**
A
| B |
C |
D
| E |
F | G | H |
I
| J | K |
L |
M
| N |
O | P
| Q |
R |
S
| T | U |
V | W | X | Y |
Z **

**A**

**AC Coupling**

Use of a special circuit to remove the static (dc) components
from the input signal to the amplifier in an instrument, leaving
only the components of the signal that vary with time.

**Ambient Temperature**

The temperature of
still air immediately surrounding a component or circuit. A
typical method to measure ambient temperature is to record the
temperature that is approximately 1/2 inch from the body of
the component or circuit.

**Analog-to-Digital Conversion
(ADC) **

The process of subdividing an analog signal into discrete time
segments, comparing the signal over those time segments to discrete
voltage levels, and reporting the results of the comparisons
in the form of digital outputs of binary numbers having a resolution
of n bits.

**Attenuation**

The relative decrease
in amplitude of a given parameter. Attenuation measurements
are common for voltage, current and power. It is usually expressed
in units of decibels (dB). For a power ratio, one dB=10Log(Pl/P2).
A dB is equal to 20Log(I1/I2) for current and 20Log(V1/V2) for
voltage ratios.

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**B**

**Band-Pass **

A range expressing the limiting frequencies for which a suitable
fraction of the maximum output of an instrument is obtained,
which for strain gage instrumentation is usually zero Hz (dc)
to the frequency at which the output is attenuated to either
-3dB (half power, reflecting 70.7% of the input signal) or -0.5dB
(about 90% power, reflecting about 95% of the input signal).

**Bobbin Core**

A core with the shape
of a bobbin or spool which contains flanges.

**Boost Regulator(DC-DC)**

A basic DC-DC switching
converter topology that takes an unregulated input voltage and
produces higher regulated output voltage. This higher output
voltage is achieved by storing energy in an input inductor and
then transferring the energy to the output by turning a shunt
switch (transistor) on and off.

**Bridge Voltage **

Voltage impressed across the power corners of a Wheatstone bridge
by the constant-voltage power supply.

**Buck Regulator (DC-DC)**

A basic DC-DC switching
converter topology that takes an unregulated input voltage and
produces a lower regulated output voltage. This output voltage
is achieved by chopping the input voltage with a series connected
switch (transistor) which applies pulses to an averaging inductor
and capacitor.

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**C**

**Close Magnetic Path**

Magnetic core shapes
designed to contain all of the magnetic flux generated from
an excited winding(s). Inductors made with these core types
are considered to be shielded inductors. Shielding, however,
is a matter of degree. Common core shapes that are considered
to have closed magnetic paths are toroids, E-cores, and most
pot cores. Shielded bobbins also offer a high degree of shielding
but most have an air gap to some degree. Common core shapes
that are considered to have open magnetic flux paths are rod
cores and unshielded bobbin cores.

**Coefficient of Thermal Expansion**

The ratio of (a) the change in length of a line segment in a
body per unit of temperature change to (b) its length at a reference
temperature.

**Coils**

Another name for inductors

**Common-Mode Noise**

Noise or electrical
interference that is common to both electrical lines in relation
to earth ground.

**Common-Mode Voltage**

A voltage (usually unwanted) appearing in common at both inputs
of an instrument with respect to the output reference (usually
ground).

**Constant-Current Power Supply
**

Power source that, when attached to the power corners of a Wheatstone
bridge , produces the same current for all values of bridge
resistance.

**Constant-Voltage Power Supply
**

Power source that, when attached to the power corners of a Wheatstone
bridge , produces the same voltage for all values of bridge
resistance.

**Copper Loss**

The power lost by current
flowing through the winding. The power loss is equal to the
square of the current multiplied by the resistance of the wire
(1^2*R). This power loss is transferred into heat.

**Core Losses**

Core losses are caused by an alternating magnetic field
in the core material. The losses are a function of the operating
frequency and the total magnetic flux swing. The total core
losses are made up of three main components: Hysteresis, eddy
current and residual losses. These losses vary considerably
from one magnetic material to another. Applications such as
higher power and higher frequency switching regulators require
careful core selection to yield the highest inductor performance
by keeping the core losses to a minimum.

**Core Saturation**

See Saturation Current.

**Curie Temperature**

The temperature above
which a ferrite core loses its magnetic properties. The core's
permeability typically increases dramatically as the core temperature
approaches the curie temperature which causes the inductance
to increase. The permeability drops to near unity at the curie
temperature which causes the inductance to drop dramatically.
The curie point is the temperature at which the initial permeability
has dropped to 10% of its original value at room temperature.

