. What is an NDIR Sensor?

lphasense IRC-A sensors use the principle of Non-Dispersive Infra-Red (NDIR) to determine gas
APPLICATION
oncentration. Each sensor consists NOTEof an AAN infrared201-06source, optical cavity, dual channel detector
nd internal thermistor. Gas diffuses into the optical cavity. Light from the infrared source passes
hrough the optical cavity where it interacts with the gas before impinging on the detector. Certain
ases absorb infrared radiation at specfic wavelengths (absorption bands). The dual channel
etector is NDIR:
comprised Gas of Concentration
an active channel andCalculation a reference channel. Overview The active channel is fitted
ith a filter such that the only
1. What is an NDIR Sensor?
light with a wavelength that corresponds to an absoption band of the
arget gas is allowed to pass through. If the target gas is present in the optical cavity the intensity
Alphasense IRC-A sensors use the principle of Non-Dispersive Infra-Red (NDIR) to determine gas concentration. Each sensor consists of an
f light passing through the filter and hitting the active channel decreases. The reference channel
infrared source, optical cavity, dual channel detector and internal thermistor. Gas diffuses into the optical cavity. Light from the infrared source
f the detector is fitted with a filter that only allows wavelengths of light where there are no
passes through the optical cavity where it interacts with the gas before impinging on the detector. Certain gases absorb infrared radiation
bsorption bands to pass through. The intensity of light hitting the reference channel is not
at specfic wavelengths (absorption bands). The dual channel detector is comprised of an active channel and a reference channel. The active
ffected channel
by theispresence of gas. The use of a reference channel allows variations in the light
fitted with a filter such that the only light with a wavelength that corresponds to an absoption band of the target gas is allowed
ntensity totopass bethrough.
compensated for. The detectors used are highly sensitive to the ambient
If the target gas is present in the optical cavity the intensity of light passing through the filter and hitting the active channel
emperature and so it is necessary
decreases. The reference channel of the todetector
constantly monitor
is fitted with a filter the temperature
that only and of
allows wavelengths compensate
light where there the
are no absorption bands
utput. The internal thermistor is used for this purpose.
to pass through. The intensity of light hitting the reference channel is not affected by the presence of gas. The use of a reference channel allows
variations in the light intensity to be compensated for. The detectors used are highly sensitive to the ambient temperature and so it is necessary
. How do I get useful
to constantly signals
monitor the from
temperature the sensor?
and compensate the output. The internal thermistor is used for this purpose.
ull details are given in Application Note AAN 202. Briefly, in order to get useful signals from the
etector in an NDIR sensor the infrared source is typically pulsed on and off at 1 to 3 Hz in a
quare wave, 50% duty cycle. Suggested frequencies are 2 Hz for IRC-A1 sensors which use
2. How do I get useful signals from the sensor?
yroelectric detectors and 3 Hz for IRC-AT sensors which use thermopile detectors. The actual
equencyFullisdetails
not are given inimportant
hugely Application Note
but AAN 202. Briefly,
it must in order to get
be stable. usefulsuitable
Using signals from the detector
circuitry in an
this NDIR sensor the infrared source
generates
is typically pulsed on and off at 1 to 3 Hz in a square wave, 50% duty cycle. Suggested frequencies are 2 Hz for IRC-A1 sensors which use
pproximately sinusoidal detector output signals from a preamplifier. It is the peak to peak
mplitudepyroelectric
of thesedetectors
signals and 3 Hz for IRC-AT sensors which use thermopile detectors. The actual frequency is not hugely important but it must
that is important. In the following discussion the use of active and
be stable. Using suitable circuitry this generates approximately sinusoidal detector output signals from a preamplifier. It is the peak to peak
eference signal refers to the amplitude.
amplitude of these signals that is important. In the following discussion the use of active and reference signal refers to the amplitude.

