For many of us, infrared thermometers are a new thing. While using one may seem pretty straightforward, the reality is that if you don’t use it correctly, you won’t get an accurate reading. You also won’t get an accurate reading if you’re using the wrong kind of infrared thermometer.
If you’ve just received your new infrared thermometer, or you’re doing your research before purchasing one, you need to know how to use it once you get it. You also need to be sure and purchase the best infrared thermometer, since different kinds are made for different purposes.
How do Thermometers Work?
In order to understand how to properly use a thermometer, it’s helpful to know how thermometers work, first. All thermometers are tools for measuring heat. All of them, no matter the type, rely on a small amount of a substance that reacts to heat in specific ways to measure temperature.
Old-school mercury thermometers, for instance, rely on the expansion of mercury when exposed to heat. Because mercury responds to heat in a predictable way, it’s easy to use it as a way to measure temperature.
The reason why this works is that heat is actually a form of energy. At the atomic level, heat is movement. If you were to take a hot object and put it under a microscope next to a cold object, you’d see that the atoms in the hot object are moving around a lot more than the ones in the cold object.
Heat also works like air- it wants to move from areas of high pressure to low pressure. To understand this, you need to remember that “cold” is really just the absence of heat- you can’t actually measure how cold something is, you can only measure how much heat something has. When something is cold, it has very little heat.
If you put a cold object next to a hot one, the heat wants to even out by warming up the cold object. The rate at which this happens depends on what those objects are made of, because some materials conduct heat better than others. Metal is more conductive than wood, and silicon and rubber materials conduct heat so poorly that they can be used as insulators.
For a long time, most thermometers used metal to measure heat. Mercury is, in fact, a metal. It’s simply metal that is liquid at normal temperatures, which makes it very responsive to heat. Other thermometers, including the ones that come built in to a lot of grills, cheap oven thermometers, and the ones that come in your Thanksgiving turkey, are bimetal thermometers.
These thermometers use two different metal strips- often steel and copper- that are attached to each other and conduct heat at different rates. As they’re heated, the combined metal strips will bend in one direction, and they’ll bend in the other direction when they’re cooled. These are popular because they’re cheap, but they’re also very inaccurate.
Thermometers that rely on metals responding to heat to measure a temperature are imprecise and bimetal thermometers especially can be off by 5-10 degrees. They also take a relatively long time to give you a temperature reading. This why professionals in fields that require regular temperature readings- chefs and doctors- almost always prefer digital thermometers.
Most digital thermometers use a sensor called a thermoresistor. These are usually a small piece of glass with two wires attached. As the glass heats up, it’s resistance to the flow of electricity changes. A small computer in the thermometer can detect that change, and uses it to calculate a much more accurate temperature reading. What’s more, these are often instantaneous readings.
How Are Infrared Thermometers Different?
You’ll often see infrared thermometers labeled as “digital infrared thermometers,” which can be confusing because digital thermometers are not the same thing as infrared thermometers. Infrared thermometers are indeed digital, meaning that they use a computer to calculate temperature, but they don’t function the same way as other digital thermometers.
All other types of thermometers have to be in direct contact in order to measure a temperature. For medical thermometers, that means they have to be touching the body- more accurately, they have to be in physical contact with the interior of the body, either in the mouth or in the rectum- to get an accurate reading of body temperature. For a meat thermometer, it has to be in physical contact with the interior of the meat, which is why they look like large needles.
What makes infrared thermometers so unique is that they can measure temperature from a distance. Exactly what that distance is will depend on the brand and type of thermometer, but it gives them a distinct advantage in many situations. If you have to take your child’s temperature, an infrared thermometer makes for a much more pleasant experience than a digital one.
Let’s go back to what heat is- it’s energy that’s manifested in the movement of atoms. As those atoms move around, they generate infrared radiation. Infrared radiation is light, it’s just not light that you and I can see. Everything generates infrared light, and the amount of infrared light that something generates varies based on how hot it is.
You’ve probably seen infrared in action before- it’s how night vision goggles and cameras work. You’ll see that technology used by everyone from nature documentary crews to the military. An infrared thermometer measures the amount of infrared light that something is generating.
How Do Infrared Thermometers Work?
The way that infrared thermometers work isn’t too different from the way that most digital thermometers work, the only major difference is that they are able to measure the temperature from a distance.
Infrared thermometers have a special lens that focuses infrared light onto a special sensor called a thermopile. The thermopile converts that light into heat, and then that heat is converted into electricity. The amount of electricity being generated is then used to calculate the temperature.
