Choosing an IR Camera
Which equipment specifications should you consider before you buy?
Over the past few years there have been big breakthroughs in the market for thermal imagers—not to mention that prices have dropped considerably. Infrared (IR) cameras are also finally being designed with the end user in mind. Advances in technology and materials get a lot of credit for this, but it once seemed that the comfort and sanity of the operator was an afterthought when it came to the camera’s form factor and menu layout.
The reality is that today’s imagers are also lighter and easier to use. Ten years ago, you really could not find a new, full-featured imager for much less than $20,000. Today, there are many fantastic choices out there with a wide range of features for building applications. Even better, the ideal thermal imager for today’s building thermographer does not necessarily need to be top of the line or the most expensive. Whether you’re a home performance contractor, weatherization crew member, or energy auditor, there are even fine choices in the $2,000–5,000 range that will certainly meet your needs.
Before You Buy
Complex as some systems may seem, all IR cameras are comprised of the same basic components: lens, detector, processing electronics, display, controls, and power supply. You’d never guess that, however, if you were to take a quick glance at a typical technical data sheet for a camera.
Thermal imager specification sheets can be confusing and difficult to understand. Some features, such as thermal sensitivity and detector size, are useful in evaluating performance, but a data sheet is not going to tell you how the camera functions and feels when you are in the field. If you are considering purchasing any type of IR camera, be sure to try it and compare it to other models before you buy.
There are a number of factors to consider in addition to cost and after-sales service. Please keep in mind as you read this that The Snell Group is vendor neutral. We do not sell equipment, nor are we a subsidiary of any IR camera manufacturer.
Equipment Specifications to Consider
Here we’ll summarize which equipment specifications are important for you to consider and which ones are not. Ultimately, it is you who will know best which camera is the right one for your job. For a list of definitions, see “Infrared Equipment Glossary.”
Thermal sensitivity. For building work, this is perhaps one of the most important specifications to evaluate. Be certain that your thermal imager is able to resolve temperature differences of 0.1°C or less on a surface. This ability is often stated as 100 milliKelvins (mK) on the specification sheet. The smaller the number, the better (that is, the more sensitive) the system. Strong consideration should be given to cameras with even lower thermal sensitivities, such as 70mK (0.07°C). A handful of 40–50mK (0.04–0.05°C) systems are also available and provide fantastic image quality and clarity. A better thermal sensitivity allows you to work more hours in a day and more days in a year. The lower sensitivities are capable of discerning the smaller temperature variations that are typically encountered in marginal inspection conditions (such as when the inside-to-outside wall surface temperature difference is low). In other words, the additional cost of improved sensitivity is an investment that can really pay off.
Instantaneous field of view (IFOV). The field of view (FOV) is a measure of the angular view path of what the camera sees. Usually measured in degrees, it determines the thermal imager’s overall viewing area and is defined by horizontal and vertical angles. For building inspections, an FOV of 20° x 20° can work well, but the actual lens size will vary by model.
The IFOV describes the spatial resolution capability of a camera. Simply defined, IFOV is the smallest target size an IR imager can discern at a given distance with a given lens and detector array. IFOV represents the size of the projection of a single detector through the lens onto the scene. It is usually specified in a camera’s technical data sheet as an angle of measurement in milliRadians or mRad. The smaller the mRad value, the tighter the angle and the better the spatial resolution of the imager.
Except for work on large buildings, spatial resolution is typically not a concern nor is it a limiting factor because we can easily move closer to increase resolution. The item to consider here, though, is what spatial resolution will you require? What is the smallest level of detail you are going to need to resolve at your inspection distances? What types and sizes of buildings are you inspecting? If your answer is mostly greater distances (where simply moving closer is not possible) or larger structures, a lower mRad value would be worth considering.
Infrared Equipment Glossary
Background or reflected temperature. The source of radiation that reflects off the target the IR instrument is viewing.
Detector array. An array that is composed of a number of individual detectors, typically 320 x 240 or 160 x 120 in size.
Emissivity. A measurement that describes a material’s ability to radiate energy by comparing it to a blackbody (a perfect radiator) at the same temperature. Emissivity settings range from 0 to 1.
FOV. Field of view, a measurement of the angle seen by the camera; the specification is typically given in degrees horizontal and vertical, such as 20° x 20°.
FPA. Focal plane array, an IR system that has an image-sensing device consisting of individual IR-sensing detectors at the focal plane of a lens.
IFOV. Instantaneous field of view, the smallest area that can be seen by the IR camera at a given distance. Also known as spatial resolution.