. Calibrating the sensor

3. Calibrating
or sensor calibration the
twosensor
parameters are needed. These are ZERO and SPAN:
For sensor calibration two parameters are needed. These are ZERO and SPAN:
ERO. This isThis
ZERO. theisratio of ofthe
the ratio theactive
active toto reference
reference signalssignals in theofabsence
in the absence of the target gas:
the target gas:

ACT0
ZERO =
REF0

here: Alphasense Application Note

where: ACT and REF are signals in zero gas.
AAN 201-06
ACT0 and 0REF0 are 0
signals in zero gas.
ZERO is a sensor specific parameter and should be determined whenever the sensor is installed (or reinstalled) in an instrument.
ZERO is a sensor specific parameter and should be determined whenever the sensor is
The sensor should be powered on and left to warm up for at least 30 minutes in zero gas. The active and reference signals should then be
installed (or reinstalled) in an instrument.
measured and ZERO determined. The temperature should also be measured and recorded.
he sensor should
PAN. This the proportion be powered on andthat
of radiation leftimpinges
to warm on up the
for active
at least 30 minutes
element of theindetector
zero gas. that The
has
ctive and reference signals should then be measured and ZERO determined.
e ability to be absorbed by the target gas. Due to filter bandwidth and fine structure in absorption The temperature
hould also
pectra therebeThis
SPAN. measured
will and
the proportion
be radiation recorded.
of radiation that impinges on the active element of the detector that has the ability to be absorbed by the target
that cannot be absorbed by the target gas (see Application Note
gas. Due to filter bandwidth and fine structure in absorption spectra there will be radiation that cannot be absorbed by the target gas (see
AN 204). SPAN can be determined as follows:
Application Note AAN 204). SPAN can be determined as follows:

ABS x
© Alphasense
SPAN = Limited Page 1 of 5 November 2014
1 − exp(
Sensor Technology −bx c300
House, ) Avenue West, Skyline 120, Great Notley Essex CM77 7AA, UK
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here: email: sensors@alphasense.com Web: www.alphasense.com
where: ABS is the absorbance (see below) at the calibration concentration
ABSx is thex absorbance (see below) at the calibration concentration
X: see Table 1 for recommended SPAN concentrations for each sensor range
X: see Table 1 for recommended SPAN concentrations for each sensor range
b and c are linearisation coefficients (see Table 1 and Application Note AAN 203).
b and c are linearisation coefficients (see Table 1 and Application Note AAN 203).

. Determination of Absorbance
bsorbance is defined as (see Application Note AAN 204):

