Thermocouple Styles

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Thermocouple in heater, industrial temperature sensor.

Thermocouples are devices that manufacturing companies use to gauge the temperature of a variety of items and materials. Thermocouples are widely used because many operations can fail due to even the smallest deviation of temperature. Due to the variety of machines and materials involved in manufacturing, there are multiple types of thermocouples that address different conditions and requirements.

Beaded Wire Thermocouples

A beaded wire thermocouple is two thermocouple wires connected by a welded bead. Beaded wire thermocouples are the simplest form of thermocouple. They provide quick measurements, and they work well with measuring the temperature of gases. Beaded wire thermocouples can also be made in small sizes, making them useful for confined or controlled environments. However, beaded wire thermocouples are vulnerable to damage from corrosive or oxidizing agents. Also, contact with metal surfaces can interfere with measurements due to exposure to electrical currents.

Thermocouple Probes

A thermocouple probe is a thermocouple wire housed inside a protective sheath. The material of the sheath determines the properties of the thermocouple probe; a sheath made of stainless steel, for example, yields a probe with minimal issues with chemical compatibility. Another factor that determines the function of a thermocouple probe is how the tip is treated. A grounded tip — a tip that touches the sheath wall — provides quick readings but is vulnerable to electrical currents that cause inaccuracies. An ungrounded tip — a tip that is separated from the sheath by insulation — reduces the risk of electrical interference. An exposed tip — a tip that protrudes from the sheath — are best suited for measuring air temperatures. One final benefit of thermocouple probes is that some models can be connected to computers via USB ports.

Surface Probes

A surface probe is a thermocouple probe with a thin, flat junction. Surface probes are used to measure the temperature of flat surfaces. Some models of surface probes are designed to rotate, making them ideal for measuring the temperature of moving surfaces.

Wireless Thermocouples

A wireless thermocouple is a computerized device that the user can configure to operate under a variety of different conditions. Though they are more expensive than standard themocouples, their versatility, their accuracy, and their compatibility with electronic devices can offset the initial cost.

Selecting the Right Thermocouple

The first task to perform prior to acquiring a thermocouple is to clearly definie how, where, and why the thermocouple will be utilized. The temperature range is a vital factor as well; thermocouples are designed for a variety of temperature ranges, and selecting the wrong thermocouple can lead to incorrect readings or damage to the thermocouple. The importance of response time should be considered; exposing the measuring part of the thermocouple leads to faster readings, but it can also present issues with accuracy in the presence of electrical charges and loops. If the thermocouple is to be used in corrosive, abrasive, oxidizing, or vibrating environments, the selected thermocouple needs to be resistant to the hostile environment. The thermocouple should complement the environment being tested, such as the surface probe for measuring the temperature of flat surfaces.