GLOSSARY
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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
Tape: A recording media for data or computer programs. Tape can be in
permanent form, such as perforated paper tape, or erasable, such as magnetic tape. Generally, tape is
used as a mass storage medium, in magnetic form, and has a much higher storage capacity than disk
storage, but it takes much longer to write or recover data from tape than from a disk.
Teflon: A fluorocarbon polymer used for insulation of electrical wires (trademark of DuPont
Company).
Telecommunication: Synonym for data communication. The transmission of information from one
point to another.
TEMPCO: Abbreviation for "temperature coefficient": the error introduced by a change in
temperature. Normally expressed in %/°C or ppm/°C.
Temperature Error: The maximum change in output, at any measurand value within the
specified range, when the transducer temperature is changed from room temperature to specified
temperature extremes.
Temperature Range, Compensated: The range of ambient temperatures within which all
tolerances specified for Thermal Zero Shift and Thermal Sensitivity Shift are applicable (temperature
error).
Temperature Range, Operable: The range of ambient temperatures, given by their extremes,
within which the transducer may be operated. Exceeding compensated range may require recalibration.
Terminal: An input/output device used to enter data into a computer and record the output.
Thermal Coefficient of Resistance: The change in resistance of a semiconductor per unit
change in temperature over a specific range of temperature.
Thermal Conductivity: The property of a material to conduct heat in the form of thermal
energy.
Thermal emf: See Seebeck emf
Thermal Expansion: An increase in size due to an increase in temperature expressed in units
of an increase in length or increase in size per degree, i.e. inches/inch/degree C.
Thermal Gradient: The distribution of a differential temperature through a body or across a
surface.
Thermal Sensitivity Shift: The sensitivity shift due to changes of the ambient temperature
from room temperature to the specified limits of the compensated temperature range.
Thermal Zero Shift: An error due to changes in ambient temperature in which the zero
pressure output shifts. Thus, the entire calibration curve moves in a parallel displacement.
Thermistor: A temperature-sensing element composed of sintered semiconductor material which
exhibits a large change in resistance proportional to a small change in temperature. Thermistors
usually have negative temperature coefficients.
Thermocouple Type Material
(ANSI Symbol)
J Iron/Constantan
K CHROMEGA®/ALOMEGA®
T Copper/Constantan
E CHROMEGA®/Constantan
R Platinum/Platinum 13% Rhodium
S Platinum/Platinum 10% Rhodium
B Platinum 6% Rhodium/Platinum30% Rhodium
G* Tungsten/Tungsten 26% Rhenium
C* Tungsten 5% Rhenium/Tungsten 26% Rhenium
D* Tungsten 3% Rhenium/Tungsten 150 Rhenium
*Not ANSI symbols.
Thermocouple: The junction of two dissimilar metals which has a voltage output proportional
to the difference in temperature between the hot junction and the lead wires (cold junction) (refer
to Seebeck emf).
Thermopile: An arrangement of thermocouples in series such that alternate junctions are at
the measuring temperature and the reference temperature. This arrangement amplifies the
thermoelectric voltage. Thermopiles are usually used as infrared detectors in radiation pyrometry.
Thermowell: A closed-end tube designed to protect temperature sensors from harsh
environments, high pressure, and flows. They can be installed into a system by pipe thread or welded
flange and are usually made of corrosion-resistant metal or ceramic material depending upon the
application.
Thomson Effect: When current flows through a conductor within a thermal gradient, a
reversible absorption or evolution of heat will occur in the conductor at the gradient boundaries.
Transducer Vibration: Generally, any device which converts movement, either shock or steady
state vibration, into an electrical signal proportional to the movement; a sensor.
Transducer: A device (or medium) that converts energy from one form to another. The term is
generally applied to devices that take physical phenomenon (pressure, temperature, humidity, flow,
etc.) and convert it to an electrical signal.
Transient Vibration: A temporary vibration or movement of a mechanical system.
