of the indicated gage pressure plus the atmospheric pressure. The
abbreviation is PSIA.
- The loss of power in an optical
fiber, resulting from conversion of optical power into heat and
caused principally by impurities, such as transition metals and
hydroxyl ions, and also by exposure to nuclear radiation.
Acceleration: A change
in velocity with respect to time
Accelerometer: A device
which converts the effects of mechanical motion into an electrical
signal that is proportional to the acceleration value of the
Acceptance angle - The
half-angle of the cone within which incident light is totally
internally reflected by the fiber core. It is equal to arcsin
Active power - A power measurement
that multiplies the voltage portion of the signal being measured
by the current that is in phase with that voltage.
Analog output - A signal generated
from a meter, for example, which can drive a recorder, an external
display, or a controlling device such as a heater, motor, etc.
Analog signals used for such purposes are typically 4-20mA ,
1-5Vdc, or similar ranges.
Apparent Power - A term only
applicable to Alternating Current (AC) circuits, it is the product
of the voltage applied times the current flow. The unit of measure
is VA, or Voltamperes.
Atmospheric Pressure: The pressure
exerted upon the earth's surface by the air because of the
gravitational pull of the earth. Standard atmosphere pressure at
sea level is 14.7 pounds per square inch (psi).
Attenuation - A general term
indicating a decrease in power from one point to another. In
optical fibers, it is measured in decibels per kilometer at a
Auto hold - The ability of a
measuring device to wait until a reading has stabilized before
holding (storing) that reading on the display.
Auto-ranging - Ability of a measuring
device to automatically
select the appropriate range of measurement.
Bandwidth - The transmission capacity
of a system.
Buffering - 1. A protective material
extruded directly on the fiber coating to protect the fiber from
the environment (tight buffering). 2. Extruding a tube around the
coated fiber to allow isolation of the fiber from stresses on the
cable (loose buffered).
Buffer Tubes - Loose-fitting covering
over optical fibers used for protection and isolation.
Bundle - Many individual fibers
contained within a single jacket or buffer tube. Also, a group of
buffered fibers distinguished in some fashion from another group
in the same cable core.
Cable Tester - A handheld electronic
device that is used to measure the electrical and physical
properties of network cabling. Used commonly to certify cabling to
known standards, or as a troubleshooting tool.
Cladding - The outer concentric layer
that surrounds the fiber core and has a lower index of refraction.
Coaxial Cable - A popular
transmission medium usually consisting of one central wire
conductor (two for twinaxial cable) surrounded by a dielectric
insulator and encased in either a wire mesh or an extruded metal
sheathing. Commonly used for Cable TV (CATV) or older computer
Cold Junction Compensation - Circuit
in a measuring device which resolves the difference between an
ambient temperature reference (used when device was calibrated)
and the actual operating temperature of the measuring device.
Conductance - The reciprocal of
resistance expressed in term of Siemans (formally mhos)
Connector - A mechanical device used
to provide a means for aligning, attaching, and achieving
continuity between fibers.
Consolidation Point - A location for
interconnection between horizontal cables that extend from
building pathways and horizontal cables that extend into work area
Continuity beeper- Audible tone
emitted from a meter when resistance measured falls below a
threshold level (typically 20-50 Ohm).
Core - The central, light-carrying
part of an optical fiber; it has an index of refraction higher
than that of the surrounding cladding.
Cosine F - Voltage and Current
sometimes do not happen together, often there is a difference. The
difference is an angle, F, a value between 0 and 90. The greater
the angle, the bigger the difference between True and Apparent
Power, the smaller the Power Factor. If Voltage and Current happen
at about the same time, F is small, the values of True and
Apparent Power are close, Power Factor approaches 1.
Criterion Sound Level - The eight
hour average weighted sound level, expressed in dB, that
corresponds to the maximum permitted daily exposure to noise as
prescribed in national and state regulations.
Cross-Connection - A connection
scheme between cabling runs, subsystems, and equipment using patch
cords or jumpers that attach to connecting hardware on each end.
Crosstalk - The unwanted transfer of
energy (signal) from one circuit to another circuit. Crosstalk
interferes with the desired data signal. Handheld cable testers
can be used to determine the level of unwanted crosstalk in
Data Acquisition - The ability of an
instrument to communicate measurement information as it occurs.
The meter must be in communication with a computer for measurement
storage to occur.
Datalogging - The ability of a meter
to store measurement information "on board" in nonvolatile memory
until such time it can be downloaded to a computer for storage,
analysis and report generation.
