Non-contact Infrared Thermometer

Updated: Sep 7

Infrared thermometers have obvious appeal—measuring the temperature of something without having to touch it or even be near it. But before you purchase an IR thermometer, there are some important questions you need to consider and some limitations you should keep in mind.

How to Use an Non-contact Infrared Thermometer in the Right Way?

A Non-contact infrared thermometer (also called clinical thermometer) is used for measuring human or animal body temperature. The tip of the thermometer is inserted into the mouth under the tongue (oral or sub-lingual temperature), under the armpit (axillary temperature), into the rectum via the anus (rectal temperature), into the ear (tympanic temperature), or on the forehead (temporal temperature). As one of the medical necessities for house living, the temperature gun is easy and convenient for body temperature measurement. Besides, this small portative machine can be used almost anywhere to anyone. The backlit screen will show you the detection body temperature only by pressing the button and put it close to one’s forehead. Maybe it sounds easy but there still something we need to notice on using the infrared thermometer. Here we would like to share something knowledge about the infrared thermometer and tips on how to choose an infrared thermometer to you.

How does a Non-contact Infrared Thermometer work?

You may be curious about how come the Non-contact Infrared Thermometer could take our body temperature so speedy with accurate degrees. Your curiosity is as good as mine. The reason why an infrared thermometer can be called for any time when an object needs to be determined is that it uses the infrared light from one object onto a detector called a thermopile. When we point the probe at our forehead or body closely, the thermopile absorbs the infrared radiation and turns it into electricity. The more infrared energy from the object, the hotter the thermopile gets. When the electricity is sent to the detector, it would tell the temperature of whatever the thermometer points at. The more electricity, the hotter the object is. This process is very fast and the determined accuracy is very good.


Non-contact Infrared Thermometer is characterized by specifications including accuracy and angular coverage. Simpler instruments may have a measurement error of about ±2 °C or ±4 °F.

The distance-to-spot ratio (D:S) is the ratio of the distance to the measurement surface and the diameter of the temperature measurement area. For instance, if the D:S ratio is 12:1, the diameter of the measurement area is one-twelfth of the distance to the object. A thermometer with a higher ratio of D to S is able to sense a more-specific, narrower surface at a greater distance than one with a lower ratio. A 12:1 rated device can sense a 1-inch circle at a distance of one foot, whereas a 10:1 ratio device achieves the same 1-inch circle at 10 inches, and a wider, less-specific circle of 1.2 inches at a distance of 12 inches.

The ideal target area should be at least twice the size of the spot at that distance, with smaller areas relative to distance resulting in less accurate measurement. An infrared thermometer cannot be placed too close to its target, or this proximity causes heat to build up in the thermometer's housing and damages the sensor. Measurement error generally only decreases with too much distance because of the effects of reflectivity and the inclusion of other heat sources within the sensor's field of view.

According to the Stefan–Boltzmann law, radiant power is proportional to the fourth power of temperature, so when the measurement surface has both hot and cold areas, the indicated temperature may be higher than the actual average temperature, and closer to fourth-power mean average.

Most surfaces have high emissivity (over 0.9 for most biological surfaces), and most IR thermometers rely on this simplifying assumption; however, reflective surfaces have lower emissivity than non-reflective surfaces. Some sensors have an adjustable emissivity setting, which can be set to measure the temperature of reflective and non-reflective surfaces. A non-adjustable thermometer may be used to measure the temperature of a reflective surface by applying a non-reflective paint or tape, with some loss of accuracy.

A sensor with an adjustable emissivity setting can also be used to calibrate the sensor for a given surface or to measure the emissivity of a surface. When the temperature of a surface is accurately known (e.g. by measuring with a contact thermometer), then the sensor's emissivity setting can be adjusted until the temperature measurement by the IR method matches the measured temperature by the contact method; the emissivity setting will indicate the emissivity of the surface, which can be taken into account for later measurements of similar surfaces (only).

How to use the Non-contact Infrared Thermometer correctly?

Before you take an Non-contact Infrared Thermometer for temperature measurement, there is something you should know about it. The Non-contact Infrared Thermometer measures an area, not just a dot. The longer distance you are aiming at, the bigger the area is for measurement. You need to know the infrared thermometer distance to spot ratio so that you could get close enough to target for measurement and get the accurate result. If you can’t achieve accurate measurements with a handheld IR thermometer, that might not rule out using an infrared temperature sensor completely. Besides, steam or dust can affect the accuracy of the IR thermometer. You’d better watch your surroundings before you take the measurement. Always keep the thermometer lens clean and no scratches. Allow two or three more times for temperature measurement to get to the most accurate results.

How to Choose a good Non-contact IR Thermometer on the market?

An IR laser thermometer is a necessity for house living. A good quality infrared thermometer could be durable as long as you take good care of it. Well, there are some aspects you need to focus on when choosing a good infrared thermometer. No matter what type of IR thermometer you decide to purchase, the accuracy would be the first place you need to focus on it. Test it times for the accuracy before purchase. Second, check the emissivity and temperature range. A thermometer emissivity affects its ability to read different materials, and you’ll get the most out of one that allows you to adjust the amount of energy it emits. An IR infrared temp gun’s temperature range directly affects what jobs you can do with it. Besides, you’d better choose the one with quick read speed and data recording functions. For the last thing, you should focus on the warranty. Thermometers can eventually break, and a warranty is a must-have feature for some thermometers.

Examples of use

Some typical circumstances are where the object to be measured is moving; where the object is surrounded by an electromagnetic field, as in induction heating; where the object is contained in a vacuum or another controlled atmosphere; or in applications where a fast response is required, the accurate surface temperature is desired or the object temperature is above the recommended use point for contact sensors, or contact with a sensor would mar the object or the sensor, or introduce a significant temperature gradient on the object's surface.

Non-contact Infrared Thermometer can be used to serve a wide variety of temperature monitoring functions. A few examples provided include detecting clouds for remote telescope operation, checking mechanical or electrical equipment for temperature and hot spots, measuring the temperature of patients in a hospital without touching them, checking heater or oven temperature, for calibration and control, checking for hot spots in fire-fighting, monitoring materials in processes involving heating or cooling, and measuring the temperature of volcanoes. At times of epidemics of diseases causing fever, such as SARS coronavirus and Ebola virus disease, infrared thermometers have been used to check arriving travelers for fever without causing harmful transmissions among the tested.

In 2020 when COVID-19 pandemic hit the world, Infrared Thermometers were used to provide safe and accurate testing. Public health authorities such as the FDA in the United States published rules to assure accuracy and consistency among the Infrared Thermometers.

There are many varieties of infrared temperature-sensing devices, both for portable and handheld use and as fixed installations.

Preparing the Person being Evaluated:

In preparation for taking a temperature measurement with an NCIT, the person using the NCIT should typically ensure that

  • The test area of the forehead is clean, dry, and not blocked during measurement.

  • The person’s body temperature or temperature at the forehead test area has not been increased or decreased by wearing excessive clothing or head covers (for example headbands, bandanas), or by using facial cleansing products (for example cosmetics wipes)



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