 Daisy Chaining - The serial control connection of
two or more mainframes in a
master/slave(s)
configuration. Also, some switching modules or cards can be daisy-chained to yield more
inputs. This term is also used in reference to control panels daisy chaining (looping)
from control panel to control panel to the final destination, the switching system.
Decibels (dB) - The logarithmic ratio between two
signal levels. In video and audio, it is normally defined as: dB=20 log10(V2/V1)
Destination - The
equipment connected to the output of a routing switcher,
crosspoint switch or switching array. Used when
defining the size of a switching array, the user must specify how many sources and
destination there are in the system. See
Source.
Differential Gain - Unwanted variations in a
video signal's chrominance subcarrier's amplitude that result from changes in the signal's
DC level, usually specified between 10% and 90% of full scale. Expressed in a percentage,
or a fraction of a percentage.
Differential Input -
An input circuit that actively responds to the difference between two terminals rather
than the difference between one terminal and ground. Often associated with
balanced input circuitry, but also may be used with an
unbalanced source. The opposite is the
single-ended
or unbalanced input.
Differential Phase
- Unwanted variations in a subcarrier's phase as a result of changes in the chrominance
signal's DC level, usually specified between 10% and 90% of full scale. Expressed in
degrees, or fractions or a degree.
Differential Output
- An output circuit where the output voltage appears between two active output terminals
rather than between one terminal and ground. Normally associated with
balanced circuitry. See
Differential Input.
Dry Circuit Switching
- Switching below specified levels of voltage and current to minimize any physical and
electrical changes in the contact junction. Also see
Cold
Switching.
Dry Reed Relay - A
glass enclosed, hermetically sealed, magnetically actuated contact. No mercury or other
wetting material is used. Typical atmosphere inside the glass enclosure is nitrogen.
DUT - Abbreviation for Device
Under Test. See UUT.
ECL Logic - Abbreviation
for Emitter Coupled Logic, a very high speed digital technology.
Electromechanical Effects - A relay that uses an
electromagnet to move an armature thereby actuating current.
EMI - Abbreviation for
Electromagnetic Interference. A term that defines unwanted electromagnetic radiation from
a device which could interfere with desired signals in test or communication equipment.
RFI (Radio Frequency Interference) and EMI are often used interchangeably.
Equalization -
Selective amplification (signal restoration) applied to a signal in order to compensate
for high frequency attenuation and other distortions encountered in long lengths of cable.
F-Type Connector - A threaded medium performance
coaxial signal connector typically used in consumer applications (TV's and VCR's). This
connector is typically usable as high as 1GHz. It is inexpensive since the pin of the
connector is actually the center conductor of the coaxial cable.
Failsafe - In terms of relay technology, when
power is lost, the relay contacts fall back to a default position.
Flatness - A term
expressed in dB to specify the consistent amplitude of a signal spanning a frequency
range. Typical expressions: Flatness is to be +/-1dB across (frequency range), OR Flatness
shall have <1.5dB peak to peak.
Floating - The condition where a common mode
voltage exists, or may exist between earth ground and the instrument or circuit of
interest. Low side of circuit is not at earth potential.
Frequency Range
- The measure of a circuit's ability to pass a full amplitude signal over a range of
signal frequencies. Normally measured between the point or points where the signal
amplitude falls to -3dB below the passband frequency. Normally defines the
"bandwidth" of a device or system.
Full Fanout -
Distributing the same signal to multiple destinations. See
Non-Blocking.
Ganged Control - A
method of control that allows the system to control multiple levels of switching with a
single command (see
Multi-Level). Such is the case
in a video system where different levels are assigned to the different colors in a video
signal (R = Red, G = Green and B = Blue). A single command will control all three levels
simultaneously.
Hostile Crosstalk - See Crosstalk.
Hostile Input - An unselected input carrying a
signal which causes unwanted interference and coupling in a desired output.
See Crosstalk.
Impedance - The
electrical characteristic of a transmission circuit expressed in ohms. The transmission
circuit (line) is usually
terminated
in a resistance such as 50 or 75 ohms (most popular).
Input Bus - A circuit path on the input side of a
switching array which connects to the inputs of one or more crosspoint switches. Each
input connector leads to an input bus.
Insertion Loss - The
attenuation of signals due to routing them through a switching module or system. Specified
as a decibel value (dB) over a frequency range. Loss could be due to the resistive,
inductive or capacitive features of the signal path, or a combination of all of these.
Insulation Resistance -The ohmic resistance of
insulation. It degrades quickly as humidity increases. Lower insulation resistance
provides a path for
leakage current to ground.
This is very critical when making measurements on semiconductor components where picoamp
measurements are being made.
K-Type Connector - A small type of threaded
coaxial signal connector typically used in higher frequency applications. This connector
is typically usable as high as 40GHz. It may be mated by an SMA connector with much lower
performance.
