Thermocouples are the most widely used temperature sensors on the planet due to their combination of wide temperature capabilities, ruggedness, and low cost. Thermocouples are used in applications that range from home appliances to industrial processes, to electric power generation, to furnace monitoring and control, to food and beverage processing, to automotive sensors, to aircraft engines, to rockets, satellites and spacecraft. When it comes to high temperatures, small size, fast response, high vibration or shock, most times you will find thermocouples providing the temperature measurements.

Thermocouples can be used for a wide variety of applications in the food and beverage industry including Clean-In-Place sensors, Penetration Probes, Oven Control, Food Chain Monitoring, Hotplate Control and Monitoring and Steam Kettle temperature control.

Extruders require high temperature and high pressures. They also have a unique threaded adapter in order to position the sensor tip in the molten plastic under the high pressure conditions found there.

Omega offers the TER/TEFE/SEFE and SERP thermocouples for use in extruders, these thermocouples, available in single and dual elements, have the unique threaded housing required for this application. Omega also offers the BT and CF products which are often used on the low pressure portions of extruders in both thermocouple and RTD versions.

Type E, K, T and N thermocouples are can be used for measuring temperatures down to -200°C, however the alloys used in these thermocouples must be specifically selected for use at these temperatures in order to meet the published accuracies. Most thermocouple manufacturers purchase their thermocouple alloys calibrated for use from 0°C and above. These same alloys can be used to -200°C, but the accuracy may deviate somewhat from the established values. Individual calibrations can be purchased so offset values can be determined.

The furnace conditions the thermocouple will be exposed to will determine the right thermocouple for the application. When selecting the right thermocouple, some of the conditions that need to be considered include:

-- Temperature capability of the thermocouple wires.

-- Temperature capability of the sheath or protective covering (metal or ceramic).

-- The atmosphere it will be used in (air, reducing, oxidizing, inhert).

-- The mounting configuration.

Measuring the temperature of molten metal is difficult due to the high temperature and severe conditions encountered. Because of the temperatures involved, Type K and N Base Metal and Types R, S and B Platinum thermocouples are the only choice for contact measurements in this area.

When base metal thermocouples are used, the wires are typically large diameter #8 or #14 AWG solid wires with ceramic insulators and ceramic and/ or metal protection tubes. The large diameter of the Type K or N wires degrade slower to allow time for measurements before the high temperature conditions degrade the wires.

The platinum thermocouple wires are typically on the order of #20 to #30 AWG Solid (See the RAT/SAT/BAT series). Unlike the base metal Type K and N wires, instead of deteriorating due to oxidation or corrosion, the platinum wires instead become soft due to long term annealing and eventually fail due to grain growth.