How do Infrared Thermometers work?

Infrared thermometers take surface temperature measurements from a distance without having to touch the object you want to measure.This makes them perfect for measuring hot, moving, sterile or hard-to-reach places.

They are versatile thermometers that are used across many industries work environments, including construction, laboratories and in manufacturing (food and non-food production facilities). Given their functionality, along with the key role they play in quality control and safety it pays to know how they work!

Before we examine in detail how Infrared Thermometers work there are two definitions worth knowing that will help you gain a better understanding.

Infrared: Infrared energy is a frequency of energy on the electromagnetic spectrum. Infrared wavelengths are longer than visible light and so are generally invisible to the human eye. Infrared light is emitted from the surface of all objects. For this reason an IR thermometer is usually used in tandem with emissivity values to arrive at a temperature measurement.

Emissivity: Emissivity is the measure of how effectivity a surface can emit energy as infrared radiation. The emissivity scale is a value ranging from 0 to 1. A value of 0 is attributed to a perfect reflector and 1 is an object that absorbs all incoming radiation and does not reflect any. As a general rule, the more reflective an object the more the emissivity value will go down. To ensure accurate results it is important to know the default emissivity setting on your IR thermometer along with the approximate emissivity of the surface you wish to measure.

Many items fall within the emissivity range of 0.95. As a result, most infrared thermometers will have a defult emissivity setting of 0.95. If you need more detail, below is a table of items often measured for emissivity complied by Instrument Choice scientists. If your product’s surface is not listed below contact an Instrument Choice scientist for help.

How Infrared Thermometers work

An Infrared thermometer measures both infrared radiation and the emissivity value of a surface.The Infrared thermometer has a lens that focuses the infrared rays and tunnels them through the thermometer to a detector known as a thermopile. Then, hey presto the thermopile converts the incoming Infrared radiation into an electrical signal that is then displayed as units of temperature! While the process sounds (and is) complicated, it all happens in a matter of seconds.

Figure 1 Three types of infrared radiation being emitted from an object and focused through the IR thermometer lens.

Distance to spot ratio

An important factor when using an Infrared thermometer is the distance-to-spot ratio. This ratio is the size of the area being measured against the distance of the thermometer from the sample. In simple terms, the area being measured becomes larger as the distance increases. Inversely, the area being measured becomes smaller as the distance decreases. Knowing your distance-to-spot ratio is important. It will help you ensure accuracy by helping you avoid taking measurements from outside of the desired area.

Here’s a simple example. If your distance-to-spot ratio of 12:1 your thermometer measures the temperature of a 1-inch diameter spot as if you are 12 inches from the surface.

Figure 2 Distance to spot ratio on an Infrared Thermometer using a 12:1 ratio as an example.

Common application for infrared thermometers

Infrared thermometers are recommended for any applications where the surface area of an object needs to be known quickly and where touching the surface is unsafe, bad practice or simply not possible. They are intended for measuring;

• Hard to reach places
• Hot surfaces
• Sterile and cleanroom environments
• Moving objects or surfaces

Choosing your infrared thermometer

Important considerations when selecting (and using) an infrared thermometer are:

• The surface intended for measuring:
• Is the surface shiny?
• Will there be large variances emissivity? If so, you may require a thermometer with adjustable emissivity.
• The distance between your thermometer and the surface area you wish to measure: Needing to measure a small area from a distance? A higher distance to spot ratio will be necessary. Measuring at close range? A low distance to spot ratio will suit your application.
• Accuracy: Ensure the accuracy of your instrument is reasonable for the intended use.
• Temperature range: Measuring extremes in temperature? Be sure to check the thermometer’s temperature range and that it is within the range you plan to measure.

Examples of infrared thermometers

Instrument Choice’s team of scientists have gathered examples of Infrared Thermometers with varying specifications as a glimpse of the various types of Infrared thermometers available from the Instrument Choice website.

Mini Non-Contact Thermometer  

Product Code: IC7218TM

This compact, non-contact thermometer is both accurate and easy-to-use. Suitable for both industrial and laboratory applications.

Distance to spot ratio: 1:1

Adjustable Emissivity: No

Temperature Range: -33°c to 110°c

Temperature Accuracy: ±2.5°c

Non-Contact Thermometer With Dual Laser Targeting  

Product Code: Dual-IR

Complete with dual laser targeting to help locate the diameter for measurement, this model boasts the highest distance-to-spot ratio of the three examples. This helps make it suited for food production facilities, industrial applications and laboratory use.

Distance to spot ratio: 12:1

Adjustable Emissivity: Adjustable from 0.1 to 1.0

Temperature Range: -50°c to 650°c

Temperature Accuracy: ±2.5°c (-50°c to 20°c)

±1% (20°c to 300°c)

±1.5% (300°c to 650°c)

FLUKE 62 MAX IR Thermometer  

Built to be tough and able to withstand a drop of up to three meters, this IR thermometer is rugged yet very accurate. Short list it if you need durability, accuracy and quick results in industrial, building and production settings.

Distance to spot ratio: 10:1

Adjustable Emissivity: 0.10 to 1.00

Temperature Range: -30°c to 500°c

Temperature Accuracy: ±1.5 °C or ±1.5 % of reading, whichever is greater (≥0 °C)

±2°c (≥-10 °C to <0 °C)

±3 °c (<-10°c)

Conclusion

It’s essential to use infrared thermometers when reading the temperature of a surface that’s too dangerous, impossible to reach, or where making contact with the surface would cause unwanted contamination. While the inner workings of infrared thermometers are complex, they give incredibly quick results and are simple to use.

Do you want more examples of Infrared thermometers? Search the Instrument Choice online store. You’ll find an extensive range of quality, cost-effective units that have been personally selected by our scientists.

Do you have questions about infrared thermometers? Need a bit more information on any of the meters listed above? Ask one of the Instrument Choice Scientists, we’re here to help! Call 1300 737 871 or email [email protected]