What kind of camera should I use?
Infrared Measurement is an ideal and simple solution for many demanding temperature measurement applications. The most difficult challenge people face is choosing the appropriate equipment and knowing how to use it properly. Aside from the thermographer, equipment is the greatest limiting factor in performing an infrared inspection and using incorrect instrumentation can significantly impact the accuracy of your infrared data.
There are no industry standards that govern the design or manufacture of thermal imagers, and prospective buyers are totally reliant on the information contained within sales brochures to determine if a piece of equipment is suitable. Manufacturers will suggest applications the equipment is suitable for, but they cannot guarantee that you will operate the camera under the conditions necessary to gather accurate data. It’s fair to say that many sales brochures are designed to appeal to the widest audience possible (to maximize sales), and often this information can be unreliable when it comes to choosing the correct equipment for your application.
When choosing equipment it is important to seek information and advice from qualified and certified professionals. Do not simply rely on what other’s tell you, as there is a great deal of misinformation when it comes to the use and application of thermal imaging equipment. Few people have formal training and the simplistic nature of the operation of a cameras leads to much misinterpretation (see training requirements).
Always consult a professional thermographer.
The following is a checklist of important camera attributes that you should understand before selecting equipment for your intended application. Price should be considered last, as a decision based on price alone may result in the purchase of equipment that is completely ineffective for your application. For your application you need to consider the following:
- Resolution and Spot Size
- Thermal Sensitivity
- Temperature Range
- Special requirements: Frame Rates, Camera Capture Speed, Real Time Video, Indoor/Outdoor Use, Screen Size and Image Display, Lenses, Memory Storage/Capture speed, Battery Operation Time
- Servicing and Support
For thermal imaging systems, one of the most critical specifications to be considered is resolution and spot measurement size. Spot size is a specification that pertains primarily to quantitative thermography. If you intend to present temperature measurement in your reporting and analysis, your camera’s resolution and resulting spot size is of ultimate importance.
Spot size will vary between different models of imagers and it cannot be changed. Although spot size is primarily a quantitative issue, it is important to understand its importance prior to purchasing an imager or prior to capturing data that may be quantitatively analyzed in the future.
When attempting to measure temperature, spot size determines a radiometer’s ability to accurately measure temperature. Spot measurement size is defined as the area from which temperature data are derived. This is a combination of an imagers detector resolution, detector pitch size, lens angle and proprietary measurement algorithms. Spot size is NOT determined by display crosshairs, laser dots, etc.
Detector Resolution is the principal determinant of spot size, as the greater the number of measurement points equates to a higher density of measurement points over a given area. Of course it is only part of the equation, as the lens angle and manufacturer’s image processing programming will determine the actual spot size over a given area.
Common resolutions include:
120×120 = 14,400 measurement points (very basic resolution)
160×120 = 19,200 measurement points (low resolution)
320×240 = 76,800 measurement points (professional resolution)
384×288 = 110,592 measurement points (high resolution)
640×480 = 307,200 measurement points (very high resolution)
Speak to a qualified professional about your target size, distance of measurement and determine the appropriate spot size for your target.
The following recommendations serve as a general guide only. Please speak to one of our qualified thermographers (hyperlinked to Contact Us page) before deciding what is appropriate for your application.
The smaller your target the more resolution you will need.
The greater the distance from your target, the more resolution you will need.
Accurate temperature measurement requires the correct spot size for the target and for measurement accuracy, the spot size must be smaller than target area.
It should be noted that it is impossible to compensate for incorrect spot size. Spot size must be appropriate at the time of measurement and/or at the time of image capture. When spot size is larger than the target, the imager will measure the target and the area beyond averaging the temperatures of both together. In some cases, this can produce temperature values that may be inaccurate by hundreds of degrees.
Low Voltage Electrical Distribution
Low Voltage Distribution presents us with target sizes as small as 2.5mm (think about the smallest target you will need to measure). As such we need to plan our measurement capabilities on the lowest common denominator, and our spot size needs to be less than 2.5mm.
