Automating Manufacturing Systems - Process Control and ...

plc glossary - 35.20
(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.
35.15 O
OCR (Optical Character Recognition) - Images of text are scanned in, and the computer will try to interpret
it, much as a human who is reading a page would. These systems are not perfect, and often rely
on spell checkers, and other tricks to achieve reliabilities up to 99%
octal - a base 8 numbering system that uses the digits 0 to 7.
Octave - a doubling of frequency
odd parity - a bit is set during communication to indicate when the data should have an odd number of bits.
OEM (Original Equipment Manufacturer) - a term for a manufacturer that builds equipment for consumers,
but uses major components from other manufacturers.
off-line - two devices are connected, but not communicating.
offset - a value is shifted away or towards some target value.
one-shot - a switch that will turn on for one cycle.
on-line - two devices are put into communications, and will stay in constant contact to pass information as
required.
opcode (operation code) - a single computer instruction. Typically followed by one or more operands.
open collector - this refers to using transistors for current sourcing or sicking.
open loop - a system that does monitor the result. open loop control systems are common when the process
is well behaved.
open-system - a computer architecture designed to encourage interconnection between various vendors
hardware and software.
operand - an operation has an argument (operand) with the mnemonic command.
operating system - software that existing on a computer to allow a user to load/execute/develop their own
programs, to interact with peripherals, etc. Good examples of this is UNIX, MS-DOS, OS/2.
optimization - occurs after synthesis and after a satisfactory design is created. The design is optimized by
iteratively proposing a design and using calculated design criteria to propose a better design.
optoisolators - devices that use a light emitter to control a photoswitch. The effect is that inputs and outputs
are electrically separate, but connected. These are of particular interest when an interface between
very noisy environments are required.
OR - the Boolean OR function.
orifice - a small hole. Typically this is places in a fluid/gas flow to create a pressure difference and slow the
flow. It will increase the flow resistance in the system.
oscillator - a device that produces a sinusoidal output.
oscilloscope - a device that can read and display voltages as a function for time.