RU2373503C1 - Zero- thermostat of modified construction - Google Patents

Abstract

FIELD: measurement technology.

SUBSTANCE: this device refers to the measurement technologies and is used for temperature control of bearing junctions of differential thermocouple contacts. Device consists of cylinder chamber with transparent wall with low thermal conduction. It is filled with working substance in the solid phase initially. Thermoelectric module is fixed between two thermal plate made of the material with high thermal conduction and one of the plates is fixed at the upper base (hot junction) of thermoelectric module, and the other has good thermal contact with the bottom base of the thermoelectric module (measuring junction). The heat from the hot junction of the thermoelectric module is brought by the heat-conducting plate to the upper base of the cylindrical chamber, and the measuring junction of the thermoelectric module cools the bottom base of the cylindrical chamber. The construction is located in heat insulating jacket, bypass pipe is used to compensate the changes in volume during phase transfer of the working substance.

EFFECT: invention improves the security of the construction and accuracy of temperature control during long operation.

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Description

The invention relates to measuring technique and is used for thermostating control junctions of differential thermocouples.

Differential thermocouples are widely used in various fields of science and technology and are distinguished by good technical characteristics. Their disadvantages include the need for thermal stabilization of the reference junctions in order to achieve high accuracy of measurements - their reference junction should be in conditions with a known temperature, as a rule, the melting point of ice (0 ° C) is chosen as the reference point. Several designs are known that allow thermostatting of reference junctions of differential thermocouples.

The principle of the design [1] is based on the use of a small-sized mercury relay, which is included in the on-off regulation circuit. The disadvantage is the high dependence of the accuracy of temperature maintenance on the accuracy of the sensor. The principle of operation of another thermoelectric system [1] is based on recording changes in the volume of water during its transition to the solid phase, for which a contact relay is used, which responds to changes in volume. The disadvantages of both designs are the large dimensions of the devices, the complexity of the control circuit and design.

A more successful solution is based on the placement of the reference junction of a differential thermocouple at the interface between the solid and liquid phases of the substance. A small-sized precision zero-thermostat [2] consists of a double-walled cylindrical chamber, the internal volume of which is filled with distilled water. The thermoelectric module is fixed by a cold junction to the upper base of the chamber and supplies heat from the hot junction to the lower base, which contributes to the formation of solid and liquid phases of water and their interface in the internal volume. However, this approach has a number of drawbacks, among them - the presence of significant convective fluxes that lead to a decrease in thermostatting accuracy, which is due to the design feature, and also contributes to uneven washing out of the lower edge of the ice mass, which reduces the positioning accuracy of the input differential junction of the differential thermocouple. The use of a free-floating float structure during long-term operation causes changes in the direction of ice growth and contributes to the appearance of the slope of the float, the displacement of the reference junction from the phase interface or freezing of the float from the sides and bottom. The device [2] allows you to organize one channel for measuring temperature, which, along with the difficulty of replacing thermostatically controlled junctions due to design limitations, is its significant disadvantages.

The aim of the invention is to eliminate the noted drawbacks and develop a null thermostat with a modified design, characterized by increased accuracy of temperature control by eliminating the influence of convective flows in the liquid phase, the ability to continuously operate in a long period of time, allowing simultaneous temperature control of several reference junctions, as well as their rapid replacement due to the presence of a number of design solutions that are easy to implement and lead to an increase in device reliability.

The device consists of a cylindrical chamber 3 having transparent walls with low thermal conductivity and filled with a working substance 4, which is initially in the solid phase. The thermoelectric module 2 is fixed between two heat-conducting plates 9 and 10 made of material with high thermal conductivity, and the plate 9 is fixed at the upper base (hot junction) of the thermoelectric module, plate 10 is in good thermal contact with the lower base of the thermoelectric module (cold junction) . The design is such that the heat from the hot junction of the thermoelectric module 2 is supplied through the heat-conducting plate 9 to the upper base of the cylindrical chamber 3, and by the cold junction of the thermoelectric module 2 through the heat-conducting plate 10, the lower base of the cylindrical chamber 3 is cooled. To reduce the influence of external factors, including reducing heat transfer with the environment, the design is placed in a heat-insulating casing 1, which is a cylindrical chamber Made of a transparent material in the optical frequency range with low thermal conductivity. To compensate for changes in the volume during phase transitions of the working substance, a branch tube 8 is used. The conductors of the supporting units of differential thermocouples 7 are placed on the clamping structure 6 of a material not wetted by water and having a density lower than the density of the liquid phase of the working substance 4, as a result of which thermocouple junctions 7 are located near the interface between the solid and liquid phases of the working substance 4. The conductors of thermostatically controlled thermocouple junctions are brought out through the outlet tube 8.

When the power of the thermoelectric module 2 is turned on, the process of ice melting in the cylindrical chamber 3 begins, and a phase boundary 5 is formed, which lies along the lower base of the clamping structure 6. The heat energy released on the hot junction of the thermoelectric module 2 is supplied through the heat-conducting plate 9 to the upper base the inner cylindrical chamber 3, and by means of a cold junction of the thermoelectric module 2, heat is absorbed from the lower base of the cylindrical chamber 3 using heat the supply plate 10. As a result of the operation of the thermoelectric module, the working substance 4 is heated in the chamber 3 on one side (above) and cooled on the other side (below). As a result of this, a phase boundary 5 is constantly present in the chamber, while the control junctions 7 of the differential thermocouples are constantly located at an ice melting temperature of 0 ° C.

The device allows thermostatic control junctions of several thermocouples to be simultaneously controlled, provides high reliability and thermostatting accuracy during continuous and long-term operation due to the use of a design that excludes the appearance of convective flows, and allows quick replacement of thermostatically controlled reference junctions of differential thermocouples. The device is small in size and easy to manufacture; it can be mass-produced together with differential thermocouples calibrated at the manufacturer.

LITERATURE

1. Kolenko EA Thermoelectric cooling devices. Moscow-Leningrad. Publishing House of the Academy of Sciences of the USSR. 1963, p. 135.

2. RF patent No. 2215270. Ismailov T.A., Aminov G.I., Evdulov O.V., Yusufov Sh.A. "Precision small-sized zero thermostat."

Claims (1)

A modified design null-thermostat containing external and internal cylindrical chambers, a thermoelectric module, a clamping structure made of a material with a density greater than the density of water and not wetted by water, on which thermostatted reference junctions of differential thermocouples are mounted, the conductors of which are brought out, an opening or a branch a tube for replacing thermocouples during operation and compensating for changes in the volume of the working substance during its phase transitions, with external and internal The cylindrical chambers are made of a material with high thermal conductivity, distilled water is located inside the inner cylindrical chamber, separated by a phase boundary into solid and liquid phases, while the clamping structure is in the ice melting (freezing) zone, the thermoelectric module is installed with the possibility of thermal contact with its junctions with the upper and lower bases of the inner cylindrical chamber, wherein the outer cylindrical chamber is in contact with the inner cylindrical chamber, characterized by Ie, that the hole or outlet pipe for replacing thermocouples during operation and compensating for changes in the volume of the working substance during its phase transitions is located at the upper base of the external cylindrical chamber, the thermocouple conductors are led out through the specified hole or outlet tube, while the external cylindrical chamber contains two heat-conducting plates, between which a thermoelectric module is fixed, and the contact of the thermoelectric module with the upper and lower bases provides Using these heat-conducting plates, the walls of the outer and inner cylindrical chambers are made transparent, and the thermoelectric module is located at an equal distance in the vertical plane from the lower base of the cylindrical chamber, as is its geometric center.