Welcome to the NEWPORT Technical Reference Glossary.
Click on the letter that corresponds to the word you wish to have
defined.
To return to glossary menu, click "Back" on your
browser tool bar.
Technical Reference
Absolute
Zero:
Temperature at which thermal energy is at a minimum defined as
0 Kelvin, calculated to be -273.15°C or -459.67°F.
Accuracy: Closeness of the actual reading to the value
of a primary calibration standard usually expressed in percent
error at 25°C.
ALOMEGA†: An aluminum nickel alloy used in the negative
leg of a Type K thermocouple.
†Registered Trademarks of OMEGA ENGINEERING, INC.
Ambient Compensation: The design of an instrument such
that changes in ambient temperature do not affect the readings
of the instrument.
Ambient Temperature: The average or mean temperature of
the surrounding air which comes in contact with the equipment
and instruments under test.
Ampere (amp): A unit used to define the rate of flow of
electricity (current) in a circuit, units are one coulomb (625
x 1018 electrons) per second.
Ammeter:
An
instrument used to measure current.
ATC: Automatic Temperature Compensation
Auto-Zero: An automatic internal correction for offsets
and/or drift at zero voltage input.
Automatic Reset: 1. A feature on a limit controller that
automatically resets the controller when the controlled temperature
returns to within the limit bandwidth set. 2. The integral function
on a PID controller which adjusts the proportional bandwidth with
respect to the setpoint to compensate for droop in the circuit,
i.e., adjusts the controlled temperature to the setpoint after
the system stabilizes.
Automatic Tuning: An automatic calculation of the optimum
PID parameters with a built-in software algorithm to eliminate
manual tuning.
AWG: American Wire Gage
BCD,
Buffered:
Binary coded decimal output with output drivers, to increase line-drive
capability.
BCD, Serial:
A digital data output format where every decimal digit is
represented by binary signals on four lines and up to five decimal
digits are presented sequentially. The total number of lines is
four data lines plus one strobe line per digit.
BCD, Parallel:
A digital data output format where every decimal digit is represented
by binary signals on four lines and all digits are presented in
parallel. The total number of lines is 4 times the number of decimal
digits.
BCD, Three-State:
An implementation of parallel BCD which has 0, 1 and high-impedance
output states. The high-impedance state is used when the BCD output
is not addressed in multiplexed parallel applications.
BIAS Current:
A very low level DC current generated by the measuring device
and superimposed on the signal. This current may introduce a measurable
offset across a very high source impedance.
Bipolar:
The ability of a panel meter or signal conditioner to display
both positive and negative readings.
Blackbody:
A theoretical object that radiates the maximum amount of energy
at a given temperature, and absorbs all the energy incident upon
it. A blackbody is not necessarily black. (The name blackbody
was chosen because the color black is defined as the total absorption
of light energy.)
Btu:
British Thermal Unit. The quantity of thermal energy required
to raise one pound of water 1°F at or near its maximum density
(391°F).
Buffer:
Any substance of combination of substances which, when dissolved
in water, produces a solution which resists a change in its hydrogen
concentration on the addition of an acid or alkali.
CMR
(Common-Mode Rejection Ratio):
The ability of a panel meter to eliminate the effect of AC or
DC noise between signal and ground. Normally expressed in dB at
dc to 60 Hz. One type of CMR is specified between SIG LO and PWR
GND. In differential meters a second type of CMR is specified
between SIG LO and ANA GND (METER GND).
CMV (Common-Mode
Voltage): The AC or DC voltage which is tolerable between
signal and ground. One type of CMV is specified between SIG LO
and PWR GND. In differential meters a second type of CMV is specified
between SIG HI or LO and ANA GND (METER GND).
Calorie:
The quantity of thermal energy required to raise one gram
of water 1°C at 150°C.
Celsius
(Centigrade): A temperature scale defined by 0°C at the
ice point and 100°C at the boiling point of water.
