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Glossary Term: Event tree analysis
A method of fault propagation modeling. The analysis constructs a tree- shaped picture of the chains of events leading from an initiating event to various potential outcomes. The tree expands from the initiating event in branches of intermediate propagating events. Each branch represents a situation where a different outcome is…
Glossary Term: Event (Intermediate)
An event that propagates or mitigates the initiating event during an event sequence (e.g., improper operator action fails to stop the initial ammonia leak and causes propagation of the intermediate event to an incident; in this case the intermediate event outcome is a toxic release)
Glossary Term: Event (Initiating)
The first event in an event sequence (e.g., the stress corrosion resulting in leak/rupture of the connecting pipeline to the ammonia tank)
Glossary Term: Event (Independent)
Events that do not affect each other (can be series or parallel).Tossing two coins (parallel) or one coin twice (series) are generally considered to be independent events.
Glossary Term: Elevation error
A type of error in temperature or pressure sensors that incorporate capillary tubes partly filled with liquid; the error is introduced when the liquid filled portion of the system is at a different level than the instrument case, the amount of error varying with distance of elevation or depression.
Glossary Term: EMI
Electromagnetic Interference: 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)”
Glossary Term: Effect Zone
The physical area in which a harmful effect is felt by a receptor. For a toxic release, the area over which the airborne concentration exceeds some level of concern. For a physical energy release, the area over which a specified overpressure criterion is exceeded. For thermal radiation effects, the area…
Glossary Term: E/E/PE
Electrical / Electronic / Programmable Electronic See 61508 and 61511.
Glossary Term: Eddy current
A circulating current induced in a conductive material by a changing electromagnetic field.
Glossary Term: Dynamic pressure
The increase in pressure above the static pressure that results from complete transformation of the kinetic energy of the fluid into potential energy in units of pressure.
Glossary Term: Dust, combustible
Dust that (when mixed with air in certain proportions) can be ignited and will propagate a flame.
Glossary Term: Duplex
Half duplex is where there is communications in both directions (transmit and receive), but in only one direction at a given instant in time. Full duplex is where there is communication that appear to have information transfer in both directions (transmit and receive) at the same time.
Glossary Term: Dual-sealing valve
A valve which uses a resilient seating material for the primary seal and a metal to metal seat for a secondary seal.
Glossary Term: Double block and bleed
A three valve configuration common in shut off applications. Two main shut off valves (block valves) operate on the main process line to stop flow. Then a third bleed valve to a vent can be opened to relieve pressure of remove the process fluid from the region between the two…
Glossary Term: Doppler effect flowmeter
A device that uses ultrasonic techniques to determine flow rate; a continuous ultrasonic beam is projected across fluid flowing through the pipe, and the difference between incident beam and transmitted beam frequencies is a measure of fluid flow rate.
Glossary Term: Diversity
applying different ways to performing a required function. Diversity may be achieved by different physical methods or different design approaches.
Glossary Term: Displacement level meter
A device that measures liquid level by means of a float and balance beam connected to a position sensor.
Glossary Term: DIN
Abbreviation for the standards institution of the Federal Republic of Germany.
Glossary Term: DCS
Digital or Distributed Control System. DCSs historically refers to larger analog control systems traditionally used for PID control in the process industries, whereas PLCs were used for discrete or logic processing. However, PLCs are gaining capability and acceptance in doing PID control while the DCS has come to mean the…
Glossary Term: Digital valve
A single valve casing containing multiple solenoid valves whose flow capacities vary in binary sequence (1, 2, 4, 8, 16, ...); to regulate flow, the control device sends operating signals to various combinations of the solenoids; applications are limited to very clean fluids at moderate temperatures and pressures.
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