RU2313771C1 - Compact zero-thermostat - Google Patents

Abstract

FIELD: the invention refers to measuring technique particularly to thermostatic arrangements for control of soldered joints of thermocouples.

SUBSTANCE: a zero-thermostat has an exterior cylindrical chamber fulfilled out of material with thermal conductivity. A thermal electrical module is joined to the upper foundation from the inner side with a hot soldered joint. The cold soldered joint of the thermal electrical module is in a good thermal contact with the cylindrical chamber fulfilled out of material with high thermal conductivity. Inside the chamber there is distilled water divided with the frontier of division on solid and liquid phases.

EFFECT: increases accuracy of thermostatic control of soldered joints of differential thermocouples and reliability in interpretation of conducted measurement.

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Description

The invention relates to measuring equipment, in particular to a thermostatic control device for control junctions of differential thermocouples.

In industry and laboratory practice, differential metal thermocouples are commonly used for remote temperature measurements. As you know, a differential thermocouple has a so-called control junction, which should be at a constant temperature. Usually, for the convenience of reading the values of the measured temperature, the control junctions of thermocouples are placed in melting ice at a temperature of 0 ° C.

In some cases, the use of melting ice is associated with certain operational inconveniences. In this regard, several variants of thermoelectric zero thermostats have been developed that ensure that the temperature is maintained at 0 °.

A known design of a null thermostat, the automatic maintenance of the temperature inside the working chamber of which is carried out by a special on-off control circuit, the temperature sensor of which is a small-sized mercury relay [1]. The disadvantage of this device is that the accuracy of temperature control depends on the accuracy of the sensor, as well as the complexity of the design and electrical circuit.

Known thermoelectric device with higher accuracy [1]. Automatic maintenance of temperature at 0 ° C in this device is based on a change in the volume of water when it freezes. This change in volume is recorded by a highly sensitive contact relay included in the control circuit, similar to that used in the previous device. Disadvantages: complex control scheme; complex device design; large dimensions.

A fairly successful solution is the approach in which the control junction of the differential thermocouple is located at the interface between the solid and liquid phases of the substance.

The small-sized precision zero-thermostat [2] implementing this approach consists of a double-walled cylindrical chamber, the internal volume of which is filled with distilled water. The thermoelectric module, fixed by a cold junction to the upper base of the chamber and supplying heat from the hot junction by means of a heat pipe to the lower base, is used to form the solid and liquid phases of water and their interface in the internal volume. The reference junction of the differential thermocouple is brought to the interface between the solid and liquid phases using a float design.

The design drawback is the difficulty in determining and indicating the current position of the phase boundary, which can lead to incorrect interpretation of the results of the measurements with the complete penetration of the solid phase or the complete freezing of the liquid phase of the working substance.

The aim of the invention is to eliminate the above disadvantages. To achieve this goal, a precision small-sized zero-thermostat is proposed, the design of which is shown in figure 1. The device consists of an external cylindrical chamber 1 made of a material with high thermal conductivity, the thermoelectric module 2 is attached to the upper base of the inner junction from the hot junction 2. The cold junction of the thermoelectric module 2 is in good thermal contact with the inner cylindrical chamber 3 made of a material with high thermal conductivity, in which the side wall has elasticity due to the small thickness. Inside the chamber 3 there is distilled water 4, divided by a phase boundary 5 into solid and liquid phases, where an annular float 6 freely floats in the liquid phase, the outer surface of which is made of a material not wetted by water, and the inner volume is filled with a material with high magnetic conductivity. In the center of the float is a control junction of the differential thermocouple 7, which must be maintained at a temperature of 0 ° C. The findings of the control junction of the thermocouple 7 through a special seal 8 brought out of the device. The control junction of the thermocouple 7 is fastened in the center of the float 6 by means of two thin nylon threads 9 fixed at their ends on the float and intersecting at its center (Fig. 2). An inductor 10 is mounted on the side wall of the inner cylindrical chamber 3 on one side, and an inductor 11 with side taps a, c and a central tap b is installed on the opposite side. The findings of the coil 10 are connected to the output of the master oscillator ZG, and the conclusions from the coil 11 are connected to the inputs of the measuring module MI, which is connected with the display device UI (figure 3).

The principle of operation of the proposed thermoelectric null thermostat is as follows. When the power of the thermoelectric module 2 is turned on, the process of freezing water in a thin-walled cylindrical chamber 3 begins and a phase boundary 5 of frozen and not frozen water is formed. The buoyant force acting on the float 6 presses the latter against the phase boundary 5, as a result of which the float is in the freezing (melting) zone of the water (i.e., at 0 ° C). The thermal energy released on the hot junction of the thermoelectric module 2 is transmitted through the walls of the outer cylindrical chamber 1 to the lower base of the thin-walled cylindrical chamber 3. As a result of the thermoelectric module, water 4 is heated in chamber 3 on one side (bottom) and cooled on the other side ( on top). As a result of this, a phase boundary 5 is constantly present in chamber 3, and the control junction 7 of the differential thermocouple is constantly located at the ice melting temperature, i.e. 0 ° C. The increase in the volume of distilled water 4 as a result of the phase transition is compensated by the elastic walls of the chamber 3.

The master oscillator ZG generates a sinusoidal signal with a frequency significantly higher than the upper cutoff frequency of the passband of the used temperature measuring device. At the same time, current flows through the coil 10 and a magnetic flux is created that intersects the coils of the coil 11, the frequency of which coincides with the frequency of the output signal from the master oscillator ZG. The float 6, the internal volume of which is made of a material with high magnetic conductivity, is used as a movable core between the coils 10 and 11 so that they together form a transformer. In this case, each possible position of the float in the internal volume unambiguously corresponds to a certain voltage value, measured with the help of the MI between the leads a-b and b-c of the inductor 11. In this way, the current position of the float, and therefore the phase boundary in the internal volume of the cylindrical chamber, is recorded 3. The display of the current position of the phase boundary is carried out using MD.

This device is easy to manufacture, reliable in operation and provides high accuracy of temperature maintenance. Using a system for measuring the current position of the phase boundary can reduce the likelihood of incorrect interpretation of the results of measurements. Since the device is small in size and inexpensive to manufacture, it can be mass-produced, along with differential thermocouples calibrated directly 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 small null thermostat containing a container filled with melting ice, brought into thermal contact with a cold junction of a thermoelectric module, hot junction coupled to a radiator, with a capacity representing a cylindrical chamber made of a material with high thermal conductivity, inside which there is distilled water, divided the boundary between the phases into solid and liquid phases, where in the liquid phase there is an annular float made of a material having a density lower than the density of water and not wetted by it, in the center of which there is a control junction of the differential thermocouple, which is fastened by means of thin kapron threads fixed with its ends on the float itself, while the control junction of the differential thermocouple is constantly in the freezing zone due to the buoyant force acting on the float ( thawing) of ice, and the thermoelectric module by cold junction is brought into thermal contact with the upper base of the cylindrical chamber, and the radiator is an external circuit an cylindrical chamber made of a material with high thermal conductivity in contact with its lower base with the lower base of the cylindrical chamber with melting ice, characterized in that two inductors are installed on the outer wall of the inner cylindrical chamber in such a way that the magnetic flux from the first of them crosses the turns of the second coil, while together with the float, the internal volume of which is made of a material with high magnetic conductivity, they form a transformer, the primary winding of which connects It is connected to the master oscillator, and the leads from the secondary winding are connected to the measuring module connected to the indicating device.

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