Ceramic
Insulation: High-temperature compositions of metal oxides
used to insulate a pair of thermocouple wires. The most common
are Alumina (Al O) Beryllia (BeO) and Magnesia (MgO) Their application
depends upon temperature and type of thermocouple. High-purity
Alumina is required for platinum alloy thermocouples. Ceramic
insulators are available as single and multihole tubes or as beads.
CHROMEGA†:
A chromium-nickel alloy which makes up the positive leg of
Type K and Type E thermocouples.
†Registered Trademarks of OMEGA ENGINEERING, INC.
Closeness
of Control: Total temperature variation from a desired set
point of system expressed as “closeness of control”
is ±2°C or a system bandwidth with 4°C, also referred
to as amplitude of deviation.
Color Code:
The ANSI established color code for thermocouple wires in
the negative lead is always red. Color code for base metal thermocouples
is yellow for Type K, black for Type J, purple for Type E, and
blue for Type T.
Compensating
Alloys: Alloys used to connect thermocouples to instrumentation.
These alloys are selected to have similar thermal electric properties
as the thermocouple alloys (however, only over a very limited
temperature range).
Compensated
Connector: A connector made of thermocouple alloys used to
connect thermocouple probes and wires.
Conductance:
The measure of the ability of a solution to carry an electrical
current.
Conformity
Error: For thermocouples and RTDs, the difference between
the actual reading and the temperature shown in published tables
for a specific voltage input.
Counts:
The number of time intervals counted by the dual-slope AD
converter and displayed as the reading of the panel meter, before
addition of the decimal point.
Connection
Head: An enclosure attached to the end of a thermocouple which
can be cast iron, aluminum or plastic within which the electrical
connections are made.
Constantan:
A copper-nickel alloy used as the negative lead in Type E,
Type J. and Type T thermocouples.
Control Mode: The output form or type of control action
used by a temperature controller to control temperature, i.e.,
on/off, time proportioning, PID.
Control
Point: The temperature at which a system is to be maintained.
Current Proportioning: An output form of a temperature
controller which provides a current proportional to the amount
of control required. It is normally a 420 milliamp current proportioning
band.
Current
Transformer (CT): A transformer designed for AC measurement
circuits. It provides isolation and a step-down current output.
Cycle Time:
The time usually expressed in seconds for a controller to
complete one on/off cycle.
dB
(Decibel): 20
times the log to the base 10 of the ratio of two voltages. Every
20 dB’s correspond to a voltage ratio of 10:1, every 10 dB’s
to a voltage ratio of 3.162:1. For instance, a CMR of 120 dB provides
voltage noise rejection of 1,000,000:1. An NMR of 70 dB provides
voltage noise rejection of 3,162/1.
Deadband
(Hysteresis): In a digital controller, there may be one switching
point at which the signal increases and another switching point
at which the signal decreases. The difference between the two
switching points is called hysteresis or deadband.
Degree:
An incremental value in the temperature scale, i.e. There
are 100 degrees between the ice and the boiling point of water
in the Celsius scale and 180°F between the same two points
in the Fahrenheit scale.
Deviation: The difference between the value of the controlled
variable and the value at which it is being controlled.
Differential:
For an on/off controller, it refers to the temperature difference
between the temperature at which the controller turns heat off
and the temperature at which the heat is turned back on. It is
expressed in degrees.
Differential
Input: A signal-input circuit where SIG LO and SIG HI are
electrically floating with respect to ANALOG GND (METER GND which
is normally tied to DIG GND). This allows the measurement of the
voltage difference between two signals tied to the same ground
and provides superior common-mode noise rejection.
Digit:
A measure of the display span of a panel meter. By convention
a full digit can assume any value from 0 through 9, a 1/2 digit
will display a 1 and overload at 2, a 3/4 digit will display digits
up to 3 and overload at 4, etc. For example, a meter with a display
span of +3999 counts is said to be a 3 3/4 digit meter.