Data hold - Function of a measuring
device which holds a displayed value when a user presses a key or
dB (Decibels) - The unit of measure
used when measuring the level of sound. Every 3dB represents
approximately double (-3dB = 1/2) the power or sound level, ie:
53dB is twice as loud as 50dB.
dB (Decibel) - In fiber optics, a
standard logarithmic unit for the ratio of the power that was
received over the power that was originally sent.
dBm - Decibels above one milliwatt. A
measure of power equal to 10 times the common logarithm of the
ratio of a given power to 0.001 watt
dBµ - Decibel referenced to a
Detector - An optoelectronic
transducer used in fiber optics for converting optical power to
electric current. In fiber optics, usually a photodiode.
Differential - In dual input
measuring devices, the differential is the displayed difference
between the two inputs. (Input A - Input B = Differential).
Diffraction - The bending of radio,
sound, or light waves around an object, barrier, or aperture edge.
Diode check - Function of a measuring
device which analyzes the operation of a diode. The two leads of
the diode are inserted into the device and the user is alerted
visually and/or audibly as to the diode's integrity.
Dispersion - A general term for those
phenomena that cause a broadening or spreading of light as it
propagates through and optical fiber. The three types are modal,
material, and waveguide.
Displacement - change of position, or
distance, usually measured from mean position or position of rest.
Usually applies to uniaxial, less often to angular motion.
Display counts - The number of
display units a meter or other device can indicate. For example, a
3-1/2 digit display can indicate from 0 - 1,999 (which is 2000
counts); a 4-1/2 digit display can indicate from 0 - 19,999; a
3-3/4 digit display can indicate from 0 - 3,999 counts, etc. If a
meter is "bi-polar" it can indicate positive and negative units
depending on the polarity of the signal being monitored. For
Duty Cycle - The ratio of the working
time to the total time of a pulse train expressed as a percent.
Elapsed Time - The period of time
between the start of a measurement series to the last measurement
observed or recorded.
Electric Power - is the rate at which
electricity does work. More work done in a set time, or the same
work done in a shorter time, both require more electrical power.
The unit of measure for electric power is the Watt . Electric
power, measured in Watts is also known as True Power.
Emissivity - A term related to
temperature measurement using Infrared radiation. Errors in IR
measurements can occur based on the color, shape and presence of
reflection on the measurement surface. A wide emissivity
adjustment should be available on an IR thermometer to allow the
user to compensate for these types of errors.
EMF/Electromagnetic radiation - Waves
generated by a magnet configuration which consists of a coil wound
around a steel core. The core is strongly magnetized when current
flows through the coil. Video monitors, power lines, and wire
harnesses are a few devices which produce electromagnetic
Entrance Facility - An entrance to a
building for both public and private network service cables
including the entrance point at the building wall and continuing
to the entrance room or space.
EMD (Equilibrium Mode Distribution) -
The steady modal state of a multimode fiber in which the relative
power distribution among modes is independent of fiber length.
Equipment Room - A centralized space
for telecommunications equipment that serves the occupants of the
building. Equipment housed herein is considered distinct from a
telecommunications closet because of its nature or complexity of
Exchange Rate - (also Doubling Rate)
Refers to the rate in which sound energy is averaged over time.
Every time the sound energy doubles, the measured level increases
by 3dB ,which most of the world uses. In the U.S., OSHA uses a 5dB
Frequency - Of a periodic wave, the
number of identical cycles per second. Usually expressed in Hertz.
Fresnel Reflection - The reflection
that occurs at the planar junction of two materials having
different refractive indices; Fresnel reflection is not a function
of the angle of incidence.
g units or gravitational units - A
way to express an acceleration, in terms of a ratio. Divide a
given acceleration by the appropriate value (9.80665 m/s2 or
386.087 in/sec2 or 32.1739 ft/sec2).
GO/NO GO Alarm - An output from a
meter or controller which is used to indicate when a preset
measurement point has been reached or exceeded. The alarm may be
visible, audible, electrical or any combination of these.
Graded-index Fiber - An optical fiber
whose core has a nonuniform index of refraction. The core is
composed of concentric rings of glass whose refractive indices
decrease from the center axis. The purpose is to reduce modal
dispersion and thereby increase fiber bandwidth.
HC (Horizontal Cross-Connect) - A
cross-connect of horizontal cabling to other cabling, e.g.,
horizontal, backbone, equipment.
IC (Intermediate Cross-Connect) - A
cross-connect between the main cross-connect and the horizontal
cross- connect in backbone cabling.
Inches of WATER GAUGE or COLUMN (IN WG or
IN WC) A unit of air pressure measurement equal to the
pressure exerted by a column of water 1 inch high.
Index of Refraction - The ration of
the velocity of light in free space to the velocity of light in a
Interconnection - A connection scheme
that provides for the direct connection of a cable to another
cable or to an equipment cable without a patch cord or jumper.
