Infrared thermometer

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An infrared thermometer 1024 Pyrometer-8445.jpg
An infrared thermometer

An infrared thermometer is a thermometer which infers temperature from a portion of the thermal radiation sometimes called black-body radiation emitted by the object being measured. They are sometimes called laser thermometers as a laser is used to help aim the thermometer, or non-contact thermometers or temperature guns, to describe the device's ability to measure temperature from a distance. By knowing the amount of infrared energy emitted by the object and its emissivity, the object's temperature can often be determined within a certain range of its actual temperature. Infrared thermometers are a subset of devices known as "thermal radiation thermometers".

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Sometimes, especially near ambient temperatures, readings may be subject to error due to the reflection of radiation from a hotter body—even the person holding the instrument[ citation needed ] — rather than radiated by the object being measured, and to an incorrectly assumed emissivity.

The design essentially consists of a lens to focus the infrared thermal radiation on to a detector, which converts the radiant power to an electrical signal that can be displayed in units of temperature after being compensated for ambient temperature. This permits temperature measurement from a distance without contact with the object to be measured. A non-contact infrared thermometer is useful for measuring temperature under circumstances where thermocouples or other probe-type sensors cannot be used or do not produce accurate data for a variety of reasons.

Examples of use

A sailor checking the temperature of a ventilation system Pyrometer 040824.jpg
A sailor checking the temperature of a ventilation system

Some typical circumstances are where the object to be measured is moving; where the object is surrounded by an electromagnetic field, as in induction heating; where the object is contained in a vacuum or another controlled atmosphere; or in applications where a fast response is required, the accurate surface temperature is desired or the object temperature is above the recommended use point for contact sensors, or contact with a sensor would mar the object or the sensor, or introduce a significant temperature gradient on the object's surface.

Infrared thermometers can be used to serve a wide variety of temperature monitoring functions. A few examples provided include detecting clouds for remote telescope operation, checking mechanical or electrical equipment for temperature and hot spots, measuring the temperature of patients in a hospital without touching them, checking heater or oven temperature, for calibration and control, checking for hot spots in fire-fighting, monitoring materials in processes involving heating or cooling, and measuring the temperature of volcanoes. At times of epidemics of diseases causing fever, such as SARS coronavirus and Ebola virus disease, infrared thermometers have been used to check arriving travelers for fever without causing harmful transmissions among the tested. [1] [2]

IR thermometer checking a person's temperature Hand holding non-contact infrared thermometer checking a person temprature. COVID-19 Concept.jpg
IR thermometer checking a person's temperature

In 2020 when COVID-19 pandemic hit the world, infrared thermometers were used to measure people's temperature and deny them entry to potential transmission sites if they showed signs of fever. Public health authorities such as the FDA in United States published rules to assure accuracy and consistency among the infrared thermometers. [3]

There are many varieties of infrared temperature-sensing devices, both for portable and handheld use and as fixed installations.

Accuracy

Infrared thermometers are characterized by specifications including accuracy and angular coverage. Simpler instruments may have a measurement error of about ±2 °C or ±4 °F.[ citation needed ]

The distance-to-spot ratio (D:S) is the ratio of the distance to the measurement surface and the diameter of the temperature measurement area. For instance, if the D:S ratio is 12:1, the diameter of the measurement area is one-twelfth of the distance to the object. A thermometer with a higher ratio of D to S is able to sense a more-specific, narrower surface at a greater distance than one with a lower ratio. A 12:1 rated device can sense a 1-inch circle at a distance of one foot, whereas a 10:1 ratio device achieves the same 1-inch circle at 10 inches, and a wider, less-specific circle of 1.2 inches at a distance of 12 inches.[ citation needed ]