Transitional Flow: Flow between laminar and turbulent flow, usually between a pipe Reynolds
number of 2000 and 4000.
Transmitter (Two-Wire): 1. A device which is used to transmit data from a sensor via a
two-wire current loop. The loop has an external power supply and the transmitter acts as a variable
resistor with respect to its input signal. 2. A device which translates the low level output of a
sensor or transducer to a higher level signal suitable for transmission to a site where it can be
further processed.
Triac: A solid state switching device used to switch alternating current wave forms.
Triboelectric Noise: The generation of electrical charges caused by layers of cable
insulation. This is especially troublesome in high impedance accelerometers.
Triple Point (Water): The thermodynamic state where all three phases, solid, liquid, and
gas may all be present in equilibrium. The triple point of water is .01°C.
Triple Point: The temperature and pressure at which solid, liquid, and gas phases of a
given substance are all present simultaneously in varying amounts.
True RMS: The true root-mean-square value of an AC or AC-plus-DC signal, often used to
determine power of a signal. For a perfect sine wave, the RMS value is 1.11072 times the rectified
average value, which is utilized for low-cost metering. For significantly non-sinusoidal signals, a
true RMS converter is required.
TTL Unit Load: A load with TTL voltage levels, which will draw 40 µA for a logic 1 and -1.6
mA for a logic 0.
TTL-Compatible: For digital input circuits, a logic 1 is obtained for inputs of 2.0 to 5.5
V which can source 40 µA, and a logic 0 is obtained for inputs of 0 to 0.8 V which can sink 1.6 mA.
For digital output signals, a logic 1 is represented by 2.4 to 5.5 V with a current source capability
of at least 400 µA; and a logic 0 is represented by 0 to 0.6 V with a current sink capability of at
least 16 mA.
TTL: Transistor-to-transistor logic. A form of solid state logic which uses only
transistors to form the logic gates.
Turbulent Flow: When forces due to inertia are more significant than forces due to
viscosity. This typically occurs with a Reynolds number in excess of 4000.
Typical: Error is within plus or minus one standard deviation (±1%) of the nominal
specified value, as computed from the total population.
UL: Underwriters Laboratories, Inc. An independent laboratory that
establishes standards for commercial and industrial products.
Ultraviolet: That portion of the electromagnetic spectrum below blue light (380
nanometers).
Unbalance: That condition which exists in a rotor when vibratory force or motion is
imparted to its bearings as a result of centrifugal forces.
Unbalance Tolerance: The unbalance tolerance with respect to a radial plane (measuring
plane or correction plane) is that amount of unbalance which is specified as the maximum below which
the state of unbalance is considered acceptable.
Undershoot: The difference in temperature between the temperature a process goes to, below
the set point, after the cooling cycle is turned off and the set point temperature.
Ungrounded Junction: A form of construction of a thermocouple probe where the hot or
measuring junction is fully enclosed by and insulated from the sheath material.
Union: A form of pipe fitting where two extension pipes are joined at a separable coupling.
Vacuum: Any pressure less than atmospheric pressure.
Velocity: The time rate of change of displacement; dx/dt.
Vibration Error Band: The error recorded in output of a transducer when subjected to a
given set of amplitudes and frequencies.
Vibration Error: The maximum change in output of a transducer when a specific amplitude and
range of frequencies are applied to a specific axis at room temperature.
Viscosity: The inherent resistance of a substance to flow.
Volt: The (electrical) potential difference between two points in a circuit. The
fundamental unit is derived as work per unit charge-(V = W/Q). One volt is the potential difference
required to move one coulomb of charge between two points in a circuit while using one joule of
energy.
Voltage: An electrical potential which can be measured in volts.
Voltmeter: An instrument used to measure voltage.
Volume Flow Rate: Calculated using the area of the full closed conduit and the average
fluid velocity in the form, Q = V x A, to arrive at the total volume quantity of flow. Q = volumetric
flowrate, V = average fluid velocity, and A = cross sectional area of the pipe.
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