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**D**

**DC-DC Converter**

A circuit or device
that converts a DC input voltage to a regulated 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 (Also see
Boost Regulator and Buck Regulator).

**DCR (DC Resistance)**

The resistance of the
inductor winding measured with no alternating current. The DCR
is most often minimized in the design of an inductor. The unit
of measure is ohms and it is usually specified as a maximum
rating.

**Differential-Input Voltage
**

The maximum voltage that can be applied across the input terminals
of a strain gage instrument without causing damage to the instrument.

**Differential-Mode Noise**

Also known as normal-mode
noise, it is an electrical interference that is not common to
both electrical lines but present between both electrical lines.

**Distributed Capacitance**

In the construction
of an inductor, each turn of wire or conductor acts as a capacitor
plate. The combined effects of each turn can be presented as
a single capacitance known as the distributed capacitance. The
capacitance is in parallel with the inductor. This parallel
combination will resonate at some frequency which is called
the self-resonant frequency (SRF). Lower distributed capacitances
for a given inductance value will result in a higher SRF value
for the inductor and vice versa (Also see SRF)

**Dynamic Loads **

Loads that vary significantly with time as measurements are
being made.

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**E**

**Eddy Current Losses**

Eddy current losses
are present in both the magnetic core and the winding of an
inductor. Eddy currents in the winding (or conductor) contribute
to two main types of losses: losses due to proximity effects
and skin effects. As for the core losses, an electric field
around the flux lines in the magnetic field is generated by
alternating magnetic flux. This will result in eddy currents
if the magnetic core material has electrical conductivity. Losses
result from this phenomenon since the eddy currents flow in
a plane that is perpendicular to the magnetic flux.

**EMI**

EMI is an acronym for
Electromagnetic Interference. It is unwanted electrical energy
in any form. EMI is often used interchangeably with 'Noise'.

**Epoxy **

A synthetic, thermal-setting resin
having excellent adhesion to a wide variety of materials, good
resistance to chemical attack and water penetration, outstanding
electrical properties, low or moderate curing temperatures,
low shrinkage on curing, and good optical properties that is
widely used in a variety of formulations for strain gage backings,
adhesives, and protective coatings as well as photoelastic adhesives
and model materials.

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**F**

**Ferrite Core**

Ferrite is a magnetic
material which consists of a mixed oxide of iron and other elements
that are made to have a crystalline molecular structure. The
crystalline structure is created by firing the ferrite material
at a very high temperature for a specified amount of time and
temperature profile. The general composition of ferrites is
xxFe2O4 where xx represents one or several metals. The most
popular metal combinations are manganese and zinc (MnZn) and
nickel and zinc (NiZn). These metals can be easily magnetized.

**Filter**

A circuit or device
whose purpose is to control electrical energy at a given frequency
or over a range of frequencies. Groups of passive components
are commonly used to construct many types of filters. These
passive components include resistors, capacitors and inductors.

**Frequency Response **

A measure of the effectiveness of an instrument to transmit
signals applied to it in terms of their frequency, typically
as the fraction of the maximum power obtained in the output
signal at a specific frequency.

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**I**

**Impedance**

The impedance of an
inductor is the total resistance to the flow of current, including
the AC and DC component. The DC component of the impedance is
simply the DC resistance of the winding. The AC component of
the impedance includes the inductor reactance. The following
formula calculates the inductive reactance of an ideal inductor
(i.e. one with no losses) to a sinusoidal AC signal.

Z= 2*Pi*f*L - L is in henries and f is in hertz. The equation
indicates that higher impedance levels are achieved by higher
inductance values or at higher frequencies. Skin Effect and
Core Losses also add to the impedance of an inductor which are
non-ideal components of the total impedance (See also Skin Effect
and Core Losses).

**Incremental Current**

The DC bias current
flowing through the inductor which causes an inductance drop
of 5% from the initial zero DC bias inductance value. This current
level indicates where the inductance can be expected to drop
significantly if the DC bias current is increased further. This
applies mostly to ferrite cores in lieu of powdered iron. Powdered
iron cores exhibit "soft" saturation characteristics.
This means their inductance drop from higher DC levels is much
more gradual than ferrite cores. The rate at which the inductance
will drop is also a function of the core shape, i.e. air gap
(Also see Saturation Current).