The ideal target area should be at least twice the size of the spot at that distance, [4] with smaller areas relative to distance resulting in less accurate measurement.[ citation needed ] An infrared thermometer should not be placed too close to its target, as this proximity could cause heat to build up in the thermometer's housing and damage the sensor. Measurement error generally only decreases with too much distance because of the effects of reflectivity and the inclusion of other heat sources within the sensor's field of view. [5] [6]

According to the Stefan–Boltzmann law, radiant power is proportional to the fourth power of temperature, so when the measurement surface has both hot and cold areas, the indicated temperature may be higher than the actual average temperature, and closer to fourth-power mean average. [7]

Most surfaces have high emissivity (over 0.9 for most biological surfaces)[ citation needed ], and most IR thermometers rely on this simplifying assumption; however, reflective surfaces have lower emissivity than non-reflective surfaces.[ citation needed ] Some sensors have an adjustable emissivity setting, which can be set to measure the temperature of reflective and non-reflective surfaces. A non-adjustable thermometer may be used to measure the temperature of a reflective surface by applying a non-reflective paint or tape, with some loss of accuracy.[ citation needed ]

A sensor with an adjustable emissivity setting can also be used to calibrate the sensor for a given surface or to measure the emissivity of a surface. When the temperature of a surface is accurately known (e.g. by measuring with a contact thermometer), then the sensor's emissivity setting can be adjusted until the temperature measurement by the IR method matches the measured temperature by the contact method; the emissivity setting will indicate the emissivity of the surface, which can be taken into account for later measurements of similar surfaces (only).

Infrared pyrometer

The most common infrared thermometer is the spot infrared pyrometer or infrared pyrometer, which measures the temperature at a spot on a surface (actually a relatively small area determined by the D:S ratio). These usually project a visible red dot onto the center of the area being measured that identifies the spot being measured, but plays no part in the measurement. The actual angular area being measured varies among instruments and is not restricted to the visible spot.

Related equipment, although not strictly thermometers, include infrared scanning systems and infrared thermal imaging cameras. Infrared scanning systems scan a larger area, typically by using what is essentially a spot thermometer pointed at a rotating mirror. These devices are widely used in manufacturing involving conveyors or "web" processes, such as large sheets of glass or metal exiting an oven, fabric, and paper, or continuous piles of material along a conveyor belt. Infrared thermal imaging cameras or infrared cameras are essentially infrared radiation thermometers that measure the temperature at many points over a relatively large area to generate a two-dimensional image, called a thermogram, with each pixel representing a temperature. This technology is more processor- and software-intensive than spot or scanning thermometers, and is used for monitoring large areas. Typical applications include perimeter monitoring used by military or security personnel, inspection/process quality monitoring of manufacturing processes, and equipment or enclosed space hot or cold spot monitoring for safety and efficiency maintenance purposes.

A photographic camera using infrared film and suitable lens, etc., is also called an "infrared camera". This only captures the near-infrared and is not sensitive to the thermal radiation from room-temperature objects.

See also

Related Research Articles

<span class="mw-page-title-main">Infrared</span> Form of electromagnetic radiation

Infrared is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with waves that are just longer than those of red light, the longest waves in the visible spectrum, so IR is invisible to the human eye. IR is generally understood to include wavelengths from around 750 nm to 1 mm. IR is commonly divided between longer-wavelength thermal IR, emitted from terrestrial sources, and shorter-wavelength IR or near-IR, part of the solar spectrum. Longer IR wavelengths (30–100 μm) are sometimes included as part of the terahertz radiation band. Almost all black-body radiation from objects near room temperature is in the IR band. As a form of electromagnetic radiation, IR carries energy and momentum, exerts radiation pressure, and has properties corresponding to both those of a wave and of a particle, the photon.

<span class="mw-page-title-main">Thermometer</span> Device to measure temperature

A thermometer is a device that measures temperature or temperature gradient. A thermometer has two important elements: (1) a temperature sensor in which some change occurs with a change in temperature; and (2) some means of converting this change into a numerical value. Thermometers are widely used in technology and industry to monitor processes, in meteorology, in medicine, and in scientific research.

