Non-contact temperature measurement at the time of coronavirus – screening of febrile conditions

Slide No: 1© Workswell www.workswell.cz
NON-CONTACT TEMPERATURE
MEASUREMENT AT THE TIME OF
CORONAVIRUS – SCREENING OF FEBRILE
CONDITIONS

CONTENTS
 Motivation
 Where to measure the temperature on your face and how to measure it
correctly
 Short introduction to thermography
 Technical standards IEC 80601-2-59 and ISO 16142
 Parameters and possibilities of thermal cameras
 Workswell MEDICAS - thermal camera for screening febrile conditions
 Black body – etalon for non-contact temperature measurement

WHAT YOU WILL LEARN
 What are the key functions of non-contact temperature measuring devices (not only
on the skin)?
 What are the key functions of thermal cameras and what is just "marketing”?
 How the thermal camera is to be set (emissivity, reflected apparent temperature,
etc.). And how to set up your device (whichever one you have).
 Important and key parameters of thermal cameras.
 Where the temperature should be measured on the human body surface and why
there.
 Technical standards IEC 80601-2-59 and ISO 16142 in response to SARS and MERS
and their requirements and recommendations.
 Thermography equations (optional but may be useful).
 Black body, the principle of why it is important for continuous recalibration
(metrological continuity).
 And I believe that many more….

MOTIVATION: NOT LIKE THAT!
 Measuring temperature in a hospital:
* First attempt: You have 37.5 °C, you cannot go there. One
moment and I will try it again.
* Second attempt: You have 35.1 °C, you are dead, so you still
cannot go there.
* Third attempt: So now its 36.2 °C. That's a piece of junk, so
move on.
 What is wrong here?
 “Thermometer”?
 Measuring procedure?
 The person being measured?
 A constellation of stars?

MOTIVATION: NOT LIKE THAT!
 Every day at Workswell we see dozens of users (firefighters,
police officers, doctors, security agency workers, etc.) call for
non-contact temperature measuring devices and encounter
very poor "measurement repeatability". The government, the
authorities and the managers of companies send these people
out unprepared for what is not a trivial matter – non-contact
temperature measurement.
 We would like to analyse this issue to show where problems with
non-contact measurement of human skin temperature can occur,
what devices to use and the requirements placed on them.

MOTTO
"One cannot win by ignoring the enemy, but only by knowing
them and using the best strategy in combat."
MUDr. Jitka Mašková Švejdová
“Using a measuring instrument does not necessarily mean taking a
measurement. Of course, this also applies to thermometers, pyrometers
and thermal cameras."
From the training of the
Thermography Centre
www.centrumtermografie.cz

THE "CURSE" OF PREVENTION AND
DIAGNOSIS
 The curse of technical diagnostics: If you rescue an aircraft whose engine
failed during the flight, you will become a hero, but if you rescue an
average of one aircraft per month with timely technical diagnostics, no one
will probably thank you too much. On the contrary, you will be considered
a troublemaker.
 To date, the Czech Republic can be considered a successful country in terms
of the deployment and application of restrictions (quarantine) leading to
the prevention of the spread of SARS-CoV-2 (SARAS 2). The effectiveness of
these measures (a relatively small number of infected people and deaths) is
paradoxically used as the "strongest" argument against it. This is in the
sense of "nothing happens".
 In other words: the high success of restrictions can lead to a false sense of
security and assurance of no need of restrictions.

WHEN YOU ARE INCOMPETENT, YOU DO NOT
KNOW IT
 If you conduct a random survey on the street and ask who is considered
competent in the field of nuclear reactors or neurological operations,
except for the real experts who will be mindful of their designation as
experts, you will find almost no one who will claim they are. Even when
asked if they can make a good sirloin steak, these people will be reticent.
Most people know that a good sirloin steak requires high craftsmanship.
 Unfortunately, in the case of temperature measurement, almost everyone
feels qualified to comment.. Temperature is such a common term,
everyone somehow "has" it ("I have a temperature", "what is your
temperature"), everyone has measured it many times, etc. But this is a big
problem.
 People are unqualified in temperature measurement, but they don't know
it!