This gives you a very accurate temperature reading and the results, like with most digital thermometers, can be nearly instant. The best part is that you can take that temperature reading from a distance. If you’re trying to figure out how hot your grill is, you can get a reading from several feet away.
Different Types of Infrared Thermometer
Infrared thermometers are used in almost any situation that requires temperature readings. They’re especially popular in industrial settings where the ability to take an accurate temperature reading from a distance is a major safety concern.
For most people, though, there are only two kinds of infrared thermometer you need to know about: medical infrared thermometers and gun-style infrared thermometers.
Gun-Style or Digital Laser Thermometers
A quick look at one of these thermometers makes it obvious why they’re called “gun-style”. These are the most common infrared thermometers, because they have a lot of uses. They can be used in scientific and industrial settings, and they also have a lot of home uses.
These can measure the temperature of a skillet on the stove or of the surface of your grill, which can make your cooking much better. They’re designed to measure very high temperatures from a safe distance, but they can measure a wide temperature range. This one can measure temperatures as low as 58 degrees, and as high as 1112 degrees. They’re excellent for cooking, auto repair, and home repair needs.
The only downside to these thermometers is that they can only measure the surface temperature of an object. It’s why you still need traditional meat thermometers for cooking- if you have to measure the interior temperature of an object, these thermometers just aren’t useful.
Medical or Forehead Infrared Thermometers
Though they’re often called forehead thermometers, that name is misleading since infrared thermometers don’t always work that way. You may remember from your own doctors visits that your temperature was often taken through your ear.
That was an infrared thermometer. The ear drum is the same temperature as the inside of your body, but it’s an incredible delicate organ. Actually touching it with a thermometer would be very painful, so an infrared thermometer takes the temperature from a little under an inch away from it.
Forehead thermometers work by measuring the temperature of the blood in your temporal artery. Like the eardrum, this blood is the same temperature as the inside of your body even though it’s very close to the surface. Also like the eardrum, it would be impossible to get a thermometer into direct contact with it. Most models of medical infrared thermometers sold for home use can be used as both an ear and forehead thermometer.
Medical infrared thermometers can’t measure as wide a range of temperatures as the gun-style thermometers, and they have to be held much closer to take a temperature, but that’s because they are measuring a very small object and they don’t need as much range.
How to Use an Infrared Thermometer
As you might have guessed by now, how you use an infrared thermometer will depend on which type of infrared thermometer you’re trying to use. While they operate along the same principle, actually using the different types of thermometer is very different.
These thermometers have a laser on them. It’s commonly thought that this laser is what’s measuring the temperature, but as we’ve already seen the thermometer is measuring infrared light, not laser light. The laser is only there to help you aim the thermometer accurately.
This means you need to know how the laser is mounted on the thermometer. Some models place it above the infrared lens, while others place it below. Depending on how the laser is placed, you’ll actually be measuring the temperature of the spot just below or above the laser, not the spot where you can see the laser dot on the surface.
Using these thermometers is fairly straightforward. Point it at whatever object you want to take the temperature of, and pull the trigger. The trigger is the “on/off” switch, pulling it turns the thermometer on, letting it go turns it off. As long as you’re holding down the trigger, the thermometer will take continuously updated temperature readings.
Just remember that if you need to take the temperature of a relatively small object you’ll want to aim the laser slightly above or below your target. For instance, if you want to take the temperature of a grill grate, you’ll want to aim the laser between the grates at the coals or burners so that the lens is actually measuring the infrared light from the grate.
There are two ways to use a medical infrared thermometer- in the ear, and on the forehead. For an ear thermometer, you first need to check the ear for wax. Too much ear wax and the thermometer won’t be able to get a good reading. Also note that, if the ear is infected, you should not use an ear thermometer.
Pull the ear up and back (or down and back for babies under 12 months old), and gently insert the thermometer. Don’t force it, and don’t push it in too far. Now, you’ll turn the thermometer on. Once it has an accurate reading, it will beep to let you know that it’s done.
For a forehead thermometer, move any hair out of the way, along with any sweat or cosmetics, since all of these can affect the reading. You also shouldn’t use these thermometers outside. Place the thermometer against the forehead and hold down the button until it beeps.
Before you use these thermometers, check the instruction booklet that comes with them. The instructions there might deviate a little bit from the ones we’ve outlined here.
Infrared thermometers have many advantages. They take quick, accurate readings with minimal discomfort. They’re easy to use, and they’re typically very affordable. As long as you buy the right type of thermometer for your needs, you’ll find that getting an accurate temperature reading has never been easier.