eBook: Automating Manufacturing Systems; with PLCs


A.14 N

NAK (Negative AKnowledgement) - an ASCII control code.
NAMUR - A european standards organization.
NAND (Not AND) - a Boolean AND operation with the result inverted.
narrowband - uses a small data transmission rate to reduce spectral requirements.
NC - see normally opened/closed
NC (Numerical Control) - a method for controlling machine tools, such as mills, using simple programs.
negative logic - a 0 is a high voltage, and 1 is a low voltage. In Boolean terms it is a duality.
NEMA (National Electrical Manufacturers Association) - this group publishes numerous standards for electrical equipment.
nephelometry - a technique for determining the amount of solids suspended in water using light.
nesting - a term that describes loops (such as FOR-NEXT loops) within loops in programs.
network - a connection of typically more than two computers so that data, email, messages, resources and files may be shared. The term network implies, software, hardware, wires, etc.
NFS (Network File System) - a protocol developed by Sun Microsystems to allow dissimilar computers to share files. The effect is that the various mounted remote disk drives act as a single local disk.
NIC (Network Interface Card) - a computer card that allows a computer to communicate on a network, such as ethernet.
NIH (Not Invented Here) - a short-lived and expensive corporate philosophy in which employees believe that if idea or technology was not developed in-house, it is somehow inferior.
NIST (National Institute of Standards and Technology) - formerly NBS.
NO - see normally opened
node - one computer connected to a network.
noise - 1. electrical noise is generated mainly by magnetic fields (also electric fields) that induce currents and voltages in other conductors, thereby decreasing the signals present. 2. a sound of high intensity that can be perceived by the human ear.
non-fatal error - a minor error that might indicate a problem, but it does not seriously interfere with the program execution.
nonpositive displacement pump - a pump that does not displace a fixed volume of fluid or gas.
nonretentive - when power is lost values will be set back to 0.
NOR (Not OR) - a Boolean function OR that has the results negated.
normally opened/closed - refers to switch types. when in their normal states (not actuated) the normally open (NO) switch will not conduct current. When not actuated the normally closed (NC) switch will conduct current.
NOT - a Boolean function that inverts values. A 1 will become a 0, and a 0 will become a 1.
NOVRAM (NOn Volatile Random Access Memory) - memory that does not lose its contents when turned off.
NPN - a bipolar junction transistor type. When referring to switching, these can be used to sink current to ground.
NPSM - American national standard straight pipe thread for mechanical parts.
NPT - American national standard taper pipe thread.
NSF (National Science Foundation) - a large funder of science projects in USA.
NSFNET (National Science Foundation NETwork) - funded a large network(s) in USA, including a high speed backbone, and connection to a number of super computers.
NTSC (National Television Standards Committee) - a Red-Green-Blue based transmission standard for video, and audio signals. Very popular in North America, Competes with other standards internationally, such as PAL.
null modem - a cable that connects two RS-232C devices.

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