Diagnostic Tools-Thermal Imaging-The Basics

Thermal imaging is a wonderful tool that not too many years ago, was rarely used because of the high cost and complexity of the equipment.  Not the case anymore.  It’s still possible to spend tens of thousands of dollars on a high-end camera, but you can buy a decent unit for under $1000.  I own a very good camera I use all the time that retails for $600.  This blog post will cover the different cameras on the market and the terminology and other basic information needed to effectively use one.

Manufacturers and Types of Cameras

There are a few different manufacturers that currently sell cameras designed for construction and building diagnostics.  The most familiar is probably Flir, but others include Seek, Fluke and Hikmicro.  I currently own a couple Flir and a Hikmicro, my first camera was an Extech, manufactured by Flir, this camera didn’t have near the capabilities of my current cameras, and the cost of that first camera was more than twice that of my newest.

There are three common types of cameras used by the construction trades, the first two are handheld and the third is an attachment for a smartphone.  The more common handheld is one most people associate with thermal imaging.  It’s viewing screen is attached above a handle with a trigger that is used to take the photos.  Newer models have touch screens to change the camera’s settings, and some have adjustable focus and interchangeable lenses.  Prices for this style handheld camera range from a few hundred to nearly ten thousand dollars for a high-end, more advanced camera.

The second handheld camera looks similar to a traditional digital camera, about the size of a smartphone.  Their size makes it easy to carry and store, mine fits nicely in my pocket.  This is the camera I use for energy audits and building diagnostics.  Though they don’t have as many features as their bigger cousin, the newer versions have decent resolution and take clear pictures.  Most of these thermal imaging cameras cost under $1000.

The last camera is the highly portable smartphone attachment.  These very small devices plug into the phone’s charge/communication port and use an app to operate the device and the phone’s memory for storage.  There is no battery, power is supplied by the phone.  Different price points of these cameras yield different features.  Prices are typically under $500.

Things you need to know

Most thermal imaging cameras are pretty simple to use.  Pull it out of the box, charge it up (unless it’s the smartphone version) and you’re ready to take some pictures, but to get the most out of the tool, you need to understand what the camera can and can’t do.  It’s best to learn some of the terminology to effectively operate, study the many settings in the camera that can be adjusted to maximize the photos, and learn about the software tools available from the manufacturers that can help produce and edit the information of the image.  The best way to get the most out of the investment is to take a class.  There are several companies offering online, in-person and even on-site training.  Formal training can greatly reduce the learning curve.

The problems that can be identified by thermal imaging in the construction industry are; missing insulation, air leaks (works best when combined with a blower door), problems with HVAC, electrical or plumbing systems, and wet or damp areas, just to name a few.  (When diagnosing moister issues, it’s best to confirm the presence of moisture by backing up the thermal image with a moisture meter reading.)  If you have a problem that can be detected by temperature differences in various materials, thermal imaging can “see” the problem.

A thermal imaging camera works by detecting temperature differences.  To get a good image while performing a building diagnostic, it’s suggested that at least 10°C or 18°F degree temperature differential be present between inside and outside the structure.  (When looking for air leaks or missing insulation.)  When looking at a thermal image though, just a one-degree temperature difference can be seen.  An example of this is the handprint photo.

The small transfer of heat from my hand to the drywall took one second to produce this image.  Sometimes an area with large single temperature can drown out small warm or cold areas that need attention.  An adjustment called level and span can help tune the picture to bring out the small, hard to see areas in some thermal images.  (We will talk more about adjusting level and span in a bit.)  How well a thermal imaging camera can see will depend on the conduction of heat across or though the material being viewed.  How well a material conducts heat, and the temperature difference has the biggest impact on the image quality.

A good camera will not only indicate temperature differences using color (or grey scale, more on that later), but it will also measure those temperatures.  Many cameras have a temperature scale listing the high and low temperature in the field of view.  This scale is called level and span and can be automatically set, or the thermographer can set the scale manually.  In the images below, this scale is shown on the right of the thermal image.  There is also a temperature indicated near the top center of the image, this is the temperature at the crosshair of the photo.

