• Fiber Optic Sensing Glossary
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  • F
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  • I
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  • L
  • M
  • N
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  • P
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A

The degree of distance of measurement results compared to its true value. The true values for DTS systems are absolute temperatures.

Active Distributed Temperature Sensing (DTS) also known as heat pulse method. A method of DTS data collection based on utilizing a heated fiber optic cable and monitoring the thermal response during the heating and/or the cooling phase. Active DTS applicable for measurement of thermal properties and directly dependent quantities (e.g. heat fluxes and soil moisture), and of advective fluxes of air and water.

The confirmation cycle defines the number of confirmations before triggering an alarm.

Photonics are moved in high frequencies and correspond to rotational decompression. The difference between the anti-Stokes and Stokes signal is a measure of temperature.

The part of Raman backscattering which shifts to a lower wavelength from the incident light. This backscattered signal is strongly temperature dependent.

See Waveguide Array.

The surveillance of man-made hoisting.

In fiber optic sensing the monitored fiber is typically divided in individual asset zones by defining a start and stop position on the sensing fiber. Zones help structure the monitored asset. Different alarm parameter sets can be defined per zone, allowing additional flexibility in sensitivity.  Zones are also frequently referred to as Alarm Zones or simply Zones. 

Explosive area (ATEX stands for "explosive atmosphere")

The decrease in magnitude of power of a signal in transmission between points. A term used for expressing the total losses on an optical fiber consisting of the ratio of light output to light input. Attenuation is usually measured in decibels per kilometer (dB/km) at a specific wavelength. The lower the number, the better the fiber. Typical multimode wavelengths are 850 and 1300 nanometers (nm); single mode, at 1300 and 1550 nm. A typical attenuation of a 50/125 µm fiber at a wavelenght of 1064 is around 0.9 dB/km. When specifying attenuation, it is important to note if it is nominal or average, room temperature, value or maximum over operating range.

Array waveguide. See Waveguide Array.

B

See Brillouin OTDR.

Backscattered Light or also backscatter. The portion of light which is scattered back to the light-emitting source during the forward propagation of a pulse through an optical fiber. This reaction happens because of the collisions of the photonics with the constitutive elements of the optical fiber.

Measure of the information-carrying capacity of an optical fiber expressed as a unit of MHz-km.

The smallest radius below which a cable should not be bent. The standard limit for fiber optic cables is 20 times the cable diameter under tension and 10 times when not under stress.

See Brillouin OTDR.

Brillouin also known as  Brillouin Scattering or Brillouin Effect. Backscattered signal used for B-OTDR measurements to obtain strain and temperature measurements along an optical fiber. The Brillouin backscatter is caused by an incident light pulse which propagate through an optical fiber. This signal is most commonly used for distributed strain sensing.

See Brillouin.

Brillouin Optical Time Domain Reflectometry. Brillouin light is one of the types of light that is reflected back to the optical source when light is transmitted through an optical fiber. Other types include Raman and Rayleigh light. B-OTDR analyses can be used to determine strain or temperature measurements. See also: OTDR, Coherent OTDR, Raman OTDR, Rayleigh scattering, Raman OFDR.

See Brillouin.

The protective layer applied over the cladding of an optical fiber. It can consist of acrylic polymer.

C

See Coherent OTDR.

An area of extremely increased temperature in the cable. It is crucial for fiber optic-based Distributed Temperature Sensing (DTS) systems to detect hotspots rapidly and identify their location to the operators so that appropriate actions can be taken.

Installations to hold cables especially used for large amounts or long cables.

For the DTS technology, calibrating of physical quantities allows inferring temperature from DTS raw signals. An accurate calibration is necessary to avoid the effects of offset, a constant shift between measured and real absolute temperatures, and slope issues, a variation with distance of DTS readings of a constant temperature. Various calibration methods exists, for example like single-ended and double-ended techniques.

Temperature scale in which 0 degrees and 100 degrees are the freezing and boiling temperatures for water, also known as centigrade.

Cladding is the layer surrounding the light-carrying core of an optical fiber. It is usually made of glass or other transparent material. Its refractive index is lower than the core and so confines light in the core.

Coherent Optical Time Domain Reflectometry. C-OTDR is used in some optical systems and is a variation of time domain reflectometry (TDR) in which the returned signal is mixed with a local oscillator and then filtered to reduce noise.

See Heatable Fiber Optic Cable.

The confirmation cycle defines the number of confirmations before triggering an alarm.

Hardware installed on cable ends to provide physical and optical cable attachment to a transmitter / receiver or another cable. A junction that lets an optical fiber or cable to be repeatedly connected or disconnected to a device such as a source or detector. For DTS the standard optical connector is E2000 8° angled.

The central component of an optical fiber. The majority of lights travels through the core of a fiber. The core has a higher refractive index than the surrounding cladding in order to maintain total internal reflection.

A coupler connects three or more fiber ends. It distributes one input between two or more outputs or combining two or more inputs into one output.

The method of transferring light into or out of an optical fiber.

Cable Rating System. See RTTR.

Conductor Temperature Monitoring Module. Subset of a full RTTR engine. It used to determine the conductor temperature during stead state based on thermal model, measured temperature and load. See also RTTR.

D

A barrier to prevent water from passing through. AP Sensing's Distributed Temperature Sensing (DTS) solution for geological and hydrological applications can not only monitor the curing temperature and thermal parameters of concrete (including roller-compacted concrete (RCC)), it can monitor the dam infrastructure as well as adjacent areas for leakage and seepage.

See Distributed Acoustic Sensing.

See Decibel.

See Dynamic Cable Rating.

The standard unit used to express gain or loss of optical power.

Identifying unwanted situations.

See Insulation.

Differential Attenuation is the difference between the loss of light intensity with distance for the anti-Stokes and Stokes Raman backscatter.

The maximum distance along the sensor fiber (starting from the DTS unit) for which the DTS unit is designed to monitor.

DAS systems, like Distributed Temperature Sensing (DTS) systems, employ fiber optic sensor cables to monitor and identify acoustic strain patterns in order to recognize potentially threatening events such as Third Party Interference (TPI) or leakage. The most advanced DAS systems collect quantitative coherent full-waveform acoustic data.