Insertion Loss - The loss of power
that results from inserting a component, such as a connector or
splice, into a previously continuous path.
Kelvin Connection - A four wire
method of connecting test leads which is designed to eliminate or
greatly reduce the effect of lead or contact resistance and thus
permitting accurate measurements of low resistance.
Laser - Light Amplification by
Stimulated Emission of Radiation. A light source producing,
through stimulated emission, coherent, near monochromatic light.
Lasers in fiber optics are usually solid-state semiconductor
LCD - Acronym for Liquid Crystal
Display. Liquid crystal is a liquid that is not isotropic, that
is, it forms patterns when polarized. The orientation of the
molecules of the liquid are arranged by the meter to form the
LED - Acronym for Light Emitting
Diode, a very common display type. An electrical current is passed
through the diode causing illumination aided by the colored lens
which surrounds them. LEDs usually have 7 light segments per digit
when used as an Alpha-numeric display. Also commonly used to
indicate ON/OFF or status functions individually. Orange-red,
green, and yellow are common LED colors.
Load - A device that is driven by the
output of a meter or other measuring/controlling device. An
example of a load is a resistor being measured by a multimeter.
The resister "loads" the meter since it becomes part of the
Local Area Network, LAN - A group of
PCs, servers, printers and similar devices connected over a
network in a relatively limited geography.
Main Cross-Connect - The
cross-connect in the main equipment room for connecting entrance
cables, backbone cables, and equipment cables.
Material Dispersion - Dispersion
resulting from the different velocities of each wavelength in an
Microprocessor - Integrated circuits
which perform many instructions per second (mathematical
equations, calibration data storage, display updates, etc.)
precisely and quickly. Microprocessors are at the heart of
computer accuracy, repeatability, and speed, providing similar
attributes to electronic measuring devices such as calibrators,
multimeters, thermometers, etc.
Min/max - A function of a measuring
device which records (saves) the highest and lowest reading it has
encountered since being reset (cleared) or powered up.
Modal Dispersion - Dispersion
resulting from the different transit lengths of different
propagating modes in a multimode optical fiber.
Mode - A possible path followed by
Multimode Fiber - A type of optical
fiber that supports more than one propagating mode.
Multiplexer - A device that sequences
access to a communcation port. Several different devices can share
a single COM port on a computer if they are multiplexed.
NA (Numeric Aperture) - The number
that expresses the light-gathering ability of a fiber.
Noise Dose - A measure of the
exposure to noise expressed as a percentage of a maximum
permissible exposure. The maximum permissible exposure (or 100%)
is prescribed in national or state regulations.
Network - A series of computers and
related devices interconnected by common communications channels
OTDR (Optical Time Domain Reflectometry)
- A method of evaluating optical fibers based on detecting
backscattered (reflected) light. Used to measure fiber
attenuation, evaluate splice and connector joints, and locate
faults. Also, the equipment used to perform such measurements
(Optical Time Domain Reflectometer).
Overload - A signal that is greater
than that which a measuring device can accurately or safely
accept. Many meters have overload protection in the form of a
fuse, or similar device, to protect the meter from such a signal.
Over range indication - Visual
display alerting the user that the signal present at the meter's
input is out of range.
Peak hold - The ability of a
measuring device to hold the highest reading until the user clears
the display. Also known as Peak Detect.
Photodetector - An optoelectronic
transducer, such as a PIN photodiode or avalanche photodiode.
Photodiode - A semiconductor diode
that produces current in response to incident optical power and
used as a detector in fiber optics.
Photon - A quantum of electromagnetic
energy; a particle of light.
PSI ( POUNDS PER SQUARE INCH) a
measure of pressure. One psi is equal to the pressure exerted by
2.31 feet of water column. exerted by 2.31 feet of water.
PSIA: Pounds per square inch
absolute. Referenced to a vacuum.
PSID: Pounds per square inch
differential. The pressure difference between two points.
PSIG (POUNDS PER SQUARE INCH):
0 psig = 14.696 psia (psi absolute) = 1.0 atmosphere.
Power Factor - is the ratio of Watts
to VA, or True Power divided by Apparent Power. This can be
expressed as a decimal or percentage, i.e.: PF=0.75 or PF=75%.
True Power is never greater than Apparent Power, so the Power
Factor is never greater than 1. Power Factor may also be expressed
as Cosine F where F is an angle between 0 and 90.
Psychrometers (Wet Bulb) - A relative
humidity measuring device which has two thermometers. One measures
ambient temperature (dry bulb), the second measures the
temperature of an element surrounded by a fibrous material
saturated with water (wet bulb). Reference tables are then used to
determine relative humidity.
