Lake Shore Model 421 Gaussmeter User’s Manual
A-4 Glossary of Terminology
magnetic air gap. The air space, or non-magnetic portion, of a magnetic circuit.
magnetic field strength (H). The magnetizing force generated by currents and magnetic poles. For most applications,
the magnetic field strength can be thought of as the applied field generated, for example, by a superconducting magnet.
The magnetic field strength is not a property of materials. Measure in SI units of A/m or cgs units of oersted.
magnetic flux density (B). Also referred to as magnetic induction. This is the net magnetic response of a medium to an
applied field, H. The relationship is given by the following equation: B = µ
o
(H + M) for SI, and B = H + 4πM for cgs,
where H = magnetic field strength, M = magnetization, and µ
o
= permeability of free space = 4π × 10
–7
H/m.
magnetic hysteresis. The property of a magnetic material where the magnetic induction (B) for a given magnetic field
strength (H) depends upon the past history of the samples magnetization.
magnetic induction (B). See magnetic flux density.
magnetic moment (m). This is the fundamental magnetic property measured with dc magnetic measurements systems
such as a vibrating sample magnetometer, extraction magnetometer, SQUID magnetometer, etc. The exact technical
definition relates to the torque exerted on a magnetized sample when placed in a magnetic field. Note that the moment
is a total attribute of a sample and alone does not necessarily supply sufficient information in understanding material
properties. A small highly magnetic sample can have exactly the same moment as a larger weakly magnetic sample
(see Magnetization). Measured in SI units as A·m
2
and in cgs units as emu. 1 emu = 10
–3
A·m
2
.
magnetic scalar potential. The work which must be done against a magnetic field to bring a magnetic pole of unit
strength from a reference point (usually at infinity) to the point in question. Also know as magnetic potential.
1
magnetic units. Units used in measuring magnetic quantities. Includes ampere-turn, gauss, gilbert, line of force, maxwell,
oersted, and unit magnetic pole.
magnetization (M). This is a material specific property defined as the magnetic moment (m) per unit volume (V).
M = m/V. Measured in SI units as A/m and in cgs units as emu/cm
3
. 1 emu/cm
3
= 10
3
A/m. Since the mass of a sample
is generally much easier to determine than the volume, magnetization is often alternately expressed as a mass
magnetization defined as the moment per unit mass.
magnetostatic. Pertaining to magnetic properties that do not depend upon the motion of magnetic fields.
1
mains. See line voltage.
Maxwell (Mx). A cgs electromagnetic unit of magnetic flux, equal to the magnetic flux which produces an electromotive
force of 1 abvolt in a circuit of one turn link the flux, as the flux is reduced to zero in 1 second at a uniform rate.
1
MKSA System of Units. A system in which the basic units are the meter, kilogram, and second, and the ampere is a
derived unit defined by assigning the magnitude 4π
× 10
–7
to the rationalized magnetic constant (sometimes called the
permeability of space).
NBS. National Bureau of Standards. Now referred to as NIST.
National Institute of Standards and Technology (NIST). Government agency located in Gaithersburg, Maryland and
Boulder, Colorado, that defines measurement standards in the United States. See Standards Laboratories for an
international listing.
noise (electrical). Unwanted electrical signals that produce undesirable effects in circuits of control systems in which they
occur.
2
normalized sensitivity. For resistors, signal sensitivity (dR/dT) is geometry dependent; i.e., dR/dT scales directly with R;
consequently, very often this sensitivity is normalized by dividing by the measured resistance to give a sensitivity, s
T
, in
percent change per kelvin. s
T
= (100/R) (dR/dT) %K, where T is the temperature in kelvin and R is the resistance in
ohms.
normally closed (N.C.). A term used for switches and relay contacts. Provides a closed circuit when actuator is in the
free (unenergized) position.
normally open (N.O.). A term used for switches and relay contacts. Provides an open circuit when actuator is in the free
(unenergized) position.
oersted (Oe). The cgs unit for the magnetic field strength (H). 1 oersted = 10¾π ampere/meter ≈ 79.58 ampere/meter.
ohm (Ω). The SI unit of resistance (and of impedance). The ohm is the resistance of a conductor such that a constant
current of one ampere in it produces a voltage of one volt between its ends.
2
pascal (Pa). The SI unit of pressure equal to 1 N/m
2
. Equal to 1.45 × 10
–4
psi, 1.0197 × 10
–5
kg
f
/cm
2
, 7.5 × 10
–3
torr,
4.191 × 10
–3
inches of water, or 1 × 10
–5
bar.
permeability. Material parameter which is the ratio of the magnetic induction (B) to the magnetic field strength (H):
µ = B/H. Also see Initial Permeability and Differential Permeability.
polynomial fit. A mathematical equation used to fit calibration data. Polynomials are constructed of finite sums of terms
of the form a
i
x
i
, where a
i
is the i
th
fit coefficient and x
i
is some function of the dependent variable.
pounds per square inch (psi). A unit of pressure. 1 psi = 6.89473 kPa. Variations include psi absolute (psia) measured
relative to vacuum (zero pressure) where one atmosphere pressure equals 14.696 psia and psi gauge (psig) where
gauge measured relative to atmospheric or some other reference pressure.
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