Calibration Method of Clinical Type Infrared

Thermometers and Estimation Uncertainty in Different

Blackbody Cavities
Melda Patan Alper (  mpatan@yeditepe.edu.tr )
Yeditepe University

Research Article

Keywords: Infrared Thermometers, Ear Thermometer, Blackbody Radiation, Temperature Metrology, Measurement
Uncertainty

Posted Date: April 4th, 2023

DOI: https://doi.org/10.21203/rs.3.rs-2761413/v1

License:   This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full
License

Page 1/14
Abstract
In recent years, radiation thermometers or infrared thermometers are frequently preferred in many different sectors
from the health sector to the iron and steel industry, food, agriculture, chemistry and automotive, due to their fast
measurement capabilities, reasonable prices, wide measurement ranges and practical use. In this study, the
calibration systems of infrared clinical radiation thermometers, which are widely used in our hospitals and homes
and become more important with the sudden expansion of their usage areas (closed areas, meeting rooms,
shopping malls, schools and offices), especially during the Covid-19 period, were investigated. The measurement
of human body temperature is an important physiological measurement used primarily for diagnosis, surgery,
especially during pandemic diseases such as covid-19, intensive care and treatment procedures. Different types of
clinical thermometers are used in body temperature measurement and we can examine these thermometers in two
groups: contact thermometers and non-contact thermometers. To have confidence in the accuracy of the
measurements of the temperature measuring device, clinical thermometers, it is important that the device is
calibrated traceable to the 1990 International Temperature Scale (ITS-90).

1 Introduction
Although measuring body temperature with optical systems is not as reliable as using traditional methods (glass
thermometer, electrical thermometer), in routine clinical applications they have largely replaced the classical
methods [1]. In the field of body temperature measurement, clinical studies in recent years have focused on
practical infrared tympanic (ear) thermometers that can measure accurately, reliably and quickly, with less invasive
contact. [2, 3]

Clinical infrared thermometers are used to measure the temperature of the tympanum (ear drum) in the range (36–
41°C), and it is important that they are properly calibrated and used. Otherwise, it may lead to bad results, wrong
diagnosis and treatment. Calibration of clinical thermometers is done using a reference source of infrared (heat)
radiation, and this is conveniently provided by a ‘black body’, a cavity with black interior surfaces kept at a uniform
temperature. The cavity then has a radiation ‘emissivity’ which is close to the maximum of 1, and the radiation
detected through a small aperture in the cavity is closely related to the cavity temperature.

An important need for accurate measurement and reliability of measurements. The most important part of the
calibration system of infrared thermometers is the blackbody. The basic optical properties of black bodies are their
emissivity and reflectivity. The infrared thermometer measurement method relies on having some knowledge of
the emissivity (emissivity) of human skin, because human skin is not blackbodies: the radiation they emit is
always less than ideal [4]. The most basic problem in measurements is the black body sources used in the
calibration of all radiation thermometers. These systems do not pose such a problem in the calibration of an
industrial type infrared or radiation thermometer because the operating range of the thermometer is not as specific
as human body temperature and does not require low uncertainty, but if you are]In measuring the temperature of
the human body, the error or uncertainty of 0.5°C is very important. For this reason, the calibration system needs to
be specially designed to measure with high precision. ASTM 1998, EN 2003, JIS 2001 measurement systems
designed for calibration depend on multiple parameters such as surface shape, paint, material from which it is
produced, and even small differences in the specified conditions can affect the measurements. [5–7] First of all, it
is important that the temperature environment into which the cavity will be placed is stable and homogeneous.
Therefore, instead of systems such as block calibrators, heat sources with high thermal conductivity such as
stirred liquid baths will play an important role in reducing uncertainty [8, 9]. In the cavity design, the cavity with the
Page 2/14
closest emissivity value (є˃0.95) to the human skin will be designed and tested [10, 11]. The material of the cavity
and the coating technique are important at the design stage. The coating process is the first stage of the process
and after the process is completed, it is necessary to determine the emissivity correctly. It is important to correctly
determine the emissivity value of the produced cavity, which directly affects the measurements, and at this stage,
emissivity determination will be performed in a traceable manner with pyrometer? measurement, which is one of
the methods in the literature [12, 13]. Just as the emissivity value of the designed measurement system is
important, the emissivity value of the clinical infrared thermometer to be calibrated is also very important. A
radiation thermometer accurately measures temperature only when its instrumental emissivity is set equal to the
emissivity of the measured surface (target). Therefore, in practice, it is important to know exactly the target
emissivity and be able to set the same value on a radiation thermometer. Infrared thermometers basically have no
means of adjusting the instrumental emissivity [14].

