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A thermal imaging camera is an instrument that takes pictures of objects which show the amount of heat is being emitted from it. These devices share the same hallmarks as a conventional digital camera except that instead of using visible light they use infrared light.
Infrared energy (heat) is emitted by every object that has a temperature above absolute zero (-273.15°C / -459.67°F). The amount of energy is directly related to the object’s temperature, so as the temperature of an object increases, the amount of infrared energy emitted rises as well. A thermal imaging camera is able to take visual image of this infrared energy which the human eye is unable to detect.
A thermal camera detects infrared energy and then converts it into electronic signals. The electronics within the camera then processes these signals and converts them into a visible image which appears on the unit’s display screen or viewfinder. Not only will an infrared camera capture an image of the infrared energy emitted by an object, but it also performs temperature calculations using the same principles as an infrared thermometer. During processing, colors are assigned based on temperatures to allow users to clearly identify the different range of temperature readings.
Known as thermography, it allows users to make non-contact measurements of an object’s temperature while at the same time displaying and storing a visual image that shows heat distribution across an object or scene.
Thermal imaging cameras are also known as thermographic cameras, infrared imagers or infrared cameras and were initially developed in the 1950s for military application. At that time they were bulky systems in part because the technology required the devices to be filled with liquid nitrogen for cooling of the detector system. The classified nature of the technology and the prohibitive expense left infrared cameras out of reach for civil and commercial applications until the mid-1960s.
The development of uncooled detectors, a lowering in prices and the advancement of infrared viewing technology has seen the availability and application of thermographic cameras expand quickly. The versatility of infrared cameras have been further enhanced with the development of advanced optics and sophisticated software interfaces.
While an infrared thermometer can measure the temperature of a single point on an object, an infrared camera can scan and measure temperature distribution over a large area and can measure multiple temperatures within an entire image. The cameras provide a total view of any situation and include instant tools and functions to be able to diagnose and analyze the full extent of problems.
In all other respects, the advantages of a thermal imaging camera are similar to that of an infrared thermometer. Their primary benefit in many applications lies in their ability to accurately and safely locate problems in electrical and mechanical systems prior to failure. Locating and fixing potential problems before component failure saves valuable time and money in terms of preventing manufacturing downtime, production losses, fires or other critical failures.
Thermal imaging cameras are the only diagnostic technology that allows a user to instantly visualize and verify heat distribution which makes them an invaluable device across many industries.
Select Features Of A Thermal Imaging Camera
There are a wide-variety of infrared cameras available to suit any application and almost every budget. Ranging in price from a few hundred dollars to in excess of $80,000.00, the functions and features obviously vary from model to model. The functional requirements and intended application for each user will largely dictate which model is best for their particular circumstances.
It is important however for a consumer not be dissuaded by the significant variances in price. The capabilities of a thermal imager in terms of temperature range, accuracy and thermal sensitivity do not typically change significantly from one model to the next. The quality of the image produced is often the difference between a lower-end model (in terms of price) and a premium one. Improved image quality does not automatically provide improved accuracy or thermal sensitivity which for most users are going to be the essential qualities of their cameras.
An in-depth review of some of these important factors to consider before buying a thermal imaging camera are discussed further in this guide. The following however is a summary of some of the main features available in various models and other functions which may be considered desirable
Resolution / Optics
Most infrared cameras have fewer pixels than normal visible-light digital cameras. Higher resolution cameras can measure smaller targets from farther away which can be an important factor where, due to safety considerations resulting from significant temperatures or hazardous environments, images need to be taken at a distance from the actual object. Resolution is discussed in further detail below as it is an important factor for users to assess prior to purchase which will largely be dependent on their intended application and budget. Of particular importance however is to distinguish between detector and display resolution. The most important factor to consider is the detector resolution.
Various models do allow for the addition of telephoto and wide angle lenses as options for added versatility increased zoom and field of range. As a general rule however the best recommendation is for consumers to buy an infrared camera with the highest detector resolution that their budget allows as these optional lenses can be quite expensive.
Image Type / Video Operation
By their very nature, the main function of thermal imaging cameras is to be able to take an infrared image of an object or scene showing the amount of heat being emitted and relevant temperature measurements.
Most models however also include a digital camera that will automatically capture a normal visual image of an object or scene as well as an infrared image. This allows users to be able to easily identify and show others precisely what the object contained in the infrared image is . Other models allow users to be able to overlay a normal visual image over an infrared image and/or have picture in picture capabilities.
