An Introduction to Infrared Thermometry

Infrared thermometry refers simply to thermometry that uses infrared light. Thermometry itself is the measurement of temperature, while infrared is light with a certain wavelength at the end of the visible light spectrum. In short, this is a method for measuring temperatures that uses infrared light.
The mechanism behind this is somewhat sophisticated and potentially complex to understand, but thankfully the thermometers themselves are very straight forward and easy to use. In this comprehensive post, we’ll be looking at how you use infrared thermometry, how it works and what the strengths and weaknesses are.

Using an Infrared Thermometer

To use an infrared thermometer, you will usually have a handheld device. These are usually around the same size as a small electric screwdriver and will have a digital readout on one end. They are also shaped similarly to electric screwdrivers, with a handle and a very distinct ‘end’.
To get a reading from these devices, all you need to do is to point the device at the desired target and then squeeze the trigger. This will then give you a readout of the temperature of that item. While this is very easy on the face of it though, there are a few things you need to understand about the process that can help you to get more accurate readings.

How to Get More Accurate Readings

The first thing to recognize, is that an infrared thermometer (also IR thermometer) will usually only measure surface temperature. That means that it is reading the temperature on the surface of the material you point it at. If you were to point it at a car windshield then, the reading you got would reflect the temperature on the glass outside the car, rather than the glass on the inside or even the temperature inside the vehicle. We will get into how IR thermometers work in a moment but for now, suffice to say that it is based on the laser rebounding off of the surface – not penetrating into it.
Another thing to consider is that any air-born particles such as dust can interfere with your readings and make them less accurate. This is because the IR thermometer will actually be reflecting off of these on the way to the desired target.

Shiny and metal surfaces will also interfere with the readings, again due to the fact that they are reflecting light back at a different rate. For that reason, it can be a good idea to cover the surfaces with a piece of masking tape, or perhaps black paint. As you may remember from science class, the color black will absorb light and as such, it will offer the perfect antidote.

Another consideration is what is known as the ratio or ‘D:S’. This refers to the distance you are standing from the target versus the size of the target itself. For instance then, if you are a long way from the target you are measuring but it is very large, then you should have no problem measuring it. Likewise, if the object is quite small but you are close to it, then you can still expect to get an accurate reading. On the other hand though, if the target is very small and it is far away, then you should expect this to harm the readings. This is something that is defined by the actual make and model of the device you purchase. The higher the D:S, the better the resolution will be and the smaller spots you’ll be able to read from a distance. We’ll look at this in more detail later but for now, note that you will generally get better readings when targeting larger items that are closer. As you might already have guessed, one of the big advantages of using IR thermometry, is that it will allow you to get readings without having to be directly on top of the material that you want to measure.

In a similar manner, you also need to consider the temperature of the object. That is to say that most IR thermometers have an upper and lower limit as to what they can measure. If you are going to be measuring temperatures at either extreme end of the spectrum, the you should first make sure that your tool is capable of performing the job.

This is actually another advantage of an infrared thermometer: they allow you to measure temperatures that would be too hot or too cold to measure safely using any other means. Because you can stay a good distance away from the actual material, they allow you to safely get a reading at a distance.

Techniques for Reading Temperatures

While the basic operation of an infrared thermometer is very simple, it’s worth noting that there are three different variations on the same technique available for those who want to use these devices to their fullest effect.

These three techniques are:
Spot measuring – This measures the ‘absolute’ surface temperature of an object. This can be useful for spotting bad connections or incorrect process temperatures.

Temperature differentials – This method will compare two different spot measurements in different locations or at the same location over a period of time. This is useful for looking for voltage imbalances, which in turn can help you to uncover a problem with a motor, transformer, grounding system and more.

Scanning – To scan, you keep your finger on the trigger and at the same time move the device gradually to aim at different areas of the target. This allows you to locate areas where there might be a problem. For example, this could point to clogged air or an overheated motor.

How Does an Infrared Thermometer Work?

The idea of a laser thermometer (as they are also known) can seem a little bit like voodoo for those who aren’t familiar with them. We are used to taking temperatures up close and personal and often this will involve inserting some kind of thermometer and leaving it there for a significant amount of time. How can it be possible to get the temperature of something so quickly and at such a distance?