SPANISH FLU: ONE, SECOND, THIRD WAVE
 Three waves of Spanish flu (H1N1 virus). The most devastating wave was
in the autumn of 1918 (the return of soldiers from the WWI front), but a
third wave followed.
are we here now?
Source of the chart: Wikipedia

WHERE TO MEASURE THE TEMPERATURE ON YOUR
FACE AND HOW TO MEASURE IT CORRECTLY

TEMPERATURE ALLOCATION ON THE
FOREHEAD – INTERIOR
 "Every time I measure a different temperature on my forehead, it
fluctuates a lot" - a question on the phone

fluctuates a lot" – here we see fluctuations from 32.5° C to 35.4° C.

FOREHEAD – EXTERIOR

fluctuates a lot" – here we see fluctuations from 38° C to 39.5° C.

FOREHEAD – EXTERIOR X INTERIOR

TEMPERATURE MEASUREMENT WITH A
PYROMETER ("LASER THERMOMETER")
 When measuring the temperature with a pyrometer, the temperature
is averaged from a large area on the forehead (it is almost impossible to
measure much with the eye). Remember the previous slide! The
temperature distribution at the front is considerably inhomogeneous.
Averaging does not make sense in this case.
 Large temperature variation on the forehead (sweat glands, blood
vessels and veins, etc.). What is measured?

INFLUENCE OF MEASURING POINT
Place of measurement: Usual value in °C Highest value in °C
Rectally 36.2 37.7
In the mouth 35.7 37.3
In the armpit 35.2 36.7
In the ear 35.8 36.9
On the forehead 35.8 36.9
 The so-called „body core temperature" cannot be measured. In practice,
we measure with different approaches in different places, and the place
and method of measurement must be taken into account when
evaluating the measured data.

SO HOW DO YOU MEASURE THE
TEMPERATURE ACCORDING TO ISO 16142?
 According to the technical standard IEC 80601-2-59 it is the area in the
media adjacent to the inner corner of the eye that is excellent for fever
screening. This is due to the temperature stability in this area, as it is
located directly above the passing carotid artery.
 This is where we can expect the least temperature changes and
manifestations of the environment (proximity to the behaviour of the
core).
Source of Fig.: Pixabay
The carotid artery and its
anatomy

"VERIFY WITH A LASER THERMOMETER"
 In practice, I quite often come across the opinion that "a verification
measurement will be performed using a laser thermometer". But it is the
same principle (as thermal camera)!
 Building expert (from training, years ago): "I providing „smart“
measurements by approaching the contact distance with a non-contact
pyrometer…"
 Pyrometer measurement is not more accurate! On
the contrary, it is an orientation measurement!
The thermal camera enables more accurate
measurements (we will explain this).
 It is not possible to measure the temperature near
the carotid artery (light in the eyes, averaging
from a large area).

INTERPRETATION OF TEMPERATURE
MEASUREMENT
 Relatively constant body temperature is necessary for the normal
functioning of the metabolism and the course of enzymatic reactions. Body
temperature is given by the result of heat intake, production and
expenditure.
 We try to place the measuring point for determining the body temperature
close to the course of large vessels. These areas but best of all the surface
parts of the body, reflect the so-called temperature body core.
 The best-known places to measure are the axilla (armpit), rectum and
mouthy.
 The core of the human body is warm-blooded (homoiothermic) – even
when there are large fluctuations in the ambient temperature, its
temperature changes only minimally. Peripheral parts of the body (skin,
limbs) behave cold-blooded (poikilothermically) and partially adjust their
ambient temperature, which prevents high heat loss.

SHORT INTRODUCTION TO THERMOGRAPHY

THEORETICAL PARENTHESIS
 We don't want to scare you with theory here. The devices (or at least ours)
are designed so that you don't necessarily need to know everything I will
say next. On the other hand, for a deeper understanding of the issue, the
following is necessary.
 But I would just like to indicate that behind the user settings it is for sure
that in the background there is certain physics (and metrology), from which
the specific form (settings or work with the device) follows, which must be
respected.
 A good device design "shields" you from the theory below.
 We will not discuss the very physical nature of thermal radiation (that
would be for another extensive lecture).

