IR-based Detec­tion of Elev­ated Body Temper­ature for Coronavirus, SARS, Ebola

The body temperature preferably is detected at the inner angle of the eye with the infrared camera. Slightest differences and thus abnormal body temperatures can be displayed and will result in alarms. Performing such health screenings, e.g. via implementing temperature checkpoints for example for employee screening, enable the acquisition of important information as a basis for decision-making for subsequent medical examinations of the selected people and thus serve to secure public areas.

Such indications must, of course, always be followed by other examination methods that allow a reliable positive or negative statement about the disease and to initiate appropriate actions!

THERMAL-CHECK at a Glance

• Reliable detection of persons with elevated body temperature

• Compliance with data protection guidelines: no collection of biometric data or ID cards, no comparison with personal registers

• Screening of several people at the same time, even when moving, with consistently high measurement accuracy

• High-resolution, repeatable measurement technology thanks to high geometrical and thermal resolution with at least (640 x 480) IR pixels for absolute precision

• Camera can be used flexibly for other measuring tasks, e.g. in research and development, quality assurance, etc.

Which Advant­ages Does the InfraTec Solu­tion also Offer When Detecting Elev­ated Body Temper­ature?

• Contactless and planar temperature measurement without external reference radiator

• Parallel checking of multiple people is possible, faces at different heights (children for example)

• Having the largest number of pixels our system can screen multiple people at the same time, faces at different heights (children for example) or distances from the camera. Only the high number of pixels gives you the same reliability over a larger field of view as required in the specifications for the size of the optimal measurement area according to IEC 80601‐2‐59

• Resolution also of smaller areas of the skin (angle of the eye) from a safe distance

• Up to ± 0.3 K measurement accuracy due to adjustable temperature difference thresholds using the reference image algorithm of the THERMAL-CHECK software

• Excellent thermal resolution of up to 0.02 K

• Display and evaluation in real time

• Reliable temperature measurements based on low noise infrared detectors and precision calibration

• Alarming at surpassing temperature thresholds

• Storage of individual settings for detection of elevated body temperature

• Easily installable all-in-one unit for continuous monitoring of persons and groups of people

• Solutions for stationary and handheld use available

• Fitting to larger external digital displays via HDMI*

Down­load flyer about IR-based health meas­ures

How Is the Ther­mo­graphic Screening Proceeded?

The thermal camera and software are ready for use in just a few steps. Here, measurement distances, which result from the device configuration, have to be kept exactly in order to avoid errors during screening itself and thus to be able to achieve a reliable result.

3. Powering Up the System

• Turn on the thermal camera approximately 30 minutes prior to use for optimal equilibrium

• Connect the thermal camera to the computer (included in the scope of delivery depending on the package) according to the instructions

• Start the THERMAL‐CHECK software

Ther­mo­graphic Screening for the Detec­tion of Elev­ated Body Temper­at­ures in Detail

Certainly, thermal cameras can neither detect a virus itself nor whether a person is carrying a virus! However, these cameras enable the precise non‐reactive, contactless measurement of surface temperatures while using the technical temperature measurement technology known as thermography or thermal imaging. Hence, they are highly suitable for the quick and easy detection of elevated body temperatures, which can be an indication of a possible virus infection. Such indications must, of course, always be followed by other examination methods that allow a reliable positive or negative statement about the disease and to initiate appropriate actions! The term "detecting a fever" in the sense of a (medical) fever diagnosis is actually not permitted as a designation for the above‐mentioned thermographic recording of elevated body temperatures with thermal cameras under strict observation: One reason is that fever is a complex medical phenomenon. The other reason is that, from a purely formal point of view, the cameras used are “only“ technical measuring devices and not medical diagnostic instruments.

Thermography systems measure surface temperatures based on the emitted heat radiation, for example the temperature of the human skin surface. However, this is different from the internal body temperature, the so‐called body core temperature. The temperature of the skin surface depends on the ambient temperature (summer, winter, direct sunlight, and so on). In addition, a light film of water can produce evaporative cooling due to perspiration. Furthermore, beards, haircuts, face masks, etc. cause many areas of the skin on the face to be optically "covered" and the heat radiation cannot reach the camera unhindered. Thus, the skin surface in most parts of the face is rather unsuitable for reliable and repeatable thermographic temperature measurement.

