Many companies in India have become reseller or seller for Thermal Imaging camera for fever detection in India and there seems to be lot of confusion/doubts about choosing the right product/solution for their requirement.
Buying tips for Infra Red Thermal Camera for body temperature detection
Here is few tips which may help people choose the right product for their requirement:
Continuous mass screening – In this screening, many people walk in lobby of hotel, malls etc. where people do not walk in a single file. It can also be a case where workers enter into a factory in multiple lines. In this, Thermal Imager Camera with visual camera a face detection would be suitable.
One by one voluntary checking – Most probably, this is the screening system which will fulfill most requirement in India. Office goers entering the office one by one, either in single line/queue or multiple lines/queues or different entry gates.
Here, a person can stand in front of Fever Detection device, gets her body temperature measured looking at the thermal camera an proceed if green lighted. Here, both Thermal Camera based fever detection system or Pyrometer based fever detection system can be used for each gate or queue.
Now the technical part. What should be minimum technical specification of thermal camera or visual camera ?
For mass screening, thermal camera should have minimum 0.5 degree accuracy in measuring temperature. Also, ideally more resolutions, better the camera, but thermal camera should have minimum 384X288 Pixels resolution.
We recommend at least 640X480 pixels for mass screening for an area of 8 meters by 6 meters from distance of 1 meter to 9 meters from the Thermal Camera, assuming the thermal camera has 12mm lens. While use of black-body may increase the accuracy of the measurement by 0.1 or .2 degrees, but it may not suitable to keep them in the open.
For one by one voluntary screening, most probably, pyromter based screening will be good enough or low resolution thermal camera like 80X80 pixels should be good enough with same accuracy as above. Most probably, the visual camera or normal camera does not matter much here except that it should have minimum resolution of 2MP.
Origin of the product : Due to lock-down and COVID19 situations, most probably, it will be good idea to buy thermal imaging systems or any product made in that country, ie for India, one should prefer Make In India mainly due to transportation/support uncertainty.
Integration with other system : Ease of integration with other systems like attendance system, display system should be considered while buying a fever detection system. So, any thermal camera manufacturer with strong software development team which can provide software integration support should be preferred.
Finally, a Fever Detection System is essentially an temperature measurement system, not a camera system. So, one should check the background of the company which makes thermal imagers if they have experience in making radiometric thermal cameras.
Few Optical Parameters one should know about Thermal Camera
While thermal camera or thermal sensor has many important technical parameters which will determine its accuracy of temperature measurement, there are some optical parameters which one should know to determine its real world usage.
Like a normal camera, Thermal Camera also has very important component, lens which will influence the temperature measurement. I will be trying to list and explain those optical parameters one should know or consider while selecting a thermal camera for specific application
1. FOV ( Field Of View) : This is one of the widely known or mentioned optical parameters or specification mentioned in any thermal camera. It can be considered as an window or a solid angle through which electromagnetic radiation will enter into the sensor of the thermal camera and the size of the window is the “field of view” of the camera for that distance.
Now, it should be evident that, as its an angle, it will get wider and wider as it goes far from the sensor. This angle of view is dependent on focal length of the lens, longer the focal length, narrower the angle of view is and shorter the focal length, wider the angle of view would be.
But the FOV is not dependent fully on the focal length of the lens, but also the sensor or detector size and its pixel pitch as well as its pixel count, both horizontally as well as vertically.
Normally, for a same pixel count, if the pixel pitch is greater, it will have greater FOV than the one with smaller pixel pitch.
Normally, all thermal camera manufacturers provide FOV calculator where one can select the camera model and compute the FOV on selection or focal length or compute the focal length requirement on selection of FOV requirement.
2. Spot size or Pixel Size At Range : This is a very important parameter for any real world, practical applications of any thermal camera of any size and shape. This will greatly impact usefulness of the thermal camera in measuring temperature.
Spot Size or Pixel Size can be defined as the real world size of the measuring object ( or portion of the measuring object) one pixel of the sensor would represent in real word measurement unit, in millimetre. For example, if a thermal camera of resolution 384X288Pixels with pixel pitch of 17micron, uses a 13mm lens, then the spot size or one pixel will represent a real-world size of 5.7mm at a distance of 4 meters from the thermal camera.
It means that, a Thermal Camera with 384X288Pixels resolution and 17mm Pixel Pitch will be able to measure temperature of object whose minimum size is 5.7mm if the object being measured is at the distance of 4 meters from the Thermal Camera.
