Lake Shore 625, User Manual

Page: 126 / 132

Lake Shore Model 625 Superconducting MPS User’s Manual
A-4 Glossary of Terminology
Kelvin Scale . The Kelvin Thermodynamic Temperature Scale is the basis for all international scales, including the
ITS-90. It is fixed at two points: the absolute zero of temperature (0 K), and the triple point of water (273.16 K), the equilibrium
temperature that pure water reaches in the presence of ice and its own vapor.
line regulation . The maximum steady-state amount that the output voltage or current changes as result of a specified change in input
line voltage (usually for a step change between 105
–
125 or 210
–
250 volts, unless otherwise specified).
line voltage . The RMS voltage of the primary power source to an instrument.
load regulation . A steady-state decrease of the value of the specified variable resulting from a specified increase in load, generally
from no-load to full-load unless otherwise specified.
lock-in amplifier . An amplifier that uses some form of automatic synchronization with an external reference signal to detect and
measure very weak electromagnetic radiation at radio or optical wavelengths in the presence of very high noise levels.
1
M . Symbol for magnetization. See magnetization.
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
0
(H + M) for SI, and B = H + 4

M for cgs, where H = magnetic field
strength, M = magnetization, and µ
0
= permeability of free space = 4

× 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 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.
microcontroller . A microcomputer, microprocessor, or other equipment used for precise process control in data handling,
communication, and manufacturing.
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 4

× 10
–7
to the rationalized magnetic constant (sometimes called the permeability of space).
negative temperature coefficient (NTC) . Refers to the sign of the temperature sensitivity. For example, the resistance of a NTC
sensor decreases with increasing temperature.
National Institute of Standards and Technology (NIST) . Government agency located in Gaithersburg, Maryland and Boulder,
Colorado, that defines measurement standards in the United States.
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 temp. 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 = 10¾

ampere/meter

79.58 ampere/meter.
ohm (

) . 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
open-loop . A control system in which the system outputs are controlled by system inputs only, and no account is taken of actual
system output.
1
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.