Archives: Terminology
This is where you can add new terminologys to your site.
Radiation, Thermal
The mode of heat flow that occurs by emission and absorption of electromagnetic radiation, propagating at the speed of light. Unlike conductive and convective heat flow, it is capable of propagating across a vacuum. The form of heat transfer that allows infrared thermography to work since infrared energy travels from the target to the detector by radiation.
Read more Qualitative Measurement
The process of obtaining and interpreting thermal images based on thermal contrast in order to identify anomalies; the purpose is more to determine where a temperature difference exists than what the temperature difference is between the target and its surroundings.
Read more Quantitative Measurement
The process of obtaining thermal images with correct temperature readings. Especially useful in situations when the exact temperature or temperature difference of the target determines whether it falls in or out of a determined criteria or range of acceptability. Also important to R & D and process control situations.
Read more Pyroelectric Detector
A type of thermal infrared detector that acts as a current source with its output proportional to the rate of change of its temperature.
Read more Photo-Detector [Photon Detector]
A type of infrared detector that has fast response, (on the order of microseconds), limited spectral response and usually requires cooled operation; photo-detectors are used in infrared radiation thermometers, scanners and imagers.
Read more Planck, Max Karl Ernst Ludwig
German physicist who incorporated quantum physics into the blackbody spectral radiance equation, giving rise to blackbody curves.
Read more Pyroelectric Detector
A type of thermal infrared detector that acts as a current source with its output proportional to the rate of change of its temperature.
Read more Pyroelectric Vidicon [PEV], Also Called Pyrovidicon
A video camera tube with its receiving element fabricated of pyroelectric material and sensitive to wavelengths from about 2 to 20 mm; used in infrared thermal viewers.
Read more Objective, Objective Lens
The primary lens of an optical system, on an infrared instrument, usually the interchangeable lens that defines the total field of view.
Read more Optical Element, Infrared
Any element that collects, transmits, restricts or reflects infrared energy as part of an infrared sensing or imaging instrument.
Read more Oversampling
Collecting samples at a rate higher than the Nyquist critical frequency, fc = 1/(2D), where D is the sampling interval. Applies to both time and spatial.
Read more Night Vision
The main difference between night vision and thermal imaging is the ability to see in total darkness. Night vision utilizes existing light sources and amplifies them, while thermal imaging is actually reading the infrared radiation coming from an object, regardless of any visible light source, and a trained thermographer can utilize this information to get accurate temperature measurements.
Read more Noise Equivalent Temperature [Difference], NET[D]
The temperature difference that is just equal to the RMS noise signal; a measure of thermal resolution; (thermal sensitivity), but not taking into account target size, characteristics of the display and the subjective interpretation of the operator.
Read more NIST, NIST Traceability
The National Institute of Standards and Technology (formerly NBS). Traceability to NIST is a means of ensuring that reference standards remain valid and their calibration remains current.
Read more Non-Gray body
An object whose emissivity varies with wavelength over the wavelength interval of interest. A radiating object that does not have a spectral radiation distribution similar to a blackbody; also called a “colored body” or “realbody”. Glass and plastic films are examples of non-graybodies. An object can be a graybody over one wavelength interval and a non-gray body over another.
Read more Measurement Spatial Resolution, IFOVmeas
The smallest target spot size on which an infrared imager can produce a measurement, expressed in terms of angular subtense (mrad per side). The slit response function (SRF) test is used to measure IFOVmeas.
Read more Medium, Transmitting Medium
The composition of the measurement path between a target surface and the measuring instrument through which the radiant energy propagates. This can be vacuum, gaseous (such as air), solid, liquid or any combination of these.
Read more Mercury Cadmium Telluride MCT [HgCdTe]
A material used for fast, sensitive infrared photo-detectors used in infrared sensors, scanners and imagers that requires cooled operation.
Read more Micro-Cooler
A small, palm size cooler based on the Stirling cycle that cools an infrared detector or focal plane array to liquid nitrogen temperature (77K).
Read more Micron [Micrometer] [m or, mm]
One millionth of a meter; a unit used to express wavelength in the infrared.
Read more Milliradian [MRAD]
One thousandth of a radian (1 radian = 180°/p); a unit used to express instrument angular field of view; an angle whose tangent is equal to 0.001; 1 mrad = 0.05729578°)
Read more Minimum Resolvable Temperature [Difference], MRT(D)
Thermal resolution; thermal sensitivity – the smallest temperature difference that an instrument can clearly distinguish out of the noise, taking into account target size and characteristics of the display and the subjective interpretation of the operator. The limit of MRTD is MDTD (minimum detectable temperature difference). MDTD is the MRTD of an extended source target, that is, a target large enough to be fully resolved by the instrument.
