SU369435A1 - METHOD OF DETECTION OF INFRINGEMENT OF THE INSULATION OF THERMAL ELECTRODES OF SURFACE TERMOPROP - Google Patents

Description

The invention relates to methods for measuring temperature using thermocouples and can be used to monitor the insulation state of thermocouples of thermocouples measuring the surface temperature of metal products (process units, equipment, etc.).

Due to the low mechanical strength of insulating materials, insulation often breaks down between one of the thermoelectrodes and metallic equipment, which is the appearance of a closed electric circuit through which thermoelectric current flows.

This current creates a voltage drop in the area of the thermoelectrode from the hot spa to the point where the insulation breaks down, which leads to a claim on the readings of the device connected to the surface thermonar.

It is impossible to detect timely deterioration of the insulation of thermoelectrodes of a surface thermocouple using a megohmmeter, since both thermoelectrodes in the area of the hot junction are electrically connected to the metal housing of the equipment.

Practically, the isolation violation is guessed only in the case of a sharp discrepancy between the readings of one of the thermocouples and the readings of the others.

2

The purpose of the invention is to ensure the operational monitoring of the insulation state of thermoelectrodes of the surface thermocouple and the timely detection of the degree of defectiveness of this insulation, as well as the determination of the magnitude of the error.

This is achieved by measuring the difference in thermo-emf. between the controlled surface thermocouple and the auxiliary thermocouples formed by the copper electrodes of the surface thermocouple with the metal of the armature, and but the deviation of the values obtained from the preliminary calibration trials obtained is about measured values.

FIG. 1 shows the occurrence of an error in the readings of a surface thermonar in violation of the insulation of its thermoelectrode; in fig. 2 - thermo-emf plots. surface thermocouples of its snomogenous thermocouples, formed by a thermoelectrodump with a metal equipment case.

Each surface thermocouple, consisting of two thermoelectrodes 1 and 2, with its hot junction 3 is caulked or welded to a metal surface 4, the temperature of which is measured.

The combination of a metal surface 4 with thermoelectrodes 1 and 2 can be considered as two auxiliary thermocouples with a well-defined dependence of temperature. on temperature. Thermoelectric power diagrams Auxiliary thermocouples are built using a control surface thermocouple, which is one of the surface thermocouples, but with enhanced and reliable insulation, guaranteed against accidental damage.

During the start-up of the technological unit from the cold state, it is possible to construct the dependence of thermopower. auxiliary thermocouple temperature, determined by the last control thermocouple.

In approximated form, graph 5 thermoelectric power. surface thermocouple and graphics 6 and

7termoe.ds Auxiliary thermocouples are shown in FIG. 2

Type of joint graphs of thermoelectric power. depends on the material of thermoelectrodes of surface thermocouples and on the metal, the temperature of which is measured (for example, for a chromel-alumine surface thermocouple with a steel case of the process unit).

To check the insulation of thermoelectrodes of any of the surface thermocouples, it is necessary to measure the thermopower. This surface thermocouple (terminals 8 and 5) and thermopower. its auxiliary thermocouples (terminals 9 and 10 and terminals 8 and //).

If the insulation of thermoelectrodes is not below the permissible level, then the measured thermoelectric power. (Eb, E, EG in fig. 2) for surface and auxiliary thermocouples are determined in the graphs of fig. 2 the same temperature t, equal to the temperature of the metal at the measuring point.

If the insulation breaks between one of the thermoelectrodes of the surface thermocouple and metallic equipment, for example, at point 12, a thermoelectric current will flow through a closed electric circuit, the value of which depends on the resistance value 13 of the insulation of thermoelectrodes.

In this case, points 3 and 12 create a voltage drop across the section of the thermoelectrode / meiad, which leads to a distortion of the readings of the potentiometer connected to the surface thermocouple (terminals

8 and .9) on one of the auxiliary (terminals 8 and J}). The readings of the potentiometer connected to the second auxiliary thermocouple (terminals 9 and 10) will remain undistorted.

Thermal emf (E), measured on an auxiliary thermocouple with a defective thermoelectrode (terminals 8 and 11), will determine on chart 7 a temperature t different from the temperature determined on schedule 6 using another auxiliary thermocouple (terminals 9,10).

In this case, an auxiliary thermocouple with a defective thermoelectrode will be on the thermopower curve. always determine the lower temperature relative to the actual one.

Thus, if auxiliary thermocouples are determined on thermopower diagrams. two different temnetureury, then the auxiliary thermocouple with a defective thermoelectrode will correspond to a lower temperature.

With loss of insulation by thermoelectrode / thermoelectric power. (fs), measured on a surface thermocouple (terminals 8-9), will determine on chart 5 the temperature t that is different from the actual one. In this case, the magnitude of the distortions of the indications of the surface thermocouple, which determines the degree of imperfection of the insulation of the thermoelectrode 1, can be determined according to the schedule of thermoelectric power, as the temperature difference determined by the surface thermocouple G and that auxiliary temperature which is greater than t.

Subject invention

The method of detecting the breakdown of the insulation of thermoelectrodes of a surface thermocouple by measuring thermoelectric power., Characterized in that, in order to timely determine whether a thermocouple is defective, and also to determine the magnitude of the error, the difference in thermal emf is measured. between the controlled surface thermocouple and auxiliary thermocouples formed by each of the electrodes of the surface thermocouple with the metal of the armature, measured values are measured by the deviation of the obtained values from the previously obtained calibration values.

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