| A |
| Absolute zero: Temperature at which thermal energy is at a minimum. Defined as 0 Kelvin or 0 Rankine (-273.15 °C or -459.67°F). |
| Absorptivity: The fraction of incident radiation absorbed by a surface, a. |
| Accuracy: Closeness of a reading or indication of a measurement device to the actual value of the quantity being measured. |
| Ambient compensation: The design of an instrument such that changes in ambient temperature do not affect the readings of the instrument. |
| Ambient temperature: The average or mean temperature of the surrounding air which comes in contact with the equipment and instruments under test. |
| Ampere (amp): A unit used to define the rate of flow of electricity (current) in an electrical circuit; units are one coulomb (6.25x1018 electrons) per second. Symbolized by A. |
| American National Standards Institute (ANSI): The United States standards body responsible for designating standards developed by other organizations as national standards. |
| B |
| Blackbody: A theoretical object that radiates the maximum amount of energy at a given temperature, and absorbs all the energy incident upon it. A blackbody is not necessarily black. (The name blackbody was chosen because the color black is defined as the total absorption of light energy.) |
| Boiling point: The temperature at which a substance in the liquid phase transforms to the gaseous phase. Commonly refers to the boiling point of water, 100°C (212°F). |
| Bolometer: Infrared thermometer detector consisting of a resistance thermometer arranged for response to radiation. |
| BTU: British thermal unit, the amount of energy required to raise one pound of water one degree Fahrenheit. |
| C |
| Calibration: The process of adjusting an instrument or compiling a deviation chart so that its reading can be correlated to the actual value being measured. |
| Calorie: Measure of thermal energy, defined as the amount of heat required to raise one gram of water one degree Celsius at 15°C. |
| Celsius (Centigrade): A temperature scale defined by 0 °C at the ice point and 100°C at the boiling point of water. |
| Color code: The ANSI established color code for thermocouple (and infrared thermocouples) wires in which the negative lead is always red. Color code for base metal thermocouples is yellow for Type K, black for Type J, purple for Type E and blue for Type T. |
| Common-mode rejection ratio: The ability of an instrument to reject interference from a common voltage at its input terminals with relation to ground, usually expressed in decibels (dB). |
| Compensating alloys: Alloys used to connect thermocouples and IR thermocouples to instrumentation. These alloys are selected to have similar thermal electric properties as the thermocouple alloys over a limited temperature range. |
| Compensated connector: A connector made of thermocouple alloys used to connect thermocouple and IR thermocouple probes and wires. |
| CPS: Cycles per second, also Hertz (Hz).
Cryogenics: The measurement of very low temperatures, i.e., below -200°C. |
| Current: The rate of flow of electricity. The unit is the ampere (A), which equals one coulomb per second. |
| D |
| Degree: An incremental value in a temperature scale. |
| Diffuse emitter: A surface that emits radiation equally in all directions. |
| DIN: Deutsche Industrial Norms, a German agency that sets engineering and dimensional standards that now have worldwide acceptance. |
| Drift: A change in an instrument's reading or setpoint value over extended periods due to factors such as time, line voltage, or ambient temperature effects. |
| Dual element sensor: A sensor assembly with two independent sensing elements. |
| E |
| Electromotive force (EMF): A measure of voltage in an electrical circuit. |
| Electromagnetic interference (EMI): electrical noise induced upon signal wires with the possible effect of obscuring the instrument signal. |
| Emissive power: Rate at which radiation is emitted from a surface, per unit surface area per unit wavelength. |
| Emissivity/emittivity: The ratio of energy emitted by a surface to the energy emitted by a blackbody at the same temperature, symbolized by e. Emissivity refers to an overall property of a substance, whereas emittvity refers to a particular surface's characteristics. |
| Error: The difference between the correct of desired value and the actual read or value taken. |
| F |
| Fahrenheit: A temperature scale define by 32°F at the ice point and 212°F at the boiling point of water at sea level. |
| Fiber optic radiation thermometer: Radiation thermometer that uses a fiber optic probe to separate the detector, housing, and electronics from the radiation gathering point itself. Used to measure temperature in hard-to-reach places or in hostile conditions. |
| Field of view: A volume in space defined by an angular cone extending from the focal plane of an instrument. |
| Freezing point: The temperature at which a substance goes from the liquid phase to the solid phase. |
| Frequency: The number of cycles over a specified time period over which an event occurs. For electromagnetic radiation, normally symbolized by u. |
| G |
| Gain: The amount of amplification used in an electrical circuit.
Ground: The electrical neutral line having the same potential as the surrounding earth; the negative side of a direct current power system; the reference point for an electrical system. |
| H |
| Heat: Thermal energy, typically expressed in calories or BTUs. |
| Heat transfer: The process of thermal energy flowing from a body of high energy to a body of lower energy via conduction, convection, and/or radiation. |
| Hertz (Hz): Unit of frequency, defined in cycles per second.
|
| I |
| Ice point: The temperature at which pure water freezes, 0°C, 32°F, 273.15°K. |
| Impedance: The total opposition to electrical flow. |
| Infrared (IR): A range of the electromagnetic spectrum extending beyond red visible light from 760 nanometers to 1000 microns. |
| Infrared thermocouple: Radiation thermometer whose output simulates that of a standard type thermocouple, typically over a more limited temperature range.
