Disadvantages of an Infrared Thermometer

An infrared thermometer is a handy tool that can help you measure temperatures in several ways. The most important feature to consider when buying one is its durability. You can carry an infrared thermometer anywhere you go, and it can also be stored in your toolbox. Infrared thermometers have many benefits, and the price has come down in recent years. However, you should know that there are still several disadvantages to these devices.

infrared thermometerDistance-to-spot ratio

An infrared thermometer’s field-of-view is a crucial parameter in determining its accuracy. The manufacturer’s specifications (also known as the distance-to-spot ratio, size-of-source effect, or field-of-view) often include a specification or a chart for measuring the spots’ sizes. As a general rule, the closer the location is to the target, the higher the accuracy.

The D:S ratio refers to the area that the infrared thermometer can accurately measure compared to the distance to the target. For example, a distance-to-spot ratio of eight:1 means that a laser pointer placed eight feet from the target would be equivalent to a circle with a one-foot diameter. A lower D:S ratio would require the thermometer to be closer to the target for the exact measurement, which could pose a safety concern if the surface being measured is extremely hot.

IR thermometers come with laser pointers to indicate the spot size. Single-laser instruments may be difficult to use, while two or more lasers may be easier to handle. Some models of infrared thermometers may have multiple lasers to indicate the entire field of view at the target distance. Distance-to-spot ratios of infrared thermometers are essential, as airborne objects may deflect infrared energy.

Field of view

The field of view of an infrared thermometer is a crucial parameter for accurate measurement. Infrared thermometers have an elliptical or circular measurement spot on solid or opaque surfaces, increasing the observation area. The device processes infrared emissions received within its FOV to produce a single temperature reading. For accurate measurement, the FOV must be smaller than the target’s area, as larger sizes will result in measures that combine the temperatures of the target and the surrounding background.

The field of view of an infrared thermometric instrument varies with its application. The instrument’s field of view is a circle in which the instrument averages the amount of infrared energy emitted by the target. Therefore, the target must be large enough to fill the field of view. Otherwise, the instrument may result in an incorrect reading. Therefore, choosing an infrared thermometer that matches your application is essential. Visit instrumentchoice.com.au/instrument-choice/meters/environment-meters/ir-thermometers for more details.


There are many differences between infrared thermometers and their counterparts. The former can tell you whether someone has a fever while the latter cannot. Both can be inaccurate, and there is a tendency to overestimate the degree of fever. For this reason, both types of thermometers must meet high standards to be used for medical diagnosis. Pharmaceutical-grade infrared thermometers are more accurate than their counterparts.

The temperature measurement accuracy of infrared thermometers depends on their distance from the target. This distance should be at least twice as considerable as the target area. If the space is too short, too close or too far, the thermometer’s accuracy will be compromised. In addition, the thermometer must not be placed too close to its target since this can lead to heat accumulation in the thermometer housing and possibly damage its sensor. As the distance between the target and the thermometer increases, measurement error reduces.

Using an infrared thermometer

If you’re interested in protecting yourself from COVID-19 or reducing your contact with sick people, you may consider using an infrared thermometer. These devices measure temperatures in the infrared spectrum, invisible to the naked eye. These tools also have several benefits, including measuring temperatures over a considerable distance. But beware – the IR range is only usable when temperatures are at or above a certain level on the surface.

IR thermometers vary in their distance-to-spot ratio, which determines the IR thermometer’s field of view at a given distance. The distance-to-spot ratio reflects the sophistication of the device’s optical system. A good D:S ratio will range from 1:1 for an inexpensive infrared thermometer up to 60:1 for a high-end thermometer. The chart below shows the field of view diameters for different D:S ratios.