Thermocouples and Thermoresistances0 pages

THERMOCOUPLES and THERMORESISTANCES Application: Temprature Measurement THERMOCOUPLES and THERMORESISTANCES Temprature measurement sensors for industrial use Figure 1: Standard Thermocouples Figure 2: Mineral Oxide Thermocouples Figure 3: Thermoresistances GENERAL CHARACTERISTICS Thermocouples (Figure 1 e 2) are components which are employed to measure the temperature. They consist of two metallic conductors, joint at one end (the so-called "junction") encapsulated into a metallic tube: if the temperature changes, the voltage that can be measured at the conductors terminals (= e.m.f., electro-motive-force) changes as well. This variation can be directly linked to the temperature that the junction is experiencing. Standard thermocouples have the junction which is in direct contact with the tube sheath (grounded-junction, see Figure 4). The metallic conductors within the tube are insulated by a fibreglass-silicon sheath. Mineral oxide thermocouples junction, on the contrary, is isolated from the tube sheath (see Figure 5). The metallic conductors are annealed into a compressed MgO powder. Also Thermoresistances are components which are employed to measure the temperature but, differently from thermocouples, the sensing element is a component, located at the end of the sensor, whose electrical resistance changes with changing temperature. This variation yields a measure of the temperature that the sensing element is experiencing. The standard construction for thermoresistances considers a 2-wires connection. For a better measurement accuracy, 3 or 4-wires connection are possible too (see Figure 6). Also for thermoresistances, both the standard (conductors insulation in fibreglass-silicone) and the mineral-oxide version (insulation made of MgO compressed powder) are possible. Figure 6: 9 9 9 9 ^Lyyyyu, 2-wires connection 3-wires connection Figure 4: grounded junction The junction of the sensing elements is made directly onto the tube sheath. Figure5: Isolated junction 4-wires connection The junction of the sensing elements is electrically and mechanically isolated from the sheath. This insures a long duration even if thermal shocks or corrosive conditions are experienced The thermocouples that Masterwatt supplies are compliant to ANSI or DIN specifications. The thermoresistances fulfil IEC or DIN requirements. ermocouples and Thermoresistanc