The prohibition of mercury in glass thermometers used in the measurement of human body temperature, has had
an important effect on the development of new clinical thermometers. The restriction of the use of liquid glass
thermometers and the high uncertainty and cost of electrical? thermometers have increased the popularity of
radiation thermometers [15, 16].

Numerous blackbody system designs have been developed (bath-type cavities, oven-type cavities, and fixed
points) that meet the radiation thermometer calibration requirements [17–20]. Blackbody systems are limited for
calibration of clinical-grade thermometers (Tympanics). Vertically oriented submersible blackbody designed from
international standards are used for contact type thermometers. While producing the blackbody cavity system in
accordance with the defined standards, the manufacturer has to provide all the parameters perfectly, otherwise the
measurements will be inaccurate, and if the laboratory that performs the post-production measurement does not
have a reference to compare or an interlaboratory comparison measurement that it can participate in the
comparison measurement, it will not be able to understand the error it made in the measurement [21]. There is no
standard calibration method and system for non-contact clinical thermometers [14]. It is seen from the studies in
the literature that standard blackbodies are used in non-contact thermometers, which are costly to produce and
depend on many parameters.

Vertically oriented submersible blackbodies are suitable for use in liquid baths and liquid baths are ideal due to
their low measurement uncertainty. Horizontal type (flat plate) blackbodies are mainly used in furnace systems
and the uncertainty of these furnaces is higher than in baths. In vertical systems, the thermometer focuses inside
the cavity and the radiation has no effect of exposure to other external effects, but in horizontal systems the
system is open, the beam is focused on a surface, it is inevitable that it will be affected by other ambient
radiations at that time [7, 14].

The first aim of the present study is to compare the measurement results of standard blackbody cavity and non-
standard low-cost and simple-to-manufacture contact IR thermometers produced in our laboratory. Another
important aim is to investigate whether it is possible to calibrate non-contact thermometers, which do not have a
standard calibration system, with an acceptable uncertainty by measuring them with these two blackbody
systems.

2 Theory

Page 3/14
Blackbody radiation, also called cavity radiation, is an object that absorbs all directed radiation and re-radiates
system-specific energy. [22–23] The measuring principle of infrared thermometers is based on black body
radiation. Emission is defined as the ratio of the energy emitted from the surface of a material to that emitted from
a perfect emitter, known as a blackbody, under the same temperature, wavelength, and visibility conditions. The
emission (ɛ) value of the objects is between 0 and 1. Emission surfaces with zero emission value have maximum
reflective surface; If the emission value of the object is 1, it is called 'black bodies' and these surfaces absorb all
the radiation. Even though an object has an emission value of 1 in theory, it is not possible in practice. [24–27].
The emissivity value of the object changes depending on some parameters related to the material of which it is
made, for example, the roughness of the surface, its oxidation state. The first condition in temperature
measurements is to determine the emissivity value correctly and to measure at the correct emissivity value.
Another important condition is that the emission value changes according to the temperature, wavelength and the
angle at which the measurement takes place [28, 29]. After determining the correct emission value, it is necessary
to convert the measured signal to temperature accurately in the measurement of radiation thermometers [30].

When we study the surfaces of bodies, no surface has an emission high enough for direct use as a blackbody
source, but we can use the concept of true blackbody radiation at a uniform temperature in a closed space. It
depends only on wavelength and temperature, and it doesn't matter what the emission of the material from which
the cavity is produced. If this were not so, the second law of thermodynamics would not work, heat could be
transferred from one part of a cavity to another without a temperature gradient.

Standard blackbody sources are used to calibrate radiation thermometers. Black bodies can be placed in a bath or
oven as a thermal medium, or black body calibrators designed for direct calibration can be used. [31].

