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Glossary Term: Linear variable reluctance transducer (LVRT)
A position sensor consisting of a centre tapped coil and an opposing moving coil attached to a linear probe; the winding is continuous over the length of the core, instead of being segmented as in an LVDT.
Glossary Term: Linear variable differential transformer (LVDT)
A position sensor consisting of a central primary coil and two secondary coils wound on the same core; a moving iron element linked to a mechanical member induces changes in self induction that are directly proportional to movement of the member.
Glossary Term: Limited variability language (LVL)
This type of language is designed for process sector users, and provides the capability to combine predefined, application specific, library functions to implement the safety requirements specifications. An LVL provides a close functional correspondence with the functions required to achieve the application. Typical examples of LVL are ladder diagram, function…
Glossary Term: Likelihood
The frequency of a harmful event often expressed in events per year or events per million hours. One of the two components used to define a risk. Note that this is different from the traditional English definition that means probability.
Glossary Term: LEL/LFL
Lower explosive (or flammable) limit. See flammability.
Glossary Term: Latent fault
A fault that is present but hidden from regular means of detection. Typically these faults can only be identified as part of an accident or a detailed proof test.
Glossary Term: Laser Doppler flowmeter
An apparatus for determining flow velocity and velocity profile by measuring the Doppler shift in laser radiation scattered from particles in the moving fluid stream
Glossary Term: Ladder diagram
Symbolic representation of a control scheme. The power lines form the two sides of a ladder like structure, with the program elements arranged to form the rungs. The basic program elements are contacts and coils as in electromechanical logic systems. Typically programs of this form fall into the limited variability…
Glossary Term: Jacketed valve
A valve body cast with a double wall or provided with a second wall by welding material around the body so as to form a passage for a heating or cooling medium. Also refers to valves which are enclosed in split metal jackets having internal heat passageways or electric heaters.…
Glossary Term: IPL
Independent protection layer or layers. This refers to various other methods of risk reduction possible for a process. Examples include items such as rupture disks and relief valves which will independently reduce the likelihood of the hazard escalating into a full accident with a harmful outcome. In order to be…
Glossary Term: I/S barrier
Intrinsic safety barrier. Physical element that limits current and voltage into a hazardous area in order to satisfy Intrinsic Safety requirements.
Glossary Term: I/O
Input/Output. Refers to the electronic hardware where the field devices are wired. Discrete I/O would have switches for inputs and send signals to solenoid valves and pumps for outputs. Analog I/O would have continuously variable process values inputs, and controller outputs.
Glossary Term: Intrinsic safety
1. A type of protection in which a portion of the electrical system contains only intrinsically safe equipment (apparatus, circuits, and wiring) that is incapable of causing ignition in the surrounding atmosphere. No single device or wiring is intrinsically safe by itself (except for battery-operated self-contained apparatus such as portable…
Glossary Term: Interlock
1. Instrument which will not allow one part of a process to function unless another part is functioning. 2. A device such as a switch that prevents a piece of equipment from operating when a hazard exists. 3. To arrange the control of machines or devices so that their operation…
Glossary Term: Interference, normal-mode
A form of interference which appears between measuring circuit terminals. See also EMI.
Glossary Term: Interference, electromagnetic
Any spurious effect produced in the circuits or elements of a device by external electromagnetic fields. NOTE: A special case of interference from radio transmitters is known as “radio frequency interference (RFI)” See also EMI.
Glossary Term: Interference, common mode
A form of interference which appears between measuring circuit terminals and ground. See also EMI.
Glossary Term: Inductance
1. In an electrical circuit, the property that tends to oppose changes in current magnitude or direction. 2. In electromagnetic devices, generating electromotive force in a conductor by means of relative motion between the conductor and a magnetic field such that the conductor cuts magnetic lines of force.
Glossary Term: Incident
The result of an initiating event that is not stopped from propagating. The incident is most basic description of an unwanted accident, and provides the least information. The term incident is simply used to convey the fact that the process has lost containment of the chemical, or other potential energy…
Glossary Term: Impedance
The complex ratio of a force-like parameter to a related velocity-like parameter - for instance, force to velocity, pressure to volume, electric voltage to current, temperature to heat flow, or electric field strength to magnetic field strength.
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