Read more Modulation
In general, the changes in one wave train caused by another; in thermal scanning and imaging, image luminant contrast; (Lmax – Lmin)/(Lmax + Lmin).
Read more Modulation Transfer Function [MTF]
A measure of the ability of an imaging system to reproduce the image of a target. A formalized procedure is used to measure MTF. It assesses the spatial frequency resolution of a scanning or imaging system as a function of distance to the target.
Read more Laser Pyrometer
An infrared radiation thermometer that projects a laser beam to the target, uses the reflected laser energy to compute target effective emissivity and automatically computes target temperature (assuming that the target is a diffuse reflector)—not to be confused with laser-aided aiming devices on some radiation thermometers.
Read more Latent Heat
Also called “hidden heat” as heat is added or removed without changing the temperature. The amount of heat required (or released) for a change of phase from solid to liquid and liquid to gas (or vice versa). The latent heat of vaporization is the amount of heat required to change one gram of liquid to vapor without change of temperature. The latent heat of fusion is the amount of heat to melt one gram of solid to liquid with no temperature change.
Read more Line Scan Rate
The number of target lines scanned by an infrared scanner or imager in one second.
Read more Line Scanner, Infrared
An instrument that scans a field of view along a straight line at the target plane in order to collect infrared radiant energy from a line on the target surface, usually done by incorporating one scanning element within the instrument. If the target (such as a sheet or web process) moves at a fixed rate normal to the line scan direction, the result can be displayed as a thermogram.
Read more Kirchoff’s Law
In thermal equilibrium the absorbtivity of an opaque surface equals its emissivity (a = e).
Read more Imager, Infrared
An infrared instrument that collects the infrared radiant energy from a target surface and produces an image in monochrome (black and white) or color, where the gray shades or color hues correspond respectively to target exitance.
Read more Image Processing, Thermal
Analysis of thermal images, usually by computer; enhancing the image to prepare it for computer or visual analysis. In the case of an infrared image or thermogram, this could include temperature scaling, spot temperature measurements, thermal profiles, image manipulation, subtraction and storage.
Read more Indirect Thermography
Thermal imaging and measurement of a surface which is indirectly affected by the target of concern. That is, the target of concern is thermally decoupled from the surface due to thermal insulation, such as an air gap or a radiant barrier.
Read more Indium Antimonide [InSb
A material from which fast, sensitive photo-detectors used in infrared scanners and imagers are made. Such detectors usually require cooling while in operation.
Read more Infrared [IR]
The infrared spectrum is loosely defined as that portion of the electromagnetic continuum extending from the red visible (0.75 mm to about 1,000 mm) . Because of instrument design considerations and the infrared transmission characteristics of the atmosphere, however, most infrared measurements are made between 0.75 and 20 mm.
Read more Infrared Focal Plane Array [IRFPA]
A linear or two-dimensional matrix of individual infrared detector elements, typically used as a detector in an infrared imaging instrument.
Read more IRFPA Imager or Camera
An infrared imaging instrument that incorporates a two-dimensional IRFPA (focal plane array) and produces a thermogram without mechanical scanning.
Read more Infrared Radiation Thermometer
An instrument that converts incoming infrared radiant energy from a spot on a target surface to a measurement value that can be related to the temperature of that spot.
Read more Infrared Thermal Imager
An Instrument or system that converts incoming infrared radiant energy from a target surface to a thermal map, or thermogram, on which color hues or gray shades can be related to the temperature distribution on that surface.
Read more Instantaneous Field of View [IFOV]
The angular subtense (expressed in angular degrees or radians per side if rectangular and angular degrees or radians if round) found by the ratio of the detector dimension divided by the instrument focal length; the projection of the detector at the target plane. In a radiation thermometer this defines the target spot size; in a line scanner or imager it represents one resolution element in a scan line or thermogram and is a measure of spatial resolution.
Read more Heat Transfer
The movement of heat from one point to another by conduction, convection and/or radiation.
Read more Fahrenheit
A temperature scale based on 32°F as the freezing point of water and 212°F as the boiling point of water at standard atmospheric pressure; a relative scale related to the Rankine scale [0°F = 459.67.R; 1 F° (DT) = 1 R (DT)].