A linear optical fiber, when combined with AP Sensing's Distributed Temperature Sensing (DTS) solutions, provides a precise, distributed heat sensor along the entire length of the sensor cable.

DVS systems, like Distributed Temperate Sensing (DTS) systems, employ fiber optic sensor cables to monitor and identify vibrations and vibration patterns in order to recognize potentially threatening events such as Third Party Interference or leakage.

A Distributed Temperature Sensing (DTS) method for measurement and calibration. Both ends of the forward optical path are required to be connected to the DTS unit. By combining the forward and reverse raw data traces, which are measured sequentially from each end, each temperature trace is delivered. It is especially useful in harsh environments or with multiple splices and/or tight bends because of the compensation of the spatially variable differential attenuation.

Downstream oil and gas processing refers to the refining, processing and purifying of these products, as well as the distribution methods, which generally use pipelines.

Dynamic Rating System. See RTTR.

See Distributed Temperature Sensing.

Two fibers in the same fiber optic cable are spliced at the further end to realizes a U-shaped configuration. Via duplexing it is possible to perform measurements utilizing either one Distributed Temperature Sensing (DTS) optical channel with one end of the optical fiber connected, or two DTS optical channels with each end of the optical fiber connected. For the connection of two DTS optical channels, measurements are taken sequentially from both ends and can be single-ended, or double-ended.

See Distributed Vibration Sensing.

A natural or artificial wall or slope, to control water levels (also known as a levee). AP Sensing's Distributed Temperature Sensing (DTS) solution for geological and hydrological applications can monitor the levee infrastructure as well as adjacent areas for leakage and seepage.

DCR (or alternatively, RTTR, Real Time Thermal Rating) is a software module using mathematical network models customized to the individual HVAC or HVDC cable installation. Based on relevant input data, such as temperature measured by the DTS, current load and thermal resistivities, it continuously computes the conductor temperature, ampacity and other important values. The network can operate at highest possible safe ampacity levels and react in case of critical asset condition.

The maximum two-way loss within the sensing fiber to and from the measured point for which the DTS unit is designed.

E

See Enhanced DTS.

Electromagnetic interference, also called radio-frequency interference (RFI) is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling or conduction.

EN 54 is a required standard for fire detection and fire alarm systems. It specifies requirements and laboratory tests for every component of such systems. AP Sensing is fully certified with EN 54-5 (for outside of Europe) and EN 54-22 (for Europe), in addition to the rest of our industry-leading number of certifications (VdS, ATEX, FM, UL and ULC).

The Enhanced DTS or eDTS uses advanced and novel techniques that combine Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS) measurements. This provides highly accurate absolute temperature measurements along the optical fiber cable by using a small spatial resolution with low noise levels, and at the same time retaining a very fast measurement response in seconds. eDTS is highly beneficial for measuring accurate temperature profiles where very long distances i.e. > 50 km need to be monitored in applications such as power cable monitoring and oil & gas pipeline leakage detection system.

"Ex zone" indicates an explosive area. Many kinds of machinery and equipment, especially opto-electronics, may only be used in explosive environments with the proper certification. AP Sensing uses a low-powered laser source, which enables us to attain ATEX certification down to Zone 0.

The amount of light lost in a passive coupler above that inherent in the splitting to multiple output ports.

The process of fighting a fire until the fire is out.

That portion of loss that is not intrinsic to the fiber but is related to imperfect joining, which arises from the splicing process itself.

F

Fire alarm control panel. A fire alarm control panel or simply fire alarm panel is the controlling component of a fire alarm system. Information from fire detection systems are received by the panel, and are used to monitor their operational integrity and provide for automatic control of equipment.

Temperature scale in which the freezing and boiling points of water are 32 degrees and 212 degrees.

A siren or other signal that is set off at the wrong time or as a test. AP Sensing's Distributed Temperature Sensing (DTS) solutions have the industry's fastest fire detection and lowest false alarm rates, even in the most challenging environments (dust, dirt, humidity, electromagnetic interference (EMI)).

See Fiber Bragg Grating.

Optical signal carrier; for Distributed Temperature Sensing (DTS) systems, the fiber acts as the sensor.

A Fiber Bragg grating is a physical reflector that is built into a short segment of fiber sensing cable. It reflects certain wavelengths and allows all others to pass. This can be useful as a filter function to block or reflect certain wavelengths.

Fiber in Metal Tube (FIMT), sometimes also known as tube encapsulated fiber (TEF). FIMT is a stainless-steel tube, often gel-filled that contains optical fibers in a hermetically sealed assembly. This type of fiber is commonly used for high temperature and harsh environment cabling.

A fiber made of glass is used to transmit light - the fiber can also be used as linear sensors. A thin wire of silica (silicon dioxide) is used to transmit optical information (e.g. laser pulses and backscatter) over long distances. It is an optical waveguide consisting of a core and a cladding to confine the light signals.

A wholesome assembled product including all components, such as optical fiber(s), strength members, and protective outer sheath, which protect the optical fiber(s) from environmental factors.

See Fiber in Metal Tube.

Discovering a fire and generating a alarm.

Instrument to monitor and survey areas where a fire could occur. AP Sensing's DTS Distributed Temperature Sensing (DTS) solution for the fire detections and special hazard market provides reliable asset protection, even in challenging environments (dirt, dust, humidity, electromagnetic interference (EMI)).

Describes the direction in which a fire is moving, for example stationary, or moving towards or away from the device. Particularly in tunnel applications, this information is very valuable to both the operators who can then take appropriate actions, and to the fire-fighting personnel who can use the information when they arrive on the scene.

Sensor cables that are filled with gels or liquids to ensure they perform in a wider range of conditions.

AP Sensing passed the strict testing procedures for Fire Detection and is certified for FM approval according to the Class 3210 Standard "Heat Detectors for Automatic Fire Alarm Signaling." By adding to our industry-leadingset of tests and certifications (including UL and UL-C, CE, VdS, ATEX and SIL-2) the FM approval assures customers that our Distributed Temperature Sensing (DTS) solutions for the Fire Detection and Special Hazards markets have been objectively tested and conform to national and international standards.