A common and acceptable resolution for this application is 160×120, which generally provides adequate measurement at 1 meter distance from a target this size. It may be possible to use a 120×120 resolution camera with an appropriate lens, although this resolution is quite low and not ideal for this application.
A professional thermographer would seek 320×240 resolution or higher for both measurement and aesthetic consistency. Typically a camera of professional resolution will allow us to measure the same target from a much greater distance, and the image quality overall is much higher allowing thermal patterns to be more easily observed.
High Voltage, Overhead Networks, Substations
With power transmission and distribution our greatest challenge is the safe working distance from our target. Usually these applications will require us to be several meters from our target 5, 10, 15, 20 meters, and in some cases our target size can be as small as 40mm (think about the smallest target you will need to measure). We generally would not consider resolutions less than 320×240 for this application and in some cases telephoto lenses will be required.
Building Sciences, Energy Loss, Moisture, Pest Management
This is a broad industry sector and the applications can range from quite simple to very demanding in terms of your equipment requirements. For most domestic applications 160×120 resolutions are sufficient. Where this resolution becomes a limitation is with larger objects or buildings (ie commercial buildings, roofing, car parks, multilevel construction), where greater areas and distances are involved and more resolution will be required.
From this thermographer’s perspective, a more important consideration is the Thermal Sensitivity, (hyperlinked to below) which is supported by the fact that most camera manufacturers will develop these models with the lowest sensitivity possible.
Mechanical and Rotating Equipment
Mechanical and Rotating Equipment such as pumps, motors, bearings, conveyor systems, hydraulics, etc are the least demanding in terms of resolution requirements. They are generally large in size, and we can get quite close in proximity (usually within a meter or two). As such most of these targets can be imaged with the lower resolution cameras, such as 120×120. In some cases, equipment may be placed in hard to reach locations (elevated) or protected by safety barriers and we may be forced to work at much greater distances. This will require higher resolutions and you will need to anticipate your access to equipment before selecting a camera.
Energy Loss, Refractory Integrity
The inspection of large vessels for energy loss or refractory/insulation integrity usually requires the use of high resolution cameras (ie greater than 320×240). This would include targets such as lagged pipelines, ductwork, steam pipes and traps, furnaces, ovens, boilers, chimney stacks / flues etc. In most cases we have to work at considerable distances from the target, and despite the object being quite large, often the target (area of interest) may be quite small. For example consider a large chimney stack. While the stack may be several meters in diameter, we may be trying to identify a missing insulation brick only centimeters in size. Cracks in vessels may only create very small localized temperature patterns which will require very high resolution.
Thermal Sensitivity is an often overlooked objective specification. The number is small, and seemingly insignificant, but has major implications to image quality and measurement capabilities.
Most uncooled cameras will have sensitivity of around 0.1°C. This is considered average. The better uncooled sensitivities are less than 0.08 and the worst are closer to 0.2°C. Thermal sensitivity has a large impact on image quality as it results in either a crisp (good) or noisy/grainy (bad) image.
From a measurement perspective, higher sensitivity means we will see more temperature variation within a narrow band of temperatures.
Those applications which benefit most benefit from a high thermal sensitivity include building sciences, veterinary/medical applications, and professional thermographer’s who need quality definition in their imaging.
The lens size or angle will have a great impact on your equipment’s measurement capabilities. The angle of a lens will determine the cameras the Field of View (FOV), and this is extremely important in determining a camera’s resolution. The lens angle will determine the concentration of pixels over a given area, or in other terms the pixel size at a given distance. It is important to understand the resolution requirements of your application so you can choose appropriate lens sizes. Make sure that your camera’s standard lens (equipped with from factory) will have a satisfactory FOV for your application.
Bear in mind, not all cameras have optional lens systems that can be changed in the field. Before choosing or purchasing a camera, it is important to know whether it has an interchangeable lens system. Being able to choose from a variety of field changeable lenses can greatly expand your measurement capabilities, and this flexibility can potentially save a lot of time and money.