Receiver - An electronic device which
converts optical signals to electrical signals.
Resolution - The smallest value a
display device can indicate. For example, if a device can display
0.0 to 100.0 RPM, the smallest measurement and, therefore, the
resolution is 0.1 RPM.
Response time - The rate at which a
measuring device responds to a change in the measured variable.
Responsivity - The ratio of a
photodetector's electrical output to its optical input in an
RH Capacitance Probe - Capacitive
device that senses relative humidity. The meter used with such a
probe senses the change in capacitance based on the moisture
encountered by the capacitor's dielectric and displays the
relative humidity based on this capacitance value.
RH Resistance Probe - Resistive
device that senses relative humidity. The meter used with such a
device monitors the resistance of the probe which changes
proportionately to th amount of moisture encountered. The meter
then displays the relative humidity based on this resistive value.
RTD - A temperature measurement
device whose resistance is proportional to temperature. 2,3, and 4
wire RTDs are available.
Single Mode Fiber - An optical fiber
that supports only one mode of light propagation above the cutoff
Single Phase - A good example of a
single phase power source is a typical AC wall outlet. This is
considered to be single phase because there is a single
alternating voltage/current available. Three-phase on the other
hand, provides three separate alternating signals.
Source - The light emitter, either an
LED or laser diode, in a fiber optic link.
Spectral Width - A measure of the
extent of a spectrum. For a source, the width of wavelengths
contained in the output at one half of the wavelength of peak
power. Typical spectral widths are 20 to 60 nm for an LED and 2 to
5 nm for a laser diode.
Splice - An interconnection method
for joining the ends of two optical fibers in a permanent or
Step-Index Fiber - An optical fiber,
either multimode or single mode, in which the core refractive
index is uniform throughout so that a sharp step in refractive
index occurs at the core-to-cladding interface. It usually refers
to a multimode fiber.
TC (Telecommunications Closet) - An
enclosed space for housing telecommunications equipment, cable
terminations, and cross-connects. The closet is the recognized
cross-connect between the backbone cable and horizontal cabling.
Thermistor - A resistive temperature
measurement device whose resistance decreases as the temperature
increases. A thermistor is a stable, compact, and rugged two
terminal ceramic-like semiconductor bead.
Thermocouple - A 2-wire temperature
measurement sensor constructed of two dissimilar metals which form
a junction. Current flows from one metal to the other in
proportion to temperature. A millivolt signal is then measured by
a thermometer or other device to display temperature.
Threshold - (also cutoff) Sound
levels below this point are excluded from dosimeter measurements.
National and state regulations determine the threshold level. OSHA
uses an 80dB level.
Tight Buffer - A cable construction
where each fiber is tightly buffered by a protective thermoplastic
coating to a diameter of 900µm.
Torque - The measure of the twisting
force generated by an object.
Traffic - The volume of data
transmitted over a LAN at any given time. Traffic is generated by
the devices and associated software applications that are running
on the network. Excessive traffic on a network can seriously
impair performance of a LAN. The NETcat and NETcat Plus allow
network managers to actively monitor 10 Base-T Ethernet network
traffic to help them configure their networks for optimal
Transducer - A device that converts
energy from one form to another. It normally applies to devices
that convert physical measurements into electrical signals.
Transducer Vibration - A device that
converts movement into electrical signals proportional to the
amount of movement.
Transistor test - A function of a
measuring device which can be used to check the operation of a
transistor. The leads of a transistor are inserted into the meter
which indicates whether the device is operational or defective.
Transmitter - An electronic package
which converts an electrical signal to an optical signal.
True Power - Electric power, measured
True RMS Voltmeter - A voltmeter that
measure an AC sine wave (voltage and current) and displays the
root mean square (rms) of each waveform cycle. Important when
measuring true power.
Var or Voltampere-reactive - The
product of Apparent Power times Sine F. This is the Reactive, or
non-work producing, component of Apparent Power. Var = Apparent
Power if F = 90 degrees, therefore Power Factor = 0 and True Power
Velocity - Rate of change of
displacement with time
Vibration Meter- A device or detector
that measures a signal from a vibration sensor. The display is
usually shown in units of displacement, acceleration or velocity.
WA (Work Area) - A building space
where the occupants interact with telecommunications terminal
equipment; i.e. PCs, telephones, and other office equipment.
Watt - The unit of measure for
Wavelength - The distance between the
same two points on adjacent waves; the time required for a wave to
complete a single cycle.
Zero adjust - Ability of a meter to
be calibrated to a null or "zero" reference ensuring accurate
readings in all ranges.
© Extech Instruments Corporation