thermocoupleThermocouples are the temperature sensors and convert thermal energy into electrical energy. A group of thermocouples connected in series forms a thermopile. Thermocouples normally work with the temperature probes. But they are also an important and some times an essential part of data acquisition systems. Being highly sensitive, thermocouples respond quickly even to minute temperature changes. Thermocouple metal type, thermocouple gauge, and thermocouple form factors are the important specifications associated with thermocouples.

Thermocouple Metal Types

There are various types of thermocouples available classified with respect to metal types. The most widely used and available metal types include base metal thermocouples and refractory metal thermocouples. Both the types are further classified into sub-types.

Base Metal Thermocouples

Base metal thermocouples include type E (constantan / chromel metals). This type senses from –2700 C to 10000. Temperature range of type J (iron / constantan) is –2100 C to 12000 C, type K (chromel / alumel) with –2700 C to 13720 C, type N (nicrosil / nisil) with –2700 C to 13000 C, and type T (copper / constantan) allows temperature range of –2700 C to 4000 C.

Refractory Metal Thermocouples

Refractory metal thermocouples include type B, type S, type R, and type W. Type B consist of platinum (30%) / rhodium. Type S platinum (10%) / rhodium, Type R platinum (13%) / rhodium, and Type W is based on tungsten / rhenium metals. Temperature range of Type B is 00 C to 13200 C, Type S is 150 C to 15680 C, Type R –500 C to 17680 C, and Type W is 00 C to 23000 C.

Thermometer Gauge

Thermometer gauge refers to the nominal diameter of thermocouple wire. Thermocouples with various Gauges are available. Some of them contain option of having more than one gauge. Normally thermocouples are specified with gauge 24 (.022 inch nominal diameter), 20 (.036 inch nominal diameter), 16 (.064 inch nominal diameter), 14 (.08 inch diameter), and gauge 8 (.16 inch diameter).

Thermocouple Form Factors

Thermocouples are available in a variety of form factors and styles. The common form factor choices include printed circuit boards, modules, integrated, and standalone devices. Product's physical style includes flexible, bare wire, full-length 1—hole, and full-length 2-hole thermocouples. In flexible thermocouples the elements are separated from each other through flexible sheathing or flexible sections. In bare wire thermocouples there is no insulating material for the protection. In full-length 1-hole thermocouples all the wires contain their own insulators. In full-length 2-hole thermocouples two wires are kept within one insulator. Common insulated devices include Teflon®, PVC (polyvinyl chloride), fiberglass, alumina, mullite, and ceramic.