3 Experiment
The basic measuring principle in temperature calibrations is based on the zeroth law of thermodynamics; If the
two systems interact with each other, they will reach thermal equilibrium after a certain period of time and have the
same temperature. For this reason, it is one of the most important steps to create this temperature environment in
the measurement setup, that is, in the calibration system. The temperature environment is created using heated
furnaces or liquid baths. In this study, special calibration baths (Fluke 7341, Hart Scientific 7037) with very low
stability and homogeneity were preferred, since it was aimed to develop a calibration system for infrared
thermometers used in body temperature measurements and since it is the most important condition that the
measurements are carried out with high accuracy and low uncertainty. In researches with liquid baths, it is known
that the stability value of an average liquid bath is around ± 0.01°C. Although there are cavity studies in the
literature for clinical thermometers, no measurement system design or study using different types of clinical
thermometers has been found. The basic principle in temperature calibrations is to compare the thermometer to be
calibrated with a reference thermometer in a temperature source, the comparison method according to ITS-90 is
used in comparison measurements. In this study, as mentioned above, a liquid bath will be used and the actual
temperature of the liquid bath will be measured by reference thermometers. All temperature measurements will be
made with the Hart Scientific and Fluke brand Standard Platinum Resistance Thermometers (SPRT), the most
sensitive thermometers that can be used.

3.1 Apparatus

Page 4/14
The main apparatus utilized consisted of water bath (Hart scientific), reference thermometer-862 PF-100 (Hart
Scientific), 3030 ear infrared thermometer (Braun), two infrared non-contact thermometers, a blackbody 1- EN
12470-5 (0.95–0.97), and blackbody 2 – regular 31cm blackbody with emissivity 0.99.
3.2 Method
The experiment was conducted using two different blackbodies: blackbody 1 (standard EN 12470-5) and
blackbody 2 (normal 31cm blackbody). This was conducted to analyse the difference between results of both data
and compare them.

The dimensions displayed in the Fig. 1 are in millimeters. The number 1 in the Fig. 1 is necessary cover for the
cavity to fit inside the bath, number 2 is surface painter inside cavity, number 3 is an opening required for the
infrared thermometer to read and number 4 is the O-Ring which is sealed connection rings. In number 2 seen in the
figure, Nextel Primer 5523 coded primer should be used to prime the structure of the paint to be used here, and the
inner surface should be primed before applying Nextel Velvet coating 811 − 21 black paint using a spray gun.

Figure 2 shows a cylindrical chamber with measurements of 44.0 mm diameter and 300 mm length painted on the
interior with black enamel paint and a widely viable Isotech blackbody target aim with dimensions of 43.8 mm
width and 18 mm thickness. According to the Isotech technical criteria, this results in an overall emissivity of 0.99.

The bath (Fig. 3-a) in which the unique cavity is placed is adjusted to the lowest temperature of the measurement
range, 36°C, and the reference thermometer is immersed to the same depth in the PRT (platinum resistance
thermometer) bath without contacting the cavity. The measurements begin at 36.0°C after the cavity has reached
equilibrium in the water bath. It is done in two sets of ten measurements at 10-second intervals using both
reference PRT and test infrared thermometers up to 41.0°C. The infrared thermometers (Fig. 3-b) which were used
in this study focused to the blackbody target at a same level. During each degree measurement, the thermometer
readings were taken every 10 seconds 20 times. The first set of measurements were conducted when the
temperature in the water bath had stabilized and reached homogeneity. To measure the temperature of the
blackbody, the infrared thermometer had to be inserted as deeply as possible into the hollow without contacting
the cavity's edges. The infrared ear thermometer was inserted at the same level as infrared thermometer. All
measurements were taken close to hollow at the same level to minimize the uncertainty. The experiment of
infrared non-contact thermometers was adjusted to two different settings: Surface and Body mode. The difference
between the two modes is that their emissivity.

4 Measurements And Results

First, blackbody 1 was used to compare the infrared ear and non-contact thermometers and their accuracy. The
following temperatures were measured using blackbodies: 36°C, 37°C, 38°C, 39°C, 40°C, and 41°C. Experimental
data consist of several categories; infrared ear thermometer tested with blackbody 1 and 2, IR non-contact
thermometer tested with blackbody 1 and 2, also with two different modes (Surface and Body) which can be
observed in Table 1. Data for the infrared ear thermometer was obtained several times to test repeatability and the
most accurate values were recorded.

