Radiation that enters an instrument from sources other than the intended target. Background radiation can enter due to reflections from the target or scattering within the instrument.

A
	Absolute Zero
	The temperature of -273.16° C, -459.69° F, or 0° K; thought to be the temperature at which molecular motion vanishes and a body would have no heat energy.

	Accuracy
	The maximum deviation in a set of measurements between the temperature indicated by a radiation thermometer and the known temperature of a reference source, including the uncertainty of the reference temperature source. The accuracy can be expressed in a variety of ways including temperature, percentage of temperature reading, or percentage of full scale temperature of an instrument.

	Ambient Derating
	Derating or decrease in accuracy of an instrument due to changes in its ambient temp from that at which it was calibrated. See also Temperature Coefficient.

	Ambient Operating Range
	Range in the ambient temperature over which the instrument is designed to operate.

	Ambient Temperature
	The temperature of the instrument. Can also refer to the temperature that gives rise to the background. See Background Radiation.

	Ambient Temperature Compensation (TAMB)
	See Reflected Energy Compensation.

	ASTM
	American Society for Testing and Materials.

	ASTM E 1256
	ASTM E1256 - 88, Standard Test Methods for Radiation Thermometers (Single Waveband Type). A standard by which Raytek products are tested and calibrated for accuracy, repeatability, resolution, target size, response time, warm-up time, and long-term drift.

	Atmospheric Windows
	The spectral bands in which the atmosphere least affects the transmission of radiant energy. The spectral bands are 0.4 to 1.8, 2 to 2.5, 3 to 5, and 8 to 14 micrometers.

B
	Background Radiation
	Radiation that enters an instrument from sources other than the intended target. Background radiation can enter due to reflections from the target or scattering within the instrument.

	Blackbody
	An ideal thermal radiator that absorbs all of the radiation incident thereon, and the radiant emission from which is quantified by Planckís Radiation Law.

C
	Calibration Procedure
	A procedure that is performed to determine and set the parameters affecting an instrument's performance in order to ensure its designed function within prescribed limits.

	Calibration Source


	Carnot Cycle
	An ideal heat engine that converts thermal energy to mechanical work with the greatest efficiency that can be achieved.

	Celsius or C
	The temperature scale in which the temperature in Celsius (TC) is related to the temperature in Kelvin (TK) by the formula; TC = TK -273.15. The freezing point of water at standard atmospheric pressure is very nearly 0?C, and the corresponding boiling point is very nearly 100?C. Formerly known as centigrade temperature scale.

	Color Temperature
	The temperature of a black body from which the radiant energy has the same spectral distribution as that from a surface.

	Colored Body or Non Gray Body
	A source of thermal emission for which the emissivity depends on wavelength and is not constant.

	Comparison Pyrometry
	Method of radiation thermometry wherein the temperature of a calibrated source is changed until the radiation received from the source is the same as that from the target to determine the temperature of the target.

	Current-Loop
	A form of communications wherein a pair of wires is used to transmit the signal as a current. Levels of 4 to 20 mA are often used to indicate the minimum and maximum signal level, respectively. Sometimes, for digital applications, various magnitudes of mA current are used to indicate a logical 1 and 0. The current loop is often characterized by a maximum impedance of the device that is connected to the loop.

D
	D:S
	Optical resolution expressed as a ratio of the distance to the resolution spot divided by the diameter of the spot.

	Deadband
	Temperature band (?) about the set point, wherein an alarm output or relay can not change state, thus providing hysteresis.

	Detector
	Transducer which produces a voltage or current proportional to the electromagnetic energy incident upon it. See also Thermopile, MCT, Thermoelectric Cooled, Pyroelectric, and Lead Selenide and Si detectors.

	Dielectric Withstand (Breakdown Voltage)
	The maximum voltage an insulator of electricity can endure without voltage electrical conduction through the material.

	Digital Data Bus
	Two or more electrical conductors connecting several transmitters and receivers of digital data.

	Digital Image Processing
	Converting an image to digital form and changing the image to enhance it or prepare it for analysis by computer or human vision. In the case of an infrared image or thermogram, this could include temperature scaling, spot temperature measurements, thermal profiles, image addition, subtraction, averaging, filtering, and storage.

	Digital Output Interval
	The time interval between transmission of packets of digital data (DOI) containing temperature and system status information.

	DIN Deutsches Institut
	The German standard for many instrumentation products.f?mung.

	Drift
	The change in instrument indication over a period of time not caused by external influences on the device.

E
	EMI/RFI
	Electro-Magnetic Interference/Radio Frequency Interference, which affects the performance of electronic equipment.

	Emissivity
	At a given wavelength the ratio of infrared energy radiated by an object at a given temperature to that emitted by a blackbody at the same temperature The emissivity of a blackbody is unity at all wavelengths.

	Environmental Rating
	A rating given (usually by agencies and regulatory bodies) to indicate the severity of the environment in which the unit will function reliably.

	External Reset (Trigger)
	Initialization of an instrument to its state at power up including signal conditioning features (Peak Hold, Valley Hold, Sample Hold, Average, (1-way RS232, etc.) via the external reset input.