<span class="mw-page-title-main">Pyrometer</span> Type of thermometer sensing radiation

A pyrometer, or radiation thermometer, is a type of remote sensing thermometer used to measure the temperature of distant objects. Various forms of pyrometers have historically existed. In the modern usage, it is a device that from a distance determines the temperature of a surface from the amount of the thermal radiation it emits, a process known as pyrometry, a type of radiometry.

<span class="mw-page-title-main">Bolometer</span> Device for measuring incident electromagnetic radiation

A bolometer is a device for measuring radiant heat by means of a material having a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley.

<span class="mw-page-title-main">Heat transfer</span> Transport of thermal energy in physical systems

Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system.

<span class="mw-page-title-main">Thermal radiation</span> Electromagnetic radiation generated by the thermal motion of particles

Thermal radiation is electromagnetic radiation emitted by the thermal motion of particles in matter. Thermal radiation transmits as an electromagnetic wave through both matter and vacuum. When matter absorbs thermal radiation its temperature will tend to rise. All matter with a temperature greater than absolute zero emits thermal radiation. The emission of energy arises from a combination of electronic, molecular, and lattice oscillations in a material. Kinetic energy is converted to electromagnetism due to charge-acceleration or dipole oscillation. At room temperature, most of the emission is in the infrared (IR) spectrum. Thermal radiation is one of the fundamental mechanisms of heat transfer, along with conduction and convection.

<span class="mw-page-title-main">Thermographic camera</span> Imaging device using infrared radiation

A thermographic camera is a device that creates an image using infrared (IR) radiation, similar to a normal camera that forms an image using visible light. Instead of the 400–700 nanometre (nm) range of the visible light camera, infrared cameras are sensitive to wavelengths from about 1,000 nm to about 14,000 nm (14 μm). The practice of capturing and analyzing the data they provide is called thermography.

<span class="mw-page-title-main">Thermography</span> Infrared imaging used to reveal temperature

Infrared thermography (IRT), thermal video and/or thermal imaging, is a process where a thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are examples of infrared imaging science. Thermographic cameras usually detect radiation in the long-infrared range of the electromagnetic spectrum and produce images of that radiation, called thermograms. Since infrared radiation is emitted by all objects with a temperature above absolute zero according to the black body radiation law, thermography makes it possible to see one's environment with or without visible illumination. The amount of radiation emitted by an object increases with temperature; therefore, thermography allows one to see variations in temperature. When viewed through a thermal imaging camera, warm objects stand out well against cooler backgrounds; humans and other warm-blooded animals become easily visible against the environment, day or night. As a result, thermography is particularly useful to the military and other users of surveillance cameras.

<span class="mw-page-title-main">Black-body radiation</span> Thermal electromagnetic radiation

Black-body radiation is the thermal electromagnetic radiation within, or surrounding, a body in thermodynamic equilibrium with its environment, emitted by a black body. It has a specific, continuous spectrum of wavelengths, inversely related to intensity, that depend only on the body's temperature, which is assumed, for the sake of calculations and theory, to be uniform and constant.

<span class="mw-page-title-main">Emissivity</span> Capacity of an object to radiate electromagnetic energy

The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation. Thermal radiation is electromagnetic radiation that most commonly includes both visible radiation (light) and infrared radiation, which is not visible to human eyes. A portion of the thermal radiation from very hot objects is easily visible to the eye.

<span class="mw-page-title-main">Passive infrared sensor</span> Electronic sensor that measures infrared light

A passive infrared sensor is an electronic sensor that measures infrared (IR) light radiating from objects in its field of view. They are most often used in PIR-based motion detectors. PIR sensors are commonly used in security alarms and automatic lighting applications.

<span class="mw-page-title-main">Temperature measurement</span> Recording of temperature

Temperature measurement describes the process of measuring a current temperature for immediate or later evaluation. Datasets consisting of repeated standardized measurements can be used to assess temperature trends.

