|  | Public Health Safety | Environmental Health

Thermocouple Methods

Thermocouples meet industrial needs for temperature measurement. The theory was developed by Thomas Seebeck in 1822, who manipulated the differences in conductivity between two metals to measure temperature. Thermocouples vary in temperature range between -508 to 4,712 degrees F, depending on the combination of metals used. The four thermocouple classifications are home body, upper crust, exotic and rarified, although most rarified thermocouples are considered obsolete.

  1. Thermocouples

    • Thermocouples use electric conductivity to determine temperature change. Each thermocouple contains two metal wires with dissimilar thermal and electrical conductive properties. Joined at the measurement junction, the wires extend toward the reference junction where they remain at the same temperature and voltage, and attach to the measuring device. The voltage change between wires determines the temperature difference, and absolute temperature is calculated using the reference temperature.

    Home Body

    • The home body class contains five types of thermocouples labeled E, J, K, N and T. Each type has a different base metal combination and all fall within the temperature range of -454 to 2,501.6 degrees F. Types E and T are used at low temperatures. J and K are used at high temperatures; however J is used in a reducing environment while K operates in oxidizing conditions. Type N was developed as an upgrade for type K.

    Upper Crust

    • Upper crust thermocouple types B, S and R are used at high temperatures and contain rare metals platinum and rhodium at varying percentages. Type B metals consist of platinum and 30 percent rhodium for the first metal, and platinum and 6 percent rhodium for the second. Type R and S have the same platinum-rhodium alloy for their first metal, but contain 13 percent and 10 percent rhodium respectively. Both use platinum alone as their second metal.

    Exotic

    • Although brittle, exotic class thermocouples type C, D and G are used at high temperatures. Predominantly used as standards and with developmental devices, exotic types use tungsten and rhenium as their metals, with only slight differences in rhenium percentage among them. They all operate within the same temperature range, however type C has an extended temperature range from 32 to 1,598 degrees F compared with the range of the others at 32 to 518 degrees F.

Environmental Health - Related Articles