sFecrveeer n ing
The Coronavirus epidemic has created a worldwide demand for infrared
cameras as fever screening tools. Explaining how to be sure that the camera
chosen can actually do the job is Glenn Wedgbrow, business development
manager at sensor manufacturer Micro-Epsilon UK
Viral epidemics such as the
By Adam Offord
current Covid-19 have
created a global demand for
infrared (IR) cameras that
are able to screen for a fever
condition in humans. Many businesses
have, or are considering, the installation
of appropriate fever screening systems
to protect their most important assets –
people. Now that staff and employees of
some companies are allowed to return to
work after protective measures have been
lifted, it is vital for these companies to
ensure that their health is not put at risk
by people who have been infected with
the virus.
A key part of any automated fever
screening system is an infrared (thermal
imaging) camera. This should be easy to
integrate into a fever screening system,
which can then be used in real-time at
point-of-entry into establishments, such
as factories, warehouses, offices, public
buildings, supermarkets, airports and
schools, to prevent people with elevated
body temperatures entering.
The basis for the effectiveness of
thermal imaging cameras as a fever
screening tool lies in the correlation of the
outside skin surface temperature with the
internal or core body temperature. And
there are two main approaches to fever
screening:
● Crowd-based fever screening: The IR
camera monitors a crowd of people at
once or sequentially. Assuming that the
majority of the measured maximum head
temperature values are coming from
healthy individuals, the exceptions with
an elevated body temperature can be
detected.
● Individual fever screening: Primarily
used at security gates and controlled
entrances, the IR camera is used to
measure people, one at a time. The Medial
Canthus (tear duct) provides the strongest
correlation between outside skin
temperature and core body temperature
and is measured more precisely from a
close distance. The tear duct is located
in both eyes in the corner next to the
nose, where the upper and lower eyelids
meet. This ‘hot spot’ is ideally suited as a
measurement point. This measuring range
has a diameter of approximately 3-4mm.
ACCURACY
With numerous IR camera suppliers
out there to choose from, it is
important to select a camera that is
fit-for-purpose, reliable and accurate
for the specific application. Most IR
cameras with a spectral response of
8-14 μm (micrometres) are specified
with an accuracy of ± 2°C or 2% of the
measurement reading, whichever is
greater, based on deployments in industrial
environments in a wide variety of ambient
conditions from 0°C to +50°C.
Many IR cameras are being promoted
today as offering accuracies of ± 0.5°C or
better. However, these accuracies cannot
be achieved without the use of a black
body reference source. The source needs
to be stable, have high emissivity and
should be positioned in close proximity to
the person to be scanned (normally, the
black body is wall-mounted and placed
directly behind the person to be scanned).
By doing this, camera uncertainties
resulting from device adjustment, ambient
temperature drift and short-term stability
can be reduced and a system accuracy of ±
0.5°C (with a confidence interval of 95% or
better) can be achieved.
Having accurately measured external
face temperatures, an IR camera-based
screening system's real value is in the
ability to determine which readings are
significantly higher than those in a given
population that are exposed to similar
ambient temperature conditions.
In order to achieve the best possible
measurement results, the following factors
should be considered before deployment: 1Use a camera with a spatial resolution
of 382 x 288 pixels or better and with
a NETD (noise equivalent temperature
difference) of 80 mK (milliKelvin) or better. 2Combine the camera with an external
black body reference source. The
accuracy of the measurement can be
increased to ± 0.5°C.
MANUFACTURING/FACILITIES – FEVER SCREENING
40 www.operationsengineer.org.uk Autumn 2020
/www.operationsengineer.org.uk