DIN
(Deutsche Industries Norm): A set of German standards recognized
throughout the world. The 1/8 DIN standard for panel meters specifies
an outer bezel dimension of 96 x 48 mm and a panel cutout of 92
x 45 mm.
DIN
43760: The standard that defines the characteristics of a
100 ohm platinum RTD having a resistance vs. temperature curve
specified by = 0.00385 ohms per ohms per degree C.
Dissipation
Constant: The ratio for a thermistor which relates a change
in internal power dissipation to a resultant change of body temperature.
Drift:
A change of a reading or a setpoint value over long periods due
to several factors including change in ambient temperature, time,
and line voltage.
Droop:
A common occurrence in time-proportional controllers. It refers
to the difference in temperature between the setpoint and where
the system temperature actually stabilizes due to the time-proportioning
action of the controller.
Dual Element Sensor: A sensor assembly with two independent
sensing elements.
Dualslope
A/D Converter: An analog-to-digital converter which integrates
the signal for a specific time, then counts time intervals for
a reference voltage to bring the integrated signal back to zero.
Such converters provide high resolution at low cost, excellent
normal-mode noise rejection, and minimal dependence on circuit
elements.
Duplex
Wire: A pair of wires insulated from each other and with an
outer jacket of insulation around the inner insulated pair.
Duty
Cycle: The total time to complete one on/off cycle usually
refers to the on/off cycle time of a temperature controller.
Exposed
Junction:
A form of construction of a thermocouple probe where the hot
or measuring junction protrudes beyond the sheath material so
as to be fully exposed to the medium being measured. This form
of construction usually gives the fastest response time.
Fahrenheit:
A temperature scale defined by 32° at the ice point and
212° at the boiling point of water at sea level.
Filter (ABC): Adaptive Bandwidth Filter–Automatically
adjusts filter time constant to adapt to noise and noise spikes.
Automatically reduces filter time constant in successive 2:1
steps to respond to step changes in the input signal.
Gain:
The amount of amplification used in an electrical circuit.
Ground:
1. The electrical neutral line having the same potential
as the surrounding earth. 2. The negative side of do power
supply. 3. Reference point for an electrical system.
Grounded
Junction: A form of construction of a thermocouple probe
where the hot or measuring junction is in electrical contact
with the sheath material so that the sheath and thermocouple
will have the same electrical potential.
Hertz
(Hz): Units
in which frequency is expressed. Synonymous with cycles per
second (cps).
Hysteresis:
(see Deadband)
Hold:
Meter HOLD is an external input which is used to freeze
the display BCD HOLD is an external input used to freeze the
BCD output while allowing the A/D process to continue operation.
Ice
Point: The
temperature at which pure water freezes, 0°C, 32°F.
Input
Impedance: The resistance of a panel meter as seen from
the source in the case of a voltmeter. This resistance has to
be taken into account when the source impedance is high; in
the case of an ammeter when the source impedance is low.
Insulated
Junction: See ungrounded junction.
Insulation
Resistance: The resistance value of the cover material of
an electrical conductor, expressed in ohms.
Integral:
A form of temperature control. See automatic reset, #2.
Interchangeability
Error: A measurement error that can occur if two or more
probes are used to make the same measurement. It is caused by
a slight variation in characteristics of different probes.
Isothermal:
A process or area that is at a constant temperature.
Junction:
The point in a thermocouple where the two dissimilar metals
are joined.
Kelvin:
Symbol
K. The unit of absolute or thermodynamic temperature scale based
upon the Celsius scale with 100 units between the ice point
and boiling point of water 0°C = 273.15K (there is no degree
(°) symbol used with the Kelvin scale).
Lag:
1.
A time delay between the output of a signal and the response
of the instrument to which the signal is sent. 2. A time relationship
between two waveforms where a fixed reference point of one wave
occurs after the same point of the reference wave.
