Infrared thermometer
Encyclopedia
Infrared thermometers infer temperature
using a portion of the thermal radiation
sometimes called blackbody radiation emitted by the object of measurement. They are sometimes called laser thermometers if a laser
is used to help aim the thermometer, or non-contact thermometers 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 be determined most of the time. They are a subset of devices more precisely called "Thermal Radiation Thermometers" or Radiation Thermometer for short.
Sometimes, especially near ambient temperatures, false readings will be obtained indicating incorrect temperature. This is most often due to other thermal radiation reflected from the object being measured, but having its source elsewhere, like a hotter wall or other object nearby - even the person holding the thermometer can be an error source in some cases. It can also be due to an incorrect emissivity on the emissivity control or a combination of the two possibilities.
The most basic design 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 configuration facilitates temperature measurement from a distance
without contact with the object to be measured. As such, the 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.
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 other controlled atmosphere; or in applications where a fast response is required, an accurate surface temperature is desired or the object temperature is above the recommended use point of a 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 to this article include:
There are many varieties of infrared temperature sensing devices available today, including configurations designed for flexible and portable handheld use, as well many designed for mounting in a fixed position to serve a dedicated purpose for long periods.
Specifications of portable handheld sensors available to the home user will include ratings of temperature accuracy (usually with measurement uncertainty of ±2 °C/±4 °F) and other parameters.
The distance-to-spot ratio (D:S) is the ratio of the distance to the object and the diameter of the temperature measurement area. For instance if the D:S ratio is 12:1, measurement of an object 12 inches (30.5 cm) away will average the temperature over a 1 inches (25.4 mm) area. The sensor may have an adjustable emissivity setting, which can be set to measure the temperature of reflective (shiny) and non-reflective surfaces.
A non-adjustable thermometer sometimes can be used to measure the temperature of a shiny surface by applying a non-shiny paint or tape to the surface, if the allowed measurement error is acceptable.
The most common infrared thermometers are the:
Related equipment, although not strictly thermometers, includes:
A photographic camera
using infrared
film
and suitable lens, etc., is also called an infrared camera.
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
using a portion of the thermal radiation
Thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....
sometimes called blackbody radiation emitted by the object of measurement. They are sometimes called laser thermometers if a laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
is used to help aim the thermometer, or non-contact thermometers 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
Emissivity
The emissivity of a material is the relative ability of its surface to emit energy by radiation. It is the ratio of energy radiated by a particular material to energy radiated by a black body at the same temperature...
, the object's temperature can be determined most of the time. They are a subset of devices more precisely called "Thermal Radiation Thermometers" or Radiation Thermometer for short.
Sometimes, especially near ambient temperatures, false readings will be obtained indicating incorrect temperature. This is most often due to other thermal radiation reflected from the object being measured, but having its source elsewhere, like a hotter wall or other object nearby - even the person holding the thermometer can be an error source in some cases. It can also be due to an incorrect emissivity on the emissivity control or a combination of the two possibilities.
The most basic design consists of a lens to focus the infrared thermal radiation
Thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits 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 configuration facilitates temperature measurement from a distance
Distance
Distance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, or an estimation based on other criteria . In mathematics, a distance function or metric is a generalization of the concept of physical distance...
without contact with the object to be measured. As such, the 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.
Some typical circumstances are where the object to be measured is moving; where the object is surrounded by an electromagnetic field
Electromagnetic field
An electromagnetic field is a physical field produced by moving electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction...
, as in induction heating
Induction heating
Induction heating is the process of heating an electrically conducting object by electromagnetic induction, where eddy currents are generated within the metal and resistance leads to Joule heating of the metal...
; where the object is contained in a vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
or other controlled atmosphere; or in applications where a fast response is required, an accurate surface temperature is desired or the object temperature is above the recommended use point of a 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 to this article include:
- Detecting clouds for remote telescope operation
- Checking mechanical equipment or electrical circuit breaker boxes or outlets for hot spots
- Checking heater or oven temperature, for calibration and control purposes
- Detecting hot spots / performing diagnostics in electrical circuit board manufacturing
- Checking for hot spots in fire fighting situations
- Monitoring materials in process of heating and cooling, for research and development or manufacturing quality control situations
There are many varieties of infrared temperature sensing devices available today, including configurations designed for flexible and portable handheld use, as well many designed for mounting in a fixed position to serve a dedicated purpose for long periods.
Specifications of portable handheld sensors available to the home user will include ratings of temperature accuracy (usually with measurement uncertainty of ±2 °C/±4 °F) and other parameters.
The distance-to-spot ratio (D:S) is the ratio of the distance to the object and the diameter of the temperature measurement area. For instance if the D:S ratio is 12:1, measurement of an object 12 inches (30.5 cm) away will average the temperature over a 1 inches (25.4 mm) area. The sensor may have an adjustable emissivity setting, which can be set to measure the temperature of reflective (shiny) and non-reflective surfaces.
A non-adjustable thermometer sometimes can be used to measure the temperature of a shiny surface by applying a non-shiny paint or tape to the surface, if the allowed measurement error is acceptable.
The most common infrared thermometers are the:
- Spot Infrared Thermometer or Infrared PyrometerPyrometerA pyrometer is a non-contacting device that intercepts and measures thermal radiation, a process known as pyrometry.This device can be used to determine the temperature of an object's surface....
, which measures the temperature at a spot on a surface (actually a relatively small area determined by the D:S ratio).
Related equipment, although not strictly thermometers, includes:
- 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 CamerasThermographic cameraA thermographic camera or infrared camera is a device that forms an image using infrared radiation, similar to a common camera that forms an image using visible light...
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 thermogramThermographyInfrared thermography, thermal imaging, and thermal video are examples of infrared imaging science. Thermal imaging cameras detect radiation in the infrared range of the electromagnetic spectrum and produce images of that radiation, called thermograms...
, 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
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
using infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
film
Film
A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...
and suitable lens, etc., is also called an infrared camera.
External links
- IRINFO.ORG - The Definitive Online Resource for Infrared Thermography
- UK Thermography Association
- Introduction to Infrared Thermometers - Omega
- Applications of Infrared Thermometers and Thermal Imagers: a free online compilation of applications from various websites and publications
- 2010 updated Radiation Thermometer pages on the About Temperature Sensors website (www.Temperatures.com) since the mid-1990s
- News of infrared and thermal imaging products & services with dedicated RSS newsfeeds
See also
- Infrared camera
- ThermographyThermographyInfrared thermography, thermal imaging, and thermal video are examples of infrared imaging science. Thermal imaging cameras detect radiation in the infrared range of the electromagnetic spectrum and produce images of that radiation, called thermograms...
- ASTM Subcommittee E20.02 on Radiation ThermometryASTM Subcommittee E20.02 on Radiation ThermometryThe ASTM Subcommittee E20.02 on Radiation Thermometry is a subcommittee of the ASTM Committee E20 on Temperature Measurement, a committee of ASTM International. The subcommittee is responsible for standards relating to radiation or infrared temperature measurement...
- Sakuma–Hattori equation