As with large range of visual light digital cameras, certain models of infrared imagers come with the ability to record video in infrared. Such a feature is not considered standard across all models, but is available subject to an individual’s requirements and budget.
Laserlight / Backlight / LED light
Most thermal imaging cameras come with a single laser pointer allowing a user to specifically target the object that needs to be measured/captured. It is important to note that often the laser pointer is offset from the camera itself so that it may not always represent the exact center of the resulting image. The laser dot will not appear in the infrared image, but for those models which allow for normal visual pictures to be taken, the laser dot will be visible.
A backlight is generally considered standard so that the LCD display is visible if working in the dark or dimly lit environments.
An LED work light to illuminate a work area is one feature that will be of particular benefit and importance for those applications where the camera will be operated in low-light environments.
In comparison to infrared thermometers where emissivity is either fixed or adjustable, infrared cameras allow for manual adjustment of emissivity. For those unfamiliar with emissivity, it is a very important factor in infrared technology that can influence the accuracy of temperature measurements. A more detailed explanation on emissivity and its impact on infrared technologies such as thermal imaging cameras can be found here.
Thermal imagers make an adjustment to take into account these factors via the emissivity settings to ensure that accurate temperature readings are obtained.
Certain models of cameras also have a feature which allow users to compensate for reflected background temperature. In environments such as a factory where there may be several pieces of machinery in operation (all in close proximity to one another and all emitting heat), the temperature reading of one machine may be influenced by the heat reflected from the others. Such a feature would therefore be important where very precise temperature readings may be required.
Compass / GPS
A common feature of infrared cameras is an in-built compass which automatically adds the camera pointing direction to images for inclusion in reports.
Similarly, some models come with a GPS function which allows geo-location data to be automatically added to each image to enable objects to be easily identifiable. This would be of particular benefit for applications within a large factory or other setting where multiple pieces of machinery are being monitored and it may be difficult to identify the specific individual object from the image alone. It also assists in those applications where reports need to be submitted to third parties.
Technological advancements in wireless connectivity in recent years has allowed certain models of thermal imaging cameras to be able to connect with mobile phone and tablet applications to enable images to be viewed online and for ease in sharing critical information with third parties without users needing to leave the field. Such a feature would be of benefit for those applications where prompt off-site analysis and reporting of results are important.
More advanced models allow for bluetooth connectivity to other test equipment which can allow users to quickly review and record multiple parameters immediately. Live video streaming and remote control operation of the camera via a mobile device are other features generally reserved for high-end models.
Voice / Text Annotations
One useful feature of some models of infrared cameras is the ability to make voice and/or text annotations for each individual image. The ability to add machinery part names, plate numbers or initial findings by audio or text avoids the requirement for users to carry paper and pen on the job to record critical information. This can be a great time saver and assist with the accurate and timely recording of findings.
Those units with voice annotation capabilities have a microphone in-built to the unit to allow for voice annotations while other more advanced models have optional headsets that can be connected for this purpose.
Image Processing Software
Each model typically comes with its own image processing software enabling:
- the generation of further temperature analysis – allowing temperature measurements at different points in any image, calculation of maximum, minimum or average temperatures from within a set area within an image, profiles, histograms and isotherms
- changes in image coloring – image can be colored in accordance with different palette options (some palettes are more suitable for specific applications)
- changes to functional settings such as emissivity or reflected background temperature
- general image enhancements including zoom and filtering
- editing of text and voice annotations
The above are examples of a few of the primary features available with many post-image processing software depending on the individual functions of the thermal imaging camera itself. The accompanying software can often be overlooked by consumers and while the features of a camera unit should be the foremost consideration of a prospective buyer, the imaging software should not be neglected as it can add another dimension in the use of the images from an analysis and reporting perspective.
Factors To Consider Prior To Purchase
One of the more important features to take into account prior to purchasing an infrared camera is the range of temperature measurements it is able to take. High-end models offer a range of between -40°C to 2000° C (-40°F to 3632°F) while more inexpensive models can reasonably expect to measure temperatures between -20°C and 250°C (-4°F to 482°F).
A camera that can measure temperatures of anywhere up to between 500°C and 650°C (932°F to 1202°F) is likely to be adequate for the vast majority of heavy-duty professional applications.
Depending on the intended application, the thermal sensitivity of a particular model can be an important factor when considering what infrared camera to buy. Thermal sensitivity refers to the ability of an infrared camera to display a high-quality image even if there is low thermal contrast in a scene. In other words, a camera which is highly sensitivity can better distinguish objects in a scene even where there is very little temperature difference between them.