<span class="mw-page-title-main">Disappearing-filament pyrometer</span>

The disappearing-filament pyrometer is an optical pyrometer, in which the temperature of a glowing incandescent object is measured by comparing it to the light of a heated filament. Invented independently in 1901 by Ludwig Holborn and Ferdinand Kurlbaum in Germany and Everett Fleet Morse in the United States, it was the first device which could measure temperatures above 1000 °C. Disappearing filament pyrometers have been used to measure temperatures between about 600 °C and 3000 °C. Like other optical pyrometers they are used to measure the temperature of objects too hot for contact thermometers, such as molten metals. Widely used in the steel and ceramics industries as well as for research, they have been almost totally superseded by electronic spectral-band pyrometers.

<span class="mw-page-title-main">Proximity sensor</span> About proximity sensor

A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact.

A flame detector is a sensor designed to detect and respond to the presence of a flame or fire, allowing flame detection. Responses to a detected flame depend on the installation, but can include sounding an alarm, deactivating a fuel line, and activating a fire suppression system. When used in applications such as industrial furnaces, their role is to provide confirmation that the furnace is working properly; it can be used to turn off the ignition system though in many cases they take no direct action beyond notifying the operator or control system. A flame detector can often respond faster and more accurately than a smoke or heat detector due to the mechanisms it uses to detect the flame.

<span class="mw-page-title-main">Infrared and thermal testing</span>

Infrared and thermal testing refer to passive thermographic inspection techniques, a class of nondestructive testing designated by the American Society for Nondestructive Testing (ASNT). Infrared thermography is the science of measuring and mapping surface temperatures.

"Infrared thermography, a nondestructive, remote sensing technique, has proved to be an effective, convenient, and economical method of testing concrete. It can detect internal voids, delaminations, and cracks in concrete structures such as bridge decks, highway pavements, garage floors, parking lot pavements, and building walls. As a testing technique, some of its most important qualities are that (1) it is accurate; (2) it is repeatable; (3) it need not inconvenience the public; and (4) it is economical."

Sensors for arc welding are devices which – as a part of a fully mechanised welding equipment – are capable to acquire information about position and, if possible, about the geometry of the intended weld at the workpiece and to provide respective data in a suitable form for the control of the weld torch position and, if possible, for the arc welding process parameters.

Active thermography is an advanced nondestructive testing procedure, which uses a thermography measurement of a tested material thermal response after its external excitation. This principle can be used also for non-contact infrared non-destructive testing (IRNDT) of materials.

References

  1. Thermal Imaging for Detecting Potential SARS Infection Archived 2016-12-26 at the Wayback Machine (also covers non-imaging infrared thermometers)
  2. "A Roissy, le "thermomètre laser" pour détecter Ebola". Libération. 2014-10-18. Archived from the original on 2018-08-18. Retrieved 2014-10-18. A peine descends d'avion, les passagers du vol Conakry-Paris ont été accueillis samedi avec des thermomètres laser pour détecter d'éventuels cas de fièvre, mesure la plus spectaculaire prise par le gouvernement pour prévenir l'éventuelle arrivée en France du virus Ebola
  3. Health, Center for Devices and Radiological (2020-06-23). "Non-contact Temperature Assessment Devices During the COVID-19 Pandemic". FDA. Archived from the original on 2020-07-26. Retrieved 2020-07-14.
  4. "Infrared thermometers explained" (PDF). FireCraft Safety.com. Archived (PDF) from the original on 2017-09-05. Retrieved 2017-09-05.
  5. Research & Development. Reed Business Information. 2004. p. 31.
  6. J. R. Barker (1 October 1985). Thermological methods. VCH. p. 192. ISBN   978-3-527-15168-4.
  7. "Stefan-Boltzmann Law". Archived from the original on 2015-05-02. Retrieved 2015-06-09.