The idea is simple. When you use IR thermometers, you benefit from the fact that every molecule in any instance of matter is vibrating at any given time (yes, that includes the ones inside you!). This is what happens to heat energy when it enters any object and if that heat becomes strong enough, then the vibrations become strong enough to break bonds, thereby turning the mass into a liquid or a gas.

This impacts on the way that light interacts with the surface area. The higher the temperature, the faster the vibrations will be and if you should point your infrared thermometer at such an object, then you would find that the this movement would actually impact on the wavelength of the light. Essentially, what is happening here is that the energy in the molecules has been passed to the wavelengths in the light, causing them to move faster, making them shorter. When the object is very cold on the other hand, this will cause it to actually ‘rob’ the short wavelength of light of the energy, thereby making it longer.
The infrared thermometer is thus equipped to be able to read the wavelength of the light returning. Of course, it already knows the wavelength of the light when it went out and as such, reading this difference will allow it to calculate an accurate reading for the temperature of the surface.

Common Misconceptions About Infrared Thermometers

An infrared thermometer is a device that looks a bit like a gun in the way you hold it and that actually produces a real laser. For that reason, it might be considered quite a ‘cool’ tool as far as DIY equipment goes.

People take a passing interest to this device often then, without really knowing what it is or what it is used for. This has led to there being numerous misconceptions regarding the way they work and just how accurate they really are.

Here are some of the most common misconceptions that are good to clear up before you get out there and start shopping for your first IR thermometer.
The laser is what does the reading…

I mentioned earlier, that an infrared thermometer could also be referred to as a ‘laser thermometer’. This is partly because many infrared thermometers actually have light built in. However, while this light is present and while it might well look like that’s what you’re aiming, the reality is that this light is really only there to help you with your aim and to make sure that you know what you’re pointing the laser at. Otherwise, it is all too easy to miss and to end up reading something else entirely! A point to bear in mind here though, is that the IR beam won’t be at exactly the same point as the LED beam. This means that if you point your device at a particular material that’s on the other side of the room, you could very easily ne a couple of degrees out, which in turn could lead to you measuring the temperature of the wrong thing!

In the vast majority of cases, the positioning will be such that the thermometer is at the bottom. This means that you should aim just slightly higher with the laser. This isn’t always the case however and as such, it’s worth checking it out personally.
Some products, such as the IR-IND are actually equipped with dual lasers. The purpose of these is to help better indicate the actual location of the infrared beam. In these cases, the real beam will usually be at an equidistant point between the two lasers.

Infrared thermometers can read internal temperatures
We’ve already touched on this but it’s important to remember it again: your IR thermometer will not be suitable for reading internal temperatures, meaning that unless the heat is bleeding out, you won’t be able to pick it up. To get an internal temperature as a mechanic – which is one of the most common applications for this kind of tool – you will likely end up using a temperature fork.

All surfaces will work the same way
This is something that is very often forgotten. Some materials will simply lend themselves better to IR thermometry than others; for instance, we’ve already seen that highly reflective surfaces can make it very difficult to get an accurate reading as they will reflect the light back more quickly. Likewise, white surfaces will also reflect light much more than black ones.

And this is where it can be useful to consider a term called ‘emissivity’…

What Is Emissivity

Emissivity measures just how able an object is to give off infrared energy and this is measured on a scale of 0.000 to 1.000.
Here, a higher number suggests that a material will absorb ambient or reflected infrared energy and light, while also emitting its own radiation. This is a good thing, as it means that other light waves will be less likely to interfere with your readings.

And in which case, most organic materials are considered to be ideal when it comes to emissivity and to be the best for getting a fast, accurate reading with a device. Of course, organic material can include anything from plants or animals, as well as things like woods. In fact, by products from plants will tend to have emissivity ratings of around 0.95. This makes them ideal for accurately reading temperatures.
At the other end of the spectrum, there are some materials that have very low emissivity ratings. These include highly polished, reflective metals. If you were to point your infrared thermometer at one of these, then you would find that there was a lot of ambient energy being passed around and that the reading was not particularly accurate or true to life.