Any object which us smaller than 5.7mm will not be measured accurately as its evident from above. Though, in practical world, I think, anything less than 11mm object will not be measured or represented well by that thermal camera.
To explain it more, size of human face is say 120mm ( W) X 160mm ( H). In order to measure this skin temperature of human face, if one uses a thermal camera with 384X288Pixels with 17micron pixel pitch and 13mm lens, if the person stands at a distance of 93 meters, one pixel would represent the whole face of that person at a lucky moment!
And if the person stands at 10 meters from the thermal camera, his face would be represented by some 11X16Pixels matrix! So, in order to measure skin temperature on face of a person, it would be advisable to stand within 10 meters of the camera in its FOV, then only a reasonably satisfactory accuracy of temperature measurement can be expected!
I have tried to explain FOV and SPOT Size in simple language and examples, but I am not sure if I have been helpful enough! I will try to write better next time!
With above two optical parameters, one should be able to select a right thermal camera for their applications. The right resolution and pixel pitch, right lens. In my next post, I will try to explain NETD in a thermal sensor which greatly effect resolution, image quality of the thermal camera!
What is Thermal Camera ?
“What is thermal Camera” could be a quite tricky question! A general perception is, a Thermal Camera is that camera which can “see in the dark” as there is temperature in the dark, though no light, while normal visual camera has capability to capture image when there is “light”.
Most probably, this definition of explanation should be good enough for ‘normal people’ who do not want to be overwhelmed by jargon of a geek
Can Thermal Camera really detect fever ?
With COVID19 pandemic affecting almost whole of the world, demand for thermal screening devices or thermal imagers have recently skyrocketed.
Thermal Cameras are being used to detect fever or elevated body temperatures in a person while entering a building, office premises of a factory.
But the question is, can thermal camera really detect fever, a medical condition in human body ?
A thermal camera can measure temperature or any object and that is all they are supposed to do. So, when they measure temperature of human body, they will measure temperature of their uncovered portion of the body.
Normally, face, neck, hands and feet remain uncovered and thermal imager can measure temperature of these areas automatically when they come in the field of view (FOV) of the thermal camera.
Now if one sees medically, a fever is measured using a thermometer in the arm pit, inside ear or inside mouth and also some other areas which remain covered.
So, in practice, it seems impossible to detect fever as a thermal imager will measure temperature of the human skin only.
Now next question would be, how accurate are the measurement of thermal imagers are! Before COVID19, most thermal imagers had accuracy of +/-2 degree C accuracy.
But post COVID19 pandemic, the accuracy of thermal imagers have increased to +/-0.3Degree C. So, one can safe, Thermal Imagers are now accurate enough to detect fever provided it gets to measure the right area of the human body!
Are Thermal Imagers useful in fever screening ?
I would say, it is very useful for the following reasons:-
It is already difficult to infer fever or any medical condition for that matter without licensed medical practitioners.
Thermal Imager is supposed to sense temperature in human body and it does well in that.
Based on the temperature provided by Thermal Imager or Thermal Scanners, its upto the competent authority to decide the next course of action if anyone has high body temperature.
Its not practical to read temperature of everyone by a medical practitioner one by one, as its very time consuming, risky for the medical practitioner as well as contrary to social distancing, a tool to fight infection. Measuring human body temperature using Thermal camera is automatic, fast, accurate.
Human intervention is needed only when elevated body temperature is detected.
If used with high resolution thermal camera and wide angle lens, a single thermal camera can scan a large area for any one for high body temperature. When used with a visual camera, this could identify the person with high body temperature for further investigation.
Using thermal camera is easy as it is goes with normal business process. No training is needed. Also software with thermal cameras can have many report and analytics which is helpful.
So, my personal opinion would be, thermal imager should be the first step in isolating person with high body temperature for further investigation. Thermal Camera is the only tool right now which can help screening large number of people.
This is particularly useful to screen people to enter factories, building or office premises. There are not many such fever detection systems, but post-Covid19, most thermal imaging companies have developed such fever screening systems.
Thermal Camera or Thermal Sensor ?
Since its called “Thermal Camera”, a normal person or a newbie in “thermal imaging” world, might think this equipment to be a camera. While the end result is an “image”, thermal cameras are actually sensors, which senses heat.
So, most probably, “Thermal Camera” could be a misnomer while “Thermal Sensors” could be the right word instead of thermal camera.
Thermal Camera is surely made in camera style in construction as well as components.