Standard Lenses, those most commonly installed from the factory are designed to appeal to the majority of applications which the camera will be used. The standard Fields of View (FOV) are generally between 20° and 26°. A 20° lens will concentrate pixels more closely than a 26° lens and as such will have greater resolution. This is of course preferred for applications where the target is small or the distance is greater. Conversely, in instances where the target is larger, or we need to work more closely a wider angle lens is preferred as we are able to fit more of the target in our Field of View. Cameras aimed more towards the electrical maintenance markets tend to have narrower field of views (for improved measurement accuracy), whereas cameras aimed more towards the building science/maintenance industries will tend to have a wider field of view (where we need to see more of the target, and are less concerned with temperature measurement).
As the name suggests, wide angle lenses increase the field of view. Most wide angle lenses are between 36° and 60°. This has the effect of increasing the view of the target. Compared to a standard lens, the viewable scene increases, the pixel size increases, and the concentration of pixels decreases. This is preferred when imaging in confined spaces or imaging large targets. This effectively reduces the (spatial) resolution over the target, reduces quantitative (temperature) measurement capabilities , but can increase qualitative aspects. Building sciences, pest management, material inspection and energy loss are typical applications that would benefit from the use of wide angle lenses.
Narrow Angle Lens (Telephoto)
As the name suggests, narrow angle lenses narrow the field of view. Most telephoto lenses are between 6° and 12°. Typically this has the effect of magnifying the view of the target. Compared to a standard lens, the viewable scene decreases, the pixel size decreases, and the concentration of pixels increases. This is preferred when measuring small components or targets over a large distance. This effectively increases the spatial resolution on the target and improves quantitative (temperature) measurement capabilities. Power Transmission and Distribution (overhead networks), large conveyor systems, aerial or vehicle surveys, refractory (chimney) surveys, and surveillance are the applications that most benefit from the use of telephoto lenses.
The temperature range and span of each range can vary considerably between models. While some imagers can measure up to 2000°C, most entry level models will only measure up to 250°C. Most professional cameras will measure in the range of -20 to 600°C or higher. Many cameras designed for building sciences or veterinary work, may only measure as high as 100°C, therefore making them unsuitable for electrical and mechanical applications.
As prices progress, so does the temperature range. The first thing to be sure of is that your camera is capable of measuring the desired surface temperature of your target. Be aware that the “optional” temperature ranges quoted in brochure will only work if the camera was ordered with this function. This option is specially added to the camera during manufacture as it generally involves the addition of filters and special calibration process. It can be quite expensive (depending on the range required), so it pays to make sure a camera has a desired range before purchase.
There may be some performance trade-offs with a specific temperature range. Typically narrow ranges improve image quality, while broad ranges can diminish a camera’s sensitivity. Also, a camera’s range may be “split” over several ranges. For example a camera with -20 to 600°C capability, might have 3 ranges to achieve this. ie -20 to 120, 100 to 300, 250 to 600. Where the concern may arise is if you needed to view a target that varied in temperature between 150 and 400°C. With the above set ranges you would be unable to view the target seamlessly in 1 single range, instead having to use range 2 and 3. This would make analysis in a single image impossible. You cannot measure a temperature outside a given range. Again it pays to speak to a qualified consultant.
There are many applications which will have special needs with respect to the operation of a camera. The following are examples where the physical characteristics of a camera are important.
Frame Rates, Camera Capture Speed, Real Time Video
Cameras capture images at a variety of speeds. Many entry level cameras are NOT real time and will blur when looking at moving targets, or when used in a scanning motion. Generally entry level cameras are less than 10Hz (10 frames per second), and must be used while stationary, on stationary objects.