The number of cycles per unit of time, denoted by Hertz (Hz). Thus 1 Hz=1 cycle per second.

Fusion splicing is the method of joining two optical fiber end to end utilizing intense heat. With this method even with very low attenuation a connection can be provided.

G

The increase in signal strength as light passes through an amplifying medium.

Loss resulting from the end separation of two axially aligned fibers.

An optical attenuator that exploits the principle of gap loss to reduce the optical power level when inserted in-line in the fiber path, e.g., to prevent saturation of the receiver.

The complete value chain from extracting gas to selling gas (upstream, to the well head, and downstream, for refining and distribution).

A computer that connects and translates protocols between disparate types of networks.

Drilled hole used to access heat from the earth

An Optical Time Domain Reflectometry (OTDR) signature caused by an optical echo that appears when light reflects off two reflective surfaces, creating a false image at double the distance from the initial event.

See Graded-index multimode fiber.

See Graded-index plastic optical fiber.

In fiber optics, “glass” usually means a silica compound unless otherwise noted.

A short part of graded-index fiber that focuses light travelling through it.

An optics fiber in whose core the refractive index changes gradually with distance from the fiber axis, rather than abruptly at the core-cladding interface. This reduces model dispersion and increases fiber bandwidth.

Graded-index multimode fiber (GI-MMF). A type of multimode fiber where the refractive index of the fiber core decreases radically towards the outside of the fiber.

A plastic multimode fiber with a bandwidth of up to 3 GHz per 100 meters.

How fine a signal can be broken into its component parts.

A conductive connection with the earth.

The rate of change of the total phase shift with respect to angular frequency, d /d , through a device or transmission medium, where is the total phase shift, and is the angular frequency equal to 2f , where f is the frequency.

The variation in travel time through a fiber for light of different wavelengths

Group index, or also known as group refractive index. In fiber optics, for a given mode propagating in a medium of refractive index (n), the group index (N), is the velocity of light in a vacuum (c), divided by the group velocity of the mode.

See Group Index.

The abbreviation for Graphical User Interface.

H

A fiber with a hard plastic cladding surrounding a step-index silica core.

Areas with difficult or dangerous environmental conditions, for example, dangerous gases or chemicals, or the risk of an explosion.

A device that measures or monitors increasing temperatures. AP Sensing's Distributed Temperature Sensing (DTS) solutions use fiber optic based technology to determine the temperature and locations along the entire sensor cable.

See Active DTS.

Heatable Fiber Optic cable, also known as hybrid cables or composite cables. A heatable fiber optic cable includes metal elements (usually copper wires) close to the fibers optics core. Sending electrical current through them, generates a distributed heat pulse along the cable. This type of cable is utilized for the Active Distributed Temperature Sensing (DTS) method.

Cables rated over 35 KV. The National Electrical Code defines any cable over 600 volts as High Voltage for the purposes of Article 710. However, Article 326 delineates the generally accepted parameters of Medium Voltage and High Voltage .

An area of of extremely increased temperature, for example, along a power cable or a fire in a tunnel. AP Sensing's Distributed Temperature Sensing (DTS) solutions quickly and precisely locate hotsopts and provide an accurate temperature profile every few seconds along the entire length of the sensor cable.

The main or largest portion of a connector to which other portions are attached or enclosed.

High voltage direct current and high voltage alternating current, in electric power transmission and distribution systems.

See Heatable Fiber Optic Cable.

Hydro comes from the Greek language and means water. Hydrology is the study of water quality, movement and distribution. AP Sensing's Distributed Temperature Sensing (DTS) solution can be applied in geological and hydrological monitoring applications to track water flow, aquifer and ground sstreams, leakage and seepage in dam infrastructures, or for research projects.

I

A test that determines the ability of fiber optic cables and cable assemblies to withstand repeated impact loads. It measures the number of broken fibers, damage to the outer sheath, and any change in the optical transmittance or attenuation.

Incident light is the light which is coupled into an optical fiber at the Distributed Temperature Sensing (DTS). It travels along the fiber from the near end to the far end of the fiber.

Index of refraction, or also known as refractive index. A quantity that indicates the slow down of the speed of light in a material. 

The refractive index of a fiber as a function of cross section.

A gel or fluid with refractive index close to the one of glass, which reduces refractive-index discontinuities that can cause reflective losses.

An index-matching material is used at optical interconnection. It has a refractive index close to the one of the fiber core. 

Additional loss in a system when a device such as a connector is inserted, equal to the difference in signal level between the input and output.

Insulation or also known as dielectric. A material having high resistance to the flow of electric current.

Power per unit solid angle.

For light, the way that waves add together, depending on their phase. Constructive interference occurs when the waves are in phase and their amplitudes add. Destructive interferenceoccurs when the waves are 180 degrees out of phase and their amplitudes cancel.

A fiber-optic sensor that depends on interference effects.

An optical device that separates a series of optical channels so alternating wavelengths emerge out its two ports. The best-known type is a Mach-Zehnder interferometer.

The number of traces that can be simultaneously kept in the internal memory of the DTS unit.

Splice losses occuring from differences in the fibers being spliced.

An international standard for quality assurance and processes. AP Sensing has the industry's most complete set of tests and certifications.

A passive fiber optic component that either allows only unidirectional passing of light or that passes only some wavelengths of light. Used in conjunction with lasers or optical amplifiers to reduce or remove backreflections.

J

In fiber optics, a jacket is the protective outer coating of the cable.

The variation in time of a received signal compared to the instance of its transmission or compared to a fixed time frame at the receiver.

A jumper is a fiber optic cable that has connectors installed on both ends.

A point in a circuit where two or more wires are connected

A semiconductor diode laser.

The layer between p-and n-doped semiconductors, where current carriers recombine and emit light in a semiconductor laser or LED.

A natural fiber of plant base formed into rope-like strands. Typically used in cables for filling the interstices to give a round cross-section.

K

A unit of absolute temperature developed by Lord Kelvin.

Connectors in which the plug and adapter are fixed in alignment to prevent rotation and fiber endface damage.

k

Tensile strength measured in thousands of pounds per square inch.

L

Light Amplification by Stimulated Emission of Radiation, a simulated source of radiation.

