[ Pobierz całość w formacie PDF ]
Sidereal Day The period of an earth's rotation with respect to the stars.
characteristics of drivers and receives for use in balanced digital
Signal to Noise Ratio The ratio of signal strength to the level of noise.
multipoint systems.
Signal Conditioning Pre-processing of a signal to bring it up to an acceptable quality
RTU Remote Terminal Unit. Terminal Unit situated remotely from the
level for further processing by a more general purpose analog
main control system.
input system.
S-Video The luminance and chrominance elements of a video signal are
Simplex Transmission Data transmission in one direction only.
isolated from each other, resulting in a far cleaner image with
Simultaneous Sampling The ability to acquire and store multiple signals at exactly the same
greater resolution.
moment. Sample-to-sample inaccuracy is typically measured in
SAA Standards Association of Australia.
nanoseconds.
SAP Service Access Point.
Single-ended See number of channels.
SDLC Synchronous Data Link Control. IBM standard protocol superseding
Slew Rate This is defined as the rate at which the voltage changes from one
the bisynchronous standard.
value to another.
Selectivity A measure of the performance of a circuit in distinguishing the
Smart Sensors A transducer (or sensor) with an on-board microprocessor to
desired signal from those at other frequencies.
pre-process input signals to the transducer. It also has the capability
Self-calibrating A self-calibrating board has an extremely stable on-board reference
of communicating digitally back to a central control station.
which is used to calibrate A/D and D/A circuits for higher accuracy.
SNA Systems Network Architecture.
Self-diagnostics On-board diagnostic routine which tests most, if not all, of a board's
SNR Signal to Noise Ratio.
functions at power-up or on request.
Software Drivers Typically a set of programs or subroutines allowing the user to control
Serial Transmission The most common transmission mode in which information bits are
basic board functions, such as setup and data acquisition. These can
sent sequentially on a single data channel.
be incorporated into user-written programs to create a simple but
functional DAS system. Many boards come with drivers supplied.
64 65
The IDC Engineers Pocket Guide Power Systems Protection, Power Quality, Substation Automation
Software Trigger Software control of data acquisition triggering. Most boards are
Sync A synchronisation, or sync, pulse ensures that the monitor
designed for software control.
displaying the information is synchronised at regular intervals with
the device supplying the data, thus displaying the data at the right
SOH Start of Header (ASCII Control-A).
location.
Space Absence of signal. This is equivalent to a binary zero.
For example, a sync pulse would be used between a camera and a
Spark Test A test designed to locate imperfections (usually pin-holes) in the
display device to reset the image to the top of the frame for the
insulation of a wire or cable by application of a voltage for a very
beginning of the image.
short period of time while the wire is being drawn through the
Synchronisation The co-ordination of the activities of several circuit elements.
electrode field.
Synchronous Transmission in which data bits are sent at a fixed rate, with the
Spatial Resolution A measure of the level of detail a vision system can display. The
Transmission transmitter and receiver synchronised. Synchronised transmission
value, expressed in mils or inches per pixel, is derived by dividing
eliminates the need for start and stop bits.
the linear dimensions of the field of view (x and y, as measured in
the image plane), by the number of pixels in the x and y dimensions
Talker A device on the GPIB bus that simply sends information onto the
of the system's imaging array or image digitiser.
bus without actually controlling the bus.
Spatial Filtering In image processing, the enhancement of an image by increasing or
Tank A circuit comprising inductance and capacitance which can store
decreasing its spatial frequencies.
electrical energy over a finite band of frequencies.
Spectral Purity The relative quality of a signal measured by the absence of harmonics,
TCP/IP Transmission Control Protocol/Internet Protocol. The collective
spurious signals and noise.
term for the suite of layered protocols that ensures reliable data
transmission in an internet (a network of packet switching networks
Speed/Typical The maximum rate at which the board can sample and convert
functioning as a single large network).
Throughput incoming samples. The typical throughput is divided by the number
of channels being sampled to arrive at the samples/second on each
Originally developed by the US Department of Defense in an effort
channel. To avoid false readings, the samples per second on each
to create a network that could withstand an enemy attack.
channel need to be greater than twice the frequency of the analog
TDM Time Division Multiplexer. A device that accepts multiple channels
signal being measured.
on a single transmission line by connecting terminals, one at a time,
Standing Wave Ratio The ratio of the maximum to minimum voltage (or current) on a
at regular intervals, interleaving bits (bit TDM) or characters
[ Pobierz całość w formacie PDF ]