It consists of lens, a sensor as well as other parameters just like a normal camera. It differs from normal camera in two ways:-
The sensor of thermal camera senses “heat” of objects while sensor of normal camera senses “light”. To be more technically correct, a common Thermal Camera will sense 700nm to 1400nm ( part of IR spectrum) wavelengths while a visual camera will sense from 400nm to 700nm ( also known as visual spectrum).
Because of the above ‘sensing’ of different wavelengths, a thermal camera can never a “color image” while a visual camera can never produce image in dark.
Apart from above two main differences, both uses lenses with different aperture, focal length based on their applications. A thermal camera will have lenses which allows to pass their spectrum, ie 700nm to 1400nm to the sensor, while a visual camera uses lens which allows to pass visual spectrum.
Other parameters like focal length, aperture remains same for both as well as their operation.
A thermal image can have “color pelleting” where one color may denote one temperature. Else normally, thermal camera will display a grey image, where lowest temperature will be dark while highest temperature will be white.
Both thermal camera and normal camera will have number of pixels. For example, 384 X 288 Pixels, 1024 X 768 pixels. Now a days, even a camera in a mobile phone comes in very large pixels, like 48 MP or more.
But the meagre 384X288 Pixels in a thermal camera is considered quite adequate.
If a Thermal Camera is used just for imaging ( ie night vision camera), then it could be easy to put mroe pixels in it, but if a thermal camera is used for radiometric ( measurement of temperature), then having more pixels means more computation and data representation. As every pixel in it will carry a temperature information.
So, most probably, if a thermal camera is used in radiometric application, it would be more meaningful if tis called Thermal Sensors while if its used for night vision, it could be a black and white camera!
Thermal Camera had been very expensive a decade ago and like every technology, its price has come down and its usage increasing. Previously, Thermal Camera used to be very expensive (some thermal cameras are still very expensive), but some thermal imagers have become affordable to industries.
It is still in very nascent stage, specially in developing countries like India while it has found decent usage and application in developed countries.
Thermal Imaging Cameras have been used mainly as night vision camera and as non-contact temperature measurement system.
While pyrometer has been around for long time as non-contact measurement system and it has been doing pretty good itself, but over the period of time, larger area were needed to be monitored for temperature profile. So, I assume, thermal camera came to market.
Thermal Camera Body Temperature
With COVID19, requirement for thermal camera seems to be exploding world wide, rightly so.
Automated Body Temperature Measurement by Thermal Camera should been mainstream for long time now. Elevated Body Temperature is one of the most visible symptoms for many diseases. Fever is a symptom not only for COVID19, but also for common flu, infection apart from so many others.
But using just Thermal Camera may not be suitable for usage, specially where the requirement automatic fever detection while entering a building or a factory. Because thermal camera images can not be used for face recognition.
So, most Thermal Camera Body Temperature measurement system comes with both thermal camera and visual camera.
This Thermal Camera Body Temperature systems can detect elevated body temperature from multiple people at the same time. It can also recognise the faces of detected person which helps identifying people with fever automatically. It saves crucial time for identifying a person with high body temperature, also it can help spread of infection.
Pyrometers with Visual camera can also be used similar way to detect temperature of one person at a time. Such products tend to be less expensive as well as help social distancing, which seems to be one of the key factors preventing spread of COVID19.
Most probably, this could be the most efficient solution for many small and medium enterprises. Its fast, its accurate and it can be integrated with existing attendance system.
Worldwide, it looks like governments will enforce Body Temperature Detection using Thermal Camera or any other IR sensor for factories, commercial building, malls,conference rooms, hotels etc.
Thermal Camera industry will get the much needed push to grow. It will also become mainstream, I think, from being exclusive products for industries and military.
With growing demand, its prices will also come down making it more affordable. So, I can see, some eco-system will develop around thermal camera soon.
Visual Camera in Body Temperature Detection System
Almost all “premium version” of elevated body temperature detection system available in the market seems to have both visual and thermal camera in it. I think, main reason to put this visual camera is to identify the person without any human intervention in case he or she is detected with elevated body temperature.
While, this argument may not hold true if she is wearing a mask or veil, but still it can give some desirable features to elevated body temperature measurement system
Both the Thermal Camera and the visual camera are places in such a way that their field of view ( FOV ) overlap each other so as to detect the face using visual camera while sensing the temperature using the thermal camera.
The visual image will be used to detect a face, then this face area will be identified in the corresponding thermal image. Then the temperature of that area will be measured using the thermal camera.
While this sound pretty neat arrangement, but it may introduce few challenges too. For example :-
- Both thermal and camera have to be aligned such a way that they have maximum overlapping area.