Launch fiber or also known as launching fiber. An optical fiber used to couple and condition light from an optical source into an optical fiber. The launch fiber is usually used to create an equilibrium model distribution in multimode fiber.

A standard for signal transmission or processing to perform certain functions. It includes standard interfaces with other layers, which perform other functions.

Unwanted loss of solids, liquids, or gases. AP Sensing's pipeline leakage detection solution uses complementary temperature sensing and acoustic sensing technologies to monitor above-ground or buried pipelines, heat-tracing pipelines and jetty pipelines for leakage detection and Third Party Interference (TPI).

Identify the source of escaping solids, liquids or gases. AP Sensing's Distributed Temperature Sensing (DTS) solution for the pipeline monitoring market additionally offers complementary acoustic sensing capabilities to ensure pipeline integrity, leakage detection, and Third Party Interference (TPI) protection.

See Linear Heat Detection.

An optical fiber or fiber bundle.

Used as an adjective, a synonym for optical, often meaning fiber-optic.

Linear heat detection (LHD) is a method for detecting hot spots along a sensor cable. Different techniques include digital cables, analog cables, pressure tube sensors and, in the case of AP Sensing, fiber optic based distributed temperature sensors.

When liquefied natural gas (LNG) is extracted it is cooled to approximately -160 °C to turn it into a liquid, which requires 1/600th of the volume of the gas state, for ease of tranportation and storage. At an LNG facility, the re-gasification terminal is where it is returned to its gaseous form, purified and typically stored in tanks in its liquid form for distribution. AP Sensing's Distributed Temperature Sensing (DTS) solution for LNG applications also monitors for leakage detection along the pipelines, cool-down monitoring at the jetty, tank annulus leakage, base slab monitoring and spill containment area monitoring.

See Liquefied Natural Gas.

Oscillation modes of a laser along the length of its cavity. Each longitudinal mode contains only a narrow range of wavelengths, so a laser emitting a single longitudinal mode has a narrow bandwidth.

A protective tube loosely enclosing a cabled fiber, often filled with gel. A type of fiber optic cable construction where the fiber is contained within a loose tube in the cable jacket.

A loose tube cable structure with buffer tubes filled with gel to restrict moisture intrusion. Mostly replaced with “dry” techniques, it is still used in areas of extreme low temperatures.

Attenuation of optical signal, normally measured in decibels. The amount of a signal’s power, expressed in dB, that is lost in connectors, splices, or fiber defects.

An accounting of overall attenuation in a system.

A laser source that requires very little power to send pulses, which has many advantages in Distributed Temperature Sensing (DTS) environments. AP Sensing uses Optical Time Domain Reflectometry (OTDR) technology as its measurement principle (the other alternative for DTS systems is Optical Frequency Domain Reflectometry (OFDR) technology). Low-powered lasers have a longer life span and have lower laser safety classifications than the high-power lasers needed for OFDR systems. Low-power laser systems are inherently safer in explosive environments; some AP Sensing devices are certified for explosive environments, e.g., ATEX directive Zone 0.

See Loose tube gel filled (LTGF).

M

An advanced leak detection method which makes enhanced use of the space and time-resolved temperature readings given by Distributed Temperature Sensing (DTS). The MLTA method extracts typical patterns from a training dataset containing long-term recording of DTS data of the installation. This allows for significant reduction of nuisance alarms due to variable temperature profiles caused by changing operation conditions and environmental effects, while maintaining sensitivity to local temperature anomalies.

Material dispersion is a pulse dispersion caused by variation of a material’s refractive index with wavelength.

Mean Time Between Failures. The average amount of operating time between failures. AP Sensing is a market leader in terms of quality, reliability, MTBF and customer support.

A method of splicing in which fibers are joined mechanically (e.g., glued or crimped in place) but not fused together.

The abbreviation for metropolitan, and is the name of many products and services relating to urban areas, in particular rapid transit rail systems. AP Sensing's Distributed Temperature Sensing (DTS) solution for the fire detection and special hazard applications provides reliable asset protection even in the most challenging environments (dirt, dust, humidity, electromagnetic interference (EMI)), remaining functional up to 1000 °C.

Tiny bends in a fiber that allow light to leak out and increase loss.

Specifies the minimum spatial distance of two consecutive result points in the measured temperature profile.

See Machine Learning Transient Alarming (MLTA).

The abbreviation for multimode (fiber). The cores of multimode fiber (where the light is transported) are relatively large. They are generally used for shorter distances than singlemode fibers.

Modal dispersion arises from variation in the times that different modes take to travel through multimode fiber.

The term mode describes in fiber optics an electromagnetic field distribution which satisfies theoretical requirements for propagation in a waveguide or oscillation in a cavity (e.g., a laser). Light has modes in a fiber or laser.

Surveillance of a selected area.

All of the components for surveillance, in particular for an AP Sensing Distributed Temperature Sensing (DTS) or other distributed optical sensing system, typically to monitor temperature and/or acoustic signal to protect valuable infrastructures (train and traffic tunnels, HVDC / HVAC power cables, pipelines and LNG plants).

See Multiple Reflection Noise (MRN).

See Mean time between failure (MTBF).

Mass Transit Railway. Also known as metro or subway, is a type of high-capacity public transport generally found in urban areas. Unlike trams or buses, these electric railway systems operate on an exclusive right-of-way.

Multimode Dispersion or also known as modal disperson. Dispersion resulting from the different transit lengths of different propagating modes in a multimode optical fiber.

Optical fiber with typically 50 or 62.5 micrometres (µm) core and 125 micrometres (µm) cladding diameter, often abbreviated as MM. The cores of multimode fiber (where the light is transported) are relatively large. They are generally used for shorter distances than singlemode (SM) fibers. This type of fiber supports more than one light propagation mode.

Multiple Reflection Noise (MRN) or also known as multipath interference. The fiber optic receiver noise which results from the interference of delayed signals from two or more reflection points in a fiber optic span.

A device which combines two or more signals into a single output.

N

See Numerical Aperture.

Numerical Aperture (NA) mismatch loss desribes the loss of power at a joint which occurs when the transmitting half has a NA greater than the NA of the receiving half. It appears when coupling light from a source to fiber, from fiber to fiber, or from fiber to detector.

