The thermometer which is carried out by this principle represents the coil of inductance in which in rather uniform field the sample from mednokaliyevy or zhelezoalyu-miniyevy alum is placed. The coil turns on in a bridge chain, and temperatures, defiant change of . a sample, leads to the change of inductance of the coil proportional to the taken temperature.
From precious metals often apply nonmetallic pipes to thermocouples (quartz, porcelain etc.), however such pipes are mechanically fragile and expensive. Porcelain pipes of structure can be used at temperatures up to 1300 — 1400 °C.
conclusions in order that it was possible to carry out its inclusion in a chain of two - three - or the four-wire line. Platinum thermometers may contain two thermoresistors which output sizes are used in various purposes in one case. For special applications also small-sized thermometers of resistance are issued.
The lengthening thermoelectrodes from copper and an alloy of TP forming the thermoidentical to the thermocouple of platinorodiya — platinum in limits to 150 °C are applied to the thermocouple of platinorodiya — platinum. The same lengthening thermoelectrodes with the changed signs of polarity apply to the thermocouple tungsten — molybdenum. For the thermocouple — alumel thermoelectrodes are produced from copper and a constantan. For the thermocouple — a thaw thermoelectrodes, but executed in the form of flexible wires are lengthening.
Nonlinearity of the characteristic and technological dispersion of parameters of thermoresistors complicates receiving linear scales of thermometers, creation of multichannel devices, ensuring the interchangeability of thermoresistors necessary at mass production of thermometers with thermoresistors. To improve a type of a scale and to provide interchangeability of thermoresistors, it is necessary to apply the special unifying and linearizing chains, both passive, and active.
Parasitic ‑... arise owing to existence of not odes-norodnostey in materials and according to the data provided in work can make for various materials 10 — 100. In particular, for a platinum wire at the extent of a of temperature of 30 mm and a temperature gradient 30 To/mm size parasitic ‑... makes 10.
The modern thermodynamics determines temperature as the size expressing a condition of the internal movement of equilibrium macroscopic system and determined by internal energy and external parameters of system. Directly temperature cannot be taken, it is only possible to judge it on the change of external parameters caused by violation of an equilibrium state thanks to heat exchange with other bodies.
Applying protective pipes from carbide of silicon and graphite, it is necessary to consider that when heating they emit the restoring gases; therefore the thermocouples placed in them (especially thermocouples on platinum bases have to be protected by in addition gas-tight cover.
The error caused by change of temperature of the line, the thermocouple and the index. In thermoelectric thermometers for measurement ‑... apply both usual millivoltmetra, and the low-impedance compensators with a manual or automatic equilibration on. a measurement limit to 100 mV.
The converter which principle of action is based on thermal processes and which natural entrance size is temperature is called thermal. Thermocouples and thermoresistors belong to such converters, metal and semiconductor. The main equation of thermal transformation is the equation of thermal balance which physical sense is that all heat arriving to the converter goes for increase of its heat content of QTC and, therefore, if heat content of the converter remains invariable (temperature and a modular state, amount of heat arriving in unit of time does not change it is equal to amount of the given heat. Heat arriving to the converter is the sum of the amount of heat of Qel created as a result of allocation in it the electric power, and amount of heat of Qto coming to the converter or given them as a result of heat exchange with environment.
Thermoresistors of the MMT-4 and KMT-4 types are put into capsules and pressurized thanks to what they can be used in the conditions of any humidity and even in liquids, being aggressive concerning the thermoresistor case.