F
	Fahrenheit or F
	Temperature measurement scale where, at standard atmospheric pressure, the freezing point of water is 32?F and the vaporization point of water is 212?F. To convert from Celsius, use F = (C x 1.8) + 32.

	Fail-safe Operation
	A measurement distance sufficiently large (typically greater than 10 times the focal distance) whereby the spot size of an instrument is growing in direct proportion to the distance from the instrument, and the field of view is constant.

	Far Field
	A measurement distance sufficiently large (typically greater than 10 times the focal distance) whereby the spot size of an instrument is growing in direct proportion to the distance from the instrument, and the field of view is constant.

	Field of View (FOV)
	The area or solid angle viewed through an optical or infrared instrument. Typically expressed by giving the spot diameter of an instrument and the distance to that spot. Also expressed as the angular size of the spot at the focal point. See Optical or Infrared Resolution.

	Focal Point or Distance
	The point or distance from the instrument at which the object is focused onto the detector within the instrument. The focal point is the place or distance at which the optical or infrared resolution is greatest.

	Full Scale Accuracy
	The temperature measurement accuracy expressed as a percentage of the maximum possible reading of an instrument.

G
	Gray Body
	A source of radiant emissions for which the emissivity is less than 1 but constant and, therefore, independent of wavelength.

I
	IEC International Electrotechnical Commission
	A European organization that coordinates and sets related standards among the European Community.

	IEEE-488
	A standard developed by Hewlett-Packard Corporation and adopted by the IEEE for digital interface between programmable instrumentation. It uses a 16-bit bus to interconnect up to 15 instruments. The standard comprises hardware and protocol options. It is also called the Hewlett-Packard Interface Bus (HPIB) or General Purpose Interface Bus (HPIB) or General Purpose Interface Bus (GPIB). The present standard is ANSI/IEEE-4881-1987.

	IFOV (Instantaneous Field of View)
	Instantaneous Field of View is the angular resolution of an imaging Field of View) instrument that is determined by the size of the detector and the lens. For a point instrument the IFOV and FOV are the same.

	Image Processing
	Converting an image to a digital form and further 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, and thermal profiles, as well as image addition, subtraction, averaging, filtering, and storage.

	Indium Antimonide (InSb)
	A material used to construct photon detectors that are sensitive in the spectral region from 2.0 to 5.5 ?m and used in infrared scanners and imagers. These detectors require cryogenic cooling.

	Infrared or Optical Filter
	See Spectral Filter or Neutral Density Filter.

	Infrared Radiation
	(IR) Radiation within the portion of the electromagnetic spectrum which extends from 0.75 to 1000 ?m.

	Infrared Thermometer
	An instrument that determines the temperature of an object by means of detecting and quantifying the infrared radiation emitted therefrom. Types include total power, wide band, narrow band, and multiple wavelengths.

	Insulation Resistance
	The property of a material to resist the flow of electrical current and expressed in Megohms (M?) as the ratio of an applied electrical potential divided by the flow of electrical current resulting therefrom.

	Interchangeability
	The ability for a head sensor to be interchanged with another of the same type without the need to recalibrate the system (also referred to as Universal Electronics). Some monitors support the interchangeability of different types of heads.

	Intrinsically Safe
	A standard for preventing explosions in hazardous areas by limiting the electrical energy available to levels that are insufficient to cause ignition of explosive atmospheres during normal operation of an instrument.

	IP Designation
	Grades of intrinsic safety protection pertaining to enclosures per the British Standard 4752. The type of protection is defined by two digits, the first relating to accessibility and the second to environmental protection. The two numbers are preceded by the letters IP.

	Isolated Inputs, Outputs
	Inputs, outputs and power supply lines that are electrically insulated or Power Supplies from each other, whereby arbitrary grounding of these lines cannot affect the performance of the instrument such as generate ground-loops or short out internal resistors.

	Isotherm
	A continuous line (not necessarily straight or smooth) on a surface (or chart) comprising points of equal or constant temperature.

J
	JIS Japanese Industrial Standard
	A technical governing body that sets standards for determining or establishing the accuracy of IR thermometers.

K
	Kelvin or K
	A temperature scale that is directly related to the heat energy within a body. Formally, a temperature scale in which the ratio of the temperatures of two reservoirs is equal to the ratio of the amount of heat absorbed from one of them by a heat engine operating in a Carnot Cycle to the amount of heat rejected by engine to the other reservoir. The temperature of the triple point of water (in this scale) is defined as 273.16? K. To convert from Celsius, K=C+273.16.

L
	Lead Selenide (PbSe)
	A material used to make photon detectors that are sensitive in the 3 to 5 ?m spectral band. These detectors require thermoelectric cooling and are used in IR thermometers, scanners, and imagers.

M
	Maximum Current
	Describes the size of a load that can be driven by an instrument with a Loop Impedance mA output. For example a 500 ohm maximum loop impedance means that the instrument can supply 10 volts at 20 mA into this load.

	MCT (Mercury Cadmium Telluride) or HgCdTe
	A ternary alloy material used to build photon detectors that are sensitive in the 3-5?m and 8-14?m regions of the spectrum and require TE cooling in the 3-5 ?m region and cryogenic cooling in the 8-14?m region.

