Noncontact temperature sensors include many different types, but all share one set of unique features: they are often involved with an optical property of materials called spectral emissivity or spectral emittance.

Just to be sure we are addressing the subject you are seeking, be aware that these devices are called by a bewildering variety of names. There’s some additional information on our original version of this website. You can see an index to it here.

They all function, or are based on, the same law of physics, Planck’s Law of the thermal emission of radiation.
(That means a lot, but mostly that there is no need for thermal equilibrium between the sensor and object of measurement to obtain a temperature measurement as is necessary in the case of contact sensors. Think about that. It is a truly significant difference with an enormous impact on one’s ability to measure temperature in various situations.)

Here’s just a few of the names used in current technical and popular literature:

ir thermometer, radiation thermometer, ir pyrometer, infrared thermometer, spot thermometer, spot radiometer* (the most popular technical misnomer), line scanner, radiation pyrometer, single waveband pyrometer, dual waveband pyrometer, ratio pyrometer, 2 color thermometer, 2 colour thermometer, two color thermometer, two colour pyrometer, radiometer, spectral radiometer, IR thermocouple, total radiation pyrometer, fiber optic pyrometer, disappearing filament pyrometer, quantitative thermal imager, dfp, optical pyro, multiwavelength pyrometer, and on and on…

Types of Noncontact Sensors

  • Radiation Thermometers

    Includes Pyrometers, line-measuring thermometers (most of the time they’re called line scanners-but all don’t scan) and infrared (IR) radiation thermometers, or, perhaps the most-misused term, spot radiometers*.

  • Thermal Imagers

    Quantitative thermal imagers are a special sub-class of these thermal imaging devices, they measure radiation temperature distributions as well as showing a false color thermal image. Thermal Night Vision Devices are another subclass of these devices, distinct from “Light Amplifying Night Vision Devices”. (The latter are beasties of an entirely different heritage and modus operandi).

  • Infrared (IR or Laser) Thermometers

    This another of the misnomers used for Radiation Thermometers that have sprung into being, as if there were a fundamental difference between them and all other types.
    Simply put: there is none, or if you prefer more colloquial language: THEY AIN’T!  (The differences are not in function, but in design, cosmetics and price and get blown out of technical relevance by those who seem to seek endless ways to differentiate their product from those of the competion! Hey, folks: a rose is still a rose by any other name!).

    Strictly speaking one could call a Radiation Thermometer that measures in the infrared region of the electromagnetic spectrum an “Infrared Thermometer”, but then it would need to be defined in that manner. In other words, every “Infrared Thermometer” is a Radiation Thermometer, but not all Radiation Thermometers are Infrared Thermometers. (Man, wouldn’t it just be a lot easier to call them what they are without all the explanations?)

  • Line Scanners (page in development)

  • Night Vision Devices (page in development)

  • Optical Pyrometers

    The old and trusty Optical Pyrometer (or Disappearing Filament Pyrometer or “Optical” or “DFP” or “Pyro”) not only refuses to go away, there’s even a next gen version on the market and one of the oldest and simplest design, the “Pyro Optical” is still around, also.

    Since it predates the original “Radiation Pyrometer” and is thus one of the very first, historic types of noncontact temperature sensors, it earned its own name and mark in the history of noncontact temperature sensors.

    Strictly speaking, it is a radiation thermometer that measures thermal radiation in a narrow spectral region of the visual portion of the Electromagnetic Spectrum near 0.65 µm. (Did you know that there is thermal radiation in the visible light range? If not, check a few more common sources like..the Sun, a flame or an incandescent lightbulb – you know, the kind that gets really hot when it’s been turned on for a little while)

  • Fiber Optic Temperature Sensors

    There’s enough uses and varieties of fiber optic-related temperature sensors these days to require a separate category for them. There really are two groups of them: Contact and Noncontact fiber optic thermometers (Funny, we’ve seen that distinction before).

  • Other Noncontact Temperature Sensors

    There’s quite a list of them, the “Other” devices, beginning with hybrid systems and multiwavelength pyrometers, errr, thermometers, already, and it’s sure to grow.

* Radiometers are designed to measure radiant power. They measure in units of Watts.  Thermometers, including radiation thermometers, measure in units called Degrees on one or more temperature scales. Watts ain’t degrees!

Some engineers will  point out that radiation thermometers are merely spectral radiometers calibrated in degrees, True enough, but they function as thermometers. If one had to insist that they be called radiometers of some sort, the more technically precise descriptive term would be “Limited Angle Spectral Radiometer Calibrated in Degrees C” or something similar.

Just to say spot radiometer is then more than a misnomer. Thermometer or radiation thermometer, or infrared thermometer seems a lot easier in words, but on the tongue also, in addition to being more precisely descriptive and technically correct.

2 comments on “Noncontact Sensors

  1. There are plenty of low cost devices on the market that will measure in the range that you request, but very few of which I am aware that will meet your inaccuracy spec.

    In fact, I am aware of only a very few highly specialized ear infrared thermometers that come close to that spec under calibration conditions, despite there being a medical device requirement for that type of accuracy in use.

    The NPL in the UK has done a lot of excellent work to develop a fixed point reference black body in the 36.3 Deg C region to test ear thermometers and they found some interesting and negative results when they did their testing.

    See their technical paper online at:

    Calibration uncertainty is just the start when you seek such miniscule measurement results; there are many error sources when attempting to make a measurement in near ambient temperature regions – it is the most difficult one for radiation thermometry.

    Two questions immediately need a clear answer: !. Is that a truly required capability, or just a fuzzy ideal, (possible time to renegotiate the full measurement requirements)? and 2. Is it obtainable within the budget of the project?

  2. I am looking for a non-contact temperature sensor that will work at low temperatures (about 20 – 70 C) with an accuracy of about 0.2 C. It would need also to work under ambient lighting. Does such technology exist and could you point me in a direction?

Leave a Reply

Your email address will not be published. Required fields are marked *