⎛I ⎞
ABS = 1 − ⎜⎜ ⎟⎟
⎝ I0 ⎠

here:
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I = ACT/REF (©ALPHASENSE LTD) Doc. AAN 201-06/SEP22
I0 = ACT0/REF0 = ZERO
 c
ABSx is the1absorbance
− exp( )
ABS−xbx (see below) at the calibration concentration
SPAN =
X: see Table 1 for recommended
c SPAN concentrations for each sensor range
1 − exp( −bx )
here: b and c are linearisation coefficients (see Table 1 and Application Note AAN 203).
APPLICATION NOTE AAN 201-06
ABSx is the absorbance (see below) at the calibration concentration
here: X: see Table 1 for recommended SPAN concentrations for each sensor range
. Determination of Absorbance
ABS
b andx is
c the
are absorbance
linearisation (see below) at
coefficients theTable
(see calibration
1 and concentration
Application Note AAN 203).
bsorbance
X: seeisTable
defined as recommended
1 for (see Application Noteconcentrations
SPAN AAN 204): for each sensor range
b and c are linearisation
. Determination of Absorbance coefficients (see Table 1 and Application Note AAN 203).
4. Determination
⎛ I ⎞ of Absorbance
ABS
bsorbance is = 1 − ⎜⎜ as
defined ⎟⎟ (see
. Determination ofI Absorbance
Absorbance is defined
Application Note AAN 204):
as (see Application Note AAN 204):
⎝ 0⎠
bsorbance is defined as (see Application Note AAN 204):
⎛I ⎞
here: ABS = 1 − ⎜⎜ ⎟⎟
I
I = ACT/REF⎛⎝ I0 ⎞⎠
ABS = 1 − ⎜⎜ ⎟⎟
I0 = ACT0/REFI 0 = ZERO
here: ⎝ 0⎠
where: I = ACT/REF
I = ACT/REF
bsorbance can
I0 =therefore
ACT0/REF0 = be
ZEROdetermined from the sensor outputs using:
here: I0 = ACT 0/REF0 = ZERO
I =Absorbance
ACT/REF can therefore be determined from the sensor outputs using:
I
bsorbance
0 = ACT /REF 0 = ZERO
can0 therefore be determined from the sensor outputs using:
⎛ ACT ⎞
ABS = 1 − ⎜ ⎟
bsorbance can therefore ⎝ REFbe × ZERO
determined ⎠ from the sensor outputs using:
⎛ ACT ⎞
ABS = 1 − ⎜ ⎟
) Determination ⎝⎛ofREF
where: ABS is the
x Gas × Concentration
ACT ZERO
absorbance
⎞⎠
(see below) at the calibration concentration
ABS X:= see 1 −Table
⎜ 1 for recommended ⎟ SPAN concentrations for each sensor range
he gas concentration
b and c⎝are
is
REF determined
× ZERO
linearisation ⎠ from (see
coefficients
theTable
following equation:
1 and Application Note AAN 203).
) Determination of Gas Concentration ⎛ 1⎞
⎜ ⎟
⎡
) Determination ⎛
he gas concentration
of ABS ⎞ ⎤
is determined
Gas
⎝c⎠
Concentration from the following equation:
⎢ ln⎜ 1 − ⎟ ⎥
5) Determination SPAN of Gas
⎠ ⎥ ⎛ 1Concentration
x=⎢ ⎝
he gas concentration is determined
⎜ ⎟
⎞ from the following equation:
⎛ − ABS b is determined
The gas
⎡⎢ concentration ⎞ ⎤⎥ ⎝ c ⎠
from the following equation:

⎢⎣ ln⎜1 − SPAN ⎟ ⎥⎦⎛⎜ 1 ⎞⎟

x = ⎢ln⎛⎜⎝1 − ABS ⎞⎟⎠ ⎤⎥⎝ c ⎠
⎡
⎢ −SPAN
b ⎥
here: x = ⎢ ⎝ ⎠⎥
ABS is⎢⎣ the absorbance
−b ⎥⎦
SPAN⎢ is the proportion ⎥ of absorbing radiation (determined during calibration (see above))
here: ⎣ ⎦
b and c are linearisation coefficients (see Table 1 and Application Note AAN 203)
ABS is the absorbance
here: SPAN
where:isABSthe
is theproportion
absorbanceof absorbing radiation (determined during calibration (see above))
b andiscSPAN
ABS the
areabsorbance
islinearisation Alphasense
the proportion coefficients
of (see
absorbing radiationApplication
Table 1 and
(determined Note
Application
during Note
calibration (see AAN AAN
above)) 203) 201-06
SPAN is thecproportion
b and of coefficients
are linearisation absorbing radiation
(see Table 1 and(determined
Application Noteduring
AAN 203)calibration (see above))
© Alphasense
b and areLimited
linearisation coefficients PageTable
(see 2 of 5 1 and Application Note AAN November 2014
ote that the cabove equation assumes a positive absorbance. If the absorbance 203)
Sensor Technology House, 300 Avenue West, Skyline 120, Great Notley Essex CM77 7AA, UK
is negative the
ollowing Note
equation should
that the above equation be used.
Tel: +44 Note
(0) 1376
assumes that
556700
a positive although
Fax: +44
absorbance. negative
(0)
If the absorbances
1376 335899
absorbance imply a negative
is negative the following gas be used. Note that
equation should
oncentration
© Alphasense they
although negative may
Limited be
email: encountered due
sensors@alphasense.com
absorbances imply a negative to temperature
Page 2 ofWeb:
5
gas concentration effects.
www.alphasense.com November
they may be encountered due 2014
to temperature effects.
Sensor Technology House, 300 Avenue West, Skyline 120, Great Notley Essex CM77 7AA, UK
Alphasense⎧ Limited ⎟⎫
Page 2Fax:
1 ⎞ 1376 556700
Tel: +44⎛⎜(0) of 5+44 (0) 1376 335899 November 2014
⎪⎡ ln⎛⎜1email:
Sensor Technology ABS
House, ⎤ ⎠Avenue
⎞300⎝ c
⎪ West, Skyline
sensors@alphasense.com
+ Tel: +44 Web:120, Great Notley Essex CM77 7AA, UK
www.alphasense.com
⎟ ⎥ (0)⎪1376 556700 Fax: +44 (0) 1376 335899
⎪⎪⎢ ⎝ SPAN ⎠⎥ ⎪
x = −⎨ ⎢ email: sensors@alphasense.com
⎬ Web: www.alphasense.com
⎪ ⎢ − b ⎥ ⎪
⎪⎢⎣ ⎥ ⎪
⎦ ⎪
⎪⎩ ⎭

