Glossary
3A: A symbol of the 3A Sanitary Standards Symbol
Administrative Council approving the construction and
use of food processing equipment.
accuracy: The maximum difference allowed between
the true value and the instrument indication, usually
expressed as a percentage of the full measurement
span or in number of scale divisions on a temperature
instrument.
adjustable union connection: A type of union
connection that allows for end-user setting of the
insertion length of a temperature probe.
air-duct stem: An industrial thermometer stem style
that exposes a portion of the glass tube directly to the
process medium.
ambient temperature: The average temperature of
the environment surrounding an instrument or process.
Not normally the controlled variable.
amp: Abbreviation for ampere: a unit of electrical flow
measurement.
armor: A protective, flexible covering over the
capillary tubing.
ASME B40.3: A voluntary industry standard
developed by the American Society of Mechanical
Engineers covering the construction and use of bimetal
thermometers.
AWG: American Wire Gage: a specification of wire
size.
bimetal thermometer: A thermometer that contains a
sensitive element consisting of two dissimilar metals
welded together in the form of a coil.
bourdon tube: The sensitive element common to
gauge type, filled system dial thermometers, it is made
from a partially flattened tube, curled and closed at one
end. The final form is most often a partial turn or “C”
shape. As temperature induced pressure enters the
open end, this tube begins to straighten and expand.
This motion is transmitted to the dial indicator through
a mechanical movement.
bulb: The sensitive portion of a filled system
thermometer, containing the thermal-active fluid that
drives the thermometer indication.
capillary tubing: Hollow tubing, connecting the
sensing bulb to the bourdon tube or bellows of a dial
thermometer or temperature recorder, which transmits
the fluid displacement or pressure changes of the
thermal-active fill.
case: The enclosure of an instrument, used to protect
and support the measuring element and other internal
mechanisms.
Celsius: A temperature measurement scale
calibrated to 0°C at the freezing point of water and
100°C at the boiling point of water at sea level.
connection: The method or point of attachment for
an instrument to a process or another device.
degree: A single unit of measure on a temperature
scale.
dial thermometer: A thermometer that uses a filled
system, consisting of capillary tubing and sensing bulb,
to measure and indicate temperature. This type of
thermometer can be installed directly or in a remote
location (also see “bimetal thermometer”.)
dialface: The instrument component that contains a
printed, graduated scale on which a pointer will indicate
a measurement reading.
DIN: Deutsches Institut für Normung e.V., a German
agency that sets engineering and dimensional
standards that are recognized worldwide.
DIN Size: An electronic equipment panel size
standard developed by DIN, where 1/4 DIN equals 96 x
96 mm and 1/16 DIN equals 48 x 48 mm, etc.
electric contact: The working mechanical
components of an electrical switch, operated by the
pointer or internal mechanism of an instrument.
extension wire: Thermocouple or RTD connection
wire used to connect the sensor to a separate display,
transmitting or controlling device. Supplied separately
from the sensor (see “leadwire”.)
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Technical Info.
bronze braided armor: A type of armor made from
bronze wire, braided or woven into a tubular shape.
BSPT: British Standard Pipe Taper: a British thread
standard.
93
Glossary
continued
Fahrenheit: A temperature measurement scale
measuring 32°F at the freezing point of water and 212°F
at the boiling point of water at sea level.
liquid fill: A fluid used to fill the case of a bimetal
thermometer to protect the internal mechanism from
vibration.
figure interval: The number of units of measure
between adjacent numeric graduations on a dialface.
mA: Abbreviation for milliampere: a unit of electrical
flow measurement. One thousandth of an amp.
fixed union connection: A type of union connection
mounted on a pressure tight seat at a specific
temperature probe insertion length.
maximum registering pointer: An indicator on the
instrument lens that is moved by the measuring pointer
in one direction only, remaining at the highest reading.
Also may be used as a minimum registering pointer.
friction pointer: A pointer style that allows for zero
adjustment by manually rotating the pointer on the
pointer shaft of the instrument.
graduations: The individual indication markings on a
dialface or measuring scale.
mercury-in-glass: A thermometer that consists of a
glass tube filled with mercury.
hermetically sealed: A case or enclosure that is airtight, thereby protecting the internal mechanisms from
the elements.
Micro Switch: A miniature, snap-action switch,
installed within a dial thermometer case that is designed
to operate low current alarms or warning lights.
Hz: An abbreviation for hertz: a unit of frequency
measurement, where one hertz equals one cycle per
second.
micrometer pointer: A friction pointer using gears as
the means of adjustment.
industrial thermometer: A thermometer that consists
of a sealed glass tube, usually filled with mercury, that is
affixed to a temperature scale.
insertion length: The length of the temperature
probe on the process side of the mounting threads.
Technical Info.
mercury actuated: A type of liquid actuation in which
the liquid is specifically the element mercury.
grounded junction: A type of thermocouple sensor
construction in which the measuring junction comes in
electrical contact with the stem material.
input signal: The sensing signal that is accepted by
a display or transmitter.
