RU2328708C1 - Compact zero-thermostat with regulated thermal current - Google Patents

Abstract

FIELD: measuring techniques.

SUBSTANCE: zero-thermostat consists of an external cylindrical case, made from material with high thermal conductivity. A thermo-electric module is joined to the upper base on the inner side by a hot junction. The cold junction of the thermoelectric module is in good thermal contact with the cylinder case, made from material with high thermal conductivity. Inside the case, there is distilled water, a solid and liquid phase section. A ring shaped bob floats freely in the liquid phase, with surface made from material that can not be washed away by water. At the centre of the bob, there is a reference junction of a differential thermocouple, which should be kept at 0°C. The reference junction of the thermocouple is fixed to the centre of the bob by two thin caproic threads. The quantity of heat, taken to the lower base of the cylindrical case, is regulated through the action of a fan with an adjustable speed of rotation, fixed to the upper base of the external cylindrical case, which allows for maintaining the position of the borders of the phase section on a given level.

EFFECT: increased accuracy of temperature control of reference junctions of differential thermocouples, longer period of continuous operation.

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Description

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

In industry and laboratory practice, differential metal thermocouples are commonly used for remote temperature measurements. As is known, 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 the thermocouples are placed in melting ice having a temperature of 0 ° C.

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

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 disadvantage is the dependence of the phase boundary position on the accuracy of the device design, temperature, humidity and other environmental parameters, which contributes to the displacement of the phase boundary beyond the permissible limits with time and limits the term of continuous operation of the null thermostat due to complete freezing / melting of the working substance (distilled water) in the internal volume of the cylindrical chamber.

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 surface of which is made of a material not wetted by water. 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). The fan 10 is attached to the upper base of the outer cylindrical chamber.

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 unfrozen 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 amount of heat supplied to the lower base of the cylindrical chamber is controlled by the action of the fan 10 with a variable speed. The rotation speed of the fan 10 is calculated so that at an ambient temperature of + 25 ° С the phase boundary 5 is located in the geometric center of the inner cylindrical chamber 3. When the phase boundary 5 is shifted along the vertical axis due to a change in the environmental parameters, the fan speed 10, which leads to a change in the amount of heat supplied to the lower base of the inner cylindrical chamber 3 so that the position of the phase boundary 5 remains unchanged.

This device is easy to manufacture, reliable in operation and provides high accuracy of temperature maintenance. The device has small dimensions and is not expensive to manufacture; it can be produced in series, along with differential thermocouples calibrated directly at the manufacturer.

Information sources

1. Kolenko EA Thermoelectric cooling devices. M.-L.: Publishing House of the USSR Academy of Sciences. 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)

Small-sized null-thermostat with adjustable heat flux, containing a tank filled with melting ice, brought into thermal contact with a cold junction of a thermoelectric module, hot junction coupled to a radiator, with a tank, which is a cylindrical chamber made of a material with high thermal conductivity, inside of which there is distilled water separated by a phase boundary into solid and liquid phases, where in the liquid phase there is an annular float made of a material having a density it is less 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 thin nylon threads fixed at its ends on the float, while the control junction of the differential thermocouple due to the buoyant force acting on the float, constantly located in the freezing (thawing) zone of ice, and the thermoelectric module by cold junction is brought into thermal contact with the upper base of the cylindrical chamber, and OP is an external 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 a fan is fixed on the upper base of the outer cylindrical chamber, so that a change in its rotation speed changes the amount of heat, supplied to the lower base of the inner cylindrical chamber, so that the amount of heat supplied to the lower base of the inner cylindrical chamber remained unchanged.

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