. Temperature Compensation
he effects of temperature on an NDIR sensor are complex and care must be taken to ensure
ffective temperature compensation. Changes in temperature affect the absorbance, SPAN and
pparent gas concentration. The complexity of temperature compensation algorithms applied to
he data depends on the accuracy required. Details are given below for two simple linear
orrections. For details of more complex corrections to improve accuracy, users are encouraged
o contact Alphasense.

.1 SPAN ONLY compensation

or sensors with high full scale values (e.g >10 % vol. CO2) it is normally sufficient to correct only
T: +44 (0)1376 556700 E: sensors@alphasense.com W: www.alphasense.com
he SPAN, using the following equation: Sensor Technology House, Skyline 120, Great Notley, Braintree, Essex CM77 7AA, UK
(©ALPHASENSE LTD) Doc. AAN 201-06/SEP22
 ⎪⎪⎢ ⎝ SPAN ⎠⎠ ⎥ ⎪⎪
xx =
=− − ⎨⎨⎢⎢ ⎝ − b ⎥ ⎬⎬
⎥⎥ ⎪
⎪⎪⎢ −b
⎪⎪⎢⎣ ⎢ ⎥⎥ ⎪⎪
Alphasense Application Note AAN 201-06
APPLICATION
Note that ⎪⎪⎩⎣the above equationNOTE
⎦ ⎪ AANabsorbance.
⎦ ⎪⎪⎭ a positive
assumes 201-06 If the absorbance is negative the
⎩ ⎭
following equation should be used. Note that although negative absorbances imply a negative gas
concentration they may be encountered due to temperature effects.