**Inductance**

The property of a circuit element which tends to oppose
any change in the current flowing through it. The inductance
for a given inductor is influenced by the core material, core
shape and size, the turns count of the coil and the shape of
the coil. Inductors most often have their inductances expressed
in microhenries (uH).

**Inductor**

A passive component designed to resist changes in current.
Inductors arc often referred to as 'AC Resistors.' The ability
to resist changes in current and the ability to store energy
in its magnetic field account for the bulk of the useful properties
of inductors. Current passing through an inductor will produce
a magnetic field. A changing magnetic field induces a voltage
which opposes the field-producing current. This property of
impeding changes in current is known as inductance. The voltage
induced across an inductor by a change of current is defined
as:

V=Ldi/dt

Thus, the induced voltage is proportional to the inductance
value and the rate of current change. (Also see Inductance).

**Input Line Filter**

A power filter placed
on the input to a circuit or assembly that attenuates noise
introduced from the power bus. The filter is designed to reject
noise within a frequency band. Typically these filters arc low-pass
filters meaning they pass low frequency signals such as the
DC power and attenuate higher frequency signal which consist
of mainly noise. Band pass or low pass filters are commonly
made up of inductor and capacitor combinations. (Also see Noise,
Attenuation, EMI and Pi-Filter).

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**K**

**Kool Mu ®**

Kool Mu ® is a
magnetic material that has an inherent distributed air gap.
The distributed air gap allows the core to store higher levels
of magnetic ~ when compared to other magnetic materials such
as ferrites. This characteristic allows a higher DC current
level to flow through the inductor before the inductor saturates.

Kool Mu ® material is an
alloy that is made up of basically nickel and iron powder (approx.
50%of each) and is available in several permeabilities. It has
a higher permeability than powdered iron and also lower core
losses. Kool Mu ® is required to be pressed at a much higher
pressure than powdered iron material. The manufacturing process
includes an annealing step that relieves the pressure put onto
the powdered metals which restores their desirable magnetic
properties. Thus, the powdered particles require a high temperature
insulation as compared to powdered iron. Kool Mu ® performs
well in switching power applications. The relative cost is significantly
higher than powdered iron.

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**L**

**Laminated Cores**

Cores constructed by
stacking multiple laminations on top of each other. The laminations
are offered in a variety of materials and thicknesses. Some
laminations are made to have the grains oriented to minimize
the core losses and give higher permeabilities. Each lamination
has an insulated surface which is commonly an oxide finish.
Laminated cores are used in some inductor designs but are more
common in a wide variety of transformer applications.

**Litz Wire**

Wire consisting of
a number of separately insulated strands that are woven or bunched
together such that each strand tends to take all possible positions
in the cross section of the wire as a whole. The current through
each individual strand is divided equally since this wire design
equalizes the flux linkages and reactance of the individual
strands. In other words, a litz conductor has lower AC losses
than comparable solid wire conductors which becomes important
as the operating frequency increases (Also see Skin Effect).

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**M**

**Magnetic Wire**

Wire used to create
a magnetic field such as those in magnetic components (inductors
and transformers). Magnet wire is nearly 100% copper and must
be made from virgin copper. It Is offered with a number of different
organic polymer film coatings.

**MPP Core**

MPP is an acronym for
molypermalloy powder. It is a magnetic material that has an
inherent distributed air gap. The distributed air gap allows
the core to store higher levels of magnetic flux when compared
to other magnetic materials such as ferrites. This characteristic
allows a higher DC current level to flow through the inductor
before the inductor saturates.

The basic raw materials are nickel,
iron and molybdenum. The ratios are: approximately 80% nickel,
2%-3% molybdenum, and the remaining is iron. The manufacturing
process includes an annealing step as discussed in the Kool
Mu ® definition. MPP stores higher amounts of energy and
has a higher permeability than Kool Mu ®.

Cores are offered in 10 or more
permeability selections. The core characteristics allow inductors
to perform very well in switching power applications. Since
higher energy can be stored by the core, more DC current can
be passed through the inductor before the core saturates. The
cost of MPP is significantly higher than Kool Mu ®, powdered
irons and most ferrite cores with similar sizes (Mso see Saturation
Current and Kool Mu ®).

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**N**

**Noise**

Unwanted electrical
energy in a circuit that is unrelated to the desired signal.
Sources of noise are most often generated by some type of switching
circuit. Common sources include switching voltage regulators
and clocked signals such as digital circuits.

