Thermocouple elements are temperature sensors that are useful over a wide range of temperatures. They are used with thermocouple temperature probes, bimetallic devices that are suitable for various temperature sensing applications. Thermocouple elements are also used with data acquisition (DAQ) systems and other temperature sensing equipment. A valuable temperature sensing tool, thermocouple elements are highly sensitive to small temperature changes and able to respond quickly to changes to the environment. Insulated devices are commonly available. Options include alumina, ceramic, fiberglass, mullite, polyvinyl chloride (PVC) and Teflon®, a registered trademark of DuPont.
Metal type is an important consideration when selecting thermocouple elements. Base metal thermocouples can measure different temperature ranges, depending on the sensor material. Each type or designation represents a specific metal type and temperature range. Type E (chromel/constantan) has a typical temperature range of -270° C to 1000° C. Type J (iron/constantan) has a temperature range of -210° C to 1200° C. Type K (chromel/alumel) has a temperature range of -270° C to 1372° C. Type N (nicrosil/nisil) has a temperature range of -270° C to 1300° C. Type T (copper/constantan) has a temperature range of -270° to 400° C. For noble and refractory metals, choices include type B (platinum 30%/rhodium) with a temperature range of 0° C to 1820° C; Type S (platinum 10%/ rhodium) with a temperature range of -50° C to 1768° C; Type R (platinum 13%/rhodium) with a temperature range of -50° C to 1768° C; and Type W (tungsten/rhenium) with a temperature range of 0° C to 2300° C.
Gauge is another important consideration when selecting thermocouple elements. Thermocouple gauge represents the nominal diameter of the thermocouple wire. Some thermocouples may be available in multiple or optional gauges. Gauge choices include 8 (nominal diameter 0.16 in), 14 (nominal diameter 0.08 in), 16 (nominal diameter 0.064 in), 18 (nominal diameter 0.048 in), 20 (nominal diameter 0.036 in) and 24 (nominal diameter of 0.022 in).
Thermocouples are available in several different styles: bare wire, full-length 2-hole, full-length 1-hole, and flexible. Bare wire devices consist of a bare wire element with no protective insulation. Full-length 2-hole insulators position both wires in a single insulator. Full-length 1-hole insulators provide each wire with its own insulator. With flexible thermocouples, thermocouple elements use flexible sheathing or a flexible section or sections.