.. Temperature
Temperature Compensation
⎧
Compensation ⎜ ⎟⎫
⎛ 1⎞

⎪⎡ ⎛ ABS ⎞ ⎤ ⎝ c ⎠ ⎪
ln 1 + on ⎟an
he
he effects of
of temperature
6. Temperature
effects ⎪⎪⎢ ⎜⎝Compensation
temperature ⎥ NDIR
on ⎠an ⎪⎪ sensor
sensor are are complex
complex and and care
care must
must be be taken
taken toto ensure
ffective
SPAN
x = − ⎨⎢ compensation.
temperature ⎥ NDIR
⎬ Changes in temperature affect the absorbance, SPAN and
ensure
ffective The
temperature ⎪⎢ compensation.
effects of temperature− b on an⎥ NDIR Changes
⎪ sensor in temperature
are complex and care must beaffect
taken the absorbance,
to ensure and
SPAN compensation.
effective temperature Changes in
pparent gas
gas concentration.
pparenttemperature The
The⎥⎦ complexity
⎪⎢⎣ the absorbance,
concentration. complexity of
of temperature
⎪SPAN and apparent temperature compensation
compensation algorithms
algorithms applied
applied to to algorithms applied to
affect gas concentration. The complexity of temperature compensation
he ⎪⎩on the accuracy ⎪⎭ required. Details are given below for two simple linear
he data
datathedepends
depends
data depends ononthe accuracy
the accuracy required.
required. Details areDetails are
given below given
for two below
simple for two For
linear corrections. simple
details oflinear
more complex corrections to
orrections.
orrections. For
For
improve
details
detailsusers
accuracy,
of more
of are
more complex
complex
encouraged
corrections
corrections
to contact
to
to improve
Alphasense. improve accuracy,
accuracy, users
users are are encouraged
encouraged
o
o contact
contact6. Alphasense.
Alphasense.
Temperature Compensation
The effects of temperature on an NDIR sensor are complex and care must be taken to ensure
.1
.1 SPAN
SPAN ONLY
effective
ONLY compensation
temperature
compensationcompensation. Changes in temperature affect the absorbance, SPAN and
or apparent gas concentration.
scaleThe complexity of temperature compensation algorithms sufficient
applied to to correct only
or sensors with
6.1 SPAN
sensors high
high full
ONLY
withdepends
the data
compensation
full
on scale
values (e.g
(e.g >10
valuesrequired.
the accuracy >10 %
% vol.
Details vol. CO2)) it
are COgiven it is
is normally
2 below normally sufficient
for two simple linear to correct only
he
he SPAN,Forusing
SPAN, sensorsthe
using
corrections. Forfollowing
the
with following
high full of
details equation:
equation:
scale values
more (e.g >10
complex % vol. COto) itimprove
corrections is normally sufficient
accuracy, to correct
users only the SPAN, using the following equation:
are encouraged
2
to contact Alphasense.
SPAN = SPAN
SPAN
6.1 SPANT = SPAN + β ((T − T
cal + β o T − Tcal ))
T ONLY compensation
cal o cal
For sensors with high full scale values (e.g >10 % vol. CO2) it is normally sufficient to correct only
where: the SPAN,
where: using
SPAN theSPAN
is the following equation: T
at temperature,
where: T