Some cameras have a setting so that the crosshair (or a circle in some cameras) can automatically move to the highest or lowest temperature seen in the field of view.  This feature can be convenient for finding the hottest or coldest part of an image while taking the photo, I typically leave the camera set so the crosshair or circle stays in the center of the field of view.

The level and span feature of a thermal imaging camera is a way to adjust the temperatures visible in the image.  Most cameras have the feature to either allow the camera to automatically chose the temperature range, or it can be set manually.  Another way the level and span can be adjusted is within reporting software from the camera manufacturer.  This is done after the photo has been taken and downloaded into the software.

Above is ann example of how level and span can change the interpretation of a photo.  This adjustment in the photos was done in the reporting software.  Notice the temperature scale on the right side of the photos.  The original photo on the left has a range of 12.2° to 30.8°.  The adjusted photo on the bottom has a much closer temperature span.  This adjustment makes it easier to see potential problem areas.

When looking at some materials, the temperature registering on the camera can be incorrect.  This happens with materials that are reflective.  Instead of reading the temperature of the material’s surface, the reflection of the surrounding surface temperatures are seen instead.  The term is called emissivity.  Emissivity is a measure of how efficiently an object radiates heat.  Shiny materials reflect heat and have a low emissivity.  A material known as a blackbody will absorb heat and have a high emissivity.  The emissivity scale ranges from 0 to 100.  This is a bit of a simplistic explanation, just be aware that the temperatures of a reflective surface may not be accurately shown on the image.  A way to accurately measure temperature on a reflective surface is to place a piece of black tape on the reflective material.  Once the tape and surface temperature have equalized, the camera can more accurately register the temperature of the reflective surface.

The emissivity of a material can be set in the camera.  Charts can be found online showing the emissivity of many materials, my camera has a few common building materials preloaded in the camera.

Photo by Brent Lammert

This image is an example of emissivity.  The shiny metal elevator door is reflecting the person in the room at the time the image was taken.  We are seeing the temperature of the person reflected in the metal, causing an inaccuracy of the actual metal temperature.

It is possible to change the image mode in either the camera or in the reporting software.  The four photos below show the four image modes found on my Hikmicro Pocket 2 camera.  As you can see, all four photos are of the same subject, just presented in four different ways.  The top photo is thermal only.  Second is the thermal with a digital picture overlay.  Hikmicro calls this thermal with a digital overlay Fusion, Flir calls it MSX.  Third is the digital only picture.  Some cameras are capable of selecting the resolution of the standard digital picture, other manufacturers have a fixed setting.  The last photo is picture in picture.  These different images were changed in the reporting software, they can also be set in the camera.

The pallet, or different ways to change the colors of the thermal image can also be selected on both the reporting software and in the camera menu.  You may be several choices depending on the camera.

The color pallet of the top photo is called lava, it is the pallet I use most often.  Second is arctic, third is grey scale and the last is rainbow.  There are other pallets as well, some are unique to a manufacturer.

My first thermal imaging cameras were only able to take photos, many newer cameras can now also take video.  The advantage is that you can move around a site, taking a video, and be less concerned about something being missed.  The drawback is that you may not be able to change some of the ways to manipulate the video in the reporting software that can be done with photos.  Settings will have to be changed in the camera before shooting the video.

Many newer cameras have the ability to transmit what they are seeing to another device.  I could be at a building diagnosis, walking the site and the homeowner could be viewing what the camera sees on their smartphone, tablet or computer.  My new Hikmicro can even cast to a TV screen.  A handy feature when you’re in a tight place, like an attic, with the homeowner also wanting to see the thermal images in real time.

These are just some of the basics of thermography.  I bought my first camera back in 2009, took a short introductory class, and was off and running.  I learned a lot by making mistakes and fiddling through the camera’s settings.  Taking a full formal class is a much better strategy to learn thermography.  The cost of the new cameras is at the point where almost anyone in the industry can afford one, and the capability of the equipment has substantially increased in recent years.  Next up, how to interpret the thermal image photos.

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