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Infrared temperature measurement


Key words Infrared temperature measurement, infrared thermometers, emissivity, food safety, quality assurance, real-time
Latest version 2013/02/14
Completed by UTCN, IRTA

How does it work?

Primary objective Online/real-time temperature measurement
Working principle Infrared (IR) thermometers for non-contact temperature measurement are sensors with wide-spread application in industrial processing and research.

IR thermometers capture the invisible infrared energy naturally emitted from all materials which are at temperatures above absolute zero (0º K). Infrared radiation is part of the electromagnetic spectrum which includes radio waves, microwaves, visible light, ultraviolet, gamma, and X-rays [2]. The IR part of the spectrum spans wavelengths from 0.7 to 1000 micrometers, but only frequencies between 0.7 and 20 micrometers are used for temperature measurement, because the current detectors are not sensitive enough to detect the very small amounts of energy.

An IR thermo device is made of a lens to focus the infrared energy on to a detector, which converts the energy to an electrical signal, that is compensated through ambient temperature variation. The result is displayed in units of temperature. The higher the emissivity of an object, the easier it is to obtain an accurate temperature measurement using infrared. Emissivity is the ratio of the energy radiated by an object at a given temperature compared to the energy emitted by a perfect radiator (or black body) at the same temperature. Values of emissivity fall between 0 and 1, the last number being the emissivity of a black body. Parameters that influence emmisivity are the material, surface structure (since part of the IR energy will be absorbed and part will be reflected) and regular geometry of the material.

Additional effects
  • Reduced detection time compared to thermocouples or digital thermometers, therefore more measurements per minute can be made.
  • The temperature sensor can be used inline for real-time monitoring.
  • The product is unharmed.
Important process parameters IR intensity, field of view, angle of measurement, response time
Important product parameters Emissivity, temperature, dimensions

What can it be used for?

Products Liquid or solid, in-flow or stationary. It can be used in cases where the object to be measured is moving, is surrounded by an electromagnetic field or controlled environment (e.g. vacuum).
Operations Temperature monitoring (through receiving, storage, cooking, holding and serving).
Solutions for short comings Non-contact infrared thermometers are used in applications where fast temperature reading without physically touching the object is needed; f.i. temperature monitoring of hot, hazardous, or hard-to-reach surfaces without contaminating or damaging the object. IR thermometers also provide advantages as lightweight, ease-of-use and rapid detection.

What can it NOT be used for?

Products It can not be used with reflective surfaces like stainless steel or aluminum. Depending on the field of view, samples with rought surface are not suitable for measurement.
Operations IR thermometers only measure surface temperature, being therefore a screening tool. When used for food applications, critical temperatures have to be measured with an internal device.
Other limitations
  • It can not be used through transparent surfaces like glass or plastics since it will measure the packaging material’s surface temperature instead.
  • The accuracy of measurement can be decreased by dust, smoke or vapors (humidity).
  • IR thermometers are designed to work at ambient temperatures, usually between 0-50oC; for their use in temperatures below or above these temperatures, they have to be preconditioned (acclimatized).
  • The temperature range of the device is normally related to the use, and can range between -64 to 500oC; the interval limits are displayed once the temperature range is over passed.
Risks or hazards Eye and skin damage can occur due to laser exposure. Therefore, direct exposure of the human eye needs to be avoided. Indirect exposure via reflective surfaces is also dangerous [3].


Maturity Designs of an infrared thermometer have existed since at least the late nineteenth century, and some concepts were first revealed in 1911 [7].

Practical measuring instruments started being available in the 1930's, being widely used in industry and research nowadays [1].

Modularity /Implementation It can be implemented in an existing production line.
Consumer aspects Not known.
Legal aspects Directive 2004/40/EC of the European Parliament and of the Council of 29 April 2004 on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields).
Environmental aspects Ease and speed of IR measurement triggered more frequent monitoring of the processes and storage temperatures, leading to decreased overall waste generation and energy costs.

Further Information

Institutes IRTA, DIL
Companies All QA Products, Calex Electronics, Comark Instruments, KELLER HCW, Land Instruments International, LumaSense Technologies, OMEGA Engineering, Optris, Raytek, Testo
  1. Gruner K.D. (2010). Principles of Non-Contact Temperature Measurement. Raytech publication, 32 pages.
  2. Rogalski A. (2011). Infrared Detectors. 2nd Edition, CRC Press, Taylor & Francis group, ISBN: 978-1-4200-7671-4, 876 pages.
  3. S. Evans. (2000). IR Thermometry boosts safety and accuracy of HVAC maintenance, Plant Engineering, 54(2): 58-62.
  4. Foster, A.M., Ketteringham, L.P., Mark J. Swain, M.J., Kondjoyan, A, Havet, M. c, Olivier Rouaud, O., Evans J.E. (2006). Design and development of apparatus to provide repeatable surface temperature–time treatments on inoculated food samples. Journal of Food Engineering, 76: 7–18.
  5. Mahnke C.W., Soucheck J.A., Insalata N.F. (1973). Measurement of Product Temperature by Use of an Infrared Thermometer. Applied microbiology 26(4): 646-647.
  6. Caniou, J (1999). Passive Infrared detection, Theory and Application. Kluwer Academic Publisher, ISBN-10: 0792385322, 623 pages.
  7. Darling, Charles R.; Pyrometry. A Practical Treatise on the Measurement of High Temperatures. Published by E.&F.N. Spon Ltd. London. 1911.

IR intensity, field of view, angle of measurement, response time Emissivity, temperature, dimensions Electro-Magnetic equipment 2.1.1 physical stabilizing, other other Proquest, Science Direct, literature review Search words: infrared temperature measurement, infrared food applications WikiSysop :Template:Review document :Template:Review status

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Created by Hte irta on 14 February 2013, at 11:12