SPANTT is the
SPAN is the SPANat
cal SPAN temperature,
+ β o (T − Tcal ) T
SPAN determined during calibration
is
SPAN the = SPANat
TSPAN cal temperature, T
SPAN o is the SPAN determined during calibration
β is the SPAN ONLY correction coefficient (see Table 1 and Application Note AAN 203)
SPANcal cal is the SPAN determined during calibration
β T is the calibration temperature
βoo is
is the calSPAN ONLY correction coefficient (see Table 1 and Application Note AAN 203)
where:
theSPANSPAN ONLY correction coefficient (see Table 1 and Application Note AAN 203)
T is the SPAN at temperature, T
T is the
Tcal is the
SPAN
calibration
calibration
is the SPAN
temperature
temperature
determined during calibration
cal cal
βo is the SPAN ONLY correction coefficient (see Table 1 and Application Note AAN 203)
.2
.2 ABS AND
ABS 6.2
AND
TSPAN
cal is the compensation
SPAN
calibration temperature
compensation
ABS AND SPAN compensation
o
o ensure
ensure
6.2
accuracy
accuracy
ABS AND
at
at
SPAN
low
low concentrations,
concentrations,
compensation
it
it may
may be
be necessary
necessary to
to correct
correct both
both the
the absorbance
absorbance and
and
To ensure accuracy at low concentrations, it may be necessary to correct both the absorbance and the SPAN. The absorbance is corrected using
he SPAN. The absorbance
accuracy at low is corrected
concentrations, using
it may the
he SPAN. The absorbance is corrected using the following equation:
To ensure be following
necessary to equation:
correct both the absorbance and
the following equation:
the SPAN. The absorbance is corrected using the following equation:
((11 −− ABS )) == ((11) =−−(1ABS
(1 −TTABS
ABS )(1(1+++ ααα(T((TT− T−− TT)cal
− ABS)()1
ABS ) ))))
cal
Alphasense Application Note
T cal
AAN 201-06
where: where:
where: where: ABS
ABST is the temperature corrected absorbance at temperature, T
T is the temperature corrected absorbance at temperature, T
PAN isABS
thenT is the
corrected
ABST isABS temperature
theisisthe
ABS as above
temperature
theuncorrected
uncorrected
corrected
corrected
absorbance
absorbance
absorbance
but to ensure
absorbance at
at temperature,
accurate compensation
temperature, T
T a different coefficient
hould ABS
be is
used α the
is (seeuncorrected
the Application
absorbance
ABS is the uncorrected absorbance Alphasense Application Note
absorbance
Note
correction AAN 203):
coefficient
coefficient (see
(seeTable
Table1 and
1 Application
and Note
Application AAN
Note 203)
AAN 203) AAN 201-06
α is theTT calabsorbance
isisthe
thecalibrationcorrection
calibration temperaturecoefficient (see Table 1 and Application Note AAN 203)
temperature
α is the calabsorbance correction coefficient (see Table 1 and Application Note AAN 203)
PAN isT SPAN
thenis the
corrected
cal is the
Tcal = SPAN
calibration
T calibration + β A (but
ascalabove T − to
temperature
temperature )
Tcalensure accurate compensation a different coefficient
hould be used (see Application Note AAN 203):
SPAN is then corrected as above but to ensure accurate compensation a different coefficient should be used (see Application Note AAN 203):
here:
SPAN
SPAN T is = SPAN
T the β A (T − Tcal ) T
SPANcalat+temperature,
SPANcal is the SPAN determined during calibration
here: βA© isAlphasense
where: the
SPANABS is the
Limited
ANDSPAN SPAN correction
at temperature, T
Page coefficient
3 of 5 (see TableNovember 2014
1 and Application Note AAN
Sensor TTechnology House, 300 Avenue West, Skyline 120, Great Notley Essex CM77 7AA, UK
203)
SPANT SPAN is thecal SPAN at
is the SPANTel: temperature,
determined during
+44 (0) 1376 556700T Fax: +44 (0) 1376 335899
calibration
T cal is the
SPAN βAis iscalibration
theABS SPAN temperature
determined during calibration
the email:
AND sensors@alphasense.com
SPAN correction coefficient Web: www.alphasense.com
(see Table 1 and Application Note AAN 203)
cal
© Alphasense
β
© Alphasense
A is Tcal is
the ABSLimited
the calibration
Limited AND temperature
SPAN correction Page 3 of 5
Page 3 of 5 (see Table 1 and Application
coefficient November
November Note2014
AAN
2014
. Calculating
Sensor
203) Technologythe temperature
House, 300 corrected
Avenue West, gas concentration
Skyline
Sensor Technology House, 300 Avenue West, Skyline 120, Great Notley Essex CM77 7AA, UK120, Great Notley Essex CM77 7AA, UK
is the calibration
Tcalcorrection Tel: +44
+44 (0)
Tel:temperature 1376
1376 556700 Fax: +44
+44 (0)(0) 1376 335899
ollowing of ABS and/or (0)SPAN, the gas
556700 concentration
Fax: 1376 can
335899be calculated. However, in
email:
email: sensors@alphasense.com
sensors@alphasense.com Web:
Web: www.alphasense.com
www.alphasense.com
rder to relate the gas concentration (in
7. Calculating the temperature corrected gas concentration % volume) at temperature, T, with the gas concentration
. Calculating
n % volume) atthe thetemperature correcteditgas
calibration temperature concentration
is necessary to employ the ideal gas law. This
Following correction of ABS and/or SPAN, the gas concentration can be calculated. However, in order to relate the gas concentration (in %
ccounts for
ollowingvolume) apparent
correction changes
of ABS and/or in SPAN,
the gastheconcentration
gas concentration with temperature (because
can be calculated. an NDIR
However, in
at temperature, T, with the gas concentration (in % volume) at the calibration temperature it is necessary to employ the ideal gas law.
ensor
rder toisrelate
sensitive the to
gas the number
concentration of molecules
(in % of
volume) theattarget gas
temperature, in the
T, cell,
with not
the the
gas % volume) so
concentration
This accounts for apparent changes in the gas concentration with temperature (because an NDIR sensor is sensitive to the number of molecules
hat
n %thevolume)
gas concentration
of the target at the at temperature,
gas incalibration temperature
the cell, not the
T, is itgiven
% volume) so that is gas
the
by:
necessary to atemploy
concentration the T,ideal
temperature, is givengas
by: law. This
ccounts for apparent changes in the gas concentration with temperature (because an NDIR
ensor is sensitive to⎧ the number of molecules ⎜ ⎟⎫
⎛ 1⎞ of the target gas in the cell, not the % volume) so
hat the gas concentration ⎪ ⎡ ⎛ ABS
at temperature, ⎞ ⎤ ⎝c⎠
⎪ is given by:
T,
⎢ ln⎜1 − ⎟⎥ T