A) Requirements for the geometrical resolution of thermal cameras

Since the regions to be measured each have a dimension of approximately (3 × 3) mm² (0.014 square inches), a high spatial resolution of 1 mm2 (1 mm is 1/25 of an inch) (size of a measurement pixel on the object to be measured) is required to reliably avoid measurement errors caused by geometric factors.

• A sufficiently large field of view is necessary to capture people of different heights without the need to constantly move the camera. This requires a certain minimum number of measurement pixels or minimum detector formats. According to IEC 80601‐2‐59, the detector of the thermal camera must have at least (320 × 240) measurement pixels, whereby the face of the test person must be covered with at least (240 × 180) pixels (here approximately 56 % of all measurement pixels). In this case, the camera would have to be repeatedly moved by hand or people would have to get on and off a step in order to be able to take a measurement.

• Considerably higher flexibility is offered by more powerful thermal cameras with considerably more than (320 × 240) measuring pixels. These enable a sufficiently large field of view (FOV), for example to take thermographs of several people at the same time. This also ensures that the facial area or the eyelid angle of each individual subject is still filled with enough measurement pixels to have a good measurement in a reasonable time.

In order to meet the criterion of high spatial resolution required by the international standard, InfraTec offers the following preferred configurations (assuming 20 cm (8 inches) to be the width of the face being screened):

This overview illustrates that with larger detector formats, there is more flexibility with regard to the number of persons that can be screened at the same time and their height (for example, (1.5 ... 2) m ((4.9 … 6.6) feet)), without having to constantly reposition the camera to meet the criterion of the required spatial resolution. To achieve more flexibility with regard to different person sizes it would also be conceivable to tilt the camera by 90° to get more pixel in the vertical. The measurement distance can, of course, be further reduced within the bounds of possibility in order to improve the spatial resolution. However, the field of view will then become correspondingly smaller and the demands on the lateral placement of the test persons will increase. The angle of incidence, which determines the relationship between the measurement distance and the field of view size, can be varied by selecting the IR lens. Compared to telephoto lenses, standard InfraTec lenses offer the advantage of a larger field of view as well as a larger depth of field, which makes it easier to keep the permissible tolerances of the measurement distance, thus ensuring a smoother screening process and higher throughput. The correct distances of the person to the lens of the selected camera can be taken from the values in table columns A and B. With the VarioCAM® High Definition, two persons can be screened at the same time due to the larger field of view (important: additional partition wall absolutely necessary).

Legend

1 Thermal camera on tripod

2 Distance from the camera to the person

3 Horizontal field of view of the camera

4 Position of the person/two persons (only possible with partition wall using VarioCAM® High Definition with XGA resolution)

5 Portable partition wall (matt) for shielding from interference radiation from the environment

B) How accurately can thermographic systems be used to measure an elevated body temperature?

Usually, absolute temperature measurement accuracies of thermographic systems are specified to ± 2 K or ± 2 % under the assumption of black body measurement and to ± 1 K or ± 1 % for very good systems. This measurement uncertainty is related to the operating temperature range of the camera, which is often specified as (‐20 ... 50) °C / (‐4 … 122) F. In room temperature environments and in restricted measurement ranges, they are much more precise (up to ± 0.8 K in HiPrec mode), but not as accurate as, for example, contact thermometers.

Solutions from InfraTec with optimised measurement accuracy: Comparative analysis, for which InfraTec systems are ideally suited, is one way of further improving measurement accuracy. With the help of the innovative thermography software THERMAL‐CHECK the moving average or median of the measured temperatures of the inner eyelid angles of the last for example 10 test persons without detected increased body temperature is continuously determined and used as a reference. This is based on the fact that test persons with elevated body temperature are a rare exception, whereas inconspicuous test persons include the objectively occurring environmental variations to which all test persons are subject in the reference. In addition, the user (operator) defines a temperature threshold of for example (1 ... 2) K above this reference value, and if this temperature threshold is exceeded, a corresponding message or alarm is issued. This comparative analysis has proven to be very robust under practical conditions. If a person should have a correspondingly higher temperature, this is reliably detected (up to ± 0.3 K accuracy). This method can be practiced with InfraTec's high‐quality thermal camera series VarioCAM® High Definition without additional aids such as reference temperature radiators.