 1xN
- This term is a type of switching configuration. It has a single input that
can be connected to multiple outputs (N), or the opposite (many inputs that
could be connected to a single output). This is a simple way to describe a
matrix
(or MxN) with
one axis having a single port.
AFV/Audio-Follow-Video
- A control mode in a routing switcher (switching array) in which the audio
inputs associated with a video input are automatically selected when the
video source is selected. That is, audio and video are always switched
together. See
Breakaway.
Audio may be either single channel or multi-channel (stereo).
ASCIII
- American Standard Code for Information Interchange. A 7-bit binary
code representing the English alphabet, decimal numbers and common
punctuation marks. Also includes "control characters" such as Carriage
Return or End of Text. An 8-bit superset of the standard ASCII codes is
often used today to include foreign characters and other symbols. These
supersets are often called Extended ASCII Character Sets.
Active
Video - The portion of a video signal that contains the visible picture
information.
BNC
- A type of coaxial connector used in situations requiring
shielded
cable for signal connections and/or controlled
impedance
applications.
BPS
- The amount of binary data sent in bits per second. Not to be confused with
baud rate. Modern
data and fax modems, for example, transmit at 14,400 bits per second using a
baud rate of 2,400 baud. This is accomplished by complex encoding methods.
Also used as a general term to define any rate that digital data flows (see
Mbps).
Balanced
Input - A differential input circuit pair with equal impedance to ground
on each side. See
Differential Input. The advantages as opposed to
single-ended transmission are noise rejection over long distances of
cabling.
Balanced
Output - A differential output circuit pair with equal source impedance
on each side. See
Differential Output.
Bandwidth
- 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 "frequency range" of a device or system.
Baseband
- An un-modulated signal or band of signals. The video signal seen on a
waveform monitor is a baseband video signal.
Baud
Rate - The signaling or symbol rate of a digital transmission path
or device. A symbol can represent more than one bit of information,
depending on the encoding or modulation scheme used to create the symbol.
Often used interchangeably with bits per second (BPS), although incorrectly.
See
BPS.
Blanking/Blanking
Interval - The period of time when a television monitor is "blanked"
while the electron beam retraces from right to left or bottom to top. In a
baseband video signal, the intervals between active video lines and between
the last active line in a field and the first active line in the next.
Ideally, a video switcher would sense when a blanking period occurs and
would switch the video signal during this time. This prevents any visually
unpleasant video effects on a monitor. This requires the video switcher to
actively monitor each of the user's video sources.
Blocking
- A term with multiple and conflicting industry usage. 1) May be used to
express the inability to connect a single input of a switching array to
multiple outputs simultaneously without any input loading or mismatches. If
multiple outputs are connected to a given input, proportional input loading
will occur. 2) In multi-stage switching arrays (tri-stage or 3-stage), it
refers to the possibility that the user may not be able to route an input to
an output at all times (blocking due to unavailable middle stages). See
Non-Blocking. It is possible that even if blocking occurs, the switching
array may be able to be reinitialized in a logical order to avoid the
blocking conditions.
Breakaway
- A routing control mode wherein an audio source can be selected
independently of the video source and vice versa.
See AFV/Audio-Follow-Video.
Break-Before-Make
- Disconnecting the present circuit before connecting a new circuit. Also
known as Break/Make.
Byte
- A grouping of 8 binary bits is called a byte.
Carry
Current - See
Cold
Switching.
Channel
Crosstalk
- Coupling of a signal from one channel to another or any other output by
conduction or radiation. Crosstalk is expressed in decibels (dB) at a
specified load impedance and over a specific frequency range or ranges. See
Crosstalk Isolation.
Coaxial
Cable - A cable that has one conductor (shield) completely surrounding
the other (center conductor), the two being coaxial and separated by an
insulator. Standard industry types have a braided shield, or a semi-rigid
copper or stainless steel shield material. Braided shield coaxial cable
offers more physical flexibility but less shielding.
Cold
Switching - Closing the relay contacts before applying voltage and
current, plus removing voltage and current before opening the contacts.
(Contacts do not make or break current.) Also see
Dry Circuit Switching. Larger currents may be carried through the
contacts without damage to the contact area since contacts will not "arc"
when closed or opened.
Common
Mode Rejection - The ability of a
differential input circuit to reject a signal common to both inputs,
normally "hum" developed by 50 or 60 Hz power line (mains) voltages.
Common
Mode Rejection Ratio (CMRR) - A measure in decibels of the effectiveness
of a circuit in rejecting a common mode voltage.
Common
Mode Voltage - The voltage common to both sides of a
differential circuit pair. The differential voltage across the circuit
pair is the desired signal, whereas the common voltage signal is the
unwanted signal which may have been coupled into the transmission pair.
Component
Video - A three-channel video signal wherein the luminance, hue and
color saturation information are carried as R, G and B (Red, Green and Blue)
signals or as one of several variations of color difference signals.
Composite
Video - A single video signal carrying combined luminance, chrominance
and raster synchronizing information.
Contact
Bounce - The intermittent and usually undesired opening of
mechanical relay contacts during closure, or closing of contacts during
opening. Contact bounce period depends upon the type of relay and varies
from .5mS for small reed relays to 10-20mS for larger solenoid types.
Solid-state or
mercury wetted
contacts (Hg) do not have a contact bounce characteristic.
Contact
Life - The maximum number of expected closures before failure. Life is
dependent on the switched voltage, current, and power. Failure is usually
when the contact resistance exceeds an end of life value. Typical failure
mode is non-closure of the contact as opposed to a contact sticking closed.
Contact
Potential
- A voltage produced between contact terminals due to the temperature
gradient across the relay contacts, and the reed-to-terminal junctions of
dissimilar metals. (The temperature gradient is typically caused by the
power dissipated by the energized coil.) Also known as contact offset
voltage, thermal EMF, and thermal offset. This is a major consideration when
measuring voltages in the microvolt range. There are special low thermal
relay contacts available to address this need. Special contacts are not
required if the relay is closed for a short period of time where the coil
has no time to vary the temperature of the contact or connecting materials
(welds or leads).
Contact
Rating - The voltage, current, and power capacities of relay contacts
under specified environmental conditions. See
Carry
Current and Switched Current.
Contact
Resistance
- The resistance in ohms or milliohms across closed contacts. Also see
Path
Resistance.
Crosspoint
Switch
- A switch which, when closed, connects the signal on an input bus to one or
more output buses. Also referred to as a
matrix
switch or switching array.
Crosstalk/Crosstalk
Isolation - Unwanted interference in an output resulting from other
input and output signals, measured in dB below the nominal signal level, and
is expressed in decibels (dB) at a specified load impedance and over a
specific frequency range or ranges. Also referred to as All Hostile or
Hostile Crosstalk. See
Channel Isolation.
Current
Surge Limiting - The circuitry necessary to protect relay contacts from
excessive and possibly damaging current caused by capacitive loads.
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