Page 5/14
 Table 1
Experimental data acquired
Reference IR Ear IR Ear IR Non- IR Non- IR Non- IR Non-
Nominal thermometer Thermometer Contact Contact Contact Contact
Value Blackbody 1 Blackbody 2 Thermometer Thermometer Thermometer Thermometer
(°C) (°C) Blackbody 1 Blackbody 2 Blackbody 1 Blackbody 1
(°C) (Surface) (Surface)(°C) (Body) (°C) (Body) (°C)
(°C)

36 36.3 36.0 35.8 35.9 37.5 37.7

37 37.0 37.1 36.8 36.9 38.5 38.7

38 37.8 37.9 37.8 38.0 39.5 39.6

39 38.9 38.9 38.8 38.9 40.6 40.7

40 40.0 39.9 39.9 39.9 41.4 41.5

41 40.8 40.8 40.9 41.0 40.5 40.6

Table 1 displays result of experimentation and data acquired. The values taken were non nominal and weren’t
comparable. Therefore, using an Excel sheet all values were recorded and then a scatter plot was inserted. A
polynomial trendline of 4th degree was inserted into the graph to get equation that will give comparable values.
Thus, by adding nominal reference values into the equation obtained the test values that are comparable were
achieved.

Figure 4 shows the infrared ear and non-contact thermometer data acquired using blackbody 1. It is observed that
infrared ear and non-contact thermometers agree with each other when using blackbody 1. Nevertheless, while
measuring the 36°C the values were much higher than that of reference. This is speculated to be due to the drift of
the ear thermometer used in research. During another research (Turkish airlines and YUKAL) this drift was
observed while conducting the research at 36°C. The same drift occurred with both blackbodies thus proving that
it was the equipment rather than a mistake during research. In an article comparing two blackbodies for an
infrared ear thermometer a drift occurred in the results of local blackbody and a standard blackbody. In this
research the same drift occurred with both blackbodies thus proving that it was the equipment rather than a
mistake during research. Therefore, this drift is assumed to have no substantial effect on the results of a
blackbody comparison in either case. Nonetheless, this indicates that while using infrared ear thermometers drifts
occur thus frequent calibration is required.

Figure 5 displays the data achieved using blackbody 2 with infrared ear and non-contact thermometer. Since the
conditions of both blackbody readings are same Figs. 4 and 5 can be compared as well. When compared one can
see that the values are similar and in agreement therefore, during calibration instead of an EN 12470-5, a standard
blackbody, a non-standard blackbody could also be used successfully.

For different blackbodies, the measurement uncertainty calculation was performed for each infrared thermometer.
Because it is not enough to know that the measured value is correct by comparing it with the reference value, it is
necessary to calculate the measurement uncertainty estimation correctly in order to ensure the reliability of the
measurements. The uncertainty calculation in this study was made according to the EA-4/02 guideline. All
parameters affecting the measurement are taken into account by adding them to the uncertainty budget. After
determining the parameters affecting the uncertainty, A and B type uncertainty parameters and distribution types

Page 6/14
were determined. After the total uncertainty value was calculated, the expanded uncertainty value was determined
at the 95% confidence level. All components that affect the measurement uncertainty of clinical type
thermometers are listed in Table 2.

Table 2
Uncertainty Budget for Infrared Non-Contact Thermometer (Body)
Uncertainty Component Uncertainty Statistical Distribution Standard Uncertainty Variance

( ºC) ( mºC)

Reference Therm. Drift (1 Year) 1.00E-03 Rectangular 5.87E-03 3.30E-05

Reference Therm.Uncertainty 2.00E-03 Normal 1.00E-03 1.00E-06

Reference Therm.Stability 0.00E + 00 Normal 0.00E + 00 0.00E + 00

Indicator Uncertainty 4.00E-05 Normal 2.00E-04 4.00E-08

Indicator Shift 1.35E-04 Rectangular 7.80E-04 6.09E-07

Blackbody Homogeneity 5.00E-03 Rectangular 5.00E-03 2.50E-05

Blackbody Stability 4.00E-03 Normal 4.00E-03 1.60E-05

IRET Repeatability 9.43E-02 Normal 9.43E-02 8.89E-03

IRET Resolution 1.00E-01 Rectangular 5.78E-02 3.34E-03

IRET Reproducibility 0.00E + 00 Rectangular 0.00E + 00 0.00E + 00

Black Body Emissivity 7.00E-02 Normal 3.50E-02 1.23E-03

Combined Standard Uncertainty, Uc 0.07

Expanded Uncertainty U = kUc = 2(0.12) 0.14 mºC

Table 3
Uncertainty Values of thermometers
Nominal IR Ear IR Ear IR Non- IR Non- IR Non- IR Non-
values therm. therm. contact therm. contact therm. contact contact
Unc. Unc. Unc. -Surface Unc. -Surface therm. Unc. - therm. Unc. -
(Reference) Body Body
(Blackbody (Blackbody (Blackbody 1) (Blackbody 2)
1) 2) (Blackbody (Blackbody
1) 2)