IFOVmeas. Instantaneous field of view measurement, the smallest area that can be measured by the system at a given instant.
Isotherm. A software function that outlines or highlights areas of apparent similar temperatures in the image.
Level. The position of the thermal span in the particular thermal range to which the radiometric thermal imaging camera is set. Similar to visual brightness.
Qualitative thermography. Thermal imaging without radiometric temperature measurement. It compares surface thermal patters, not temperature differences.
Quantitative thermography. Thermal imaging with radiometric temperature measurement.
Radiometric. The response of the detector to IR radiation is calibrated so that temperatures can be inferred from the amount of radiation detected. If a camera is fully radiometric, temperatures can be read anywhere in the image. Other cameras have only a center spot that is calibrated for measurement.
Thermal sensitivity. Typically listed in milliKelvins or one-thousandth of a Kelvin.
Visual image capture. A useful and common feature of many imagers is a built-in visual camera that captures a picture and links it to the saved IR image—a must for complete reports. If the camera has a built-in light to help illuminate the scene, that is a plus, too. Some visual cameras are better than others, but most will provide decent visual documentation to show where the IR image was captured.
You might also consider using a separate, high-quality, digital visual camera. The advantage of taking a high resolution visual image is that you can blow it up and zoom in to see essential details that might be missed while on-site. If, however, you also are planning to use these images for reporting, consider that it can take longer to create the final report as you spend time pairing up the thermal and visual images. That is time that eats into your bottom line, so it may not be worth the trade-off.
On some models, the visual camera has a picture-in-picture feature that shows a thermal view in the center of the display screen surrounded by a visual image that frames the IR shot. Be aware, though, that the alignment of the visual and thermal images is better on some models than on others. Manufacturers are using new parallax alignment techniques to help address this issue.
Voice or text annotation. Stand-alone digital voice recorders have been around for a while, but it is the integrated voice recorder built into the camera that allows building thermographers to work more efficiently. This facilitates note taking in the field, but can also expedite report writing back at the office. Since the voice file is tied to the captured thermal and visual images, all you have to do is open the file in the report software, play back your notes, and type them into your report. No pens, clipboards, or cumbersome stand-alone recorders to carry around. An integrated voice recorder also helps you to keep your notes organized. No longer will you have trouble deciphering handwritten notes, nor will you have to figure out what audio file goes with what thermal image, as you would if you were using a stand-alone voice recorder.
Some IR cameras have a text annotation feature, but these are not currently as flexible or useful as the integrated voice recorder. However, they can be helpful for basic note taking, especially if you set up the feature in the camera’s software before you begin the inspection. You can create categories and tag category labels to the images as you save them. But until cameras start coming with an on-screen keyboard, we think voice annotation is the way to go.
Image analysis and reporting software. Most IR cameras work with a free, basic software package provided by the manufacturer. With this software, you can typically perform simple image adjustments, add analysis and comments, export individual shots with adjusted temperature scales, change color palettes, and generate basic reports of multiple images at a time. You may find that some manufacturers offer a more robust software program at an additional cost, but these packages typically offer far more features than what is needed to generate effective reports. Also know that software will likely require that your computer have Word or Adobe installed as the report wizards generally export the final report file to one of these formats.
Size of detector array. This relates to the number of pixels or sensors on your camera’s detector. While the IR cameras available for building applications are a long way from the 5–8 megapixel visual arrays we are used to seeing on most smart phone cameras today, many of them are more than adequate for most building diagnostic work. More pixels generally mean greater detail. Excellent IR systems for home weatherization are now being made with 120 x 120, 160 x 120, and 320 x 240 focal plane arrays (FPAs). This translates to 14,400, 19,200, and 76,800 pixels respectively. FPAs smaller than 120 x 120, while cheaper, do not provide sufficient spatial resolution for building diagnostics and are not recommended. FPAs larger than 320 x 240 do produce an impressive image, but they are more expensive, and they are bigger than you need for most residential work. If, however, you are primarily inspecting larger buildings (multifamily units, high rise apartments/offices, or industrial facilities) the bigger array size is worth considering.
Ease of use. An IR camera must be simple and easy to use—image adjustment, focusing, and basic operation must be intuitive. This is an important point, one that is often overlooked. Avoid complicated menu systems. Avoid cameras on which the most frequently used adjustments—focus, level/span, and image capture—are cumbersome to execute. Pick up the camera and feel its weight. Could you hold it comfortably for an hour or two? Is it balanced properly, or is your wrist or arm strained? Does it allow for one-hand operation when you are in a tight space or have a poor viewing angle? Could you use it if you were wearing gloves outdoors in a cold climate? These are just some of the important questions to consider.
