 Output
Bus - An output circuit path leading from the output(s) of one or more
crosspoint switches arranged in a crosspoint switching array. Typically,
only one crosspoint switch at a time can feed a signal to an output bus.
Each output connector is fed from an output bus.
Path
Resistance - The resistance of a complete signal path, including the
switching element's contact resistance, any PC board circuit resistance and
connector terminal resistance and or cabling.
Also
see Contact Resistance.
PECL
Logic - Abbreviation for Positive Emitter Coupled Logic, a very high
speed digital technology. Also see
ECL.
Piezoelectric Currents - The current caused by
mechanical stress to the insulating materials or connectors. To minimize this problem in
low current or voltage measurements, the stress must be removed from the insulators, and
materials with a low piezoelectric effect must be used.
Propagation Delay - The specified amount of time
for a signal to pass through a previously closed signal path. The delay must be
considered, for example, when the signal is used to synchronize other signals, or is being
used in a Clock / Data configuration. This is due to both the electrical length of the
signal path, and any active components in the signal path.
RGB - A three-component video
signal in which all the colors in a scene or image are conveyed as three primary colors
(Red, Green and Blue) on three separate channels. Some times, the Green signal also
carries the Sync information as well. Many high resolution video monitors have RGB inputs.
RS-232 - An asynchronous serial data interchange
standard. RS-232 links between equipment are normally limited to 50 feet (16 meters). Also
referred to as RS-232C (most popular revision).
RS-422 - A more robust serial digital data
interchange standard utilizing individual differential signal pairs for data transmission
in each direction. Depending on data transmission rates, RS-422 can be used at distances
to 4,000 feet (1,275 meters). Also referred to as RS-422A (the most popular revision).
RS-485 - A very robust serial data interchange
standard. An RS-485 communications channel is a party-line (multi-drop) digital signal
and, like RS-422, is balanced. It is very immune to interference, making it more reliable
in demanding environments. It is usable at distances of 4,000 feet and beyond.
Redundant Power
Supply - A second power supply circuit sometimes specified for systems used in
critical applications. Redundancy is useful where unexpected power failures can cause a
major system to fail, often at great expense. Redundant power supplies could be fed from
different AC power (mains) circuits for maximum system reliability. Power supplies are
usually "diode or'ed" and should be hot swappable. A "redundant
capacity" supply is usually a single supply with built-in redundancy
included and is not hot swappable, but each supply voltage is duplicated
allowing the user to schedule down time to replace the supply.
Relay - An electrically controlled mechanical
device that opens and closes electrical contacts when a voltage (or current) is applied to
a coil. A relay provides isolation of control signals from switched signals.
Return Loss - A measure
of the undesirable signal reflections from an imperfectly
terminated transmission line.
Expressed in dB. Also see
VSWR.
SMA - A small type of threaded coaxial signal
connector typically used in higher frequency applications. This connector is typically
usable to 26GHz.
Self-Terminating -
A switching configuration which automatically terminates a signal path when it is not
connected to any other signal path. It is usually most important to terminate unused
inputs to a unit to assist in reducing noise and improve crosstalk isolation.
Settle Time - The time required for establishing
relay connections and stabilizing user circuits. For relay contacts, this includes
contact bounce.
Shielding - A metal
enclosure or gasket for a circuit, or a metal shield surrounding wire conductors (coaxial
or triaxial cable) to lessen interference, interaction, or current leakage. The shield is
usually grounded.
Single-Ended Input
- A circuit that responds to the voltage on one input terminal and ground.
See Differential Input.
Single-Ended Output - A circuit whose output is
developed between one output terminal and ground.
See
Differential Output.
Slave - A mainframe that is
serially connected to a controlling mainframe (master). The slave is controlled from a
master.
See Master / Master Mainframe.
SMB / SMC - Types of small coaxial signal
connectors typically used in high frequency applications. SMC threads to the mating
connector while the SMB "snaps" to the mating connector.
Solid State Relay
- A relay that switches electric circuits by use of semiconductor elements without moving
parts or conventional contacts.
Source - The equipment
providing a signal to the input of a routing switcher, crosspoint switch, or switching
array. See Destination.
Switched Current -
The maximum current level that can be reliably handled while opening and closing contacts.
Also see Carry Current.
Sync - A abbreviation for synchronizing, as in
synchronizing pulses. The timing pulses in a video signal which identify lines, fields and
frames.
Sync-On-Green - An
RGB
signal format in which the sync information for all three channels is included on the
green channel.
Syntax - The language "spoken" by
devices communicating with each other.
Terminated/Termination/Terminator
- An impedance used to terminate a transmission line. For example; cables used for video
distribution should be terminated with a 75 ohm resistor (terminator) at the last
connector on the receiving end if it is not already terminated internally.
Thermal EMF - See
Contact Potential
TNC - A threaded type of BNC coaxial connector.
Tri-Stage
Matrix - A switching architecture that utilizes input stages,
mid-stages and output stages in an efficient multi-stage matrix. Larger
switching arrays are better served by this type of design since multiple
signal paths are available for redundancy, the number of actual hardware signal
crosspoints is reduced, and the physical size and cost of the unit is dramatically
reduced. This design is not cost effective in switching arrays smaller
than 32x32.
Triaxial Cable - A cable with three conductors:
one conductor surrounded by an inner shield and an isolated outer shield. Generally, the
inner shield is connected to a guard potential and the outer shield to signal LOW or
ground.
Trigger - An external stimulus that initiates one
or more instrument functions. Trigger stimuli include; a front panel button (TAKE), an
external input voltage pulse.
TTL Logic - Abbreviation for
Transistor-Transistor Logic, a very typical medium speed digital technology.
Twinaxial Cable - A cable with three conductors:
one twisted pair of conductors surrounded by an outer shield.
Un-Balanced - A
transmission circuit with an impedance to ground. See Differential Input. This is also
referred to as a
single-ended transmission
line. Most analog signals over 100MHz are single ended. The compliment to this type of
transmission line is differential.
UUT - An abbreviation for Unit
Under Test. Also see
DUT (Device Under Test ).
Voltage Clamping - The circuitry necessary to
protect relay or solid-state switching elements from excessive voltage. A possible source
of this excessive voltage could be caused by switching current into inductive loads.
VSWR - Abbreviation for
Voltage Standing Wave Ratio. The loss due to the mismatch introduced into the signal by
the load or source signal path characteristics. Expressed as a ratio of the highest
voltage to the lowest voltage found in the signal. Also expressed as
Return Loss in dB. The Return Loss expression is the
more modern term.
VXI - A newer electrical and
mechanical standard (based on the VME standard, with Extensions for Instrumentation)
mainly utilized in the ATE industry to assist different vendor's equipment to work
together in a common control and packaging environment.
Wideband - 1) an
adjective describing the characteristics of a communications circuit or channel that can
carry a large quantity of information at a high rate. 2) In video applications, a
circuit or system with sufficient bandwidth to convey very high resolution information in
an image (video) signal. For reconstructed video images from a computer, the required
bandwidth is half the pixel clock rate.
See
Nyquist Frequency.
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