RU227175U1 - Thermoelectric converter - Google Patents

Abstract

The utility model relates to thermometry and can be used to improve the accuracy of temperature measurements using thermoelectric temperature converters (thermocouples). The thermoelectric converter includes two thermocouples, which are placed inside an electrically insulating tube; according to the utility model, each thermocouple consists of two thermoelectrodes with standardized thermoelectric characteristics, and the working junctions of the thermocouples are combined into a common working junction, which ensures electrical contact of the thermoelectrodes of each thermocouple. The technical result of the utility model is to improve the quality of thermal technological processes by increasing the accuracy of process temperature control.

Description

The utility model relates to thermometry and can be used to improve the accuracy of temperature measurements using thermoelectric temperature converters (thermocouples). When operating thermocouples, under the influence of various production factors, a drift occurs in the thermoelectric properties of the thermoelectrode materials in the thermocouple. In turn, this causes the actual static characteristic of the thermocouple to deviate from the nominal static characteristic, which reduces the accuracy of temperature measurement.

The following devices are known to improve the accuracy of temperature measurement using thermoelectric converters.

A thermoelectric converter is known (RF patent No. RU 94700 U1, class G01K 7/02, G01K 15/00, 2010), containing one or two working thermocouples, structurally made in one protective case and an additional channel inside the protective case, in which there can be a reference thermocouple is placed. Periodic installation of a reference thermocouple allows you to compare the readings of the working and reference thermocouples, as well as correct the resulting deviation in the readings of the working thermocouple. The disadvantage of this approach is the difficulty of assessing the accuracy of thermocouples located in hard-to-reach places, as well as the periodic nature of assessing the accuracy of temperature measurement.

There is a known temperature meter with self-diagnosis of malfunctions of sensitive elements during operation (RF patent No. RU 86306 U1, class G01K 7/04, 2009), containing three series-connected temperature-sensitive elements (the first thermocouple, a thermoresistance and a second thermocouple), and the working junctions of the thermocouples are connected with corresponding thermal resistance terminals. Thermal resistance measurement is performed using a four-wire circuit using thermocouples as conductors to supply current and measure voltage. As a result, the temperature meter allows you to obtain three temperature values: from the first and second thermocouples, as well as from the thermal resistance. The disadvantage of this solution is the limited temperature measurement range (up to 600°C when using thermal resistances), as well as the influence of the current passed through the thermocouple thermoelectrodes on the accuracy of temperature measurement.

The design of a thermoelectric converter consisting of three thermoelectrodes is known (US patent No. US 6239351 B1, class H01L 35/28, 2001). The inventive converter includes a thermocouple made of materials with standardized thermoelectric characteristics (for example, chromel-alumel) and an additional reference thermoelectrode made of a stable material (for example, platinum), which are combined into a single working junction. The proposed design allows, in addition to measuring the thermoelectromotive force (TEMF) value of the thermocouple, to obtain two additional TEMF measurements for each temperature measurement. Additional thermal electromotive force occurs in pairs of thermoelectrodes formed between the thermocouple thermoelectrodes and the reference thermoelectrode (for example, chromel-platinum, alumel-platinum). The algorithm for assessing the measurement accuracy for a given three-electrode transducer is based on comparing the values of additional thermoelectric forces with the reference values obtained during preliminary calibration of the transducer. The disadvantage of this approach is the need for individual calibration of each three-electrode converter used to obtain a table of reference values of additional thermoelectric forces and the absence of a method for increasing the accuracy of temperature measurement using the proposed thermoelectric converter design.

The closest to the claimed utility model is a three-electrode thermoelectric converter (patent RU 2 129 708 C1, IPC G01K 15/00, G01K 7/02, publ. 04/27/1999), which consists of a thermocouple with standardized thermoelectric characteristics and an additional thermoelectrode made of resistant influencing factors of material production. The working junction of the thermocouple is combined with an additional thermoelectrode, while along the length of the thermoelectric converter the thermoelectrodes are electrically isolated from each other. As a result, a three-electrode thermoelectric converter allows one to measure one main and two additional TEMF values, from each of which the temperature is calculated. Temperature calculation based on the thermoelectric power of the main thermocouple and additional thermoelectrode pairs is performed using inverse conversion functions obtained during individual calibration of the thermoelectric converter. To assess the accuracy of temperature measurement using this thermoelectric converter, the obtained calculated temperatures for the main thermocouple and additional thermoelectrode pairs are compared. The disadvantage of the proposed solution is the need for individual calibration of each three-electrode thermoelectric converter before operation in order to obtain inverse conversion functions for calculating temperatures for additional thermoelectrode pairs.

The purpose of the utility model is to increase the accuracy of temperature measurement using a thermoelectric converter without preliminary calibration of each individual thermoelectric converter.