Image display. A high-quality LCD display screen is essential to diagnosing an image. The size of these screens varies considerably among cameras, so be sure to look at a couple of different models. Larger displays are helpful if more than one person is viewing an image, as when you are trying to communicate the problem to the homeowner, or training a crew member on the job. One downside to an LCD display screen is that it can be challenging to use outdoors on both sunny and cloudy days. Many manufacturers provide sun shields or visors that can be slipped over the display screen to help reduce glare. You will also still find some models that offer both an LCD display and a viewfinder. This is something to consider if you will be working outside more often than not.
Optional lenses. While telephoto lenses are not usually necessary for residential work, the option to add a wide-angle lens can be helpful for inspections in tight spaces. An indoor scenario would be one where you can’t view enough of a wall in a small bedroom without standing in the hallway. An outdoor scenario would be one set in a high-density residential neighborhood, where yards are small (or the spacing between buildings is tight), which limits the viewing distance. The ability to change lenses is worth considering, but know there is an additional cost and that not all cameras have that option.
Focus. Cameras come in several varieties, including Fixed Focus, Manual Focus and Motorized/Auto focus. Fixed focus imagers, while convenient, can have trouble with clarity when looking at objects either very near or far. Motorized/Auto focus cameras are nice for their simple function, which allows for quick, one-hand operation on some models. One drawback is that you might find it difficult to fine tune the image to your liking. Many thermographers seem to enjoy the control one has over image clarity with a manual focus where the operator is able to “dial it in.” This is something you need to test for yourself and is often a personal preference. There is really no wrong type of focus method as long as you get the right focus.
Batteries. In the past, most IR cameras did not last more than 60–90 minutes before they needed a fresh battery. Today, almost all new cameras on the market have run times that average three to four hours, or even more, depending on the model, on how it is used, and on settings such as the brightness of the LCD screen. Batteries may be either removable or built in. If you have a choice, we’d suggest an IR camera with a removable battery, for those long inspection days where one battery won’t suffice.
Image palette. Many thermographers prefer using either a grayscale or a monochromatic palette. Avoid working with a rainbow color palette in the field. A rainbow palette can make it difficult to focus and is not as intuitive as a monochromatic palette set to positive polarity, where lighter is hotter and darker is colder. When inspecting with a rainbow palette in the past, we’ve often found ourselves struggling to decide whether yellow was warmer than red, or red hotter than orange. Make it easy on yourself; less is more when it comes to colors.
Frame rate. Frame rate is measured in hertz (Hz); it indicates the camera’s ability to capture moving targets. The higher the frame rate, the better the camera’s ability to render and capture moving objects. Lower frame rates are less tolerant of movement and will blur the image if you pan across a scene too quickly. That said, 9 Hz systems have become widely available and can work just as well as 30 Hz and 60 Hz systems if you hold the camera steady. While the ability to capture moving targets is important for industrial thermographers who are inspecting certain types of rotating equipment (motor shafts, bearings, or couplings), it is far less important in building applications, where our targets are stationary.
Laser pointer. This feature is certainly not required, but the laser pointer can help to guide you visually around a room, giving you a general idea of where you are looking. While the laser does not necessarily line up with the spot temperature displayed on the screen, it can be useful if you like to see the place you’re pointing to on a wall or ceiling.
Image storage. Images are saved electronically either on a small removable Secure Digital (SD) or compact flash memory card, or on internal storage. All can work, but whichever one you choose, make sure you can download it to your computer. When considering a camera, think realistically about how many images you need to store before downloading. Most SD cards now hold at least 2 gigabytes—more than enough space for your typical inspection day. Digital radiometric video capture in MPEG4 format or something similar is starting to show up on some systems and will add another useful dimension to reporting and analysis. You will find a few IR cameras that also offer a composite video output. This is nice to have for conducting demonstrations with your thermal imager and LCD projector. With the right couplers, you can also record this feed to either a camcorder or a digital video recorder. Granted, the captured data don’t have radiometric or span or level adjustment capabilities, but these data are useful for some reporting needs.
Radiometric measurements. Today, most infrared cameras are radiometric in that they display a thermal image and provide apparent surface temperature measurements. Many come with at least one fixed temperature spot in the center of the screen. While the ability to record temperature values is typically not necessary for most buildings work, having at least one spot measurement can be useful.
