阅读说明：本技术 一种建立超低频电压标准及实现量值传递的系统及方法 (System and method for establishing ultralow frequency voltage standard and realizing magnitude transmission ) 是由 石照民 潘仙林 张江涛 宋�莹 丁香 王嵘瑜 于 2019-09-23 设计创作，主要内容包括：本发明涉及一种建立超低频电压标准的方法,基于双加热丝热电变换器输出热电势的平方特性,建立超低频电压交直流转换系统,实现两路幅值相等的正交低频电压信号与直流电压的等效转换,将超低频电压溯源到直流电压标准,建立超低频电压标准,解决了10Hz以下交流电压无法实现交直流转换的难题,为10Hz以下的交流电压测量提供了溯源标准。本发明还结合差分采样系统,以其中一路低频电压为参考标准,通过差分采样测量被测低频电压与超低频电压标准之间的差值对被测低频电压进行校验,实现了超低频电压标准的量值传递。(The invention relates to a method for establishing an ultralow frequency voltage standard, which is characterized in that an ultralow frequency voltage alternating current-direct current conversion system is established based on the square characteristic of thermoelectric potential output by a double-heating-wire thermoelectric converter, equivalent conversion between two paths of orthogonal low frequency voltage signals with equal amplitude and direct current voltage is realized, the ultralow frequency voltage is traced to the direct current voltage standard, the ultralow frequency voltage standard is established, the problem that alternating current-direct current conversion cannot be realized by alternating current voltage below 10Hz is solved, and the tracing standard is provided for alternating current voltage measurement below 10 Hz. The invention also combines a differential sampling system, takes one path of low-frequency voltage as a reference standard, and verifies the measured low-frequency voltage by measuring the difference value between the measured low-frequency voltage and the ultra-low frequency voltage standard through differential sampling, thereby realizing the magnitude transmission of the ultra-low frequency voltage standard.)

1. The ultralow-frequency voltage alternating current-direct current conversion system comprises an upper computer (1), a direct current voltage source (2), a standard direct current voltmeter (3), an orthogonal signal generator (4), a first follower (5), a second follower (6), a first alternating current-direct current conversion switch (7), a second alternating current-direct current conversion switch (8), a double-heating-wire thermoelectric converter (9) and a nanovolt meter (10), wherein the upper computer (1) is respectively connected with the direct current voltage source (2), the direct current standard voltmeter (3), the orthogonal signal generator (4), the first alternating current-direct current conversion switch (7), the second alternating current-direct current conversion switch (8) and the nanovolt meter (10) through an IEEE-488 bus to realize system automation control, and the orthogonal signal generator (4) is respectively connected with the first alternating current-direct current conversion switch (7) through the first follower (5) and the second follower (6), The second alternating current-direct current conversion switch (8) is connected, the direct current voltage source (2) is respectively connected with the direct current standard voltmeter (3), the first alternating current-direct current conversion switch (7) and the second alternating current-direct current conversion switch (8) are connected with the double-heating-wire thermoelectric converter (9), and the double-heating-wire thermoelectric converter (9) is connected to the nano-volt meter (10).

2. A method for establishing an ultra low frequency voltage standard using the ultra low frequency voltage ac to dc conversion system of claim 1, comprising the steps of:

A. the upper computer (1) controls the orthogonal signal generator (4) to output two paths of orthogonal low-frequency voltage signals U with equal amplitude_AAnd U_BThe direct current voltage source (2) outputs a positive direct current voltage signal U_DC+；

B. The upper computer (1) controls the first alternating current-direct current conversion switch (7) and the second alternating current-direct current conversion switch (8) to be switched to an alternating current state;

C.U_Aand U_BThe signals are respectively input into a first alternating current-direct current conversion switch (7) and a second alternating current-direct current conversion switch (8) after passing through a first follower (5) and a second follower (6), and are input into a double-heating-wire thermoelectric converter (9) after passing through the first alternating current-direct current conversion switch (7) and the second alternating current-direct current conversion switch (8);