Interchangeability error: A measurement error that can occur if two or more sensors are used to make the same measurement. Caused by slight variations from sensor to sensor. |
| Intrinsically safe: An instrument in which electrical energy is limited such that it will not spark or otherwise ignite a flammable mixture. |
| ISA: Formerly the Instrument Society of America, now referred to as the International Society for Measurement & Control. |
| J |
| Joule: Basic unit of thermal energy. |
| Junction: The point in a thermocouple where the two dissimilar metals are joined. |
| K |
| Kelvin: Absolute temperature scale based on the Celsius scale, but with zero K defined at absolute zero. 0°C corresponds to 273.15°K. |
| L |
| Linearity: The deviation of an instrument's response from a straight line. |
| Linescanner: Device that uses a series of moving mirrors to measure temperature or other properties at various points across a moving web or surface. |
| Loop resistance: The total resistance of a complete electrical circuit.
|
| M |
| Measuring junction: The thermocouple junction referred to as the hot junction that is used to measure an unknown temperature. |
| Melting point: The temperature at which a substance transforms from a solid phase to a liquid phase. |
| Micron (mm): One millionth of a meter. |
| Milliamp (mA): One thousandth of an ampere. |
| Millivolt (mV): One thousandth of a volt. |
| N |
N = N factor (= 14388/(lT))
Narrow-band radiation thermometer: Radiation thermometer that measures radiation in a tightly controlled range of wavelengths, typically determined by the optical filter used. |
| Noise: Any unwanted electrical interference on a
signal wire. |
| Normal-mode rejection ratio: The ability of an instrument to reject electrical interference across its input terminals, normally of line frequency (50-60 Hz).
|
| O |
| Ohmeter: A device used to measure electrical resistance. |
| Optical isolation: Two networks or circuits in which an LED transmitter and receiver are used to maintain electrical discontinuity between the circuits. |
| Optical pyrometer: Infrared thermometer that measures the temperature of very hot objects by the visible wavelength radiation given off. |
| P |
| Phase: A time-based relationship between a periodic function and a reference. |
| Photon detector: Radiation thermometer detector that releases electric charges in response to incident radiation. |
| Polarity: In electricity, the quality of having two oppositely charged poles, one positive and one negative. |
| Power supply: A separate unit or part of a circuit that provides power to the rest of a circuit. |
| Primary standard: The standard reference units and physical constants maintained by the National Institute of Standards & Technology (NIST) upon which all measurement units in the United States are based. |
| Pyroelectric detector: Radiation thermometer detector that changes surface charge in response to received radiation. |
| Pyrometer: Device used to measure the infrared radiation (hence temperature) given off by a body or surface. |
| R |
| Radiation: The movement of energy in the form of electromagnetic waves. |
| Range: An area between two limits within which a quantity is measured, stated in terms of a lower and upper limit. |
| Rankine: Absolute temperature scale based on the Fahrenheit scale, but with zero R defined at absolute zero. 0°F corresponds to 459.67°R. |
| Reference junction: The cold junction in a thermocouple circuit that is held constant at a known or measured temperature. |
| Reflectivity/reflectance: The fraction of incident radiation reflected by an object or surface. |
| Radio frequency interference (RFI): Noise induced upon signal wires by ambient radio-frequency electromagnetic radiation with the effect of obscuring the instrument signal. |
| Repeatability: The ability of an instrument to give the same output or reading under repeated, identical conditions. |
| Resistance: The resistance to the flow of electric current, measured in ohms, W. |
| S |
| Secondary standard: A standard of unit measurement derived from a primary standard. |
| Sensitivity: The minimum change in a physical variable to which an instrument can respond. |
| Span: The difference between the upper and lower limits of a range, expressed in the same units as the range. |
| Spectral filter: A filter that allows only a specific bandwidth of the electromagnetic spectrum to pass, i.e., 4-8 micron infrared radiation. |
| Spot size: The diameter of the circle formed by the cross section of the field of view of an optical instrument at a given distance. |
| Stability: The ability of an instrument or sensor to maintain a consistent output when a constant input is applied. |
| Sterling cycle: Thermodynamic cycle commonly used to cool thermographic detectors. |
| T |
| Thermal detector: Radiation thermometer detector that generates a signal based on the heat energy absorbed. |
| Thermocouple: The junction of two dissimilar metals through which a measurable current flows depending on the temperature difference between the two junctions. |
| Thermography: The presentation and interpretation of two-dimensional temperature pictures. |
| Thermometry: The science of temperature measurement. |
| Thermopile: an arrange of multiple thermocouples in series such that the thermoelectric output is amplified. |
| Thermowell: A closed-end tube designed to protect a temperature sensor from harsh process conditions. |
| Transmittance/transmissivity: The fraction of incident radiation passed through an object. |
| Two-color pyrometer: A radiation thermometer that measures the radiation output of a surface at two wavelengths, thus reducing any effects of emissivity variation with wavelength. |
| V |
| Volt (V): The electrical potential difference between two points in a circuit. One volt is the potential needed to move one coulomb of charge between two points while using one joule of energy. |
| W |
| Wavelength: Distance, from peak to peak, of any waveform. For electromagnetic radiation in the infrared region, typically measured in microns and symbolized by l. |
| Working standard: A standard of unit measurement calibrated from either a primary or secondary standard which is used to calibrate other devices or make comparison measurements. |
| Z |
| Zero offset: The non-zero output of an instrument, expressed in units of measure, under conditions of true zero. |