2. Aligning both camera may not be very easy if both the cameras are of different resolution and sensor size. Normally, thermal camera have lower resolution than the visual camera.
3. The pitch size of the sensors of thermal and visual cameras also differ.
4. The resolution of thermal camera should be much higher than the thermal camera.
5. It may introduce a minimum working distance as they require overlap zone, unlike single thermal camera system which just have minimum focus distance.
This kind of dual camera system offers one advantage, that is automatic face recognition. Apart from that, I do not see any other advantage though. Auto face Recognition may help it become attendance system too. But then, RF ID based attendance system can blunt this advantage.
Personally, I will always prefer single camera system which has just the thermal camera or thermal sensors like LTE-384F, which is tripod mountable. As for attendance, I would use RF-ID based proximity card.
With visual camera, some people may have privacy issues too, specially if such system is installed in public places.
Having a visual camera is surely a nice feature as visual cameras are not very expensive. With visual camera, the elevated body temperature detection system becomes a complete solution with temperature detection, face recognition system.
Thermal Camera as Night Vision Camera
Thermal camera is being increasingly used a “Night Vision” camera and rightly so. Night Vision has much wider real world usage/application then “con-contact temperature measurement”.
Thermal Cameras of Thermal sensors are capable of doing both. And as for developers point of view, using thermal camera as night vision device is much simpler, and faster to manufacture or calibrate too.
When a Thermal Camera is used as a night vision device, it does not require to measure temperature. So, the temperature calibration, compensation and related processing is not required.
It makes life of a Thermal Camera manufacturer or developer much easier. All it has to do is, provide corrections and produce an image as sharp as possible.
Temperature Measurement requires sharp image before temperature is computed. So, if a thermal imaging camera is used as “Night Vision Device”, It works just like normal camera, with either fake color palette or black and white images.
It will still require ambient compensation to produce “good images”, but it still becomes much simpler to operate for the thermal imaging camera.
Normally, when a thermal imaging camera is used as “night vision device”, it can have lenses with long focal length. For example, it may have 50mm, 75mm, 100mm, 150mm, 200mm or even 300mm.
With long focal length, it can see further and further. Its generally accepted that, any thermal imaging camera using LWIR ( 8-14 Micron Wavelength) can “see” scene upto 15KM with suitable lens in un-cooled operation. Longer focal length lens could be very expensive.
Cooled Thermal Imaging cameras can have longer distance, but are normally more expensive and takes longer to start.
Using thermal cameras as night vision devices have one main advantage, that is, its non-intrusive. Unlike traditional night vision devices, which normally uses image intensifiers and IR rays ( invisible to human eye, but visible to camera or IR detectors) to illuminate scene can be detected.
As thermal imaging cameras use emitted IR from the scene objects to “see” scene, its impossible to detect if it is being monitored.
Another advantage is range. It can see longer than other traditional night vision devices by using lenses with long focal lens.
This is one of the reasons why Thermal Cameras are being increasingly used as gun-sights. With thermal camera based gun-sights, a shooter or a sniper can use his weapon both day and night.
Hunting ( illegal in India as well as many countries) weapons also use thermal imaging based night vision device which gives them night hunting capability. Also, forest officials use them to count wild animals during night time when nocturnal animals become active.
In future, we hope to see increasing usage of thermal camera as night vision device.
Fever Screening Tender Specification in India
Recently, I came across a tender specification of which says smart thermal camera with real-time video and body temperature screening system which made me think about body temperature screening systems being sold or deployed in India.
Here is the screenshot of the tender document which outlines the specification of the “Body Temperature Screening System”
Body Temperature Screening
The specification number 1 and 2 makes sense as they are going to be useful for record keeping as well as any future analysis.
While all thermal cameras can detect hot spot, I am not sure what is the requirement of the connecting it to mobile or tablet while I can understand it could be connected to TV, smart or otherwise!
Specification 4 asks for power backup which is understandable again, but I wonder why should a thermal camera have 128GB of SD card built into it! While I am not aware if any thermal camera can work independently as body temperature screening system without PC based software!
Specification 6 says, provision of mobile based application! I am not sure how can a mobile process thermal camera data and generates alarms real time. Or why should one use Mobile Phone for a Body Screening devices while there are options of using industrial grade PCs or any other similar rugged equipment ?
Specification 7 Now says about CMS software ( I am assuming CMS stands for Camera Management Software) which can access multiple cameras over LAN! Well, All thermal Cameras normally have either Ethernet or USB. And any Industrial Grade Thermal Cameras will have Ethernet connectivity!
