Touchless Infrared Thermometers: How Do They Work and Are They Accurate?

by Garber Metrology

Companies use touchless infrared thermometers to measure the temperature of people and objects. With the COVID-19 pandemic and the increased need to check body temperature, many organizations now rely on the accuracy of touchless infrared thermometers in their daily operations. While touchless infrared thermometers are incredibly accurate, they sometimes need calibration services to ensure they are still delivering accurate results.

If you use touchless infrared thermometers or plan to use them, learn more about how they work, what makes them accurate and why it is important to calibrate them.

What Are Infrared Thermometers?

Infrared thermometers are devices used to measure infrared temperature. They infer temperature by measuring the thermal radiation from a person or object and allow users to measure temperature without any contact with a person or object. They offer an excellent alternative to probe-type or thermocouple sensors when these sensors can’t reach an object or receive an accurate result.

You can often find these thermometers used in circumstances where an electromagnetic (EM) field surrounds an object or when an object is moving. You might also see no-contact thermometers employed when a company needs a fast reading or an object is held in a controlled atmosphere, like a vacuum.

How Do Non-Contact Thermometers Work?

Non-contact infrared thermometers are complex devices that deliver accurate temperature measurements. These devices utilize an object’s infrared radiation to determine its temperature. If you want to know how infrared thermometers work, find out more about what infrared radiation is and how touchless infrared thermometers use this radiation to take an object’s temperature below:

Infrared Radiation

The first step in learning how touchless infrared thermometers work is understanding infrared radiation. Any object without an absolute zero temperature contains moving atoms. The speed at which these atoms move directly correlates to the object’s temperature. When an object has a higher temperature, the atoms move faster, and when it has a lower temperature, they move slower. As the atoms move, they emit infrared radiation.

Since infrared radiation’s wavelength is longer than visible light’s wavelength, people can’t see it. However, when something gets incredibly hot, you may see signs of it, such as a metal object glowing white or red. Though infrared radiation can’t be seen, people can still feel it. For example, campfires, sunlight and radiators all put out infrared radiation that we can feel in the form of heat.

Because infrared radiation can tell us about an object’s temperature, it can be used to measure temperature. Manufacturers design infrared thermometers to detect an object’s infrared radiation and the heat it produces, converting those readings to an infrared temperature measurement.

How Infrared Thermometers Measure Temperature

Since an object’s infrared radiation can provide information about its temperature, many companies use infrared thermometers to read temperatures. Infrared light works much like visible light, as it can be absorbed, focused or reflected. An infrared thermometer contains a lens tasked with focusing an object’s infrared light onto the thermometer’s thermopile.

The thermopile is a type of detector made of thermocouples connected in a parallel arrangement or a series. As the lens focuses the infrared light onto the thermopile’s surface, the detector absorbs it. After absorption, the device converts the infrared light into heat, and then the thermometer produces a voltage output proportionate to the object’s incident infrared energy. Once the device produces the voltage output, the detector uses the output to give an accurate temperature reading, which it displays on the thermometer’s screen.

This process is complex, but it usually only takes a few seconds to complete. By using a non-contact infrared thermometer, you can quickly receive a temperature reading of an object or person.

What Are Non-Contact Infrared Thermometers Used For?

Many companies and organizations use non-contact infrared thermometers for a variety of applications. These devices can be used to take the temperature of a person and objects, like mechanical and electrical equipment. For example, if an operator needs to measure the temperature of a hot motor, they can use a touchless infrared thermometer to get an accurate reading from a safe distance.

Recently, thermometer manufacturers have seen greater demand for no-contact thermometers due to the public health concerns surrounding the COVID-19 virus. Many health facilities use infrared thermometers to take a patient’s temperature before they enter a building. This scan can help prevent sick people from entering an enclosed environment where they could infect others with COVID-19 or another virus.

How Do Infrared Forehead Thermometers Work?

Since COVID-19 has made temperature checks a vital part of many organizations’ day-to-day operations, many companies are turning to infrared forehead thermometers. These infrared thermometers are usually handheld. A user can point them at another person’s forehead to take their temperature, with the process only taking a few seconds. Infrared forehead thermometers determine a person’s temperature by utilizing an algorithm that takes the forehead’s temperature and then translates it into an oral equivalent temperature reading.

Since these thermometers are non-contact, they help keep an organization’s staff at a distance while taking someone else’s temperature. Oral thermometers require staff members to interact more closely with someone else and necessitate more cleaning requirements, but no-contact thermometers are an excellent alternative. Infrared thermometers also do not require people to remove facial masks while a staff member takes their temperature, helping everyone stay safer.

Are Non-Touch Thermometers Accurate?

When operators use touchless infrared thermometers correctly, they work and are very accurate. A key to a non-contact thermometer’s accuracy is its ability to account for different emissivities. An object’s emissivity refers to the way it gives off thermal radiation. An object’s emissivity is measured on a 0.00 to 1.00 scale.

Since objects have different emissivities, the best and most accurate infrared thermometers have an adjustable emissivity rather than a fixed emissivity to account for the differences. Thermometers featuring an adjustable emissivity lets users modify their thermometer to a particular object and receive an accurate result. For example, reflective surfaces usually have lower emissivity compared to non-reflective surfaces. A thermometer with adjustable emissivity can be set to better account for a reflective surface’s lower emissivity.