A unit of measure equal to one billionth of a meter.

The optical power reflected from one or more input ports, back to another input port.

See Noise Equivalent Power (NEP).

See Nanometer.

Noise in a cable or circuit is any extraneous signal that tends to interfere with the signal normally present in or passing through the system.

The optical input power to a detector required to generate an electrical signal equal to the inherent electrical noise.

Nonzero dispersion-shifted fiber single-mode is an optical fiber with the wavelength of zero chromatic dispersion shifted outside the C-band. Some types have zero dispersion near 1500 nm, others near 1625 nm.

Numerical Aperture (NA) indicates the sine of half the angle over which a fiber can accept light. This is multiplied by the refractive index of the medium containing the light. For air the index is almost equal to 1.

See NA Mismatch Loss.

O

Optical Frequency Domain Reflectometry, a process to analyze wavelength and characteristics. OFDR is an alternative method to Optical Time Domain Reflectometry (OTDR). In order for OFDR measurements to be effective the backscatter signals detected during the entire measurement time are measured as a function of frequency in a complex fashion, and then subjected to Fourier transformation.

Upstream oil and gas is considered to be a process in the oil and gas industry (together with midstream and downstream) that includes searching for new fields, drilling exploratory wells, and recovering the oil, gas or liquefied natural gas (LNG). Typically the oil or gas is also processed, purified and made ready for distribution.

Improving the efficiency of oil and gas reservoir extraction and production. AP Sensing's Distributed Temperature Sensing (DTS) solution for well and reservoir monitoring lets operators better manage reservoirs, wellbores and completions. Temperature profiles can be monitored thoughout the entire well or at user-selected locations.

The complete value chain of extracting oil to selling oil (upstream, to the well head and downstream. for distribution and refinery).

The humidity range in which the device (the Distributed Temperature Sensing (DTS) instrument, not the sensor cable) can measure accurately.

Environmental temperature range and humidity range of the DTS unit, within which the specifications apply.

The temperature range in with the device (the DTS unit, not the cable) can measure accurately.

Optical groundwire. A special wire that has a data transfer function in addition to the functions of a ground wire.

An optical signal transmitted at one wavelength. WDM systems transmit multiple channels at separate wavelengths.

An optical fiber is usually made of silica and transmits signal at very high bandwidths over long distances through a process known as total internal reflection. It is constructed with a core surrounded by the cladding.

Industry standard is E2000 8° APC (angled polished connector).

An optical path indicates the path travelled by the light in the optical fiber(s). If the forward optical path is intended, it follows the direction of the emitted light. The end of the forward optical path can be the far end of the fiber cable. If a duplex configuration is applied, it can also be the near end of the fiber.

Optical return loss (ORL) is the sum of the amount of light reflected from all optical fibers and components. The fiber, connectors, or splices in an optical system can cause the reflection.

An optical component that separates or connects a conduct line.

Sometimes used as a synonym for optical fiber. It can also apply to planar light waveguides.

See Optical return loss (ORL).

Optical Time Domain Reflectometry: an optical laser pulse propagating through the fiber sends scattered light back to the transmitting end, where it is analyzed. The position of the scatterd light (temperature reading) is determined by measuring the arrival timing of the returning light pulse, similar to a radar echo. AP Sensing employs OTDR technology, which is also the technology of choice for the telecoms industry, together with low-powered laser sources, for long product lives and the ability to use them in hazardous (explosive) areas.

A cable and conductor made from aluminum installed above ground.

P

Passive Component doesn’t require outside power.

Passive Distributed Temperature Sensing (DTS). It is the standard method of the collection of temperature data along an optical fiber using DTS instrumentation, without artificially heating the fiber cable as opposed to the active DTS methods.

Passive optical network is a fiber-optic distribution network with no active components between the switching office and the customer.

See Plastic-Clad Silica.

Partial discharge. In electrical engineering, partial discharge (PD) is localized dielectric breakdown (which does not completely bridge the space between the two conductors) of a small portion of a solid or fluid electrical insulation (EI) system under high voltage (HV) stress, which is invisible to the human eye.

See Polyethylene (PE).

Pipelines and associated installations are often located in remote areas and need to be monitored for perimeter intrusion and other Third Party Interference (TPI) activities. Examples of these activities include construction, underground tunneling, subsea hazards, rock falls, motor vehicles, train traffic, walking, machinery digging, manual digging, and intrusion, such as climbing over a fence. AP Sensing offers perimeter protection solutions to ensure intelligent event detection for various applications.

Pipelines and associated installations are often located in remote areas and need to be monitored for perimeter intrusion and other Third Party Interference (TPI) activities. Examples of these activities include construction, underground tunneling, subsea hazards, rock falls, motor vehicles, train traffic, walking, machinery digging, manual digging, and intrusion, such as climbing over a fence. AP Sensing offers perimeter protection solutions to ensure intelligent event detection for various applications.

The study of electromagnetic energy wherein the basic unit is the photon. The word photonics is a mixture of photon and electonics.

Plastic-Clad Silica (PCS) Fiber. A step-index multimode fiber in which a silica core is surrounded by a lower-index plastic cladding.

Polyethylene (PE) is a thermoplastic used to jacket aerial and direct buried cables.

Polypropylene is a thermoplastic similar to PE. However, it is stiffer and with a higher softening point.

Polyurethane (PU) is a thermoplastic material used in cable jackets derived from the polymerization of ethylene gas.

Polyvinyl chloride (PVC) is a multi-purpose thermoplastic jacket material used in the manufacture of riser-rated cable and cordage.

Polyvinylidene fluoride (PVDF) is a dielectric fluoropolymer. PVDF is resistant to corrosive chemicals and radiation, therefore often used to jacket stranded cable.

A cable to transport electricity. AP Sensing's power cable monitoring solutions ensure that operators of HVDC / HVAC networks, offshore windparks area cables, substation and transformer equipment, and offshore substation export cables (together with our RTTR, or real time thermal rating engine) can operate at the highest possible safe ampacity level.

Power transformers are used to increase or decrease voltages in electric power applications.