Limits
of Error: A tolerance band for the thermal electric response
of thermocouple wire expressed in degrees or percentage defined
by ANSI specification MC96.1 (1975).
Load:
The electrical demand of a process expressed as power (watts),
current (amps) or resistance (ohms).
Loop
Resistance: The total resistance of a thermocouple circuit
caused by the resistance of the thermocouple wire. Usually used
in reference to analog pyrometers which have typical loop resistance
requirements of 10 ohms.
LSD
(Least-Significant Digit): The rightmost active (non dummy)
digit of the display.
MSD
(Most-Significant Digit): The
left-most digit of the display.
Manual
Reset (Adjustment): The adjustment of a proportioning controller
which shifts the proportioning band in relationship to the setpoint
to eliminate droop or offset errors.
Manual
Reset (Switch): The switch in a limit controller that manually
resets the controller after the limit has been exceeded.
Maximum
Operating Temperature:
The maximum temperature at which an instrument or sensor can
be safely operated.
Measuring
Junction: The thermocouple junction referred to as the hot
junction that is used to measure an unknown temperature.
Microvolt:
One millionth of a volt, 10-6 volts.
Mil: One thousandth of an inch (0.001),10-3.
Milliamp:
One thousandth of an amp, 10-3 amps, symbol mA.
Millimeter:
One thousandth of a meter,10-3 meters, symbol
mm.
Millivolt:
One thousandth of a volt, 10-3 volts symbol mV.
Mineral-insulated
Thermocouple: A type of thermocouple cable which has an
outer metal sheath and mineral (magnesium oxide) insulation
inside separating a pair of thermocouple wires from themselves
and from the outer sheath. This cable is usually drawn down
to compact the mineral insulation and is available in diameters
from .375 to .010 inches. It is ideally suited for high-temperature
and severe-duty applications.
Multiplex:
A technique which allows different input (or output) signals
to use the same lines at different times, controlled by an external
signal. Multiplexing is used to save on wiring and I/O ports.
N/C
(No Connection): A
connector point for which there is no internal connection.
NEMA
1/ UL Type 1: Intended for indoor use, to provide a degree
of protection against contact with the enclosed equipment and
against limited amount of falling dirt.
NEMA 4/ UL Type 4: A standard from the National Electrical
Manufacturers Association which defines enclosures intended
for indoor or outdoor use primarily to provide a degree of protection
against windblown dust and rain, splashing water, and hose-directed
water.
Testing - Hosedown: Enclosure is subjected to
a stream of water from a hose which has a 1 inch diameter nozzle
and which delivers at least 65 gallons per minute from a distance
of 10 to 12 feet for a minimum of 5 minutes.
NEMA
7/ UL Type 7: A standard from the National Electrical Manufacturers
Association, which defines explosion-proof enclosures for use
in locations classified as Class 1, Groups A, B. C or D, as
specified in the National Electrical Code.
NEMA
12/ UL Type 12: A standard from the National Electrical
Manufacturers Association, which defines enclosures with protection
against falling dirt, circulating dust, and dripping non-corrosive
liquids.
Testing - Drip: Enclosure is subjected to a drip
pan which produces both splashing and dripping.
Testing - Atomized Water: Enclosure is subjected
to a spray of atomized water by using a nozzle that produces
a 3" round diameter spray, 12" from closure. The air
pressure is at 30psi.
NEMA-size
Case: An older US case standard for panel meters, which
requires a panel cutout of 3.93 x 1.69 inches.
NMR
(Normal-Mode Rejection): The ability of a panel meter to
filter out noise superimposed on the signal and applied across
the SIG HI to SIG LO input terminals. Normally expressed in
dB at 50/60 Hz.
Nicrosil/nisil:
A nickel chrome/nickel silicone thermal alloy used to measure
high temperatures. Inconsistencies in thermoelectric voltages
exist in these alloys with respect to the wire gage.
Noise:
An unwanted electrical interference on the signal wires.
NPT:
National Pipe Thread.