Read more Field of View [FOV]
The angular subtense (expressed in angular degrees or radians per side if rectangular, and angular degrees or radians if circular) over which an instrument will integrate all incoming radiant energy. In a radiation thermometer this defines the target spot size; in a scanner or imager this defines the scan angle or picture size or total field of view (TFOV).
Read more Fiber Optic, Infrared
A flexible fiber made of a material that transmits infrared energy, used for making non-contact temperature measurements when there is not a direct line of sight between the instrument and the target.
Read more Filter, Spectral
An optical element, usually transmissive, used to restrict the spectral band of energy received by an instrument’s detector.
Read more Flame Filter
A filter of a specific waveband used to minimize the effects of flame, enabling the IR camera to “see” through the flame. The specific waveband is a region where the transmittance of flame approaches unity. Center wavelengths are typically 3.9 mm for shortwave instruments and 10.6 mm for longwave.
Read more Focal Plane Array [FPA]
A linear or two-dimensional matrix of detector elements, typically used at the focal plane of an instrument. In thermography, rectangular FPAs are used in “staring” (non-scanning) infrared imagers. These are called IRFPA imagers.
Read more Focal Point
The point at which the instruments optics image the infrared detector at the target plane. In a radiation thermometer, this is where the spot size is the smallest. In a scanner or imager, this is where the instantaneous field of view (IFOV) is the smallest.
Read more Foreground Temperature [See Instrument Ambient Background]
Temperature of the scene behind and surrounding the instrument as viewed from the target.
Read more Frame Repetition Rate
The time it takes an infrared imager to scan (update) every thermogram picture element (pixel); in frames per second.
Read more Full Scale
The span between the minimum value and the maximum value that any instrument is capable of measuring. In a thermometer, this would be the span between the highest and lowest temperature that can be measured.
Read more Effective Emissivity [e]
(also called emittance, but emittance is a less preferable term because it was formerly used to describe radiant exitance)
The measured emissive value of a particular surface under existing measurement conditions (rather than the generic tabulated value for the surface material) that can be used to correct a specific measuring instrument to provide a correct temperature measurement.
Read more Effusivity, Thermal [e]
A measure of the resistance of a material to temperature change
E = ÖkrCp cal Cm2 °C-1 sec½
where:
K = thermal conductivity
r = bulk density
Cp = specific heat
Read more Emissivity [e]
The ratio of a target surface’s radiance to that of a blackbody at the same temperature, viewed from the same angle and over the same spectral interval; a generic look-up value for a material. Values range from 0 to 1.0. Alternatively, the ratio of a flat, optically polished, opaque target surface radiance to that of a blackbody at the same temperature, viewed from the same angle and over the same spectral interval. The latter definition characterizes the property of the material. When used this way, emittance is used to characterize the material when it is other than flat, optically polished and opaque.
Read more Emittance [e]
The ratio of a target surface’s radiance to that of a blackbody at the same temperature, viewed from the same angle over the same spectral interval; a generic look-up value for a material. Values range from 0 to 1.0.
Read more EMI/RFI Noise
Disturbances to electrical signals caused by electromagnetic interference (EMI) or radio frequency interference (RFI). In thermography, this may cause noise patterns to appear on the display.
Read more Environmental Rating
A rating given an operating unit (typically an electrical or mechanical enclosure) to indicate the limits of the environmental conditions under which the unit will function reliably and within published performance specifications.
Read more Exitance, Radiant [Also Called Radiosity]
Total infrared energy (radiant flux) leaving a target surface. This is composed of radiated, reflected and transmitted components. Only the radiated component is related to target surface temperature.
Read more Detector, Infrared
A transducer element that converts incoming infrared radiant energy impinging on its sensitive surface into a useful electrical signal.
Read more Diffuse Reflector
A surface that reflects a portion of the incident radiation in such a manner that the reflected radiation is equal in all directions. A mirror is not a diffuse reflector.
Read more Diffusivity, Thermal, [a]
(Note: same symbol as absorptive, may be confusing.) The ratio of conductivity (k) to the product of density (r) and specific heat (Cp) [a = k/rCp cm² sec‑1]. The ability of a material to distribute thermal energy after a change in heat input. A body with a high diffusivity will reach a uniform temperature distribution faster than a body with lower diffusivity.
