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DA -
Department Of the Army
dB -
Decibel. A unit used to express
relative difference in power or intensity, usually between two acoustic or
electric signals, equal to ten times the common logarithm of the ratio of
the two levels. Decibels indicate the ratio of power output to power input
dB = 10 log10 (P1/P2).
DC -
Direct Current. Electrical current that flows in one direction only.
DC-DC Converter - A circuit or device that converts a DC input
voltage (usually unregulated) to a regulated DC output voltage. The output
voltage may be lower, higher, or the same as the input voltage. Switching
regulator DC-DC circuits most often require an inductor or transformer to
achieve the regulated output voltage. Switching regulator circuits can
achieve a higher level of power efficiency when compared to non-switching
techniques.
Delta
Connection - A standard three phase connection with the ends of
each phase winding connection in series to form a closed loop with
each phase 120 electrical degrees from the other. In this system,
three power carrying conductors are used, sometimes with a fourth
safety ground wire.
Delta-Delta - The connection
between a delta source and a delta load.
Delta-WYE - The connection
between a delta source and a WYE load.
Derating -
Utilizing a component or piece of equipment intentionally below its
specified rating to allow for variations in operating parameters
such as temperature.
DHS -
Department of Homeland
Security
DOD -
Department Of Defense
DOE -
Department Of Energy
DON -
Department Of the Navy
Double Conversion - A UPS design in which
the primary power path consists of a rectifier and inverter. Double
conversion isolates the output power from all input anomalies
such as low voltage, surges and frequency variations by converting
AC to DC to AC. See Online UPS.
Dropout Voltage - The
voltage at which a device fails to operate properly or safely.
Computer systems will reboot, reset, or lose data when line
voltage falls below approximately 95-100 Volts AC.
See Brownout.
Dual Source Input - In
this case, the UPS has both a primary and secondary source
feeding it. If either source fails, the other takes over with no
break. If they both fail, the batteries take over with no break.
Dry
Contact - Isolated contacts through which the end user supplies
an external circuit. UPS dry contacts provide basic communication
capabilities such as monitoring and shutdown.
Dynamic
regulation - The ability to hold
the controlled level to specification while other parameters vary, i.e.
dynamic voltage regulation while the load is changing.
Earth ground
- A low impedance path to earth for the
purpose of discharging lightning, static, and radiated energy, and to
maintain the main service entrance at earth potential.
Efficiency - The ratio of the output power from the
UPS to the input power from the utility. The mathematical formula
is: Efficiency = Po/ Pi Where "Po" equals power output,
"Pi" equals power input, and power is represented by watts. This shows the percentage
of the input power that is available as useful output power. For
example, a UPS that is 85% efficient delivers 85% of the utility
power it receives to the load. The remaining power takes the form of
dissipated heat.
EIA
- Electronic Industries Alliance. An organization that helps set
standards in the electronics industry.
Electrician
- Refers to an installation
electrician qualified to install heavy-duty electrical components in
accordance with local codes and regulations. May not qualified to maintain
or repair electrical equipment; compare to Technician.
Electromagnetic
- A magnetic field caused by an electric current. Power lines cause
electromagnetic fields that can interfere with nearby data cables.
Electromechanical
- A mechanical device which is controlled by an electric device.
Solenoids and shunt trip circuit breakers are examples of
electromechanical devices.
Electrostatic
- A potential difference (electric charge) measurable between two
points which is caused by the distribution if dissimilar static charge
along the points. The voltage level is usually in kilovolts.
Electrostatic
Discharge (ESD) - Current produced by two objects having a static
charge when they are brought close enough to produce an arc or discharge (static
electricity). The effects of static discharge can range from simple
skin irritation for an individual to degraded or destroyed semiconductor
junctions for an electronic device.
Electrostatic
Shield - A metallic barrier or shield between the primary and
secondary windings of a transformer which reduces the capacitive
coupling and thereby increases the transformers ability to reduce
high frequency noise.
See Faraday Shield.
EMF
- Electromotive force or voltage. See Voltage.
EMC
- Electro Magnetic Compatibility. The requirement for both
electromagnetic emissions and susceptibility of a piece of equipment
to comply with a governing set of standards.
Emergency Shutdown - Used to
instantly or quickly shutdown all of the electrical power available
to the UPS, the power supply and/or the load. An emergency shutdown device is usually
used during a crisis to prevent damage to the UPS and the load. The
local control switch or switches are commonly referred to as the EPO or
Emergency Power Off. Some installations require a Remote Emergency Power Off
(REPO) capability as part of their security/safety system.
EMI/RFI
- Electro Magnetic Interference/Radio Frequency Interference. Electrical
energy emitted by one electrical device that may disturb the normal
operation of another device. The interference is either radiated emissions
(RE) from the
surface of a device or conducted emissions (CE) via its electrical connections.
EMI/RFI
Filter - A device that suppresses
or reduces the level of EMI/RFI emitted by electrical or electronic
equipment.
EPO
- Emergency Power Off. See Emergency Shutdown.