Offset:
The
difference in engineering units between the setpoint and the
actual process temperature. Also, referred to as droop.
Ofhc:
Oxygen-free high-conductivity copper. The industrial designation
of the pure copper used in a Type T thermocouple.
Ohmmeter:
An instrument used to measure electrical resistance.
OMEGALLOY†:
A nickel chrome/nickel silicone thermal alloy used to measure
high temperatures. Inconsistencies in thermoelectric voltages
exist in these alloys with respect to the wire gage.
†Registered Trademarks of OMEGA ENGINEERING, INC.
On/off
Controller: A controller whose action is fully on or fully
off.
ORP:
Oxidation Reduction Potential
Overshoot: The number of degrees that a process exceeds
the setpoint temperature when coming up to the setpoint temperature.
PH(S)
(Standard pH Scale):
The conventional standard pH scale established on the basis
that an individual ionic activity coefficient can be calculated
from the Debye-Hückel law for primary buffers.
PID: Proportional, Integral, Derivative--A three-mode control
action where the controller has time proportioning integral
(auto reset), and derivative action.
PPM:
Abbreviation for “parts per million”, sometimes used
to express temperature coefficients. For instance, 100 ppm is
identical to 0.01%.
Platinel:
A non-standard, high temperature platinum thermocouple alloy
whose thermoelectric voltage nearly matches a Type K thermocouple
(trademark of Englehard Industries).
Platinum:
A noble metal which in its pure form is the negative wire of
Type R and Type S thermocouples.
Platinum
6% Rhodium: The platinum-rhodium alloy used as the negative
wire in conjunction with platinum 30% rhodium to form a Type
B thermocouple.
Platinum
10% Rhodium: The platinum-rhodium alloy used as the positive
wire in conjunction with pure platinum to form a Type S thermocouple.
Platinum
13% Rhodium: The platinum-rhodium alloy used as the positive
wire in conjunction with pure platinum to form a Type R thermocouple.
Platinum
30% Rhodium: The platinum-rhodium alloy used as the positive
wire in conjunction with platinum 6% rhodium to form a Type
B thermocouple.
Platinum
67: To develop thermal emf tables for thermocouples the
National Bureau of Standards paired each thermocouple alloy
against a pure platinum wire (designated Platinum 27 prior to
1973, and currently Platinum 67). The thermal emf’s of
any alloy combination can be determined by summing the “vs.
Pt-67” emf’s of the alloys, i e. the emf table for
a Type K thermocouple is derived from the Chromel vs. Pt-67
and the Alumel vs Pt-67 values.
Primary
Standard (NBS): The standard reference units and physical
constants maintained by the National Bureau of Standards upon
which all measurement units in the United States are based.
Probe:
A generic term that is used to describe many types of temperature
sensors.
Process Meter: A panel meter with sizeable zero and span
adjustment capabilities, which can be scaled for readout in
engineering units for signals such as 420 mA, 1050 mA and 1-5
V.
Process Variable (PV): The parameter that is controlled
or measured. Typical examples are temperature, relative humidity,
pressure flow, level, etc. The high process variable is the
highest value of the process range, expressed in engineering
units. The low process variable is the lowest value of the process
range.
Proportioning
Band: A temperature band expressed in degrees within which
a temperature controller’s time proportioning function
is active.
Proportioning
Control Mode: A time-proportioning controller where the
amount of time that the relay is energized is dependent upon
the system’s temperature.
Proportioning
Control Plus Derivative Function: A time proportioning controller
with a derivative function The derivative function senses the
rate at which a system’s temperature is either increasing
or decreasing and adjusts the cycle time of the controller to
minimize overshoot or undershoot.
Proportioning
Control Plus Integral: A two-mode controller with time proportioning
and integral (auto reset) action. The integral function automatically
adjusts the temperature at which a system has stabilized back
to the setpoint temperature, thereby eliminating droop in the
system.