The lower the thermal sensitivity, the more accurate temperature measurements the camera is able to read. It will also produce more detailed images. Those cameras which have very low sensitivity specifications will show more color / temperature differences and can increase their accuracy as well.
Thermal sensitivity specifications can range from between sensitivity specifications range between 0.25°C and 0.05°C. For most inspection and engineering applications, thermal sensitivity of 0.1°C is likely to be more than sufficient, however it will ultimately depend on individual circumstances.
A more detailed explanation of thermal sensitivity is provided further in this guide.
There are deviations between different manufacturer’s and models, but as a general rule there are three resolution standards with infrared cameras:
- Low Resolution – ≤ 160×120 (19,600 pixels)
- Medium Resolution – 320×240 (76,800 pixels)
- High Resolution – 640×480 (307,200 pixels)
Pixel resolution on thermal imaging cameras is therefore considerably less than a standard digital camera. As previously mentioned, image quality does not influence the accuracy or thermal sensitivity of a camera. For certain applications and users however this is going to be an important consideration.
Since the highest resolution available is relatively modest when compared to digital cameras, users of thermal imaging cameras will almost always print and display the full resolution. For those applications where high-quality images are essential, pixel resolution will become an important consideration. One benefit of a camera with a higher resolution is the ability to zoom into an object while maintaining good image quality. This will be of particular importance where a user needs to take images of objects from a significant distance.
Thermal Sensitivity Explained
The thermal sensitivity of infrared camera is a factor which influences the accuracy of the unit. It is generally measured by a parameter referred to as Noise Equivalent Temperature Difference (NETD) and measures the smallest temperature difference that an infrared camera can detect in conjunction with the electronic circuit noise from the unit itself.
Those cameras with an NETD which is low are able to detect the smallest temperature differences between objects in an image and provide higher resolution images with increased accuracy. The ability to detect even the smallest of temperature differences is important in most thermal imaging applications. At its most basic, the camera will be able to “see” more in all of the circumstances.
Thermal sensitivity is measured in milliKelvins (mK). Those cameras with values at the lower end of the scale are more sensitive. Values generally range between 0.25°C (250mK) and 0.05°C (50mK). Cameras with a specification of 0.05°C (50mK) are twice as sensitive as a camera with 100mK. The bottom line is that those infrared imagers which have a lower sensitivity rating will be more accurate and are able to show more colors representing the relevant temperature differences.
Applications for Thermal Imaging Cameras
As the technology becomes more affordable, the applications for thermal imaging cameras continues to grow. In a relatively short period of time these diagnostic tools have become compact and lightweight with a model in most manufacturers ranges that will suit the budgets of most users
To a large extent, thermal imagers are much like a conventional camcorder and digital camera and are simple to use. Some background knowledge of the technology and features of the unit (many of which are described in this guide) will however certainly assist users to be able to make the most of their camera and obtain optimal performance.
The following is a list of typical applications for thermal imaging cameras. It is not an exhaustive list by any means, but gives a good indication of their growing popularity.
Building and Construction
- locate services on site
- detect missing or deficient insulation
- determine ingress of moisture in roof, insulation and walls
- detect faults in electrical components
- inspect solar panels on rooftops
- fault finding in supply lines
- detect blocked or broken pipes
Electrical & Electronics
- assist in inspections and identifying hot spots/failures of:
- electrical equipment
- mechanical equipment
- heating/cooling equipment
- fuse boxes
- battery banks
- circuit breakers
- inspect equipment when under load and look for differences between like components under similar load conditions
Inspect and detect failures in mechanical installations such as:
- conveyor belts
- For the detection of people in search and rescue operations
- See areas of heat through smoke and darkness during a fire (both body heat and source of fire)
- Spot smouldering fires inside walls and other hot spots
Detection of viruses such as SARS and Ebola and diseases such as breast cancer and arthritis.
The future for thermal imaging cameras and their applications are bright. As an example, BMW has recently introduced thermal imaging cameras into certain models of its vehicles in an effort to reduce the rate of accidents during nighttime driving. Advances in renewable energy technologies have also seen an increase in the use of infrared diagnostic technologies with solar panel, wind turbine inspections and other related applications.
While the cost of infrared technology has, until recently, largely left thermal imaging cameras outside the hands of the regular consumer, this is fast changing. Some of the applications listed below can be equally used within the home or in small business and not just by professionals within large-scale industry.
As the costs of thermal imagers continue to decrease it can be expected that additional applications and a new set of consumers will readily take up the benefits that these diagnostic instruments can provide.