MEASUREMENT PARAMETERS
 A thermal camera does not measure the temperature directly but
determines it based on the measured intensity of thermal radiation and
the parameters entered.
 There are five measurement parameters:
 Emissivity
 Reflected apparent temperature
 Three parameters for modelling the effect of the atmosphere:
 distance, atmospheric humidity, atmospheric temperature
 Emissivity and the reflected apparent temperature are especially significant
(the influence of the atmosphere can be discarded).
 The effect of the "reflected apparent temperature" decreases with
increasing emissivity…

MEASUREMENT PARAMETERS – HUMAN
SKIN
 Emissivity of human skinis between 0.97 and 0.98 (It is usually stated
differently according to the source of measurement with a slight variance
with little impact on the measurement result. The magnitude of emissivity
does not depend on the colour of the skin ("colour" does not exist for
thermography) but on the surface (roughness, porosity, etc.). The
maximum (and theoretical) value of emissivity (of any surface) is 1. So, we
are very close.
 Reflected apparent temperature: this can be directly measured by the
direct or indirect method according to ISO 18434-1 or estimated as air
temperature (room temperature). This is an approximation, but due to the
high emissivity of the skin, it is not such a big problem.
 Atmospheric correction: this can be neglected due to the small measuring
distance (the distance is then set to zero).

ILLUSTRATIVE EFFECT OF EMISSIVITY
The surface temperature of an insulated panel house is approximately homogeneous.
However, on the thermogram, it appears that the places with the inscription are up to
5°C cooler. This measurement error is caused by the different emissivity of the colours of
the inscription compared to the colours of the masonry.

THERMOGRAPHY EQUATION
1. thermal radiation from the surroundings that is reflected from the measured
surface, 2. the surface of the measured object, which is the source of the measured
thermal radiation, 3. the atmosphere, which both attenuates thermal radiation
from the measured surface (own and reflected), and also itself radiates thermal
radiation, 4. thermal camera lens
The thermography equation describes what radiation falls into the thermal camera and
its effect on the measured value.

The reflected apparent radiation
from the surrounding object,
reflected from the surface of the
measured object.
The total
radiant flux that
hits the thermal
camera lens.
The actual radiation
of the atmosphere.
The actual radiation of the object,
attenuated by the atmosphere.
The only part of the equation that
we WANT to measure!

The influence of
the atmosphere is
negligible for
many applications
(underlined
symbols).
Reflected thermal
radiation.
The actual thermal
radiation of the
measured object.
The actual thermal radiation of an object is what we WANT to measure, the reflected
(thermal) radiation is what causes us problems, and the aim is to ELIMINATE it as
much as possible. The smaller the total thermal radiation of the measured object in
the total, larger errors can be attempted to be corrected during the measurement,
despite the efforts to correct the determination of the reflected apparent
temperature.

TECHNICAL STANDARDS IEC 80601-2-59 AND ISO
16142

MERS AND SARS - HISTORY
 IEC 80601-2-59:2017 – Part 2-59: Requirements for the basic safety and
essential performance of screening thermographs for human febrile
temperature screening.
 ISO 16142-1:2016 – Recognised essential principles of safety and
performance of medical devices — Part 1: General essential principles
and additional specific essential principles for all non-IVD medical
devices and guidance on the selection of standards.

MERS AND SARS - HISTORY
 These technical standards were created as a response to the disease SARS
(2002, Kuang-tung) and MERS (2012, Saudi Arabia, Qatar) caused by the
coronaviruses SARS-CoV and MERS-CoV.
 Although these diseases have not spread much, they are real objects of
fear. For example, for MERS, mortality is estimated at up to 50%!
 According to the information from WHO,MERS reappeared in January 2020
in Saudi Arabia. In 2014, it was confirmed that the virus was spread to
humans from camels.
 The occurrence of SARS was first reported on November 16, 2002 from the
Chinese province of Kuang-tung. Over the following months, the disease
spread to more than 30 countries, infecting more than 8,000 people and
directly killing 774.