Proportioning
Control with Integral and Derivative Functions: Three-mode
PID controller. A time-proportioning controller with integral
and derivative functions. The integral function automatically
adjusts the system temperature to the setpoint temperature to
eliminate droop due to the time-proportioning function. The
derivative function senses the rate of rise or fall of the system
temperature and automatically adjusts the cycle time of the
controller to minimize overshoot or undershoot.
Protection
Head: An enclosure usually made out of metal at the end
of a probe where connections to the probe are made.
Protection
Tube: A metal or ceramic tube closed at one end into which
a temperature sensor is inserted. The tube protects the sensor
from the medium into which it is inserted.
Range:
An area between two limits within which a quantity is measured.
It is usually expressed by stating the lower limit first and
then the upper limit.
Rankine
(°R): An absolute temperature scale based upon the Fahrenheit
scale with 180° between the ice point and boiling point
of water. 459.67°R = 0°F.
Rate
Action: The derivative function of a temperature controller.
Rate
Time: The time interval over which the system temperature
is sampled for the derivative function.
Ratiometric
Measurement: A measurement technique where an external signal
is used to provide the voltage reference for the dual-slope
A/D converter. The external signal can be derived from the voltage
excitation applied to a bridge circuit or pick-off supply, thereby
eliminating errors due to power supply fluctuations.
Reference
Junction: The cold junction in a thermocouple circuit which
is held at a stable known temperature. The standard reference
temperature is 0°C (32°F); however, other temperatures
can be used.
Relay
(Mechanical): An electromechanical device that completes
or interrupts a circuit by physically moving electrical contacts
into contact with each other.
Form “A”–A single-pole, single-throw (SPST)
relay with normally open (NO) and common contacts. These contacts
close when the relay coil is energized. They open when power
is removed from the coil.
Form “B”–A single-pole, single throw (SPST)
relay with normally closed (NC) and common contacts. These contacts
open when the relay coil is energized. They close when power
is removed from the coil.
Form “C”–A single-pole, double-throw relay
with normally open (NO), normally closed (NC) and common contacts.
Relay
(Solid State): A solid state switching device which completes
or interrupts a circuit electrically with no moving pans.
Repeatability:
The ability of a probe or instrument to give the same output
or reading under repeated identical conditions.
Resistance:
The resistance to the flow of electric current measured in ohms.
For a conductor resistance is a function of diameter, resistivity
(an intrinsic property of the material) and length.
Resistance
Ratio Characteristic: For thermistors, the ratio of the
resistance of the thermistor at 25°C to the resistance at
125°C.
Resistance
Temperature Characteristic: A relationship between a thermistor’s
resistance and the temperature.
Resolution:
The input corresponding to a one-unit change in the least
significant digit. (Good resolution is not necessarily equal
to good accuracy.)
Response
Time (Time Constant): The time required by a sensor to reach
63.2% of a step change in temperature under a specified set
of conditions. Five time constants are required for the sensor
to stabilize at 100% of the step change value.
RTD:
Resistance Temperature Detector.
SCR:
Silicon
Controlled Rectifier.
Seebeck Coefficient: The derivative (rate of change)
of thermal emf with respect to temperature normally expressed
as millivolts per degree.
Seebeck
Effect: When a circuit is formed by a junction of two dissimilar
metals and the junctions are held at different temperatures,
a current will flow in the circuit caused by the difference
in temperature between the two junctions.
Seebeck
EMF: The open circuit voltage caused by the difference in
temperature between the hot and cold junctions of a circuit
made from two dissimilar metals.
Secondary
Standard: A standard of unit measurement derived from a
primary standard.
Sensitivity:
The minimum change in input signal to which an instrument
can respond.
Setpoint:
The temperature at which a controller is set to control
a system.
Settling
Time: The time taken for the display to settle within one
digit of the final value when a step is applied to the meter
input.
Sheath
Thermocouple: A thermocouple made out of mineral-insulated
thermocouple cable which has an outer metal sheath.