Transferring and allocating electricity. AP Sensing's Distributed Temperatue Sensing (DTS) solution for power cable monitoring, together with our Real Time Thermal Rating (RTTR), or Dynamic Cable Rating (DCR) engine lets operators monitor and protect their networks and operate them at the highest possible safe ampacity level.

Predefined actions to undertake in case an alarm occurs, e.g., traffic signaling, ventilation activation, or activating fire suppression systems.

The quantification of the smallest variation of a quantity that an instrument is able to detect and properly measure above the noise. Regarding a Distributed Temperature Sensing (DTS) system, it is the smallest fluctuations in temperature which can be resolved. It is an index of the repeatability (in both space and time) of a measurement. It can be a synonym for resolution but not accuracy.

The plastic coating which is applied directly to the cladding surface of the fiber. It has the purpose to preserve the integrity of the surface.

See Polyurethane (PU).

Pulse dispersion describes the spreading out of pulses as they travel along an optical fiber.

See Polyvinyl chloride (PVC).

See Polyvinylidene fluoride (PVDF).

Q

A series of four separately insulated conductors. They are usually twisted together in pairs. The term quad also describes a series-parallel combination of transistors with increased reliability because failure of one transistor will not disable the entire circuit.

Quad fiber cable is a specific type of fiber optic cable. It has four single cables enclosed in an extruded jacket of polyvinyl chloride (PVC), with a rip cord for pulling back the jacket to access the fibers.

Acording to the ISO norm family, quality is the "degree to which a set of inherent characteristics fulfils requirement." Other definition for quality can be find in the ISO 9001/14001/45001.

Quantization in fiber optics describes the process of converting the voltage level of a signal into digital data before or after the signal has been sampled.

Quantum efficiency indicates the fraction of photons which strikes a detector that produces electron-hole pairs in the output current.

A quaternary is a semiconductor compound made of four elements (e.g., InGaAsP).

A digital signal with four significant conditions.

Quick disconnect describes a connector or splice which permits rapid locking and unlocking of mating parts.

R

Raman Optical Frequency Domain Reflectometry. See also: Raman OTDR.

See Raman OTDR.

A type of structure used to house electronic components which permits a customized setup of equipment.

Sir Chandrasekhara Venkata Raman (7 November 1888 - 21 November 1970) was an Indian physicist and Nobel laureate in physics recognised for his work on the molecular scattering of light and for the discovery of the Raman effect, which is named after him.

Named for the Indian physicist C.V Raman, who first published observations of this effect in 1928. It describes how light wavelengths are changed when they are deflected by molecules. With AP Sensing's use of OTDR technique an optical laser pulse propagating through the fiber sends scattered light (reflected from the silicon of the fiber) back to the transmitting end, where it is analyzed.The intensity of the Raman signals is a measure for the temperature along the fiber. Raman wavelengths are shifted further from the incident wavelength of the Brillouin backscatter.

Raman Optical Frequency Domain Reflectometry. See also Raman OTDR.

Raman Optical Time Domain Reflectometry. Raman scattering, or light scattering, occurs in the optical fibers. Optical Time Domain Refelectometry (OTDR) and Optical Frequency Domain Reflectometry (OFDR) are the 2 main measurement principles for distributed sensing technology. The OTDR method, which is used by AP Sensing, was developed over 20 years ago and it is the standard used in the telecoms industry. It also means that low-powered laser sources can be used (compared to OFDR systems), so that the Distributed Temperature Sensing (DTS) devices can be used in hazardous or explosive areas. Alternative OFDR systems require much higher-powered lasers and need to use more complex algorithms to determine temperature and location. See also: OTDR, Raman, Coherent OTDR, B-OTDR.

Rayleigh Scattering or Rayleigh Effect. Reflections with the same wavelength of the laser source. In an optical fiber Rayleigh scattering is caused by microscopic densitiy and refractive index variations. The Rayleigh backscatter is  most commonly used for Distributed Acoustic Sensing (DAS).

When liquefied natural gas (LNG) is extracted it is cooled to approximately -160 °C to turn it into a liquid, which requires 1/600th of the volume of the gas state, for ease of tranportation and storage. At an LNG facility, the re-gasification terminal is where it is returned to its gaseous form, purified and typically stored in tanks in its liquid form for distribution. AP Sensing's Distributed Temperature Sensing (DTS) solution for LNG applications also monitors for leakage detection along the pipelines, cool-down monitoring at the jetty, tank annulus leakage, base slab monitoring and spill containment area monitoring.

RTTR (or alternatively, DCR, Dynamic Cable Rating) is a software module using mathematical network models customized to the individual HVAC or HVDC cable installation. Based on relevant input data, such as temperature meaured by the DTS, current load and thermal resistivities, it continuously computes the conductor temperature, ampacity and other important values. The network can operate at highest possible safe ampacity levels and react in case of critical asset condition.

Facility to improve the quality of materials by cleaning and removing unwanted substances, typically for petroleum oil, natural gas or liquefied natural gas (LNG).

Refraction describes the bending of light as it passes between materials of different refractive indices.

See Index of Refraction.

Refractive-index gradient describes the change in refractive index with distance from the axis of an optical fiber.

ROV crafts that are telecommanded, especially used underwater in the oil and gas industries.

Repeatability is the precision or resolution at which a measurement can be repeated in time and space. The index of repeatability for a Distributed Temperature Sensing (DTS) system is provided by the temporal resolution.

A receiver-transmitter combination which detects and amplifies a weak signal forretransmission through another length of optical fiber.

The number of pulses or data bits per second.

Surveillance of oil and gas fields, dams, dykes, and underground water sources.

Improving the efficiency of oil and gas reservoir extraction and production. AP Sensing's Distributed Temperature Sensing (DTS) solution for well and reservoir monitoring lets operators better manage reservoirs, wellbores and completions. Temperature profiles can be monitored thoughout the entire well or at user-selected locations.

The smallest change that can be distinguished with a measurement.

Radio-frequency interference. See EMI.

The ability to maintain performance despite harsh or changing conditions.

Roll-off is an Optical Time Domain Reflectometry (OTDR) trace of a fiber that gradually rolls off due to nonreflective breaks.

See Remotely Operated Vehicles.

See Real Time Thermal Rating.

S

Steam assisted gravity drainage. Water vapors are pressed into a well or reservoir to facilitate the extraction of oil or gas.