36°C ± 0.14 ± 0.14 ± 0.23 ± 0.14 ± 0.14 ± 0.14

37°C ± 0.14 ± 0.16 ± 0.14 ± 0.18 ± 0.17 ± 0.15

38°C ± 0.17 ± 0.14 ± 0.17 ± 0.14 ± 0.17 ± 0.14

39°C ± 0.17 ± 0.17 ± 0.14 ± 0.14 ± 0.16 ± 0.18

40°C ± 0.14 ± 0.15 ± 0.17 ± 0.14 ± 0.17 ± 0.14

41°C ± 0.19 ± 0.14 ± 0.16 ± 0.14 ± 0.14 ± 0.14

Page 7/14
Table 3 provides all uncertainties of all thermometers and their arranged settings. According to the standards of
ASTM 1998, EN 2003 and JIS 2001 an infrared thermometer should be reliable within the range of ± 0.2°C [8]. This
value is in accordance withing experiment operating range of 36°C to 41°C as the standard operating range is
35.5°C to 42°C. The result of same degree but different conditions show slight difference however, this is an
uncertainty resulting from the positional difference while conducting the experiment. As it was confirmed in
previous research that the positioning of the thermometer on blackbody results in a difference up to 0.2°C.
Because it was measured and conducted by hand the position of thermometers was not precise and following on
each step. Therefore, the uncertainties of the thermometers and different categories have slight variance.

5 Conclusion
In summary, it has been found that a low-cost non-standard black body designed for the calibration of radiation
thermometers is suitable for use in the calibration of clinical thermometers. It was observed that the standard
cavity, on the other hand, affected the measurements due to the problem in the coating thickness during the
production phase and caused a deviation at the lowest temperature value of 36°C. It has been determined that
providing standard parameters at the production stage causes the production process to prolong and some
deviations in the measurements. It was a development that was detected during this study that clinical
thermometer measurements could be measured with the same precision, except for radiation thermometers with
ordinary black spray paint used inside the non-standard cavity.

However, the results of the designed cavity were good agreement with the results of contact and non-contact
thermometers, and their expanded uncertainties did not exceed 0.2°C as stated in the manufacturer's declarations.
In summary, we can say that the obtained results provide a valid and effective method for ensuring traceability of
the designed cavity for calibration purposes.

Declarations
Acknowledgements
I wish to thank Dr. Richard Rusby from National Physics Laboratory (NPL) for help and comments. I would also
like to thank Maria Aiordachioaiei for help during this study.