	Minimum spot size
	The diameter of the smallest object for which an instrument can meet its performance specifications.

N
	NEMA
	National Electrical Manufacturer?s Association. Among its activities, sets US standards for housing enclosures, similar to IEC IP.

	NET
	See NETD.

	NETD (or NE?T)
	Noise Equivalent Temperature Difference or the change in temperature of a blackbody target that fills the radiometer FOV which results in a change in the radiometer signal equal to the rms noise of the instrument.

	Neutral Density Filter
	An optical or infrared filter for which the transmission is constant and not a function or wavelength.

	NIST Traceability
	Calibration in accordance with and against standards traceable to NIST (National Institute of Standards and Technology, USA). Traceability to NIST is a means of ensuring that reference standards remain valid and their calibration remains current.

O
	Optical or Infrared Resolution
	The ratio of the distance to the target divided by the diameter of the circular (or spot) for which the energy received by the thermometer is a specified percent age of the total energy that would be collected by an instrument viewing a calibration source at the same temperature. The distance to the target is generally the focal distance of the instrument. The percentage energy is generally 90?95%.

	Optical Pyrometer
	A system that, by comparing a source whose temperature is to be measured to a standardized source of illumination (usually compared to the human eye), determines the temperature of the former source.

	Output Impedance
	Describes the impedance of the thermometer that is experienced by any device connected thereto. To achieve accurate readings, the input impedance of a device connected to the thermometer must be much greater than the output impedance of the thermometer.

P
	Peak Hold
	Output of the maximum temperature measurement indicated by an instrument during the time duration for which this display mode has been active.

	Photondetector or Quantum Detector
	A type of detector in which the photons or quanta of energy interact directly with the detector to generate a signal.

	Pyroelectric Detector
	Thermal detector that has a signal generated by means of the pyroelectric effect wherein changes in temperature of the detector generates an electrical signal.

	Pyrometer
	A broad class of temperature measuring devices, originally designed to measure high temperature, but some are now used in any temperature range. Includes radiation pyrometers, thermocouples, resistance pyrometers, and thermistors.

R
	Radiance Temperature
	The temperature of a black body which has a radiance equal to the radiance of the object at a particular wavelength or wavelength band.

	Radiant Energy
	The electromagnetic energy emitted by an object due to its temperature.

	Radiation Thermometer
	A device used to measure the temperature of an object by quantification of the electromagnetic radiation emitted therefrom. Also, a radiometer calibrated to indicate a blackbody?s temperature.

	Rankine or R
	The absolute temperature scale related to Fahrenheit in the equivalent manner Kelvin is to Celsius. R = 1.8 x K, or also R = F + 459.67.

	Reference Junction or Cold Junction
	Refers to the thermocouple junction that must be known in order to infer the temperature of the other or thermocouple measurement junction.

	Reflectance
	The ratio of the radiant energy reflected from a surface to that incident on the surface.

	Reflected Energy Compensation
	A variable used to achieve greater accuracy by compensating for background IR energy that is reflected off the target into the instrument. If the temperature of the background is known, the instrument reading can be corrected.

	Relative Humidity
	The dimensionless ratio of the actual vapor pressure of the air to the saturation vapor pressure (abbreviated RH). Percent relative humidity is expressed as the product of RH and 100. For example an RH of 0.30 is a percent relative humidity of 30%.

	Repeatability
	The degree to which a single instrument gives the same reading on the same object over successive measures under the same ambient and target conditions. The ASTM standard E 1256 defines it as the sample standard deviation of twelve measurements of temperature at the center of the span of the instrument. Generally expressed as a temp difference, percent of full scale value, or both.

	Resolution
	See Temperature Resolution, Optical Resolution, or Spatial Resolution.

	Response Time
	The time for an instrument?s output to change to 95% of its final value when subjected to an instantaneous change in target temperature corresponding to the maximum temperature the instrument can measure (per ASTM E 1256). The average time required for software computation within the processor is also included in this specification for Raytek products.

	RS-232
	Recommended Standard (RS) 232 is a standard developed by the Electronic Industries Association (EIA) that governs the serial communications interface between data processing and data communications equipment and is widely used to connect microcomputers to peripheral devices. [Ref. 1] The present revision is EIA-RS-232-D, which defines the interface between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE) employing serial binary data interchange. The standard does not define the protocol or format of the binary stream. The standard comprises three parts: electrical characteristics, interface mechanical characteristics, and functional description of the inter change circuits. The equivalent international standard is Comite Consultatif International Telegraphique et Telephonique (CCITT) V.24.

	RS-422
	A recommended standard developed by EIA that defines a balanced interface and is an expansion of RS-423 that increases the data rate to 10 Mbps.

	RS-423
	A recommended standard developed by EIA that defines an unbalanced interface and is an expansion of RS-232 and provides improvements included increased connecting cable lengths, increased data rates, and use of multiple receivers on line.

	RS-485
	A recommended standard developed by EIA that is an improvement over RS-422 in that it allows an increase in the number of receivers and transmitters permitted on the line.