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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.
Glossary Term: Digital/Discrete I/O
Input or output that senses or sends either “on” or “off” (1 or 0) signals to the field. For example a discrete input would sense the position of a switch as energized or de-energized. A discrete output would turn a pump or light on or off.
Glossary Term: DP (Differential pressure) transmitter
A transducer designed to measure the pressure difference between two points in a process and transmit a signal proportional to this difference, without regard to the absolute pressure at either point. Often used to measure flow by the pressure difference across a restriction in the flow line or to measure…
Glossary Term: Differential gap
The smallest increment of change in a controlled variable required to cause the final control element in a two position control system to move from one position to its alternative position.
Glossary Term: Diaphragm valve
A valve with a flexible linear motion closure piece that is forced into the internal flow passageway of the valve body by the actuator.
Glossary Term: Diagnostic coverage
A measure of a system’s ability to detect failures. This is a ratio between the failure rates for detected failures to the failure rate for all failures in the system.
Glossary Term: Diaphragm
A sensing element consisting of a thin, usually circular, plate which is deformed by pressure differential applied across the plate.
Glossary Term: Design pressure
The maximum allowable working pressure permitted under the rules of the relevant construction code. See also pressure, design.
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