TECHNICAL STANDARDS IN RESPONSE TO
THE MERS AND SARS RISK
 Requirements for the parameters of thermal
cameras
 Uncertainty of measurement, use of black
body
 Geometric resolution (lens x sensor resolution)
 Visualisation (pallet)
 Black body parameters (temperature stability,
uncertainty, size (20x20px), emissivity, etc.)
 MRTD, re-calibration co 5s
 and others.
 The environment in which the measurement is to be taken.
 Measurement procedure, setting of measurement parameters, etc.

EFFECTIVE CESSATION OF MERS INFECTION
– SOUTH KOREA 2015
Using effective measures, the spread of MERS in South Korea in 2015 was quickly
stopped.

PARAMETERS AND OPTIONS OF THERMAL
CAMERAS

BASIC PARAMETERS OF THERMAL CAMERAS
 The basic parameters of a thermal camera that need to be discussed
regarding the accuracy of measuring body temperature (of course, on the
skin) are:
 Uncertainty of measurement (this concerns not just the device but the whole
measurement chain)
 Resolution (we will explain why) and iFOV (resolution x lens)
 Other parameters of the thermal camera, which must also be
considered, are the spectral range, temperature range (should not be
too wide), NUC technique, sFFC calibration in production, NETD, MTDR,
etc.
 These are almost always LWIR thermal cameras with a spectral range of
7 - 14 μm, in which the glass is impermeable (i.e. it cannot be
measured through glasses)!

BASIC PARAMETERS OF THERMAL CAMERAS
The microbolometer is a
sensor of the Workswell
MEDICAS thermal camera.
Resolution 640 x 512
(Workswell MEDICAS) is one
of the highest resolutions on
the market for thermal
cameras. In the area of body
temperature screening, this
is almost the highest
resolution of a mass-
produced system.

INFLUENCE OF THERMAL CAMERA
RESOLUTION ON MEASUREMENT ACCURACY

FIELD OF VIEW AND RESOLUTION PER PIXEL

"HOMEOPATHIC MEASUREMENT"
 On most materials from "very serious suppliers", you will find temperature
measurement of people with glasses. How does this function? I DON'T KNOW and I
never will.
 What does the green cross point to in the thermogram? Maximum temperature?
Hard to say.

 On most materials from "very serious suppliers", you will find temperature
measurement of people with glasses. How does this function? I DON'T KNOW
and I will never know.
 Besides, there is a risk that the person will not be recognised (AI algorithms
do not work 100%) and the risk assessment will fail.

 Temperature alarms are definitely more appropriate (than just face
recognition), as they do not indicate the one temperature assigned to a face,
as we see in the picture, but theTEMPERATURE FIELD!
 Consideration: if the camera evaluates the maximum temperature, how does
it cope with the reflection of the apparent temperature on the glasses (low
emissivity) and in the case of warm objects from the surroundings, if average,
how does it cope with the reflection of the colder surroundings?

"ESPECIALLY SINCE IT HAS ARTIFICIAL
INTELLIGENCE (AI)"
 It is not clear on what the data the rectangles are based on. Two of the people are
wearing glasses, which is not suitable for a marketing presentation due to the
requirement of the IEC 80601-2-59 standard and can create the impression that people
wearing glasses can also be measured by the system. For the figure at the back (detail
on the right), their entire face is almost covered by a veil/respirator and their glasses. If
the temperature in the rectangle is obtained by averaging, the apparent lower
temperature on the glasses is likely to be included in the average. The face detection
function does not change the above.

"HOMEOPATHIC MEASUREMENT" PAPER
CAN WITHSTAND EVERYTHING
 Such low measurement uncertainties are not even reported for scientific
research thermal cameras (with a cooled sensor) that are very expensive. The
uncertainties are almost the same for all the thermal cameras mentioned.

HOW DOES THIS MEASUREMENT (NOT)
WORK?

