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Non-contact infrared thermal imagers for mass fever screening (Part 2 of 3)

How to tell whether the infrared thermal imager system is a good one?

Thermal imager system is comprised of following components:
  • Thermal imager (Infrared), usually the one with a smaller lens.
  • Visual camera (RGB), usually the one with a larger lens.  
  • An image processing unit, similar to a DVR/NVR in CCTV system 
  • Black body radiator (or black body radiation source) is a box-size powered device which provides a constant K number for thermal imager to compare and provide a close to accurate absolute reading
  • A display and alert system is same as what a security system should have.

Technology is evolving fast, components manufacturers are competing with each other by keeping upgrading their resolution, processing speed and shrinking the size. Each component has its own core technologies. 

Thermal Imager 
For commercial applications, uncooled thermal imager is commonly used, graded by a number called NETD (sensitivity, the lower the better) and the resolution pixel number; e.g. 160 x 120 or 320 x 240 pixels, the higher number gives higher cost. 

NETD (Noise Equivalent Temperature Difference), in mK unit (1000th K), is the number correlates to the distribution of background noise (standard derivation); the smaller number means smaller  +/- tolerance of measured temperature. 

The K measurement from thermal imager refers to the K compares with the background environment which is also changing. That is why they need a known temperature as a reference in order to provide an absolute temperature reading. This reference can be provided by a Black body radiator. 

This black body radiator source provides a very simple function, a steady K usually set at 37.5C in real practice, yet comes with a very expensive price which is almost the same as the thermal camera. 

Image processing unit
Image process unit (IPU) is just a small computer with a combo of hardware and software to processes the digital signals from thermal and RGB cameras, recognizes the human parts, performs thousands of IR data statistics on each pixel per second, encode/decode, and correlate both images together. 

The best option is to have this program can be running on an embedded system placed inside the camera body with conventional digital video outputs directly to display, but there are lower-cost systems that run on a rugged PC outside. The former is more reliable, plug and play and independent on the PC environment.

The cost of a thermal image system is way more expensive than an IP CCTV camera system is because of this IPU. It requires super-fast processing power and a mathematical model to process these two digital signals. The complexity is far beyond the typical encoding/decoding function of what typical video chipsets provide. 

To deal with this vast amount of temperature and pixel data and patterns, each manufacturer of this system has its own IPs as the core technology. And here comes the novel use of machine learning. 

CPU, GPU, and now NPU (Neural Processing Unit)
Since the outbreak of SARS in 2003, manufacturers have been developing a proprietary machine-learning algorithm or deep learning by NPU or infrastructure developed by Intel, Huawei, etc. Having the intelligence developed in the camera, so-called edge computing, can save a lot of cost by using entry-level PC. It does not rely on a powerful external PC with expensive high-end CPU/GPU to provide an acceptable response time. This is a very important concern especially for multiple cameras with high-res dual-lens (IR and RGB) cameras.


Non-contact infrared thermal imagers for mass fever screening (Part 1 of 3)

Since the outbreak of Coronavirus, people have been advised to refrain from work or school, and minimize social contact, wear masks and be vigilant to hand hygiene. Other than those health workers and medical professionals, there is a lot of people taking risks going to their workplace to keep this city running.

Early detection of fever people (febrile people) and segregation is a must to prevent the spread of infectious diseases (COVID-19 or influenza) in workplaces or schools.

The best method will be a test kit per person, to perform an accurate screening, daily before going to work. However, it wouldn't be possible in any future.

According to the news reports and CDC reports, coronavirus cases come with high fever and dry cough, though not all. Elevated body temperature is one of the possible warnings of coronavirus.

How to enforce a body temperature check in your premise?

How to enforce a body temperature check for every visitor before they are entering public transports, buildings, factories, and schools?

There are different methods to check the temperature; they also come with different "normal body temperature".

  1. Mercury thermometer
  2. Infrared ear probe thermometer 
  3. Infrared forehead thermometer  
  4. Infrared thermal imaging 

Guideline of thermometers

What temperature you are measuring?

Fevering people have a higher core (body) temperature which simply refers to the blood temperature in brain and heart. While the mercury thermometer (oral method) remains the most accurate method and best reference to body core temperature of all, it is impossible to use this as a screening measure.

Infrared ear probe thermometer is simply not an effective way due to the close-contact of operators, the use of consumable, and the lack of accuracy due to many reasons.

Skin temperature can be measured at a distance by using infrared sensors in both handheld and camera settings. Infrared forehead thermometer measures forehead skin temperature may provide a slightly better accuracy reading if it is performed by a well-trained staff and regular black-body calibration.

Still, it is still far from practical to have students/workers lining up in rush hours for a forehead scanning; exposing the staff to have close contact is also a problem.

The final solution goes to Infrared Thermal Imaging

Infrared thermal imaging is widely adapted since the SARS outbreak in 2003, it measures multiple points of skin temperatures, at a distance up to 5-10m. The sensitivity has been greatly improved by both using better sensors and better algorithms or models since the data captured is huge.

By passing through a thermal camera, without stop by any counter or even slow down, hundreds of data points samples are taken on visitor's forehead, face, hands, legs, and any exposed skin. It is unnoticeable by visitors.

Infrared Thermal Imaging is well-proven and reliable

An uncooled infrared thermal imager can easily take over 50 readings/sec over 384 x 288 pixels, which is a 5.5M data/sec.

More data points mean machine intelligence can work out all the statistics throughout the whole human body to provide the best estimate to the true core body temperature.

The A.I. training model can be trained by the numerous sample on both body readings and surroundings at every minute to offset any change in environments.

Surveillance camera companies are now providing a wide range of infrared thermal imaging solutions to the market.

This is why Infrared Thermal Imaging counters are commonly seen in airport arrival halls during the outbreak of the diseases.

(IMPORTANT NOTE: You can only ever measure the temperatures of the surfaces with a thermal imager; you cannot look into something or through something.)