Besides the fact that they’re shaped like a gun and have a built-in laser, infrared thermometers are just plain cool. They’re very fast (instantaneous), provide a good indication of temperature and allow you to collect data at a distance. The problem is, you’ve got to look past the novelty – and learn how to use them properly – before they’ll give you excellent temperature returns.
Here are three of the most common misconceptions about infrared thermometers:
#1 The laser reads the temperature
This is just plain wrong. The laser pointer in an infrared thermometer is a guide that indicates where you’re pointing the instrument. When measuring the heat coming from an A/C duct (for example), the laser helps to steady your aim and ensure that you’re close to the area you’re trying to temp.
Depending on the make and model, an infrared thermometer is actually reading the temperature above, below or around where you see the laser. Some infrared thermometers, like the IR Pro Series and the IR-IND are equipped with two lasers. They provide an indication of the infrared radiation being measured between the laser points. And depending on your infrared’s optics, the diameter of the area being measured will change as you get farther away from your target. This is called the optical range.
(Hint: Understanding optical range will greatly improve the accuracy of your temperature measurements. Keep your eyes open for a future post where we’ll take a closer look at what exactly optical range is and how it affects your temperature readings.)
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#2 An infrared thermometer will tell you the internal temperature
This is another myth worth busting. An infrared thermometer is a surface temperature tool – period. If you’re grilling, baking, smoking or roasting you’re going to need a penetration probe to tell you the internal temperature of the food you’re cooking. An infrared will only give you the surface temperature of the food, and depending on your optical range, the temp of the surrounding grill, skillet, oven, etc.
Ideally, you would use infrared thermometers to temp the surface of hot oil, a cast iron skillet, a saute pan, even chocolate, and soup. However, whipping out your infrared “laser gun” to temp burgers on the grill may have you explaining to your guests why they’re undercooked.
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#3 All surfaces are created equal
As a matter of fact, just the opposite is true. Not all surfaces are created equal. Depending on what you’re pointing your infrared gun at you’re likely to get variations in emitted infrared energy. This variation is called emissivity. Emissivity is a measure of a material’s ability to emit infrared energy. It is measured on a scale from just about 0.00 to just below 1.00.
Generally, the closer a material’s emissivity rating is to 1.00 (such as cast iron), the more that material tends to absorb reflected or ambient infrared energy and emit only its own infrared radiation. Most organic materials, including the byproducts of plants and animals, have an emissivity rating of 0.95. These are ideal surfaces for accurate temperature readings.
Substances with very low emissivity ratings, like highly-polished metals, tend to be very reflective of ambient infrared energy and less effective at emitting their own electromagnetic waves. If you were to point an infrared thermometer with fixed emissivity at the side of a stainless steel pot filled with boiling water, for example, you might get a reading closer to 100°F (38°C) than 212°F (100°C). That’s because the shiny metal is better at reflecting the ambient radiation of the room than it is at emitting its own infrared radiation.
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What is fixed emissivity?
Fixed emissivity is a setting in some infrared thermometers (usually of 0.95 or 0.97) that attempts to simplify their operation while leaving them suitable for most material surfaces, including almost all foods. Other infrared thermometers come with adjustable emissivity settings, so you can more accurately prepare your thermometer for the type of surface being measured, particularly when measuring non-organic surfaces.