TYPES OF DEVICES
1) Pyrometer
Note: The laser has no
measurement function, it
only shows where it is
measured on the surface.
2) Handheld x stationary
thermal camera -without
metrological continuity
using black body
3) Thermal camera with
metrological traceability
using a black body

WORKSWELL MEDICAS
THERMAL CAMERA FOR SCREENING FEBRILE
CONDITIONS

BLACK BODY - METROLOGICAL CONTINUITY
 Workswell MEDICAS thermal camera& Black body. Two of the most
important components in the system.

PARAMETERS OF THE WORKSWELL MEDICAS
THERMAL CAMERA
SDK card port Ethernet HDMI

ADJUSTABLE LEVELS
 Three levels of temperature:
 Low temperature and normal temperature
 Increased temperature
 Fever
Workswell MEDICAS????
Temperature alarms:

FULLY RADIOMETRIC THERMAL CAMERA
 Facial recognition is not a required function of the system. On the contrary,
it is redundant. In the image on the right, the elevated temperature is
precisely localised, pixel by pixel…
 Probably, no one will ever explain to me how the temperatures in the image
on the left are measured where there are people with glasses (that is, with
a detected face). Can the temperature be measured correctly at all here?
 Therefore, the number of screened persons is not limited with MEDICAS!
Workswell MEDICAS
????

FULLY RADIOMETRIC THERMAL CAMERA
 The radiometric thermal camera does not need any facial recognition. It
measures the temperature everywhere; there is no need to identify the
face. The thermal camera accurately indicates by an alarm (isotherm)
where the limit temperature has been exceeded!
 On the contrary, where is the temperature measured during facial
recognition? The camera shows one number, but how did the camera
come up with this? Is it an average value, the maximum? Where is it
located and how significant is it?
???? Workswell MEDICAS
???? - where can the
temperature be measured
on this person?

FINALLY, CHOOSING A THERMAL CAMERA
 It is much easier and cheaper to add relatively redundant functions to a
thermal camera than to offer a sufficiently high-quality thermal camera
with sufficient resolution and sufficient measurement accuracy.
 One "magical" temperature reading should not replace a fully
radiometric thermal camera
 In addition, AI algorithms quite often
fail. Although a good assistant, it
cannot be "left to them".
 From the point of view of the security
of the situation, the thermal camera
acts more like a thermal imaging frame
at an airport than anything else.

BLACK BODY - THE STANDARD FOR NON-
CONTACT TEMPERATURE MEASUREMENT

BLACK BODY - METROLOGICAL CONTINUITY
 Each measurement is a "comparison
with a standard".
 The standard for non-contact
temperature measurement is (among
other things, but above all) the so-
called “black body“
 We will not run into theoretical
thermography here, so will only state
that the black body is a source of
defined thermal radiation.

TECHNICAL BLACK BODY
 In technical practice, we do not have a body with𝜀 = 1 available, but only
black bodies that are close to this value, i.e. for example𝜀 = 0,99.
 Such a “black body” is called: technical black body.
 Cavity black body x plate black body.
Black body is a body that completely absorbs all incident electromagnetic
radiation on its surface, regardless of the wavelength of this radiation.
Therefore, the absorption of a black body is one (α = 1). Thus, the
emissivity of the black body (𝜀 = 1) is also unitary, and the black body is
thus the "most efficient emitter" of thermal radiation.

EXAMPLE OF BLACK BODY CONSTRUCTION
 Due to multiple reflections, the incident infrared radiation is attenuated.
This also achieves high emissivity because (in a thermodynamic
equilibrium) the following equation applies (high emissivity is achieved
despite high absorption:
EMISIVITY = ABSORPTION

BLACK BODY – METROLOGICAL CONTINUITY
 The black body continuously recalibrates the thermal camera and thus
maintains high measurement accuracy.

BLACK BODY
 The thermal stability of a black body is a critical parameter, which
determines the uncertainty of the entire metrology chain.

THANK YOU FOR YOUR ATTENTION

Non-contact temperature measurement at the time of coronavirus – screening of febrile conditions

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Non-contact temperature measurement at the time of coronavirus – screening of febrile conditions