In these transducers the change of resistance of wire or tape is used from platinum for determination of temperature. They are named the capacitance-resistance detectors of temperature. It is not necessary from here, that other metals can not be used for taking temperature, however most often platinum pickoffs are used in such transducers.
The sensitiveness of capacitance-resistance temperature transducers is very subzero, and a dynamic reaction is enough slow (by virtue of construction of device). They are subject to destruction at vibrations and shots.
Dependence of resistance on a temperature was first fully certain for the industrial platinum thermometer of resistance in BOFS in 1904 for the range of temperatures from - 220 to + 1050 °C.
There are two basic types of platinum wire capacitance-resistance transducers : the probe and pickoff assembled on a surface immersed on Wednesday. Wire elements are usually set on ceramic basis with a minimum pull and, as a rule, covered by protective material, preventing them from influence of environment.
The construction of model platinum wire probe is shown on a fig. 1(a), and the temperature pickoff assembled on a surface on a fig. 1(b). Transducers with pellicle pickoffs (fig. 1, c), metallic foil, located on an insulating base, is used in which, are not so widespread, as wire, although the sphere of their use broadens constantly, as they have small sizes, improved dynamic reaction, higher sensitiveness and relatively subzero cost.
Platinum capacitance-resistance transducers usually join in one of shoulders of bridge of Óèòñòîíà, which high exactness of measuring is provided by means of. Certainly, not high resistance of device (about 100 Ohm) creates problems during his commutation with a measuring apparatus, as resistance of wires, connecting transformer with a measuring chart, can be commensurably with resistance of transformer.
Platinum resistance thermometers are now used everywhere. They are deservedly considered the most stable and reliable contact temperature sensors. However, in practice the accurate temperature measurements they came only in the 20th century. The first international practical temperature scale was adopted in 1887 BIPM scale hydrogen gas thermometer constant volume based on the fixed points of melting ice and boiling water. On this scale, was grawerowanie mercury-in-glass thermometer, which was then used for standards of length and to other areas where required accurate measurement of temperature. The extension of the range scale and search for carriers of the scale, convenient to use and provides good reproducibility and stability of measurement results that led to the creation of platinum resistance thermometers. The choice of platinum as the material for the reference resistance was due to the high corrosion resistance of this metal, chemical inertness, good ductility, ability to clean to a very high degree of purity. An important role is also played by the high resistivity of platinum and a high temperature coefficient of resistance.