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Thermocouples
- Thermocouples are pairs of dissimilar
metal alloy wires joined at least
at one end, which generate a net
thermoelectric voltage between
the two ends according to the
size of the temperature difference
between the ends, the relative
Seebeck coefficient of the wire
pair and the uniformity of the
wire's relative Seebeck coefficient.
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Thermistors
- Thermistors (Resistance Thermometers)
are instruments used to measure
temperature by relating the change
in resistance as a function of
temperature.
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Radiation Pyrometer
- A device to measure temperature
by sensing the thermal radiation
emitted from the object.
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Radiation Thermometers
(Optical Pyrometers and Infrared
Thermometers) - Optical Pyrometers
are devices used to measure temperature
of an object at high temperatures
by sensing the brightness of an
objects surface.
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Resistance
Temperature Detectors (RTDs)
- RTD's (Resistance Temperature
Detectors) are precision, wire-wound
resistors with a known temperature
resistance characteristic. In
operation, the RTD is usually
wired into a specific type of
circuit (wheatstone bridge). They
are nearly linear over a wide
range of temperatures and can
be made small enough to have response
times of a fraction of a second.
They require an electrical current
to produce a voltage drop across
the sensor that can be then measured
by a calibrated read-out device.
The output of this circuit can
be used to drive a meter which
has been calibrated in temperature,
or to operate a relay to sound
an alarm or shut down the motor.
The Platinum RTD is the most accurate
and stable temperature detector
from zero to about 500°C. It can
measure temperatures up to 800°C.
The resistance of the RTD changes
as a function of absolute temperature,
so it is categorized as one of
the absolute temperature devices.
(In contrast, the thermocouple
cannot measure absolute temperature;
it can only measure relative temperature.)
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Fiber Optic
Temperature Sensors - Optical-based
temperature sensors provide accurate
and stable remote measurement
of on-line temperatures in hazardous
environments and in environments
having high ambient electromagnetic
fields without the need for calibration
of individual probes and sensors.
Optical temperature
sensor systems measure temperatures
from -200C to 600C safely and
accurately even in extremely hazardous,
corrosive, and high electro-magnetic
field environments. They are ideal
for use in these conditions because
their glass-based technology is
inherently immune to electrical
interference and corrosion. Since
there is no need to recalibrate
individual sensors, operator and
technician safety is greatly enhanced
as the need for their repeated
exposure to field conditions is
eliminated.
Probes are made
from largely non-conducting and
low thermal conductance material,
resulting in high stability and
low susceptibility to interference,
and in increased operator safety.
Optical cables also have a much
higher information-carrying capacity
and are far less subject to interference
than electrical conductors.
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Silicon Temperature
Sensors - Integrated circuit
temperature sensors differ significantly
from the other types in a couple
of important ways. The first is
operating temperature range. A
temperature sensor IC can operate
over the nominal IC temperature
range of -55 C to +150 C. Some
devices go beyond this range while
others, because of package or
cost constraints, operate over
a narrower range. The second difference
is functionality. A silicon temperature
sensor is an integrated circuit,
including extennsive signal processing
circuitry within the same package
as the sensor.
