highe absolu e
e o alues as a esul o exci a ion equi emen s.
The p oposed solu ion has a wide measu emen ange, and
he e o e he p ope ies o he esul s a e discussed in pa s.
Table IX compa es he accu acy wi h o he op ical senso
solu ions. Wang e al. [38] decla ed a measu emen esolu ion
o 0.13 ◦C. The esolu ion o ou solu ion a ies wi h he
measu emen me hod applied. Wi h he ampli ude me hod
(low empe a u es and BBR), he esolu ion is de e mined by
a 16-b ADC. The esolu ions o he p oposed solu ion a
low empe a u es a e 0.136 ◦C and 0.026 ◦C using he BBR
me hod. Resolu ion o he ime-based luminescence me hod is
de i ed om he inpu cap u e module’s 1-MHz clock signal;
he esul ing esolu ion o he ime-based me hod is 0.039 ◦C.
Jinling and Junhai [28] s a ed ha he luminescence
ime me hod was no sui able o nega i e empe a u e
measu emen , which we also con i m in ou s udy, whe e he
ampli ude-based app oach is used in he empe a u e ange
−40 ◦C o65◦C. The s udy in [28] used he ime-based
me hod up o 600 ◦C, bu in ou solu ion, he measu emen
ange is ex ended o 820 ◦C by using he BBR me hod.
Zhao e al. [27] p esen ed a low- empe a u e ange senso
(0 ◦C–90 ◦C) wi h a maximum e o o 0.45 ◦C using he ime-
based me hod. Ou solu ion combines wo me hods wi hin his
ange, esul ing in a highe absolu e e o o 4.27 ◦C, al hough
he absolu e e o s ill sa is ies au omo i e equi emen s since
engine ope a ing empe a u es all ou side his ange.
The s udy [39] decla ed a empe a u e ange o 200 ◦C
o 1000 ◦C, wi h a esolu ion o 0.45 ◦C and hys e esis
o ±4◦C. Hys e esis ela es o he absolu e e o , as he
di e ence be ween he measu ed alue and he ue alue
migh di e acco ding o he hys e esis o ±4◦C. We did
no analyze hys e esis in ou solu ion, al hough we used he
BBR me hod in he high- empe a u e ange, and he e o e he
esolu ion is app oxima ely en imes highe , esul ing mainly
om using a di e en app oach o es ima ing empe a u e.
VI. CONCLUSION
The p esen ed case s udy clea ly demons a ed he op ical
senso ’s ull unc ionali y o applica ion in an EGT mea-
su emen ange. The solu ion sa is ies au omo i e indus y
s anda ds, and he senso design is ully compa ible wi h
cu en ly used senso s in dimensions, encapsula ion, powe
equi emen s, and so on. The expe imen s applied d op-down
es s s a ing om a high empe a u e o analyze he senso
ac oss a b oad empe a u e ange. Fo his eason, we did no
e alua e he hys e esis o he p oposed senso .
The combina ion o luminescence and BBR p inciples co -
e s he ope a ing empe a u e spec um o he equi ed applica-
ion and he e o e p o ides high accu acy ac oss he ope a ing
empe a u e ange. The p oposed solu ion ully e lec s he
ad an ages o op ical-based senso s, which includes esis ance
o elec omagne ic in e e ence, en i onmen al iendliness,
and small size. The solu ion was es ed up o 820 ◦C, which is
nea he uppe - empe a u e limi o glass op ical ibe s. This
limi could be aised signi ican ly by using a sapphi e op ical
ibe , which has a mel ing poin o 2040 ◦C [8]. The s udy
[40] used sapphi e ibe s in an en i onmen wi h empe a u es
up o 1500 ◦C. Howe e , sapphi e op ical ibe would also
inc ease he p ice o he senso , and he e o e o solu ions in
en i onmen s up o 820 ◦C, low-cos glass op ical ibe s a e a
mo e cos -e ec i e op ion. Al hough op ical ibe empe a u e
senso s a e no widely used, mainly because o hei high
cos , hey pe mi empe a u e measu emen whe e o he mo e
common empe a u e measu emen p inciples ail o canno be
used in p inciple o o sa e y easons.
The nex s ep in ou esea ch is moun ing he senso in o an
exhaus sys em in an expe imen al ca and a de ailed analysis
o he e ec on ehicle ope a ion. Fu u e wo k will also en ail
pe manen ins alla ion on a ehicle, wi h moni o ing conduc ed
a a ious mileage in e als and eco ding o he e ec on
senso pe o mance unde en i onmen al in luences such as
poo oad condi ions. Addi ional es s mus be pe o med o
assess whe he he senso is able o eliably de ec co ec
empe a u e h oughou he yea wi h changes in ambien con-
di ions, he p esence o humidi y, and o he ac o s. Rise and