Numerical aperture. The light-gathering ability of a fiber. It defines the maximum angle to the fiber axis at which light will be accepted and propagated through that fiber. Also, numerical aperture describes the angular spread of light from a central axis, as in light exiting fiber, being emitted from a source, or entering a detector.

A special fastener for joining fiberboard sheet material to wood framing. [ISA-RP60.11 1991]

Negative acknowledgment. This code indicates that the last block transmitted was in error and that the receiver is expecting a retransmission.

A plate attached to a control valve that bears the name of the manufacturer and a listing of the valve's specifications. [ANSI/ ISA-75.05.01 2000]

In fiber optics, the loss of power at a joint. It occurs when the transmitting half has a numerical aperture (NA) that is greater than that of the receiving half, as when coupling light from source to fiber, from fiber to fiber, or from fiber to detector.

Normenarbeitsgemeinschaft f r Me -und Regelungstechnik in der Chemischen Industrie. A committee founded in 1949 by several large chemical companies from Germany, The Netherlands, and Switzerland to standardize industrial practices in process measurement and control. A subcommittee published a set of guidelines for structured batch control in 1986, which were accepted throughout the European chemical industry with strong support worldwide. NAMUR looks at batch automation from the process activity viewpoint and views activities such as charge, mix, heat/ cool, and the like,...