References
1. R.S. Burnham, R. S., McKinley, D.D. Vincent, Am J Phys Med Rehabil. 85(7):553–558 (2006) DOI:
10.1097/01.phm.0000223232.32653.7f
2. R. Hajela, Journal of Evolution of Medical and Dental Sciences, vol. 9, no. 8, p. 555–561 (2020) DOI:
10.14260/jemds/2020/124
3. V. Pecoraro, D. Petri, G. Costantino, A. Squizzato,·Moja L., Virgili G., Lucenteforte E., Internal and Emergency
Medicine 16(4): 1071–1083. (2020) DOI: 10.1007/s11739-020-02556-0
4. F. Sánchez-Marín, S. Calixto-Carrera, C. Villaseñor-Mora, Journal of Biomedical Optics 14(2), 024006 (2009)
DOI:10.1117/1.3086612.
5. T. Fukuzaki, J. Ishii, T. Kojima, “Quality System for Measurement of Infrared Ear Thermometers in Japan”,
National Metrology Institute of Japan / AIST, Tsukuba, Japan
Page 8/14
 6. BS EN 12470-5:2003 Clinical thermometers – Part 5: Performance of infra-red ear thermometers
7. ASTM International, Designated E1965-98V (Reapproved 2016), Standard Specification for Infrared
Thermometers for Intermittent Determination of Patient Temperature
8. I. Pušnik, J. Drnovšek, Physiol. Meas. 26, 1075 (2005) DOI: 10.1088/0967-3334/26/6/016
9. I. Pušnik, A. Miklavec, Instrumentation Science and Technology. 37(5): 516–530 (2009) DOI:
10.1080/10739140903149061
10. P. Castro, R. Lecuna, M. Manana, M.J. Martin, D. Campo, Sensors. 20, 7126 (2020) DOI: 10.3390/s20247126
11. A. Manoi, U. Norranim, Y. Kaneko, J. Ishii, Int J Thermophys. 35:485–492 (2014) DOI: 10.1007/s10765-014-
1619-z
12. J. Ishii, Translation from Synthesiology. Vol.1 No.1, p.47–58 (2008) https://doi.org/10.5571/syntheng.1.47
13. J. Song, X. P. Hao, Z.D. Yuan, Z. L. Liu, L. Ding, International Journal of Thermophysics. volume 39, Article
number: 85 (2018) https://doi.org/10.1007/s10765-018-2404-1
14. S. Boles, I. Pušnik, M. L. Dubhaltach, D. Fleming, I. Naydenova, S. Martin, Measurement. Volume 106, Pages
121–127 (2017) DOI:10.1016/j.measurement.2017.03.023
15. I. Pušnik,. “Development and analysis of systems for evaluation of metrological parameters and assurance of
traceability of non-contact thermometers, doctorate thesis”, University of Ljubljana, Faculty of Electrical
Engineering (2004)
16. I. Pušnik, Physiol. Meas. 25 699 (2004) DOI: 10.1088/0967-3334/25/3/010
17. K. D. Hill, AIP Conf. Proc. 684 (2003) 669–674 DOI: 10.1063/1.1627204
18. P. R. Dekker, E. Van Der Ham, Int. J. Thermophys. 29, 1001–1013 (2008) https://doi.org/10.1007/s10765-008-
0420-2
19. G. J. Kim, et al. Physiol. Meas. 35 753 (2014) DOI: 10.1088/0967-3334/35/5/753
20. C. W. Park, Y. S. Yoo, B. H. Kim, S. Chun, S. N. Park, Int J Thermophys 32:7 1622–1632 (2011) DOI:
10.1007/s10765-011-0962-6
21. T. Kolat, F. Liebmann, The Journal of Measurement Science Volume 8, Issue 1 (2013) DOI:
10.1080/19315775.2013.11721631
22. R. Simpson, G. Machin, H. McEvoy, R. Rusby, Journal of Medical Engineering & Technology. 30:4, 212–217
(2006) DOI:10.1080/030919006007711530
23. Preston- Thomas H., 1990. “ITS-90 - The International Temperature Scale of 1990”, Metrologia, 27,107
24. www.npl.co.uk
25. Quinn T J 2013 Temperature (New York: Academic)
26. Young H D, Freedman R A 2016 University Physics with Modern Physics (Fourteenth Edition Pearson)
27. F. Sakuma, L. Ma, SICE. Annual Conference, IEEE, 37, 5–16. (2003)
28. A. Merlone, L. Iacomini, A. Tiziani, P. Marcarino, Measurement.. 40, 422–427 (2007)
DOI:10.1016/j.measurement.2006.06.006
29. C.E. Gibson, B. K. Tsai, A. C. Parr, 1998 NIST Measurement Services: Radiance Temparature Calibration
30. H. Yoon, P. Saunders, G. Machin, A.D. Todd, 2018, BIPM, Guide to the Realization of the ITS-90 Radiaiton
Thermometry

Page 9/14
Figures

Figure 1

EN 12470-5 Standard Blackbody (1) [6]

Page 10/14
Figure 2

Blackbody (2) designed by Yukal (Isotech blackbody target)

Page 11/14
Figure 3

a) EN standard blackbody inside the bath and b) infrared thermometers

Page 12/14
Figure 4

Comparison of Infrared ear and non-contact thermometer using blackbody 1 within the temperature range of 36-
41°C

Page 13/14
Figure 5

Comparison of Infrared ear and non-contact thermometer using blackbody 2 within the temperature range of 36-
41°C

Supplementary Files
This is a list of supplementary files associated with this preprint. Click to download.

Author.docx

Page 14/14