Read more D* [Detectivity Star]
Sensitivity figure of merit of an infrared detector–detectivity expressed inversely so that higher D*s indicate better performance; taken at specific test conditions of chopping frequency and information bandwidth and displayed as a function of spectral wavelength.
Read more Direct Thermography
Thermal imaging and measurement of a surface whose thermal signature is, or is directly affected by the target of concern. That is, the target of concern has little or no thermal insulation between it and the surface measured.
Read more Display Resolution, Thermal
The precision with which an instrument displays its assigned measurement parameter (temperature), usually expressed in degrees, tenths of degrees, hundredths of degrees, etc.
Read more Calibration
Checking and/or adjusting an instrument such that its readings agree with a standard. Calibration removes instrument systematic error and quantifies the instrument random error.
Read more Calibration Check
A routine check of an instrument against a reference to ensure that the instrument has not deviated from calibration since its last use.
Read more Calibration Accuracy
The accuracy, to which a calibration is performed, usually based on the accuracy and sensitivity of the instruments and references used in the calibration.
Read more Calibration Source, Infrared
A blackbody or other target of known temperature and effective emissivity used as a calibration reference.
Read more Capacitance, Thermal
This term is used to describe heat capacity in terms of an electrical analog, where loss of heat in analogous to loss of charge on a capacitor. Structures with high thermal capacitance lose heat more slowly than those structures with low thermal capacitance.
Read more Capacity, Heat
The heat capacity of a material or structure describes its ability to store heat. It is the product of the specific heat (cp) and the density (r) of the material. This means that denser materials generally will have higher heat capacities than porous materials.
Read more Celsius [Centigrade]
A temperature scale based on 0°C as the freezing point of water and 100°C as the boiling point of water at standard atmospheric pressure; a relative scale related to the Kelvin scale [0°C = 273.12 K. 1 C° (DT) = 1 K. (DT)]
Read more Conductance, Thermal
A measure of the ability of a material of defined thickness and cross-sectional area to conduct heat. Related to the material property, thermal conductivity. The inversed of thermal resistance (C = 1/R).
Read more Conduction, Thermal
The only mode of heat flow in solids, but can also take place in liquids and gases. It occurs as the result of atomic vibrations (in solids) and molecular collisions (in liquids and gases) whereby energy is transferred from locations of higher temperature to locations of lower temperature.
Read more Conductivity, Thermal, [K]
A material property defining the relative capability to carry heat by conduction in a static temperature gradient. Conductivity varies slightly with temperature in solids and liquids and with temperature and pressure in gases. It is high for metals (copper has a K of 380 W/m-°C) and low for porous materials (concrete has a K of 1.0) and gases.
Read more Convection
The form of heat transfer that takes place in a moving medium and is almost always associated with transfer between a solid (surface) and a moving fluid (such as air), whereby energy in transferred from higher temperature sites to lower temperature sites.
Read more Atmospheric Windows [Infrared]
The spectral intervals within the infrared spectrum in which the atmosphere transmits radiant energy well (atmospheric absorption is a minimum.). These are roughly defined as 3-5 µm and 8-14 µm.
Read more Artifact
A product of artificial character due to extraneous agency; an error caused by an uncompensated anomaly. In thermography, an emissivity artifact simulates a change in surface temperature but is not a real change. A hot solar reflection or a cold reflection due to narcissus would be examples of artifacts.
Read more Apparent Temperature
The target surface temperature indicated by an infrared point sensor, line scanner or imager before temperature corrections are made.
Read more Ambient Temperature Compensation
Correction built into an instrument to provide automatic compensation in the measurement for variations in instrument ambient temperature.
Read more Ambient Temperature
Temperature of the air in the vicinity of the target (target ambient) or the instrument (instrument ambient).
Read more Ambient Operating Range
Range of ambient temperatures at which an instrument is designed to operate within published performance specifications.
Read more Accuracy [of Measurement]
The maximum deviation, expressed in % of scale or in degrees Celsius or Fahrenheit, that the reading of an instrument will deviate from an acceptable standard reference.
Read more Absorptivity, a [Absorptance]
The proportion (as a fraction of 1) of the radiant energy impinging on a material’s surface that is absorbed into the material. For a blackbody, this is unity (1.0). Technically, absorptivity is the internal absorptance per unit path length. In thermography, the two terms are often used interchangeably.
Read more Absolute Zero
The temperature that is zero on the Kelvin or Rankine temperature scales, also the temperature at which a material is at its lowest energy state.
Read more