The sampling resolution is the sampling interval spacing along an optical fiber which is collected by a Distributed Acoustic Sensing (DAS) or a Distributed Temperature Sensing (DTS) system.

Spread reflection, in particular light scattering occurs when light rays are deflected from a straigh path.

Leakage water surveillance. AP Sensing's Distributed Temperature Sensing (DTS) solution for geological and hydrological applications is ideally suited for aquifier and ground water stream monitoring, analysis of thermal stress in dams and dykes, providing excellent subsurface visualization.

Fiber Optic - Linear Heat Detection - LTS 200 / LTS 240 Sensor Control Unit. Instruments are comparable to AP Sensing's Distributed Temperature Sensing (DTS) devices. In cases where AP Sensing has replaced these devices, the AP Sensing device was able to work with installed sensor cables and was easily integrated into the previous SCADA and IT systems.

A device that measures a physical quality and converts it into a signal that can be read by an instrument. For example, AP Sensing's Distributed Temperature Sensing (DTS) devices work together with fiber optic sensor cables to analyze back-scattered laser light to determine temperature and interpret acoustic signals along the entire length of the cable.

Specifies the measurable temperature range of the particular type of optical fiber being used as a sensor.

Sheath describes the outer protective layer of a fiber optic cable.

A suddenly and dramatic change of condition or parameters.

The ratio of signal to noise, measured in decibels; an indication of analog signal quality.

Silica Glass is used in standard optical fibers. This type of glass is made mostly of silicon dioxide.

A method of calibration and measurement for collecting temperature signatures from one end of an optical fiber.

The slope width is defined as the spatial distance between the measured 10 % and 90 % levels of the slope, with 0 % and 100 % being the stationary temperature levels before or after the step.

Singlemode (fiber). Compared to multimode fiber, singlemode fiber has a relatively small core (where the light is transported) and is more often used for longer distances. The core diameter is usually 8 or 9 µm. This type of fiber supports only a single light propagation mode.

An optical pulse that naturally keeps its original shape as it travels along an optical fiber.

See Synchronous Optical Network (SONET).

Specifies the slope width of a measured step temperature profile (rising or falling). It is the minimum distance which a distributed sensing system needs in order to measure a step change in a signal along the optical fiber. Regarding Distributed Temperature Sensing (DTS) systems, it is usually calculated as the distance needed to differentiate between 10 % and 90 % of an applied temperature step.

Special sensor cables designed for more extreme conditions, e.g., very low or very high temperatures, with gel or liquid fillings, or steel or aluminum casings.

A permanent junction between two fiber ends.

A housing to protect a fusion-spliced fiber.

The ratio of power emerging from output ports of a coupler.

In a Distributed Temperature Sensing (DTS) temperature measurement, the standard deviation statistics are based on an ambient temperature evenly distributed over the operating temperature range, and a sensing fiber temperature evenly distributed over the sensing fiber temperature range, over the measurements "i" (the index of a sufficiently large sample).

A coupler with more than three or four ports.

A step loss is a sharp loss in intensity of light propagation along an optical fiber. This usually happens because of the connectors and fusion splices, and is visible as a step in the Stokes and anti-Stokes signatures. If the step loss between the Stokes and anti-Stokes optical signals diffierentiate from each other, a step artefact on the temperature trace could happen, which appears from the location of the step loss until the end of the sensing fiber. Double-ended configurations normally automatically account for step losses.

A step-index fiber with a core large enough to carry light in multiple modes.

A step-index fiber with a small core which is capable of carrying light in only one mode. This type typically has zero dispersion at 1310 nm.

The technology in which the scattered oscillations go in the opposite direction as the conducting ray.

Stimulated raman scattering describes the interactions between light and atoms in a transparent material that convert energy from one wavelength to another.

Photonics are moved in low frequencies and correspond to rotational stimulation. The difference between the anti-Stokes and Stokes signal is a measure of temperature.

It is the part of the Raman backscattering which is shifted to a higher wavelength from the incident light. This type of backscatter is not strongly temperature dependent.

Measuring stress or expansion along an optical sensor fiber.

Surveillance of structures and the condition of facilities to detect damages.

Cable installations underwater to transport electrical current. AP Sensing's Distributed Temperature Sensing (DTS) sytems are ideally suited for monitoring subsea applications.

A standard for fiber-optic transmission.

T

T coupler is a coupler with three ports.

See Time Division Multiplexing (TDM).

Time Domain Reflectometry. TDR is used to determine the characteristics of electrical lines by observing reflected waveforms, for example to localize faults or other discontinuities in electric systems.

Tube encapsulated fiber. See Fiber in Metal Tube (FIMT).

Specifies the variations in the measured temperature at points along the sensor cable held at uniform temperature. Temperature resolution TRes is calculated as: TRes = StDevtrue,i{ Hi }. The temperature resolution is defined as standard deviation over distance. It can be also calculated in time for a fixed point along the optical fiber.

Temporal resolution describes the time required to collect an individual signature along an optical fiber.

Tensile strength describes the pull stress which is required to break a given specimen.

Terminator is an optical plug with the fiber dead ended so that there is no reflectance. It measures component reflectance using the Optical Time Domain Reflectometry (OTDR) and also reduce Fresnel reflections at open connector ports.

Continuous monitoring and analyzing of results and data, especially with regard to AP Sensing's fiber-optic based distributed optical sesnsing solutions.

Visualization of temperature conditions in, for example, oil wells, geothermal wells or within industrial processes.

The temperature range in which a material will perform its function without undue degradation.

An electrical device that can act as a temperature sensor. Thermocouple are most widely used in certain industrial processes or in thermostats. For large infrastructures they do not have the accuracy, reliability, durability, immunity to dust, dirt, electromagnetic interference (EMI) and humidity when compared to Distributed Temperaure Sensing (DTS) devices.

The minimum current required to sustain laser action in a diode laser.

Time division multiplexing (TDM). A digital technique for combining two or more signals into a single stream of data by sharing time.

A gradient-based detection method which utilizes analysis of the temperature history and analysis of the ambient temperature for each position. The results are combined mathematically to determine a measure of unusual behavior and trigger an alarm when a certain threshold is exceeded. This method achieves a higher sensitivity than classic detection, and smaller changes in temperature can be detected.