94
measuring junction: The thermocouple junction
known as the hot junction that is used to measure the
process temperature.
minor division: The number of units of measure
between adjacent graduation markings on a dialface.
mm: Abbreviation for millimeters: a unit of linear
measurement.
movement: The instrument component that
mechanically translates the motion of the sensitive
element into the rotary motion of the pointer.
mV: Abbreviation for millivolt: a unit of electromotive
force measurement. One thousandth of a volt.
intrinsically safe: An instrument or device that will
not produce any spark or thermal effects under normal
or abnormal conditions that will ignite a specified gas
mixture.
non wetted part: A component not in contact with the
process media.
leadwire: Thermocouple or RTD connection wire that
is integrated into the temperature sensor.
NPT: National Pipe Taper: an American thread
standard.
liquid actuated: A method of dial thermometer
construction in which the temperature is measured and
indicated by utilizing the coefficient of thermal expansion
of a fluid in the sensor and thermal system.
O.D.: Outside diameter.
ohm: A unit of electrical resistance. Often represented
by the Greek symbol omega (Ω).
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Glossary
continued
output signal: The resulting voltage, amperage or
pressure from a measurement device, often used as
input by another instrument or control valve.
pneumatic: Worked by or filled with compressed air
or other similar gases.
pointer: The indicator on a dial type analog
instrument, such as the hands on a clock.
pressure: A measure of force distributed over a
surface area.
psi: Abbreviation for pounds per square inch: a unit of
pressure measurement.
range: The low and high limits of a measurement
scale.
Reaumur: A temperature measurement scale
measuring 0°R at the freezing point of water and 80°R
at the boiling point of water at sea level.
red set hand: An indicator permanently affixed to the
instrument dialface to identify a predetermined reading
limit.
reference junction: The cold junction of a
thermocouple, which is the attachment point to a
controller or indicator.
ring: The exterior component on a thermometer that
attaches the window to the case.
RTD: Resistance Temperature Detector: a variable
resistor that will change its electrical resistance in direct
proportion to changes in temperature in a precise,
repeatable and nearly linear manner.
span: The difference between the high and the low
limits of the measuring range of an instrument.
spiral armor: A type or armor made from a formed
strip of metal that interlocks itself into a flexible tubular
shape.
spirit fill: An organic fill, contained inside the tube of
an industrial thermometer, used in place of mercury.
temperature recorder: A thermometer designed to
continuously measure and permanently record the
temperature of a specific application or condition over a
predetermined period of time.
temperature sensor: A device or component for
measuring temperature, used in conjunction with an
electronic display or controller.
terminal block: An electrical hookup point installed
within a connection head.
thermal system: The sensing bulb, capillary tubing
and bourdon tube (or bellows) assembly of a dial
thermometer or temperature recorder, containing the
system actuation thermal-active fill. A permanently
sealed system.
thermocouple: An electronic sensing device made
from two dissimilar metals that generate electrical
voltage directly in proportion to changes in temperature.
thermometer: An instrument designed to measure
and indicate the temperature of a specific application or
condition.
thermowell: A pressure tight receptacle designed to
receive a temperature sensing element (usually by
means of a threaded connection) and provided with
external threads, flanges or other means for pressure
tight attachment into a vessel or pipe.
transmitter: A temperature instrument that is
designed to convert a thermocouple or RTD signal to a
mA signal and pass the signal to an electronic indicator
or controller.
tube: The hollow glass chamber inside an industrial
thermometer that contains the mercury or spirit fill.
U-Clamp: A “U” shaped component and attachment
hardware for mounting a thermometer case into a panel
cutout without using bolt holes in the panel.
union connection: A type of threaded connector that
freely swivels about a temperature sensor allowing for
threaded connection into a well or hub without rotating
the sensor and connecting tubing, wire, etc.
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Technical Info.
spring loaded: A thermocouple or RTD stem that is
not welded to the fitting and uses an internal spring to
allow the stem to bottom out inside a thermowell.
stem: The portion of a thermometer or temperature
sensor that is inserted into the process.
95
Glossary
continued
unit of measure: Smallest integer on the
measurement scale for which the scale is named.
USDA: United States Department of Agriculture: a
government organization responsible for developing the
inspection standards of agricultural products.
Vac: Abbreviation for volts alternating current: a unit of
electromotive force measurement.
vacuum: Pressures below ambient atmospheric
pressure.
vapor actuated: A method of dial thermometer
construction in which the temperature is measured and
indicated by utilizing the vapor pressures generated
from a fluid in the sensor and thermal system.
Vdc: Abbreviation for volts direct current, a unit of
electromotive force measurement.
weatherproofed case: A sealed, environmentally
resistant instrument case.
wetted part: A component in contact with the process
media.
window: The clear portion of an instrument case
front, usually made from plastic or glass, through which
the measurement indication is read.
Technical Info.
zero adjustment: The act of realigning the pointer
with the dialface graduations, an aspect of the
calibration procedure.
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