Common Terms Used in the Switching and Electronics Industry

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.

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.
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.
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.
Full Fanout - See Non-Blocking
Hostile Crosstalk - See Crosstalk.
Hostile Input - An unselected input carrying a signal which causes unwanted
interference and coupling in a desired output. See Crosstalk.
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 form 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.
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 - An abbreviation for Mean Time To Repair, a theoretical period of time
need to repair a piece of equipment given certain circumstances.
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 charactoristics. Typically usable to
12.5GHz, but some manufacturers offer connectors usable to 18GHz.
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

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.
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.
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.
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 typicall 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.
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.
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