⎡ T ⎤ ⎪⎪⎢ ⎜⎝ SPANT ⎟⎠ ⎥ ⎪⎪
xT = ⎢ ⎥ ⎨⎧⎢ ⎥⎤ ⎜⎝ c ⎟⎠ ⎬⎫
⎛ 1⎞
⎣Tcal ⎦ ⎪⎡⎢ ⎛ −ABS b ⎞ ⎪
⎪ ⎢ ln⎜⎜1 −
T
⎟⎟ ⎥⎥ ⎪
⎡ T ⎤ ⎪⎪⎢⎣⎢ ⎝ SPANT ⎠ ⎥⎦⎥ ⎪⎪
xT = ⎢ ⎥ ⎩⎨
⎣Tcal ⎦ ⎪⎢⎢ −b ⎥ ⎭⎬
⎥ ⎪
⎪⎢ ⎪
T: +44 (0)1376 556700 ⎪
⎣ sensors@alphasense.com⎥⎦ W:⎪www.alphasense.com
⎩E: ⎭ Sensor Technology House, Skyline 120, Great Notley, Braintree, Essex CM77 7AA, UK
(©ALPHASENSE LTD) Doc. AAN 201-06/SEP22
 APPLICATION NOTE AAN 201-06

8. Summary of Coefficients

Table 1. IRC-A1 : Standardised Linearisation and Temperature Compensation Coefficients (assuming calibration at 20°C)
Range Linearisation Coefficients Temp. Comp. Coefficients
Sensor Gas
(SPAN Conc.) b c βO βA
0 to 5000 ppm
IRC-A1-IAQ CO2 4.1 x 10-4 0.897 N/A 0.0009 0.0005
(4000 ppm)
0 to 5 % Vol
IRC-A1-Safety CO2 0.520 0.680 0.0021 0.0009 0.0014
(4 % Vol)
0 to 20 % Vol
IRC-A1-Combustion CO2 0.491 0.613 0.0024 0.0009 0.0020
(16 % Vol)
0 to 100 % Vol
IRC-A1-Industrial CO2 0.698 0.302 n.d n.d n.d
(100 % Vol)

Table 2. IRC-AT : Standardised Linearisation and Temperature Compensation Coefficients (assuming calibration at 20°C)
Range Linearisation Coefficients Temp. Comp. Coefficients
Sensor Gas
(SPAN Conc.) b c βO *βA
0 to 5000 ppm
IRC-A1-IAQ CO2 3.25 x 10-4 0.9363 0.00001 0.00056 0.00001
(4000 ppm)
0 to 5 % Vol
IRC-A1-Safety CO2 0.5411 0.6716 tbd 0.00056 tbd
(4 % Vol)
0 to 20 % Vol
IRC-A1-Combustion CO2 1.0459 0.2932 tbd 0.00056 tbd
(16 % Vol)
0 to 100 % Vol
IRC-A1-Industrial CO2 tbd tbd tbd tbd tbd
(100 % Vol)

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