How to select right Infrared ‘IR’ Thermometer?

Last updated on January 22nd, 2021 at 03:28 am

IR ‘Infrared’ thermometer is one of the most useful temperatures measuring instruments and it is used in almost all industries.  IR thermometer measures temperature based on the thermal radiation of the object. Thermal radiation is also referred to as black body radiation.  The thermometer measures infrared energy emitted by the object and after adjusting it with the emissivity of the object it determines the temperature of the object. As no physical contact is need with quick measurement possibility it is a very popular.

IR Thermometer

There are numbers of IR thermometers available in the market with a different specification and price range. Selecting the right IR thermometer is a challenging task based on our requirements and achieving maximum benefits with the use of IR technology.

Lets discuss how to select right IR thermometer for your application:-

1 D: S (Distance to Spot Size): As IR thermometers are contactless it is important to know what we are measuring. Normally laser beam is added to the IR thermometer to locate the measuring area. It is important to note that the laser spot is not the exact point of measurement but just the identification of the area of measurement. The area of measurement changes with the change in distance of the use of the thermometer. If the distance is increased the spot area being measured will increase and it will start measuring temperature of large suface. The capability of measurement of spot size with respect to distance is defined as D:S (Distance to spot size).  Eg if in specification of the thermometer it is mentioned that the distance to spot ratio is 12:1, it means the thermometer can measure a one-inch diameter spot when it’s 12 inches from the target. For increasing or reducing spot size distance of thermometer can be adjusted accordingly. Thermometer D:S varies from 1:1 on the least expensive to 60:1 for expensive models. Higher D:S will provide you better control of the area being measured.

Distance to Spot area

2 Emissivity : As IR thermometers measure IR radiation being emitted by the body and the IR radiation depends on the emissivity of the surface. It is important to select the right emissivity for correct temperature measurement. Emissivity is a measure of how effectively a surface emits infrared radiation. The emissivity scale ranges from a relative value of 0 to 1. where 1 represents the perfect black body emitter, while 0 represents zero thermal radiance.

Emissivity indicator in IR Thermometer

Most organic objects fall close to 0.95 on the emissivity scale. For this reason, many IR thermometers are pre-set at an emissivity of 0.95.  However, objects with much lower emissivity ratings, such as polished metal, will give false temperature readings. This problem can be sorted out by putting a piece of non-reflective tape (such as electrical tape) over the shiny surface or applying some flat paint to give you a target from which you can get a better measurement. Depending on the use of IR thermometer fixed emissivity, 3 steps (high medium & low) emissivity or variable emissivity IR thermometer can be selected.

Temperature measurement with non reflective tape

3 Temperature range: the thermometer is designed to be operated between lower and higher temperature limits. It is important to check if the temperature to be measured is the in-between range of the thermometer range before procurement.

4 Accuracy & repeatability: just like another thermometer accuracy of the thermometer is important and must be selected based on our requirement. Accuracy of measurement also differ in between different temperature range of the thermometer therefore for the right selection of thermometer, measuring range of temperature should be at the max accuracy level of instrument.

5 Repeatability – it is often used to describe the variation in successive measurements of the same variable taken under the same conditions, variation should be low and repeatability of the instrument should be high for better results.

6. Unit of measurement: in most of the thermometer unit of temperature measurement is Deg C or Deg F or both, before selecting right thermometer unit of measurement must be checked. some thermometers are having both temperature units and may be beneficial if reading to be taken in both units. apart from unit display resolution must also be checked for getting precise reading.

7. Operating Conditions: Operating temperature range is important for the proper functioning of the thermometer. it must be checked before selection. While operating the IR thermometer it must be noted that thermometer temperature must be normalized to the atmospheric temperature for correct measurement. Humidity and altitude also plays role in operating conditions, to be checked if the IR thermometer is used for any extreme conditions.

8 IP rating: IP or ingress protection rating is the level of protection offered by an electrical enclosure, against solids and liquids, based on the environmental use of a thermometer, IP rating should be specified or selected. An IP rating consists of two digits, the first one for intrusion protection, and the second one is for moisture protection. IP54 is commonly used as it means equipment is protected from dust and splashing of water.  For more detail click here.

9 Laser Safety: Laser is used for guiding the measuring target,  if leaser is used in the IR thermometer, laser safety to be considered while selecting thermometer especially if it is being used in medical or food applications. For more detail click here

Laser radiation warning

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