Thermocouples are heat sensors and temperature controls used to measure temperature in a wide range of industrial, commercial and residential applications. Thermocouples, often called temperature probes or temperature sensors, consist of two dissimilar metals connected at two points.
According to Seebeck's principle, a voltage is always created between two dissimilar metals, and the voltage changes in proportion to exterior temperature changes; thermocouples harness this reaction to measure temperature changes. Thermocouple instruments have a basic construction, consisting of two metal wires connected at the base and with a bead at the tip. Type K thermocouples, the most universal type of thermocouple, are constructed of chromel (chromium and nickel alloy) and alumel (aluminum and nickel alloy) wires; type K thermocouples have relatively high temperature resistance and can be found in many everyday devices. For industrial purposes, high temperature thermocouple assemblies may be used in kilns, ovens, plastic extrusion machines, pressure chambers, water tanks, heat exchangers, parts washers and many other processors as water heater thermocouples, furnace thermocouples and in most temperature sensitive applications. Residential and commercial thermostats and temperature switches commonly use thermocouples as well. Thermowells and thermocouple wires are thermocouple accessories used to isolate the thermocouple device from damaging heat sources and to extend the reach. Alternatives to thermocouples include resistance temperature detectors, or RTDs, and thermistors which are used for high accuracy applications.
Most thermocouple assemblies are sheathed, that is covered with a protective tubing and insulator of sorts. There are three possible thermocouple 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 to a change in temperature, and provides a 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 due to their low cost, simple construction and ease of installation. Most thermocouples have a wide temperature range, good repeatability and short response time; RTDs tend to measure with tighter accuracy than thermocouples, but they do not have nearly as high heat capacity and are more costly. Thermocouples are generally not sensitive enough for certain precision laboratory and testing applications, in which case thermistors and RTDs are used instead. The main types of thermocouples offer a broad range of application options which are not always met by other types of temperature sensors.
Welded Tube Skin Thermocouple - Thermo Sensors Corporation
Metal Sheathed Thermocouple Element - Thermo Sensors Corporation
Thermocouple - Thermal Devices
Boiler Tube Thermocouple - Thermocouple Technology, Inc.
Surface Mount Thermocouple - Thermal Devices
General Purpose Thermocouple - Thermal Devices
- The temperature of the
air surrounding the equipment.
- Any metal other than precious metal, such as copper, aluminum, lead, nickel and tin.
-- British thermal unit; a unit for measuring a quantity of heat. 1 btu is the amount of heat required to raise the temperature of 1 pound of water 1°F.
- Adjusting the equipment so readings and accepted measurements are correlated so the value is accurate.
(centigrade) - A temperature scale defined by 0 °C at the ice point and 100 °C at boiling point of water at sea level.
- Established by ANSI to distinguish wires for thermocouples.
- Alloys with similar thermoelectric properties to the alloys in the thermocouple, used to connect the thermocouple to the instrument.
- The difference between the value of the controlled variable and the value at which it is being controlled.
-The temperature scale defined by 32° at the ice point and 212° at the boiling point of water at sea level.
- Unit of thermal energy.
- In a thermocouple where two different metals are joined.
- Expressed in BTU per pound. The amount of heat needed (absorbed) to convert a pound of boiling water to a pound of steam.
- A metal with high resistance to chemical effect, especially corrosion and solution by organic acids; occasionally called precious metal.
- A generic term that is used to describe many types of temperature sensors .
- Metal containing a coating consisting of material with a high melting point. Used in high temperature capacity thermocouple devices.
--The transmission of energy by electromagnetic waves and may become thermal energy when absorbed and increase in the temperature of the absorbing body.
- Stands for Resistance Temperature Detectors.
- The minimum change in a physical variable to which an instrument can respond.
- Thermodynamic cycle commonly used to cool thermo graphic detectors.
- A measurement of heat equal to 100,000 btu.
- Measures the difference in potential created at the junction of two different metal wires which feed from the measuring instrument.
- Many Thermocouples grouped together in a series to increase the thermoelectric output.