Uses for Infrared Thermometers

We have already seen that infrared thermometers can be an indispensable tool for mechanics as it will allow them to test the heat of any given implement and to look for things that are perhaps overheating or that aren’t distributing their heat evenly. Likewise, this could be used to find issues inside or behind walls for a builder or electrician, or even to get the temperature of certain areas of a computer chassis, in order to see if the CPU or GPU might be getting too hot and being forced to underclock.

Again, it’s important to note with these kinds of applications, that the overheating will need to change the temperature on the surface of said item in order for it to show up on the IR thermometer. Usually though, this will happen and that means that you can use the thermometer to scan for issues.
IR thermometers can also be particularly useful in cooking, where they might be used to check that the surface of something you are cooking has reached a satisfactory level. For example, if you are cooking beef steak and your objective is simply to burn off any surface bacteria while enjoying the beef largely blue; then you need to be able to quickly get a reading for the surface of the meat.

Again though, you need to remember that this will not tell you internal temperature. When cooking chicken then, if you want to check that the meat is cooked through, it is preferable to use a temperature fork.

While not every home needs an infrared thermometer, there are definitely a number of different uses for the typical DIYer. These include:
Finding faulty terminations that are situated in high power electric circuits

  • Finding overloaded circuit breakers
  • Capturing process temperature readings for later analysis
  • Finding hot spots in electronic equipment
  • Finding leaks inside sealed vessels
  • Looking for issues with steam traps
  • And much more!

Buying an IR Thermometer

If you have decided that IR thermometers have a place in your tool kit, then there are several things to consider when looking for your own device.

Temperature Range
The first thing to consider is the temperature range. As mentioned, an IR thermometer will always have limits in terms of what it can measure. This is very important to take into account, seeing as it won’t be much use to you if the thing you need to measure is too hot to measure.
So what is normal? Well, most infrared thermometers should be able to measure temperatures within a range of -50 degrees Celsius, all the way up to 500 degrees. This should be more than enough for the vast majority of applications around the home and even in a wide range of professional settings.
That said, some models will be able to go as high as 1,000 degrees Celsius. This is most likely to be useful in a research setting. Either way, all that matters is that the temperature range encompasses all the different temperatures that you are likely to be measuring at any given time.

Emissivity

Different devices will have different approaches to emissivity (which if you recall, refers to the amount of infrared light that is absorbed or reflected from a target object). The key thing to note here, is that some objects will come with a ‘fixed emissivity’, while others will have an adjustable one.

Because different surfaces have different levels of emissivity, this needs to be reflected in the way that the light is calculated on its return. IR thermometers with adjustable emissivity will generally have slightly more versatility from their tool.

Distance to Spot Ratio
We’ve already discussed what the D:S is and you have probably already recognized that this is a very important detail to look out for when shopping for an infrared thermometer. This higher this number, the easier it will be for you to measure small items that are far away.
The extent to which this matters will once again depend on your intended use and on your workflow. Do you often find yourself needing to get temperatures from things that you can’t reach? If so, do they tend to be small or are they larger surface areas? This becomes particularly important in lines of work where perhaps you may not be able to get up close and personal with the intended target.

Other Considerations
Of course, there are many other considerations to take into account and precautions to take prior to making a purchase. For instance, you should always take care to read reviews and to look at customer feedback for any given product before making a purchase. This is highly important, seeing as even a product that sounds good on paper can sometimes end up being inaccurate or particularly sensitive to dust and ambient light.
Price is also something that a lot of people are going to need to consider. Ultimately, the aim is to look for something that fits in your budget and that does everything you need it to without costing more than necessary.

Design is important too. Not only do you want a gadget that you spent money on to look nice but you also want it to be comfortable to hold with an ergonomic grip that won’t hurt when you’re using it over long periods. Again, the best way to tell this is to look at reviews.

Finally, think about things such as the clarity of the screen, extras that might be included such as carry cases and how the batteries hold up over time. Consider the brand too and whether there is a warranty.As we said at the start though, these devices are actually pretty simple and there isn’t all that much to consider when making your purchase. They don’t need to break the bank and even a basic model should be able to serve you well and help you to take quick and accurate measurements, even at a distance.

Take your time shopping around and this will prove to be a useful addition to your repertoire. You’ll wonder how you ever used to make do without one!