Basic (Qualitative) Use of a Thermal Imager.




Ah! A thermal image of my morning cup of tea. That image shows heat emitted doesn't it? I took that image using my Seek Thermal XR camera. This an entry level microbolometer, or in lay person's terms: a thermal imager.

I felt it necessary to post this instructable to let folks know some capabilities of microbolometers such as mine and also to help dispel myths on thermal imagers. I'm a level 2 certified Infraspection Institute Thermographer and part of my job is to use imagers like these to do troubleshooting and maintenance. You dont have to be certified to use a thermal imager but if you understand how it works and its limititations plus uses then a mighty tool you will have!

Thermal imagers will only give you an indication of the SURFACE of a target, not the internal temperature. It cannot see beneath any surface. Seeing through walls or anything is the stuff of movies (remember the original Robocop movies?) and not the reality of this device type.

Please note that this is an introductory instructable. I do not cover calibration or quatitative analysis.

Step 1: The Seek Thermal XR!

This imager is a game changer in terms of its low cost. At approximately 300USD off Amazon, I wanted it within the first 5 minutes of reading its specs and the product reviews. Its clipped onto an android or iphone and is also powered by the host phone. The app is free.

At a resolution of 206x156, low frame rate and a 20degree field of view, you may think that this imager is not so good. Reality is, once you know what to use it for and how to apply it, it will be your best friend for hunting down problems in many systems (electrical, mechanical, process).

Step 2: Attempting to Get the Best Possible Image.

First thing we were taught with the use of thermal imagers is that the temperature readings calculated in the processors are usually not correct. This is because of the difference between an imager's preset emissivity and the actual emissivity of the materials under inspection. Also errors arising from (including but not limited to):

1. loading from the sun or other nearby heat sources.

2. angle used for imaging may not be not optimum.

3. reflectance due to the type of surface the material(s) have.

Most thermal imagers come with a focus ring to allow manual focusing of the image, or the higher end units have auto focus. Getting a good focus and paying attention to the distance to spot ratio (basically dont stray far from your measured target else accurancy drops) are important.

Being perpendicular to the traget helps alot to get a cleaner image and more accurate temperature readings.

Take for example the visual image of a UPS cooling fan. The first thermal image is blurry and not focused. The second image is focued and offers more detail for troubleshooting (eg. failing fan bearing). Here is an excellent example of the resolution difference between a standard visual camera and an entry level thermal imager. You need to appreciate the limitation of resolution and the ability to now "see" hot and cold spots. Higher end (and extremely expensive) thermal imagers will give better resolutions.

Step 3: Knowing Your Target Emissivity.

The perfect black body (this is the actual definition so please no jokes) has an emissivity of 1. An imager set to this emissivity value will give a fairly accurate reading on the target's surface temperature.

Real world objects have a range of emissivity values. The table attached has examples of these values. Basically shiny surfaces have low values and are difficult to read. Why? Infrared radiation, like visible spectrum, is reflected by shiny surfaces. Taking a thermal image of a shiny copper busbar will give a reflection of heat sources and even the thermographer taking the images! Standing in front of a mirror with your thermal imager will give you an image of yourself. Reflections are very bad for good imaging and also accuracy of the temperature readings. Blocking off external infrared sources will help in addition to standing at an angle from perpendicular.

Here is a good example I made right here in my office. The lock for my overhead bin is shiny. The thermal image says the key hole is 34C! This is a wrong temperature due to infrared radiation reflected from a nearby light. The thermal imager lied to me because I did not apply it properly. Dont let this happen to you!

Remember thermography is a science AND an art!

Step 4: Troubleshooting!

Knowing what the normal operating temperatures on a system is critical to knowing if something is wrong. Makes sense yeah? This is actually one of the hardest part of thermography: establishing baseline data.

Motor bearing running hot due to failure, belt not properly tensioned on a pulley, heat being lost due to degenerating insulation on a furnace, imbalance of current on a three phase supply in a panelboard, winding failure in a dry type transformer, water leak inside of a wall are a few examples of how powerful even a basic thermal imager is when it comes to picking up problems.

Take for example the last image. This is a three phase circuit breaker. The middle phase clearly shows higher heat than the other two. Use of a clamp ammeter confirmed severe loading on that phase.

Remember that thermography is the fastest means to find problems but you must use follow up (different) techniques to get to the real source of the problem(s). For example a bearing running abnormally hot, use vibration analysis to give you more information. Components in the system that pulley is part of will have a part to play in its abnormal heating!

Step 5: Taking Care of Your Imager and Being a Proud Owner.

Scheduled calibration will keep your imager accurate and manufacturer recommended cleaning will keep your troubleshooting device working well for many years.

Dont use it as a toy (for non thermographers). Don't point it at the sun and expect it to work properly after. Even the lowest cost thermal imager is an invaluable tool!

Here I had some fun and took a thermal of one of my doggies. LOL.

PS: All thermal imagers will make a clicking noise. Dont throw it away and think its broken! They need to do this to refresh the image onto the internal sensor. No different than the micro movements our eyes have to make to refresh images on our retinas.



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    10 Discussions


    2 years ago


    With the release of Seek's Pro series there will be a lot more thermal imagers in use. This is a good introduction. Thank you.

    1 reply

    3 years ago

    This is very cool and knowing how cheap they are I'm prone to getting onone , in the future, but I have to say it's not a thing of movies. I left active duty 17 years ago and we had units that could see though walls at 2000 meters given contrasting conditions obviously. But , they were around $50k at the time.

    1 reply

    Reply 3 years ago

    Wow OK. There is no thermal imager that can penetrate walls. The physics behind how they work prevent such a capability. Thermal imaging works only on the surface of an object, not beyond that surface.


    4 years ago

    Thank you v much for the entirely new (to me) info. Do you think it'd work for home heat loss imagery?

    1 reply

    Reply 4 years ago

    Thank you and most definitely you Can. It's a very common application.

    dangerous dan

    4 years ago

    Okay, I want one of these!
    this will make me an order of magnitude more effective at my job!

    1 reply

    My friend, I HIGHLY recommend you get one off amazon. The other version of seek thermal imager is cheaper than the XR. However you just cant go wrong with a 300USD price tag for a thermal imager.