Latching - In relay or
switching technology, this refers to the ability to keep the contact status in place even
if power is removed from the equipment.
Leakage Current -
Error current that can degrade sensitive measurements. Even high resistance paths between
low current conductors and nearby voltage sources can generate significant leakage
currents. Leakage in insulating material, micro-contamination on insulating surfaces, and
moisture (humidity) can have catastrophic effects on picoamp and sub-picoamp (femtoamp)
measurements.
Looping Input - An
input which passes a video signal in and out of a device without terminating the cable or
affecting the signal quality. Looping inputs use two connectors normally wired together
with no active components between them. If the looping feature is not used, a 75 ohm
terminator should be placed on the second connector, or a provision for switching in a 75
ohm termination internally.
Low Thermal - See
Contact Potential.
Mbps - Megabits per second
(millions of bits per second). A measure of digital data transmission rate.
Mainframe - A unit which
accepts modules and/or cards. Typically in Universal Switching's equipment, the Mainframe
unit provides control and power to the modules installed.
Master / Master Mainframe
- A mainframe that has control of other mainframes (slaves) in a serial chain. A
master/slave combination has one bus address and appears as one mainframe with increased
capacity.
Matrix - An arrangement of
signal circuits in which input buses are represented by parallel vertical lines and output
buses as overlapping horizontal lines (or visa versa), forming a grid-like array.
Crosspoint switches at each crossing point connect inputs to outputs. Also referred to as
a switching array, or crosspoint switch.
MxN -
This term is another way to express a type of switching configuration. It
is the same as a matrix or
crosspoint
switch where a number of inputs (M) can connect to a number of outputs
(N). This term is common since when giving the dimensions of a matrix, it
is usually is expressed as the number of input (M) by the number of
outputs (N). For example, a matrix with 8 inputs and 32 outputs would
commonly be expressed as an 8x32 matrix. The MxN term is also used since
it doesn't explicitly indicate "in" and "out" since
some type of matrices are bi-directional. When one axis has only a single
port, this is commonly expressed as a
1xN
array.
Mercury Wetted Relay - A
reed relay in which the contacts are wetted by a film of mercury (Hg). Usually has a
required operating position to avoid liquid mercury from shorting the contacts; other
types are position insensitive. This type of relay is usually higher power and longer
life, but at a higher dollar cost. Another benefit of this type of contact is the
repeatability of contact resistance and virtually no
contact
bounce.
MTBF - An abbreviation of Mean
Time Between Failure, a theoretical period of time between failures in equipment based on
stresses in environment, temperature, levels of quality and other parameters.
MTTR MTTR
- An abbreviation for
Mean Time To Repair, a theoretical period of time need to repair a piece of equipment
given certain circumstances.
Multi-Level - Usually
indicating that separate levels of switching are included different levels are required.
This is typical when switching RS-232 type data lines. These could be up to 25 levels
deep. Some types of video signals are divided into different levels, one for each primary
color (Red, Green and Blue). For most applications of this nature, this type of switching
array is
gang controlled.
Multiplexer - Being able to connect a single
sources to any multiple destinations (one at a time), or the opposite. Also referred to as
a Scanner.
N-Type Connector - A larger threaded coaxial
connector with high power handling and good high frequency characteristics. Typically
usable to 12.5GHz, but some manufacturers offer connectors usable to 18GHz.
Noise Figure - An
expression of noise generated with in a device specified in dB. This parameter is important
in RF application such as a receive antenna switching system and IF signal routing. The
lower the noise figure, the better.
Non-Blocking
- A term
with multiple and conflicting industry usage. 1) May be used to express the ability
to connect a single input of a switching array to multiple outputs simultaneously without
any input loading or mismatches. This usually results in a constant signal loss because of
the use of power dividers (signal splitters) to configure the non-blocking switching
array. Non-blocking switching arrays can also be achieved using impedance shifting in
place of power dividers. Also referred to as Full Fanout. 2) In multi-stage
switching arrays (tri-stage or 3-stage), it refers to the ability to route an input to an
output at all times (no blocking due to unavailable middle stages).
NTSC - National Television
Standards Committee. This organization developed the original NTSC standard for color
television used in North America, Japan and many other countries.
Noise - Any unwanted electronic signal, or an
unwanted audible sound (from fans or cooling devices).
Nyquist Frequency
- If an analog signal is sampled at a rate more than twice that of its highest frequency
component, it can be properly reconstructed when reconverted back to the analog domain.
The required sampling rate is called the Nyquist frequency. Conversely, the analog
bandwidth required to accurately transmit a properly reconstructed sampled image is one
half the image sample (pixel clock) rate. See
Wideband.
Back to the TOP
If you would like to submit additional
terms and definitions, we encourage sending us email:
support@uswi.com
|