Signal
Conditioner: A circuit module which offsets attenuates,
amplifies linearizes and/or filters the signal for input to
the A/D converter. The typical output signal conditioner is
+2 Vdc.
Single-ended
Input: A signal-input circuit where SIG LO (or sometimes
SIG HI is tied to METER GND. Ground loops are normally not a
problem in AC-powered meters, since METER GND is transformer-isolated
from AC GND.
Span:
The difference between the upper and lower limits of a range
expressed in the same units as the range.
Span
Adjustment: The ability to adjust the gain of a process
or strain meter so that a specified display span in engineering
units corresponds to a specified signal span. For instance,
a display span of 200°F may correspond to the 16 mA span
of a 420 mA transmitter signal.
Spare:
A
connector point reserved for options, specials, or other configurations.
The point is identified by an IE#) for location on the electrical
schematic.
Specific
Heat: The ratio of thermal energy required to raise the
temperature of a body f ° to the thermal energy required
to raise an equal mass of water 1°.
SSR: Solid State Relay: (see Relay, Solid State).
Stability:
The quality of an instrument or sensor to maintain a consistent
output when a constant input is applied.
Super
Cooling: The cooling of a liquid below its freezing temperature
without the formation of the solid phase.
Super
Heating: 1. The heating of a liquid above its boiling temperature
without the formation of the gaseous phase. 2. The heating of
the gaseous phase considerably above the boiling-point temperature
to improve the thermodynamic efficiency of a system.
PFA:
A fluorocarbon polymer used for insulation of electrical wires
.
TEMPCO:
Abbreviation for “temperature coefficient”: the error
introduced by a change in temperature. Normally expressed in
%/°C or ppm/°C.
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.
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:
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).
Standard
thermocouple types are:
|
Thermocouple
Type (ANSI Symbol)
|
Material
|
|
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/Platinum 30%
|
|
Rhodium
|
|
|
G*
|
Tungsten
Tungsten 26/ Rhenium
|
|
C*
|
Tungsten
5°/O Rhenium Tungsten 26%
|
|
Rhenium
|
|
|
D*
|
Tungsten
3% Rhenium Tungsten 25%
|
|
Rhenium
|
|
| *
Not ANSI symbols |
| †
Registered Trademarks of OMEGA ENGINEERING,
INC. |
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.
Transmitter (Two-wire): A device which is used to transmit
temperature data from either a thermocouple or RTD 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.
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-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.
LS-TTL Compatible: For digital input circuits, a logic
1 is obtained for inputs of 2.0 to 5.5 V which can source 20 pA,
and a logic 0 is obtained for inputs of 0 to 0.8 V which can sink
400 uA. 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
uA; and a logic 0 is represented by 0 to 0.8 V with a current
sink capability of at least 16 mA. “LS” stands for low-power
Schottky.
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.
LS-TTL Unit Load: A load with LS-TTL voltage levels, which
will draw 20uA for a logic 1 and -400 uA for a logic 0.
Undershoot:
The
difference in temperature between the temperature a process goes
to below the setpoint, after the cooling cycle is turned off,
and the setpoint 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 lining where two extension pipes
are joined at a separable coupling.
Zero Adjustment:The ability to adjust
the display of a process or strain meter so that zero on the display
corresponds to a non-zero signal, such as 4 mA, 10 mA or 1 Vdc.
The adjustment range is normally expressed in counts.
Zero Offset: 1. The difference expressed in degrees between
true zero and an indication given by a measuring instrument. 2.
See Zero Suppression.
Zero Power Resistance: The resistance of a thermistor or
RTD element with no power being dissipated.
Zero Suppression: The span of an indicator or chart recorder
may be offset from zero (zero suppressed) such that neither limit
of the span win be zero. (Example: a temperature recorder which
records a 100° span from 400° to 500° is said to have
400% zero suppression.
|
|
