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About Thermocouples
Thermocouples are temperature measuring devices. They
consist of two dissimilar metals connected at two points. When one point
is at a different temperature than the other a current or voltage is
developed and used in measurement. Thermocouples are widely used and
can be found in many everyday devices. For industrial purposes thermocouple
assemblies can be found in furnaces, pressure chambers, kilns, food production
ovens and most temperature sensitive applications. Common elements used
in thermocouples are copper, nickel, and silver.
Each of the metals used in thermocouples have specific capacities for
measuring certain temperature ranges. There are three functional classes
of thermocouple assemblies based on the metal used. Base metal thermocouples
are good for measuring temperatures under 1000 degrees Celsius. Noble
metal thermocouples measure up to about 2000 degrees. Lastly, Refractory
metal thermocouples can handle upward of 2600 degrees Celsius. Most thermocouple
assemblies are sheathed and are one of three junction types: grounded,
ungrounded or exposed. In an exposed thermocouple, the tip of it protrudes
out beyond the sheath, exposing it directly to the surrounding environment.
This provides fast response and reading of the temperature, but this
type of reading is limited to non-corrosive and non- pressurized situations.
Thermocouples often work together as part of a larger measurement or
other data
acquisition
system. These systems are often computerized and
have automated capabilities. They gather information from one or more
signal inputs or sensor sources such as thermocouples and convert this
information into a digital form for further analysis.
While there are alternatives to thermocouples they are the most popular
temperature measuring device. Some of the advantages to using a thermocouple
are their low cost, wide temperature range, good repeatability and their
short response time. Thermocouples are generally not sensitive enough
for certain applications. It is important to evaluate the application
environment before purchasing or replacing a thermocouple. Some things
to consider when looking at thermocouples are the size and dimensions
needed, the number of thermocouple pairs, operating temperature and plug
requirements.
Featured
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http://www.microwaves101.com/encyclopedia/thermocouples.cfm
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Types of Thermocouples
- are used for the temperature
measurement of piping and other cylinder shaped entities.
- sense heat which has wavelengths longer than
red visible light and shorter than microwaves.
- register changes in resistance as changes in temperature.
- are wires made of a different homogeneous metal or alloy,
joined at one end to form a measuring junction.
- gauge temperatures with a bridge measurement.
- gather information on the change in resistance
of a metal wire element.
- is a resistance temperature detector with a pair
of different metals joined at two points so a voltage results
when the
junctions are at different temperatures.
- measure the temperature of a material or substance.
- are semiconductors with varying resistance that relates
to temperature.
- are a collection of tubes,
wires and insulators. Often included to in classification with heating
elements.
( heating-elements.com )
- are used to protect temperature sensors.
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