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You may ask just how accurate are these infrared thermometers?


There are many IR thermometer on Facebook, Amazon and online with prices ranging from R 800 up to R 4000.  Many peoples first thought is that the cheap ones are probably not accurate.  If you had to take a look on Amazon you will notice that all the reviews of the cheaper models are overwhelmingly positive.  So what is the difference between a cheap and an expensive Infrared thermometer gun?

Looking at the specs, inexpensive ones have adjustable emissivity and accuracy of within 1% degree celsius. The expensive one also has similar accuracy and adjustable emissivity. What you lose with more inexpensive models is durability and a broader range of temperatures.  Furthermore, the primary difference between many of them is the ratio of spot size to distance.  An IR non-contact thermometer is essentially a single point of data. The ratio of spot size to distance is what determines the accuracy.  For domestic or office use the more inexpensive ones are perfectly suited to the purpose.

If you truly want or need extremely high accuracy you should consider an actual thermal camera. Obviously much more expensive but very much more accurate over a given area. Even an inexpensive 120 x 120 sensor is taking 14,400 data point readings at one time and converting that data into a false-colour image that can be manipulated to show the temperature of any one pixel.



Factors that can influence the accuracy


One must bear in mind that there are various factors that can influence the accuracy of all thermometers in general. These factors include whether a person has been exercising or just climbed out of a hot car.  Think for a moment about a person who has been trying to catch a flight in an airport for which they are late, they may have just run down a concourse.  If a person has taken anti-inflammatories or other medication to suppress their symptoms this could give a false low reading.



How is IR used to determine temperature?

All matter emits energy in the form of IR (heat). If there is a temperature difference between objects, including the surrounding environment, then this gradient can be measured and used. If the object in question is at the same temperature as its surroundings, the net radiation energy exchange will be zero. In either case, the characteristic spectrum of the radiation depends on the object and the surrounding absolute temperature. Handheld IR thermometers take advantage of this “radiation dependence” on temperature to produce a value for the targeted object and to display the results for the operator to read.

IR light works like visible light—it can be focused, reflected or absorbed. Handheld IR thermometers typically use a lens to focus light from one object onto a detector, called a thermopile. The thermopile absorbs the IR radiation and turns it into heat. The more IR energy, the hotter the thermopile gets. This heat is turned into electricity. The electricity is sent to a detector, which uses it to determine the temperature of whatever the thermometer is pointed at. The more electricity, the hotter the object. The higher the temperature, the more electricity sent to the detector, the higher the reading.

Handheld Infrared Thermometer Advantages

Handheld IR thermometers are fast, accurate and convenient—ideal for remote monitoring. The noncontact feature allows temperature measurements to be taken without touching the product being tested. This is not only important for the safety of the worker but also limits potential product contamination.

The response time (detection to display) of an IR thermometer is typically about one-half second. Maximum measuring distance is determined by the quality of the internal optics and atmospheric conditions. A handheld IR thermometer can only measure the surface temperature of an object and not the internal temperature. Because the maximum measuring range and accuracy can be affected by atmospheric conditions (water vapor or carbon dioxide) the maximum range is generally limited to approximately 100 feet.


The accuracy of the handheld IR thermometer is primarily determined by the distance-to-spot ratio (D/S Ratio). This ratio is the size of the area being evaluated by the IR thermometer as it relates to distance. In other words, the area being measured becomes larger as the distance increases. The smaller the target, the closer you should be to it. This ratio will have a significant impact on the accuracy or precision of the reading. If the target you are measuring is six inches in size, and your handheld infrared thermometer has a D/S ratio of eight to one, then the maximum distance at which you can reliably measure the temperature of the target is 48 inches (8:1 x 6 = 48). Beyond this distance, not only is the target being measured, but whatever else falls within the “spot” is being measured as well. This means that if a very hot object is the target, and it is in cooler surroundings, then measurements taken beyond the maximum distance will include cooler elements, lowering the “average” of what is in the “spot.”