Thermoconverters and devices of temperature
Use expansion thermometers, the thermoimpendence converters (TC), thermoelectric and manoyometrichesky thermoconverters and devices to temperature measurement. In the remote systems of transfer of indications with thermoimpendence converters and thermoelectroconverters use secondary devices — ratiometers, automatic bridges, millivoltmeters and potentiometers.
Thermometers of expansion serve for temperature measurement in rooms of fresh air, etc.
The sensing device represents the cylinder with liquid when which heating liquid extends and its column rises in the reading device.
The provision of the end of the column concerning the scale of the thermometer corresponds to temperature of the environment in which there is the cylinder.
Thermoimpendence converters (GOST 6651 — 78) apply in systems where it is required to take high temperatures and to remotely transfer indications. The principle of operation of such converters is based on property of metals to change the resistance at change of temperature.
Sensing devices of thermoconverters carry out from the playotina (TSP) or copper (TSM). The platinum or copper wire is reeled up on the framework. The framework sizes depending on the design of the termoyopreobrazovatel can be from 60 to 100 mm. The framework with the sensing device of 1 (fig. 1) is placed in the body of the protective armature made, as a rule, of stainless steel.
Wires pass in the isolating ceramic beads 3 and are connected to clips of the 5th head of the termoyopreobrazovatel of resistance. To the communication link the converter is connected through omental consolidation 4. On technology pipelines the converter is inserted into the slot and strengthened the union 6. Mounting length of thermoconverters is from 10 to 3150 mm, diameter of the protective armature — from 10 to 300 mm.
Direct current characteristics of transformation are standardized (GOST 6651 — 78) and express dependence of resistance of the sensing device on the taken temperature. The characteristic is designated 1P, 100P, 10M, 100M, etc. The number (1, 10, 100) designates sensing device resistance at 0 °C (1, 10, 100 Ohms), and the letter — sensing device material.
On measurement accuracy converters release five classes which designate Roman numerals. Platinum thermoimpendence converters apply to temperature measurement in the range minus 260 - plus 1100 °C, and copper - minus 200 - plus 200 °C.
Use of converters is limited both because of rather nizyoky maximum temperature, and because of the considerable sizes of the karyokas of the sensing device.
Thermoelectroconverters apply to temperature measurement in limits up to 1800 °C (GOST 6616 — 74).
Operation of the thermoelectroconverter is based on the following principle. If to solder two rods from different metals, and then soldered (hot) and the free (cold) ends to place on Wednesdays with different temperatures, then between the free ends of rods there is the potential difference. The free ends connect to the receiver of current and receive the electric circuit in which there is the source э. of the village Termoyoelektrodvizhushchaya t force. aa. of page in the chain depends on the difference of temperatures in which the free and soldered ends of the converter, and from properties of metals or alloys of which rods are made are placed.
In the industry use converters from the following alloys the chromel-kopel (CK), the chromel alumel (CA), the platinorody-platinum (PP), platinorody (30% of rhodium) - platinorodiya (6% of rhodium) (PR). Each type of the thermoelectric converter (HK, CA, software, PR) has the grading characteristic — dependence between razniyotsy temperatures hot and the cold ends and the t arising between them. aa. of page.
The thermoelectroconverter is arranged anayologichno to the thermoimpendence converter (fig. 2). The sensing device placed in the body 1 represents the seal of thermoelectrodes soldered to the silver disk (the hot end). Thermoelectrodes produce from the metals or alloys stated above. Thermoelectrodes are brought via channels of the isolating beads to clips of the head 3. To the body of devices or pipelines the thermoelectroconverter fix unions or flanyoets.
The complexity of use of thermoelectroconverters consists in need of stabilization of temperature of their free (cold) ends. If temperature of the cold ends, i.e. ambient air temperature, changes, and temperature taken in the point of immersion of the hot end will remain invariable, values of t. aa. of page will change too. The systems of measurement to fluctuations of temperature of the cold ends reach Nechuvstvitelyyonosti by thermostating of the cold ends of the thermoelectroconverter, electric compensation of temperature influences in the installation site of the thermoelectroconverter or electric compensation of temperature influences in the installation site of the secondary device.
Generally put into practice the last way at which the connecting line between the thermoelectroconverter and the vtorichyony device is mounted special compensation wires. For each type of the thermoelectroconverter the opredelenyony brand of compensation wires is established. At connection of cold konyots of the thermoelectroconverter to compensation wires between each thermoelectrode and the wire the additional termoyopara is formed. Materials of compensation wires and the way of their connection choose such that t. aa. of page of each additional thermocouple were equal among themselves and included opposite. In this case summaryony t. aa. of page will depend only on the difference of temperatures of hot konyoets of the thermoelectroconverter and the free ends of the compensation wires connected on the entrance of the secondary device. In the secondary priyobor install the device which automatically makes the amendment, to value of t. aa. of page depending on temperature at which there are free ends of compensation wires in the device. Manometric thermometers (GOST 8624 — 80) apply to temperature izmeyoreniye in zones of devices. The principle of their action is based on dependence between temperature and liquid pressure or gas at the fixed volume. The measuring system of the thermometer is filled with the zhidyokost or gas.
The thermocylinder 7 (fig. 3a) is submerged on Wednesday which temperayotura will be measured. By means of the capillary the 6th thermocylinder 7 is connected to the manometer 9. At change of temperature of the environment, the thermocylinder is submerged in kotoyory, pressure of the liquid filling system or gas changes. Through the capillary the 6th this pressure is brought to the pruzhiyena of 1 (fig. 3b) soldered to the body 8. At temperature increase of the termobalyolon the 7th pressure of the gas filling system increases and under its action the manometrical pruyozhina is untwisted. At reduction of temperature the spring respectively twists. Through draft the 4th movement of the end of the pruzhiyona is transferred to the tribko-sector mekhayonizm. The arrow 2 moving on the scale is got on axis 5 of the pinion it is proportional to change of pressure.Top