Ethernet
- A baseband LAN specification invented by Xerox Corporation and developed
jointly by Xerox, Intel, and Digital Equipment Corporation. Often referred to as a contention-based topology because workstations are
in competition for channel bandwidth. For this reason, Ethernet uses a
cable-sharing process called Carrier Sense Multiple Access with Collision
Detection (CSMA/CD). Ethernet has become a series of standards
produced by IEEE referred to as IEEE 802.3.
ETL
- Electrical Testing Laboratories. A US independent safety agency that
sets standards for product safety. See UL, CSA, CE, VDE and TÜV.
ETM
- Elapsed Time Meter. A time measurement device that is counting time only
when a piece of equipment is energized. Typically used to log total
operational hours of the equipment for maintenance and event logging.
Fahrenheit
(°F) - An English measure of temperature level, degrees Fahrenheit.
Farad
(F) - Unit of measurement for capacitance.
Faraday
Shield - A grounded electrostatic shield
that reduces coupling capacitance in transformers. The shield, which
effectively reduces output common mode noise, is placed between the
primary and secondary windings of a transformer.
Fault Current - The level of current
that can flow if a short circuit is applied to a voltage source.
Fault
Tolerance - The ability of a system to continue operating in
the event of a fault.
FCC
- Federal Communications Commission. The FCC specifies the maximum amounts
of EMI and RFI that electrical equipment is permitted to generate in Part
15 of the FCC Rules and Regulations.
Ferroresonant Transformer -
Transformer in which part of the core is driven into saturation by a
resonant tank circuit. The output of the transformer, taken from the
saturated portion, is relatively immune to variations in input
voltage.
Firmware - Software that is
stored in semiconductor memory such as ROM, EPROM or EEPROM.
Firmware is typically an embedded instruction set to control the
operation of logical hardware found in monitoring and/or control
systems.
Flame
retardant - The materials will not
support combustion on their own and will in fact help suppress combustion.
This applies to the battery case materials, wire insulation, switches,
circuit breakers, fuse holders, and connector bodies.
Float
Charging - The battery charging mode for which sealed lead acid
batteries are designed. The float voltage is the ideal maintenance voltage
for the battery which maximizes battery life. When the float voltage is
applied to a battery, a current known as the float current flows into the
battery, exactly canceling the battery's own internal self-discharge
current. Sealed lead acid batteries require float charging at least
occasionally or they will become permanently degraded by a process called
sulfation. Maximum lifetime is obtained when a sealed lead acid battery is
permanently float charged.
Flyback Converter - Also
called a buck-boost converter, this topology typically uses a single
transistor switch and eliminates the need for an output inductor.
Energy is stored in the transformer primary during the first half of
the switching period when the transistor switch is on. During the
second half or flyback period when the transistor is off, this
energy is transferred from the transformer secondary. Also see Boost
Regulator, Buck Regulator, Bridge Converter, Forward Converter,
Push-Pull Converter and Resonant Converter.
Flux - The lines of force of a
magnetic field.
Forward Converter - Also
called a Buck-Derived converter, this topology, like the flyback
converter, typically uses a single transistor switch. Unlike the
flyback converter, energy is transferred to the transformer
secondary while the transistor switch is on, and stored in a output
inductor. See Boost Regulator, Buck Regulator, Bridge Converter,
Flyback Converter, Push Pull Converter and Resonant Converter.
Forward Transfer Impedance -
The amount of impedance placed between the source and load with
installation of a power conditioner. With no power conditioner, the
full utility power is delivered to the load; even a transformer adds
some opposition to the transfer of power. On transformer based power
conditioners, a high forward transfer impedance limits the amount of
inrush current available to the load.
Frequency - The
number of cycles (oscillation positive and negative) completed in
one second. Defined as Hertz (Hz). In North America, utility power
is generally 60 cycles per second or 60 Hertz. Many countries based
on European standards use 50 Hertz. Aircraft typically use 400
Hertz.
Frequency
Converter
- A unit that changes the power from one frequency to another frequency (i.e. from 120
VAC, 400 Hz input
to 120 VAC, 60 Hz output). Input and output voltages may also be converted
as well.
Frequency Variations - A change in frequency from the normally stable utility frequency of 50 Hz,
60 Hz or 400 Hz. This may be caused by erratic
operation of emergency generators or unstable frequency power sources. For
sensitive electronic equipment, the result can be data corruption, hard
drive crash, keyboard lockup and program failure.
Full
Bridge Converter - Converter topology that typically operates as
forward converter but uses a bridge circuit, consisting of four switching
transistors, to drive the transformer primary. Also see Bridge Converter.
Full
Height (FH) - Refers to a computer
device that requires a full size drive bay or space, typically 5.25”
wide
Fuse
- A one-time overcurrent protection device employing a fusible link that
melts (blows) after a certain current level is exceeded for a certain
length of time.
Full
Load - The greatest load that a circuit is designed to carry
under specific conditions; any additional load is considered an
overload.
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