The technical result of the utility model is to improve the quality of thermal technological processes by increasing the accuracy of process temperature control.

The claimed technical result is achieved by measuring temperature using the claimed thermoelectric converter, including two thermocouples, which are placed inside an electrically insulating tube, characterized in that each thermocouple consists of two thermoelectrodes with standardized thermoelectric characteristics, and the working junctions of the thermocouples are combined into a common working junction, providing electrical contact of thermoelectrodes of each thermocouple.

The essence of the utility model is illustrated by graphic materials, where:

fig. 1 - diagram of a thermoelectric converter;

fig. 2 - an example of connecting a thermoelectric converter to a measuring transducer and performing measurements;

fig. 3 - test results of the utility model.

The thermoelectric converter (Fig. 1) consists of two thermocouples with standardized thermoelectric characteristics. The first thermocouple includes thermoelectrodes A and B, the second thermocouple includes thermoelectrodes C and D. For each of the thermocouples, their nominal static characteristics are known and standardized - the dependence of the thermoelectromotive force (TEMF) on temperature. The thermocouples are placed inside an electrically insulating tube 1, which ensures that there is no electrical contact between the thermocouple thermoelectrodes. The working junctions of thermocouples AB and CD are combined into a common working junction 2, which provides electrical contact of all thermoelectrodes at one point, and allows the formation of a thermoelectric converter with the following pairs of thermoelectrodes: AB, CD, AC, AD, BC, BD.

The thermoelectric converter works as follows.

According to the theory of thermoelectricity (Rogelberg, I.L. Alloys for thermocouples / I.L. Rogelberg, V.M. Beilin. - M.: Metallurgy, 1983), thermocouple TEMF occurs independently in each thermoelectrode

(1)

Where - temperatures of the working and free junctions of thermocouple AB, respectively; - absolute thermoelectric power of materials of thermoelectrodes A and B, respectively; - integral thermoelectric power of each thermoelectrode, which occurs when the temperature differs from before along the thermoelectrodes.

By combining the working junctions of two thermocouples into a common junction, it becomes possible to measure the TEMF vector

, (2)

where AB and CD are pairs of thermoelectrodes with normalized thermoelectric characteristics (main thermoelectrode pairs); AC, AD, BC, BD - additional thermoelectrode pairs that arise when two thermocouples are combined with a common junction.

Temperature calculations for the main thermoelectrode pairs AB and CD are performed using normalized inverse conversion functions, for example, according to GOST 8.585-2001. Temperature calculations for additional thermoelectrode pairs AC, AD, BC, BD can be performed using the calculated inverse conversion functions. The coefficients of the calculated inverse functions are determined based on the tabulated values of the thermoelectric power of individual thermoelectrodes relative to the reference thermoelectrode using the least squares method (for example, based on data from Thermocouple reference tables based on IPTS-68 - National Bureau of Standards, 1974).

The calculated temperature values are combined into a vector: Calculation of temperature measurement result in the proposed thermoelectric converter is carried out on the basis of the vector as a weighted average

, (3)

Where - weight of the temperature value of each th thermoelectrode pair as part of a thermoelectric converter. Weight values can be assigned based on reference data or calibration certificates from the thermoelectrode wire manufacturer, depending on the sensitivity of each thermoelectrode pair.

The useful model can be implemented, for example, for the following combinations of thermocouples with normalized thermoelectric characteristics in the medium temperature range: chromel-alumel-nichrosil-nisil (HANN), chromel-copel-iron-constantan (CCZhK), chromel-alumel-chromel-copel ( HAHK). A four-channel aluminum oxide straw is used as an electrical insulating tube.

An example of connecting a thermoelectric converter to a measuring transducer is shown in Fig. 2, where the precision signal converter “TERKON” was used as a measuring transducer (https://termexlab.ru/#!/ru/product/terkon-preobrazovatel-signalov-ts-i-tp-pretsizionnyij-252000/). Each pair of thermoelectrodes is connected to a separate measuring channel “TERKON”, which carries out synchronous measurement of the TEMF vector according to (2).

The test results of the thermoelectric converter HANN in accordance with the claimed utility model (Fig. 3) confirm the increase in the accuracy of temperature measurement relative to individual thermocouples XA and NN. Table 1 (Fig. 3) shows the comparison of the measurement result with temperatures And for two thermocouples as part of a thermoelectric converter. Actual working junction temperature and free junction measured using reference thermocouples. As a result, the resulting deviation from the actual temperature of the working junction at a given free junction temperature less than deviation And .

Claims (1)

A thermoelectric converter comprising two thermocouples, which are placed inside an electrically insulating tube, characterized in that each thermocouple consists of two thermoelectrodes with standardized thermoelectric characteristics, and the working junctions of the thermocouples are combined into a common working junction, providing electrical contact of the thermoelectrodes of each thermocouple.