The specification 8 beats me! Why do you need a two way communication in thermal camera ? I can understand the specification 9 though!
Now this specification does not mention anything about technical specification of thermal camera or anything technical requirement for body screening! That the Thermal Camera has to be capable of temperature measurement with certain accuracy! This specification is absent altogether! While this specification must be the main technical specification for any body temperature screening system!
Assuming, this body screening device will be used for elevated body temperature detection during this COVID19 time, this technical specification should have mentioned about temperature measurement. and accuracy of measurement which should be at least -/+0.5 Degree C.
Without this requirement in the thermal camera, most probably, this body screening device is not only an eyewash, but it could also put people at risk!
I think, government agencies or offices should consult thermal camera specialists or companies for required specification for elevated body temperature measurement systems.
Minimum Technical Specification For Human Body Temperature Screening System
Technical specification for human body screening system in India, I thought I would try to put up specifications which are minimum technical requirement for such systems. It may not be complete and totally exhaustive list, but I think this could be good enough to start with.
- It should be dual camera system ie It should have both Thermal Camera and Visual Camera. Why ? Because : Thermal camera is to measure human body ( face skin) temperature measurement and the visual camera for face detection. Face Detection and Face Recognition are two different thing altogether and should not be confused with one another. Automatic face detection helps identify the person who has high body temperature.
- Thermal Camera resolution must be 384X288 Pixels or higher, Why ? While Thermal Cameras with both 80X80 pixels and 160X120 Pixels may be able to detect high body temperature in a human face which is of approx 8-14CM width and 10-17CM in height ( just a general figure) with suitable length, but 384X288 Pixels will out form and offer more flexibility than 160X120 Pixels / 80X80 Pixels ones. Higher resolution Thermal camera require at least 1GBPS Ethernet which may be expensive.
- Thermal Camera should be able to measure temperature from 20 to 50 Degree C.
The accuracy of temperature measurement should be minimum +/- 0.5 Degree C without black body (Reference Object with a black surface of fixed temperature) and should be +/- 0.4 Degree C with a Black Body.
This specification simply says that, the measured temperature error could be upto 0.8 Degree with black body and upto 1 degree without black body. This accuracy should provide enough indication of a person who has high body temperature which may require further medical investigation to ascertain presence of fever.
Very important to note here is, all industrial Thermal Cameras had normally accuracy of +/- 2 Degree C before pre-covid19 era! Also, this accuracy should be maintained at ambient temperature from 20 Degree C to 50 Degree C, depending on the location where the Human Body Temperature Screening is being deployed.
In open area in northern India like an entry gate in a power plants ( or any othe rplants), factories, the ambient temperature could rise upto 45 Degree C during days and goes below 25 Degree C. But while installing inside air conditioned airport building, malls, office entrance , it could be pleasant ambient temperature at 28 Degree C or less.
- Operating Temperature should be from 0 Degree C to 50 Degree C and it should be customised depending on area/location of deployment. The accuracy of the Thermal Camera should remain same.
- Certificate of temperature measurement accuracy from an NABL ( National Accreditation Board for Testing and Calibration Laboratories) Accredited laboratory should be a must. Without this, most probably, the temperature measurement would be just an eyewash and could put people at risk.
- Thermal camera should have spectral range of 8014 Micron and should have NEDT less than <40mK at f1.0, 30 Hz 300K. This specification is an indicator of the temperature measurement accuracy. It could be cooled or un-cooled.
- Lens FOV ( Field Of View) for thermal camera should be around from : H:22 to 50 Degree V: 18 Degree to 40 Degree.
- Visual Camera should be industrial grade as normally all thermal cameras are of industrial grade. It should have at least 1.3MP so that face detection or any other image processing becomes easier.
- Both these cameras should be housed in a proper enclosure ( preferably IP65) so that they have same over-lapping FOV which will be the measurement area.
- Thermal and Video camera should have preferably Ethernet connectivity so that it can be monitored from a distance or videos could be taken to a control room with ease.
- PC based Windows or Linux Software which is capable of live video display, or optional face detection, saving image and temperature data and generate alarms when any high body temperature, say 37.5 Degree C is detected.
- The software should have configurable emissivity option. This could be important when people wear heavy make-up on face. It is good idea to have face detection facility in the software but that is not a must.
- Black-body is a desirable and should be useful in an airport, malls etc. It may not be very useful for plants, factories without arranging proper shade for it.
I have tried to mention some technical specification for human body temperature screening system here and I welcome everyone to add their desirable or expected specification in the comment section.
I welcome any suggestion to improve this post in the comment section!