The main problem we have with temperature measurements in building applications is that new thermographers often pay far too much attention to the temperature value and not enough attention to what the image is actually telling them. Not to mention the fact that temperature measurements can be fraught with error. In building inspections, IR is most often about qualitative differences on the wall surface (Is that area hot or cool?). The fact that the wall happens to be 72.3°F (22°C) at a particular point does not really tell you anything if you’re trying to evaluate insulation performance or air leakage. It is more about the thermal patterns that you detect on the wall.
Insulation and dew point indicators. These two features require data input from the user that may be inaccurate—making them potentially misleading and dangerous to use. The insulation indicator purports to locate areas in the building where there is inadequate or deficient insulation. The operator is directed to enter into the camera the outdoor temperature, indoor temperature, and insulation level percentage. The imager then calculates an insulation temperature value and places a colored isotherm over the suspect area on the display screen.
Infrared Standards for Building Inspections
In addition to proper training, all thermographers should be familiar with the following standards for conducting IR building inspections:
- ISO 6781. “Thermal Insulation, Qualitative Detection of Thermal Irregularities in Building Envelopes, Infrared Method” (www.iso.org)
- ASTM C-1060. “Thermographic Inspection of Insulation Installations in Envelope Cavities of Frame Buildings” (www.astm.org)
- ASTM E-1186. “Air Leakage Site Detection in Building Envelopes and Air Barrier Systems” (www.astm.org)
- RESNET. “Interim IR Guideline for Thermographic Inspections of Buildings” (www.resnet.us)
- Canadian GSB 149-GP-2PM. “Manual for Thermographic Analysis of Building Enclosure” (www.tpsgc-pwgsc.gc.ca/ongc-cgsb/index-eng.html)
- Canadian NMS Section 02 27 13. “Thermographic Assessment–Building Envelope” (www.pwgsc.gc.ca)
Our concern is that this feature does not take a number of variables into account. Ambient air temperature is by no means the only driver of heat transfer through a wall. The surface-to-surface temperature difference across the wall system is not the same as the ambient air temperature difference in many instances.
Also, does the thermographer understand what the state of heat transfer is through the wall? Is it steady state or is it transient?
Differences in the thermal capacitance of the building materials could be one reason. It is also possible that the temperature difference from inside to outside might have flipped during the day and not yet stabilized in the opposite direction. How about solar loading on the outside wall surface? What type of insulation is in the wall? What is its density? We feel these questions are not being sufficiently considered with this feature. This is why thermographers need to be trained to think critically during an inspection and not have a computer with limited information make the decisions for them.
With the dew point indicator, the thermographer enters relative humidity and temperature values. The indicator highlights points on the wall where condensation may be present or may form. We are also concerned this feature is overly simplistic; but more importantly, again it takes critical thinking out of the inspection process. While we’ve heard from some thermographers in the field that they find the dew point indicator useful, we strongly advise you to use either of these with great caution.
If you are considering buying an IR camera, The Snell Group is more than willing to help you through the decision-making process. Contact the authors by phone at (800)636-9820 or by e-mail at firstname.lastname@example.org and email@example.com.
Flir — www.flir.com/US
Fluke — www.fluke.com
Monroe Infrared Technology — www.monroeinfrared.com
Palmer-Wahl — www.palmerwahl.com
Testo — www.testo.us
Proper Training and Qualification
IR cameras may be affordable and easy to use, but you still need to be qualified to operate them properly. That includes having the right training and the right amount of experience. Thermographers who are qualified do better work, get better results, and work more efficiently. Unfortunately, as a few models have now broken the $2,000 barrier and prices continue to drop, some people are asking whether similarly priced IR training is still necessary. Our response? Well, anyone can buy a framing hammer. They too are easy to use and inexpensive, but it takes a skilled carpenter to know how to frame a wall correctly. The same is true with an IR camera. Just like an unskilled carpenter, you can do quite a bit of damage with a thermal imager if you use it improperly. Being successful with this technology not only requires great camera skills, but also an in-depth understanding of heat transfer, radiation physics, inspection conditions, and building science. (See “Infrared Standards for Building Inspections” for additional inspection standards.) Without a solid foundation in training and experience, expect to make mistakes. Some may be costly.
Infrared’s Bright Future
The number of choices today for a full-featured, inexpensive, IR camera is astounding. Now is the time to analyze your current needs and see if investing in one makes sense. Do your homework, look at—and try—several systems. You’ll be glad you did.
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