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**O**

**Operating Temperature Range**

Range of ambient temperatures
over which a component can be operated safely. The operating
temperature is different from the storage temperature in that
it accounts for the component's self temperature rise caused
by the winding loss from a given DC bias current. This power
loss is referred to as the 'copper' loss and is equal to:

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**P**

**Power Loss = (DCR)(1^2)dc**

This power loss results
in an increase to the component temperature above the given
ambient temperature. Thus, the maximum operating temperature
will be less than the maximum storage temperature:

Maximum Operating Temperature
= Storage Temperature - Self Temperature Rise

**Permeability (Core)**

The permeability of
a magnetic core is the characteristic that gives the core the
ability to concentrate lines of magnetic flux. The core material,
as well as the core geometry, affect the core's 'effective permeability.'
For a given core shape, size and material, and a given winding,
higher permeability magnetic materials result in higher inductance
values as opposed to lower permeability materials.

**Pi-Filter**

A filter consisting of two capacitors connected in parallel
with a series inductor. These filters are commonly found near
DC-DC converters to filter ripple current and voltage.

**Powdered Iron Core**

Powdered iron is a
magnetic material that has an inherent distributed air gap.
The distributed air gap allows the core to store higher levels
of magnetic flux when compared to other magnetic materials such
as ferrites. This characteristic allows a higher DC current
level to flow through the inductor before the inductor saturates.

Powdered iron cores are made
of nearly 100% iron. The iron particles are insulated from each
other, mixed with a binder (such as phenolic or epoxy) and pressed
into the final core shape. The cores are cured via a baking
process. Other characteristics of powdered iron cores include:
they are typically the lowest cost alternative and their permeabilities
typically have a more stable temperature coefficient than ferrites
(Also see Saturation Current.)

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**Q**

**Q**

The Q value of an inductor
is a measure of the relative losses in an inductor. The Q is
also known as the 'quality factor' and is technically defined
as the ratio of inductive reactance to effective resistance
and is represented by:

Q=X/Re=2*Pi*f*L/Re

Since X and Re are functions
of frequency, the test frequency must be given when specifying
the Q. X typically increases with frequency at a faster rate
than Re at lower frequencies, and vice versa at higher frequencies.
This results in a bell shaped curve for Q vs frequency. Re is
mainly comprised of the DC resistance of the wire, the core
loss and the skin effect of the wire. Based on the above formula
it can be shown that the Q is zero at the self resonant frequency
since the inductance is zero at this point (Also see SRF.)

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**R**

**RFI**

RFI is an acronym for
Radio-Frequency Interference. It is an older and more restrictive
term that is used interchangeably with 'EMI' (Also see EMI.)

**Rated Current**

The level of continuous
DC current that can be passed through the inductor. This DC
current level is based on a maximum temperature rise of the
inductor at the maximum rated ambient temperature. The rated
current is related to the inductor's ability to minimize the
power losses in the winding by having a low DC resistance. It
is also related to the inductor's ability to dissipate this
power loss in the windings. Thus, the rated current can be increased
by reducing the DC resistance or increasing the inductor size.

For low frequency current waveforms
the RMS current can be substituted for the DC rated current.
The rated current is not related to the magnetic properties
of the inductor (Also see Incremental Current and Saturation
Current).

**Reactance**

The imaginary part
of the impedance (Also see Impedance).

**Ripple Voltage**

The periodic alternating
voltage imposed on the voltage output of a switching voltage
converter. The ripple voltage is normally specified as a peak-to-peak
value.

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**S**

**Saturation Current**

The DC bias current
flowing through tile inductor which causes the inductance to
drop by a specified amount from the initial zero DC bias inductance
value. Common specified inductance drop percentages include
10% and 20%. It is useful to use the 10% inductance drop value
for ferrite cores and 20% for powdered iron cores m energy storage
applications.

The cause of the inductance to
drop due to the DC bias current is related to the magnetic properties
of the core. The core, and some of the space around the core,
can only store a given amount of magnetic ~ density. Beyond
the maximum flux density point, the permeability of the core
is reduced. Thus, the inductance is caused to drop. Core saturation
does not apply to 'air-core' inductors (Also see Incremental
Current and Permeability).

**SRF (Self Resonant Frequency)**

The frequency at which
tile inductor's distributed capacitance resonates with the inductance.
It is at this frequency that the inductance is equal to the
capacitance and they cancel each other. The inductor will act
purely resistive with a high impedance at the SRF point. The
distributed capacitance is caused by the turns of ~re layered
on top of each other and around the core. This capacitance is
in parallel to the inductance. At frequencies above the SRF,
the capacitive reactance of the parallel combination will become
the dominant component.

