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Lake Shore Model 325 Temperature Controller User’s Manual
A-2 Glossary of Terminology
coercive force (coercive field) . The magnetic field strength (H) required to reduce the magnetic induction (B) in a magnetic material
to zero.
coercivity . Generally used to designate the magnetic field strength (H) required to reduce the magnetic induction (B) in a magnetic
material to zero from saturation. The coercivity would be the upper limit to the coercive force.
Constantan . A copper-nickel alloy of which the negative lead of Type E, J, and T thermocouples are composed.
cryogenic . Refers to the field of low temperatures, usually –130 °F or below, as defined by 173.300(f) of Title 49 of the Code of
Federal Regulations.
cryogenic fluid . A liquid that boils at temperatures of less than about 110 K at atmospheric pressure, such as hydrogen, helium,
nitrogen, oxygen, air, or methane. Also known as cryogen.
1
cryostat . An apparatus used to provide low-temperature environments in which operations may be carried out under controlled
conditions.
1
cryotronics . The branch of electronics that deals with the design, construction, and use of cryogenic devices.
1
Curie temperature (Tc) . Temperature at which a magnetized sample is completely demagnetized due to thermal agitation. Named for
Pierre Curie (1859 – 1906), a French chemist.
current source . A type of power supply that supplies a constant current through a variable load resistance by automatically varying its
compliance voltage. A single specification given as “compliance voltage” means the output current is within specification when the
compliance voltage is between zero and the specified voltage.
curve . A set of data that defines the temperature response of a temperature sensor. It is used to convert the signal from the sensor to
temperature.
Curve 10 . The voltage vs. temperature characteristic followed by all DT-400 Series silicon diode temperature sensors.
degree . An incremental value in the temperature scale, i.e., there are 100 degrees between the ice point and the boiling point of water
in the Celsius scale and 180 degrees between the same two points in the Fahrenheit scale.
demagnetization . When a sample is exposed to an applied field (H
a
), poles are induced on the surface of the sample. Some of the
returned flux from these poles is inside of the sample. This returned flux tends to decrease the net magnetic field strength internal to
the sample yielding a true internal field (H
int
) given by: H
int
= H
a
– DM, where M is the volume magnetization and D is the
demagnetization factor. D is dependent on the sample geometry and orientation with respect to the field.
deviation . The difference between the actual value of a controlled variable and the desired value corresponding to the setpoint.
1
Dewar flask . A vessel having double walls, the space between being evacuated to prevent the transfer of heat and the surfaces facing
the vacuum being heat-reflective; used to hold liquid gases and to study low-temperature phenomena.
1
Invented by Sir James
Dewar (1842 – 1923), a Scottish physical chemist.
differential permeability . The slope of a B versus H curve: µ
d
= dB/dH.
differential susceptibility . The slope of a M versus H curve:

d
= dM/dH.
dimensionless sensitivity . Sensitivity of a physical quantity to a stimulus, expressed in dimensionless terms. The dimensionless
temperature sensitivity of a resistance temperature sensor is expressed as S
d
= (T/R)(dR/dT) which is also equal to the slope of R
versus T on a log-log plot, that is S
d
= d lnR / d lnT. Note that the absolute temperature (in kelvin) must be used in these
expressions.
drift, instrument . An undesired but relatively slow change in output over a period of time, with a fixed reference input. Note: drift is
usually expressed in percent of the maximum rated value of the variable being measured.
2
electromagnet . A device in which a magnetic field is generated as the result of electrical current passing through a helical conducting
coil. It can be configured as an iron-free solenoid in which the field is produced along the axis of the coil, or an iron-cored structure
in which the field is produced in an air gap between pole faces. The coil can be water cooled copper or aluminum, or
superconductive.
electrostatic discharge (ESD) . A transfer of electrostatic charge between bodies at different electrostatic potentials caused by direct
contact or induced by an electrostatic field.
error . Any discrepancy between a computed, observed, or measured quantity and the true, specified, or theoretically correct value or
condition.
2
excitation . Either an AC or DC input to a sensor used to produce an output signal. Common excitations include: constant current,
constant voltage, or constant power.
Fahrenheit (°F) Scale . A temperature scale that registers the freezing point of water as 32 °F and the boiling point as 212 °F under
normal atmospheric pressure. See Temperature for conversions.
feedback control system . A system in which the value of some output quantity is controlled by feeding back the value of the
controlled quantity and using it to manipulate an input quantity so as to bring the value of the controlled quantity closer to a desired
value. Also known as closed-loop control system.
1
four-lead . measurement technique where one pair of excitation leads and an independent pair of measurement leads are used to
measure a sensor. This method reduces the effect of lead resistance on the measurement.
GaAlAs . Gallium-aluminum-arsenide semiconducting material used to make the special Lake Shore TG family of diode temperature
sensors.
gamma . A cgs unit of low-level flux density, where 100,000 gamma equals one oersted, or 1 gamma equals 10
–5
oersted.