There are many applications where a faster frame rate will be required, otherwise the image will be blurred and distorted. When monitoring rotating or moving equipment, or when the thermographer themselves is moving (walking or in a vehicle), you will need a faster frame rate. Higher speed frame rates are usually above 30hz, with the faster rates at 50 or 60Hz.
If you have an application which occurs in a very short time interval, ie less than a few seconds, then you will also need to consider video capture in real time. This is where a camera is able to gather several seconds or minutes of streaming video (usually at 30 frames per second), and can then break each frame down individually for analysis. This is mostly found in
high end professional cameras With this kind of application you should definitely seek the advice of a seasoned professional who has performed this kind of measurement.
Indoor or Outdoor Use
If you are going to use your camera outdoors then special attention should be given to the type of viewing options the camera provides. Most external LCD screen are adversely affected by Sunlight, so much so, that they are virtually impossible to see in bright sunlight. Many entry level cameras provide some kind of sunshield which slide over the screen to form a protective tunnel. This is a crude but relatively effective remedy for short term use. Some models do offer a day bright screen, which is specially lit to provide better viewing in outdoor elements. These are also quite effective, but the best solution is an internal LCD or CRT viewfinder otherwise known as an eyewell.
This solution is found in most professional cameras which offer both an external :LCD screen for indoor use, and an internal viewfinder (eyewell) for use outdoors in Sunlight. If you perform extended work outdoors, the latest internal viewfinders offer low radiation OLED (organic LED) viewfinders which make it much more comfortable for use over long periods of time.
Screen Size, Onscreen display and Image Display
There is a great variety of screen sizes and display resolutions, and the appropriateness of each is completely up to the end user’s personal preference. Screen sizes are measured diagonally across the screen and will range from as small as 2 inches to 5 inches. Subjective characteristics to keep in mind when looking for an appropriate screen size are:
Can I see the screen properly?
Am I able to read all the small numbers clearly. Can I see the difference between an 8 and a 0 ?
Can I see sufficient detail in the image (ie for high sensitivity applications).
What is it like outdoors?
Bear in mind that in general, the larger the screen the higher the power consumption. If long battery life is an important factor having a smaller screen, or perhaps energy saving (screen saver) functions will be of benefit.
Is there enough information on-screen?
The amount of data represented on-screen is also an important consideration for many applications. It may be important to have specific data in front of the operator at all times. Information such as the emissivity, image range, temperature range or filter, hot seeking cursors or other temperature related information may need to be instantly recognized by the operator.
Why does it look better on the camera than on the PC?
Always bear in mind the image display is usually NOT the same as the detector resolution. In most cases (especially when larger screens are in use), the image will be enhanced or digitally increased in size to be presented on the camera’s screen. Many 160×120 native resolutions (detector) will be enhanced to 320×240 or 640×480 on the rear screen of the camera for display purposes. This only serves to aesthetically enlarge the image and has no effect on measurement capabilities. Often this enhancement is not carried through to the software, whereby the image will open in it’s native format. It pays to always compare the on-screen performance to the downloaded image to avoid getting a false sense of image quality. How the image looks in the PC software will be the best representation of how it will look for the customer when you prepare the report!
Software should be one of the most important selection criteria for any infrared thermography system, yet most times it is overlooked or at best, an afterthought. The report (output) is the most important part of any infrared survey, and the software is the primary means of generating that report.
The most important thing to realize is that each camera can only be used with the software provided by it’s own manufacturer. You cannot simply open any infrared image with any software. Manufacturer’s specifically design their software to meet the needs of their target audience. That may be for professional thermographers, plant maintenance personnel, building inspectors, or research fellows and medical practitioners. Software designed for scientific research may have excellent analysis capabilities, but it’s reporting function for electrical distribution surveys may non existent. As such, trying to manage large volumes of data from switchboard surveys may be extremely time consuming and prohibitive with such software. Conversely, software designed for high volume data collection may be ineffective for mapping the surface areas of large surface material objects (like in the building industry). Software, like cameras varies greatly, and it choosing the appropriate software is just as important as the hardware.