How Distance-to-Spot Ratio Affects No-Contact Thermometer Accuracy

To receive an accurate reading from a touchless thermometer, it is crucial to understand they need to be at a certain distance from an object to measure its temperature correctly. To know how far away you can be, you will need to know the thermometer’s distance-to-spot ratio, which refers to the length the thermometer can be from an object to measure its temperature accurately.

You will often see infrared thermometers with 4:1, 8:1, 30:1 and 50:1 ratios, with the larger ratios allowing users to employ thermometers farther from an object or person. The ratio’s first number indicates how many inches away the thermometer can be, and the second number stands for how many square inches of an object’s surface area it can measure.

So, a thermometer with an 8:1 ratio can accurately take an object’s temperature when 8 inches away from it. Generally, companies and organizations do not need thermometers with high ratios unless the measured object is extremely hot and staff members need to keep a safe distance from it during measurement.

How to Check If Your Thermometer Is Accurate

Companies utilize a few different methods to check the accuracy of their thermometers. A blackbody is usually the best choice, but some companies also use a thermocouple or another trusted infrared thermometer to check a thermometer’s accuracy. Find out more about some of the main methods companies utilize to check the accuracy of non-contact infrared thermometers below:

1. Use Another Trusted Infrared Thermometer

When you don’t think an infrared thermometer is delivering accurate results, you can check it against another trusted infrared thermometer. In this method, you will have both thermometers measure the same area of thermal energy. If their measurements are the same, you can be confident your infrared thermometer is delivering accurate results. If their measurements are different, you can adjust the calibration of the infrared thermometer in question to match the trusted thermometer’s calibration.

For this method to work, you’ll have to ensure you can trust the infrared thermometer you’re using. If you don’t have a trusted thermometer, comparing the measurements of two untrustworthy thermometers could cause inaccurate results. It is also crucial to measure the same surface area of an object, as measuring two different areas could result in different measurements.

2. Employ a Thermocouple

Some companies use an instrument called a thermocouple to check the temperature of an object and compare that reading with an infrared thermometer’s temperature reading. If the non-contact infrared thermometer’s temperature reading is off, you can adjust it so it gives the same measurement as the thermocouple.

A drawback to this method is that thermocouples aren’t as accurate as infrared thermometers when used alone. They tend to experience more wear during their use, and if you use this method, you have to first verify the thermocouple’s accuracy. Thermocouples can also vary widely in quality, so it’s important to use only the best if you want to employ it to verify an infrared thermometer’s accuracy.

3. Utilize a Blackbody

Companies regularly use blackbody calibrators to ensure infrared thermometers are calibrated properly and are as accurate as possible. A blackbody serves as a type of perfect emitter, emitting the maximum amount of infrared energy for a temperature. It also plays the role of a diffuse emitter, radiating infrared radiation in every direction at the same intensity. Currently, there’s no completely perfect blackbody available, but many models are close enough to provide an appropriate base for proper calibration.

A blackbody calibrator comes with an empty cavity featuring a small target opening. Inside the blackbody, you can find a tube or conical-shaped radiation source stored in a furnace, heat or bath pipe. Since the blackbody’s emissivity serves as a known value, a company can have an infrared thermometer take the blackbody’s temperature and see if it accurately reflects the known value. If it doesn’t accurately reflect the value, a company can calibrate the thermometer to meet it.

Since blackbody calibrators tend to be more expensive and difficult to operate, companies generally send their thermometers to a company specializing in calibration to ensure their devices are accurate. A blackbody calibration tends to give the most accurate results, so many companies rely on it.

Importance of Touchless Thermometer Calibration

Whether you’re taking the temperature of an object or a person, you need your thermometer to give you accurate results. Too high or low temperatures in a piece of machinery can indicate a need for repairs, and an inaccurate thermometer could cause you to miss them. Inaccurate readings could also slow production if they indicate something could be wrong with a piece of equipment, causing you to halt production while the equipment goes through an inspection.

Besides the need for accurate temperature readings in machinery, COVID-19 has made accurate body temperature readings even more important. Inaccurate results can result in public health hazards, as it’s crucial to screen people who are coming into a workplace or health facility for fevers. An improperly calibrated thermometer could miss people with fevers, causing a virus to spread between people.

Touchless thermometer calibration ensures your thermometers deliver accurate results you can trust. Because accuracy is so important to so many companies’ and organizations’ operations, proper calibration is crucial. Regardless of whether you need to screen people for fevers or want to keep your machinery running at its best, you likely want to make proper touchless thermometer calibration a priority. When you receive infrared thermometer calibration services, you can have peace of mind knowing your thermometers are reading temperatures accurately.

Contact Garber Metrology for Temperature Calibration

At Garber Metrology, we help many companies accurately calibrate their non-contact infrared thermometers. We use blackbodies and radiometrically calibrated calibrators to measure touchless thermometer accuracy. Our experienced calibration technicians ensure our temperature calibration services are fast and comply with the strictest regulations. We can handle your calibration needs in-house or on-site, giving you plenty of flexibility. When you turn to us for your thermometer calibration needs, we’ll make sure your infrared thermometers are as accurate as possible.

Review our humidity and temperature calibration services today. If you have any questions or want to request a free quote, feel free to contact us.

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