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Control and Instrumentation GlossaryWe have 17 entries in our Glossary for this letter. D&ID Duct and Instrument Diagram - the HVAC equivalent of a P&ID An air distribution diagram which typically includes HVAC equipment; instrumentation; connections to other systems; duct sizes etc Further Reading Damping The suppression of oscillation. Achieved using viscosity of a fluid for viscous damping, and the induced current in electrical conductors for magnetic damping. Further Reading DCS Distributed Control System A control system with multiple processors and I/O subsystems connected by a network. Further Reading Dead Time The interval between the initiation of a change in the input and the start of the resulting observable response. Further Reading Deadband The range through which an input can be changed without causing an observable response. Further Reading Decibel (dB) Unit for expressing a logarithmic measure of the ratio of two signal levels. Further Reading DEMKO Testing institute and Notified Body based in Denmark. Further Reading Dew Point Warm gas (e.g. air) can hold more water vapour than a cool gas. If the gas is cooled sufficiently it will reach a temperature where the gas becomes saturated and condensation will form. At this temperature the gas is said to have reached its dew point. Further cooling will allow further moisture to condense. Further Reading Dielectric An insulating material that can sustain an electric field but resists passage of electric current. Further Reading Dielectric Constant A number that expresses the degree of non-conductivity of different substances Further Reading DIN - Deutsche Industrie Normen German industrial standards Further Reading Dither An oscillation of small magnitude often introduced to overcome the effects of friction; hysteresis or clogging Further Reading Double Block and Bleed Double Block and Bleed consists of the closure of two block valves in series with an intermediate bleed valve used to provide isolation of process from maintenance personnel Can be constructed from individual valves or in a single purpose built unit. Further Reading Drift Undesired change in the input-output relationship over a period of time. Further Reading DTI The UK's Department of Trade and Industry Further Reading Duplex Name given to a family of stainless steels which have a near equal mix of austenite and ferrite. Duplex stainless steels exhibit high strength and excellent corrosion resistance. Further Reading Stainless Steel Guide Dynamic Range Ratio of the largest to the smallest signal level a circuit can handle. Usually expressed in dB Further Reading |
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