Also, tile Q of the inductor
is equal to zero at the SRF point since the inductive reactance
is zero. The SRF is specified in Mhz and is listed as a minimum
value on product data sheets (Also see Distributed Capacitance.)

**Shielded Inductor**

An inductor designed
for its core to contain a majority of its magnetic field. Some
inductor designs are self shielding. Examples of these are magnetic
core shapes which include toroids, pot cores and B-Cores. Magnetic
core shapes such as slug cores and bobbins require the application
of a magnetic sleeve or similar method to yield a shielded inductor.

It should be noted that magnetic
shielding is a matter of degree. A certain percentage of the
magnetic field will escape the core material. This is even applicable
to toroidal cores as lower core permeabilities will have higher
fringing fields than will high permeability toroidal cores (Also
see Closed Magnetic Path.)

**SI Units **

Units of measurement based on International System of Units,
including seconds of time, meters of distance, and kilograms
of mass. From these, newtons of force and joules of work and
energy are derived. Temperature is measured on the Celsius scale.

**Skin Effect**

Skin effect is the
tendency for alternating current to flow near the surface of
the conductor in lieu of flowing in a manner as to utilize the
entire cross-sectional area of tile conductor. This phenomenon
causes the resistance of the conductor to increase. The magnetic
field associated with the current in the conductor causes eddy
currents near the center of the conductor which opposes the
flow of the main current flow near the center of the conductor.
The main current flow is forced further to the surface as the
frequency of the alternating current increasing (Also see Litz
Wire.)

**Storage Temperature Range**

Range of ambient temperatures
over which a component can be stored safely (Also see Operating
Temperature Range.)

**Switching Frequency**

The operating frequency
of a switching regulator.

**Switching Regulator**

A circuit that is designed
to regulate the output voltage, from a given input voltage,
by using a closed control loop design. The most common switching
regulator types involve a magnetic component, such as an inductor
or transformer, that is used to store and transfer energy to
the Output by having the current switched on and off (Also see
Boost Regulator and Buck Regulator.)

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**T**

**Tape Wound Cores**

Cores made by rolling strips of alloy iron into a toroidal
shape. The metal strips have a precisely controlled thickness
which are coated with a very thin insulation material to prevent
the metal in the layers to make contact with each other. The
finished cores have an outside coating to protect the metal
layers and they are offered in a variety of material mixes.
Tape wound cores are capable of storing high amounts of energy
and contain a high permeability. Their major disadvantage is
that they are relatively expensive when compared to other core
types (Also see Toroidal Inductor.)

**Temperature Rise**

The increase in surface
temperature of a component in air due to the power dissipation
in the component. The power dissipation for an inductor includes
both copper and core losses.

**Toroidal Inductor**

An inductor constructed
by placing a winding(s) on a core that has a donut shaped surface.
Toroidal cores are available in many magnetic core materials
within the four basic types: Ferrite, Powdered iron, Alloy and
High Flux, and Tape Wound. Characteristics of toroidal inductors
include: self shielding (closed magnetic path), efficient energy
transfer, high coupling between windings and early saturation.

**Transducer **

Any device or element for converting an input signal into an
output signal of a different form, commonly a device for converting
a physical variable (force, pressure, displacement, etc.) into
electrical signals.

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**V**

**Voltage Injection **

Method of zero-balancing an instrument by injecting a voltage
of opposite sign but like magnitude into the output from an
unbalanced Wheatstone bridge .

**Volt Microsecond Constant**

The product of the
voltage applied across the winding and the time for the magnetizing
current to reach 1.5 times the linear extrapolation of the current
waveform. This constant is a measure of the energy handling
capability of a transformer or inductor. It is dependent upon
the core area, core material (including the saturation flux
density of the core), the number of turns of the winding and
tile duty cycle of the applied pulse.

**Volume Resistivity (Core)**

The ability of a core
to resist the flow of electrical current either through the
bulk of the material or on its surface. The unit of the volume
resistivity is Ohm-cm. Core volume resistivity becomes an issue
in Inductor designs where the leads/termina1s come in contact
with the core material. This type includes axial and radial
inductors that have leads epoxied into the core. As for core
materials, high permeability ferrites present the most concern
as their volume resistivity is typically the lowest.

Under certain conditions, a low
resistive path can be realized between two inductor terminals
if they are in contact with a low resistivity core. The inductor,
under these conditions, will lose its higher impedance characteristics.

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