Total reflection of light travelling back into a material when it strikes the interface with a material having a lower refractive index at an angle below a critical value.

Third Party Interference. TPI is usually referred to as external third party events in proximity of an asset, either by accident or on purpose. Examples are digging and drilling activities at construction sites close to an underground pipeline or power cable, anchoring near subsea cables or unauthorized trespassing or intruding into a protected area.

A combination of transmitter and receiver providing both output and input interfaces with one device.

Transmitter is a light source packaged with drive electronics to produce an optical signal.

Transverse modes describe modes across the width of a waveguide, fiber, or laser. It is different from longitudinal modes, which are along the length of a laser.

See Time Space Gradient (TSG) Alarming.

See Fiber in Metal Tube (FIMT).

Transport facility underneath the ground. AP Sensing's Distributed Temperature Sensing (DTS) solutions for the fire detection and special hazard markets offer reliable asset protection in train and traffic tunnels, even in the most challenging environments (dirt, dust, humidity, electromagnetic interference (EMI)).

U

U-bend usually describes the bending of 180 degrees of two fibers splices at the far end of a fiber cable. With this type of bending, the forward optical path is doubled within the same cable and allows an easy application of the methods requiring a U-shaped configuration.

U-shaped configuration is the deployment of a fiber cable with both ends of the forward optical path connected to a Distributed Temperature Sensing (DTS) instrument. This can be realized by u-bending either two fiber optics (at the far end) or the cable itself (at half of its length). This configurations indicates temperature signatures mirrored at the U-bend and allows performing measurements in two directions. The u-shaped configuration is necessary for the double-ended method.

See Underwriter’s Laboratory (UL).

A UL certification ensures customers that our Distributed Temperature Sensing (DTS) solutions have been objectively tested to ensure physical and environmental safety for our customers. The UL certification adds to our industry-leadingset of tests and certifications (including UL-C, CE, VdS, FM, ATEX and SIL-2).

A UL-C certification ensures Canadian customers that our Distributed Temperature Sensing (DTS) solutions have been objectively tested to ensure physical and environmental safety for our customers. The UL-C certification adds to our industry-leadingset of tests and certifications (including UL, CE, VdS, FM, ATEX and SIL-2).

UPC is specific to singlemode applications. It refers to the endface geometry of a connector ferrule as well as performance characteristics (-55 dB return loss).

A transmission line in which voltages on the two conductors are unequal with respect to ground, i.e., a coaxial cable.

Buried cables, especially high voltage transmission and distribution power cables.

A nonprofit laboratory which examines and tests devices, materials and systems for safety, not for satisfactory operation.

See Ultra Physical Contact (UPC).

The process within of oil and gas production that involves the extraction of oil and gas from the earth; the hydraulic engineering.

Tunnels for power distribution, typically used in cities. AP Sensing's Distributed Temperature Sensing (DTS) solution for power cable monitoring lets you monitor and protect your power infrastructure in utility tunnels, HVDC /HVAC underground power cables, joints and terminations and in subsea and substation equipment.

V

Variable Optical Attenuator (VOA). An attenuator in which the attenuation can be varied.

Vault is a storage product allowing for excess cable slack and splice case.

An international organization for safety and security. which tests and certifies products in the fire detection and safety market.

A large craft made for navigation on water.

Continuous oscillation.

Electromagnetic radiation visible to the human eye at wavelengths of 400 to 700 nm.

A visible fault locator is a device that couples visible light into the fiber to allow visual tracing and testing of continuity. Some are bright enough to allow finding breaks in fiber through the cable jacket.

See Variable Optical Attenuator (VOA).

The term most often used to designate electric pressure which exists between two points and is capable of producing a flow of current when a closed circuit is connected between the two points.

W

Waveguide describes a structure that guides electromagnetic waves along its length. An optical fiber is an optical waveguide.

Waveguide array or also known as array waveguide (AWG). An array of curved planar wave-guides which separates many optical channels at once.

The part of chromatic dispersion which arises from the different speeds light travels in the core and cladding of a single-mode fiber.

A parameter of the light wave. It is the distance (in meters) between two adjacent peaks in a wave.

Wavelength isolation or also known as far-end crosstalk. A WDM’s isolation of a light signal in the desired optical channel from the unwanted optical channels.

A wavelength selective coupler is a device which couples the pump laser wavelength into the optical fiber while filtering out all unwanted wavelengths. It is usually used in erbium-doped fiber amplifiers.

Wavelength-Division Multiplexing (WDM). Multiplexing of signals by transmitting them at various wavelengths through the same fiber.

See Wavelength-Division Multiplexing (WDM).

WDM coupler is a passive device designed to either optimally combine light of multiple predetermined wavelengths into a single core; or to optimally sort and segment those wavelengths and couple them separately into output fiber cores.

A wavelength region where fibers have low attenuation. It is used for transmitting signals.

The difference (in dB) between the power budget and the loss budget (i.e. the excess power margin).

X

The frequency range between 8.0 and 8.4 GHz.

XLPE stands for cross-linked polyethylene, which is widely used to insulate medium- and high-voltage power cables.

Y

A tee coupler variation in which incident light is split between two channels that branch out like a Y from the input.

Yield is the percentage of completed splices or assemblies that pass specifications and are good the first time. The higher the yield (e.g., 95 %), the greater the installed cost benefit.

Yield strength describes the minimum stress at which a material will start to physically deform without further increase in load.

Yield value is the stress, either normal or shear, at which a marked increment in deformation occurs without an increase in load.

Z

A fiber with zero chromatic dispersion which is shifted to 1550 nm.

The wavelength at which net chromatic dispersion of an optical fiber is nominally zero. This happens where waveguide dispersion neutralizes material dispersion.

A zipcord is a separable, two-fiber, breakout-style cable.

In fiber optic sensing the monitored fiber is typically divided in individual zones by defining a start and stop position on the sensing fiber. Zones help structure the monitored asset. Different alarm parameter sets can be defined per zone allowing additional flexibility in sensitivity.  Zones are also frequently referred to as Alarm Zones or Asset Zones.