D. reading thermoelectric potential E output by the double-heating-wire thermoelectric converter (9) by the nano-volt meter (10)_a1；

E. The upper computer (1) controls the first alternating current-direct current conversion switch (7) and the second alternating current-direct current conversion switch (8) to be switched to a direct current state;

F. the standard DC voltmeter (3) measures the DC voltage signal U_DC+Amplitude, U_DC+The power is respectively input into a thermoelectric converter (9) with double heating wires after passing through a first alternating current-direct current conversion switch (7) and a second alternating current-direct current conversion switch (8);

G. reading thermoelectric potential E output by the double-heating-wire thermoelectric converter (9) by the nano-volt meter (10)_d+；

H. The upper computer (1) controls the direct current voltage source (2) to output a negative direct current voltage signal U_DC-Wherein U is_DC-＝-U_DC+Measuring a DC voltage signal U by a standard DC voltmeter (3)_DC-Amplitude, U_DC-Respectively pass through a first AC/DC conversion switch (7) and a second AC/DC conversion switch (8) and then are outputEntering a double-heating wire thermoelectric converter (9);

I. reading thermoelectric potential E output by the double-heating-wire thermoelectric converter (9) by the nano-volt meter (10)_d-；

J. The upper computer (1) controls the first alternating current-direct current conversion switch (7) and the second alternating current-direct current conversion switch (8) to be switched to an alternating current state;

K. reading thermoelectric potential E output by the double-heating-wire thermoelectric converter (9) in an alternating current input state by a nano-volt meter (10)_a2；

L. comparison E_a1+E_a2And E_d++E_d-When E is large or small_a1+E_a2＝E_d++E_d-Then low frequency voltage signal U_AAnd U_BThe effective value U is obtained by calculation according to the formula (1)

M, when E_a1+E_a2≠E_d++E_d-The dc voltage is adjusted by equations (2) and (3):

and repeating the processes A to M until E is guaranteed_a1+E_a2＝E_d++E_d-At this time, the low-frequency voltage signal U_AAnd U_BThe effective value U is obtained by calculation according to the formula (4)

Therefore, equivalent conversion between the ultralow frequency alternating voltage and the direct current voltage is realized, the alternating current voltage is traced to the direct current voltage standard, and the ultralow frequency alternating current voltage standard is established.

3. An ultralow-frequency voltage standard magnitude transfer system comprises an upper computer (1), a direct-current voltage source (2), a standard direct-current voltmeter (3), an orthogonal signal generator (4), a first follower (5), a second follower (6), a first alternating-current/direct-current conversion switch (7), a second alternating-current/direct-current conversion switch (8), a dual-heating-wire thermoelectric converter (9), a nano-volt meter (10), an alternating-current voltage source (11) and a differential sampling system (12), wherein the upper computer (1) is respectively connected with the direct-current voltage source (2), the direct-current standard voltmeter (3), the orthogonal signal generator (4), the first alternating-current/direct-current conversion switch (7), the second alternating-current/direct-current conversion switch (8), the nano-volt meter (10), the alternating-current voltage source (11) and the differential sampling system (12) through an IEEE-488 bus, so that automatic control of, the orthogonal signal generator (4) is connected with the first alternating current-direct current conversion switch (7) and the second alternating current-direct current conversion switch (8) through the first follower (5) and the second follower (6) respectively, meanwhile, one channel of the orthogonal signal generator (4) is connected with one channel of the differential sampling system (12), the alternating current voltage source (11) is connected with the other channel of the differential sampling system (120), the direct current voltage source (2) is connected with the standard direct current voltmeter (3), the first alternating current-direct current conversion switch (7) and the second alternating current-direct current conversion switch (8) respectively, the first alternating current-direct current conversion switch (7) and the second alternating current-direct current conversion switch (8) are connected with the double-heating wire thermoelectric converter (9), and the double-heating wire thermoelectric converter (9) is connected to the nano-volt meter (10).

4. A method for implementing ultra low frequency voltage normal magnitude transfer using the ultra low frequency voltage normal magnitude transfer system of claim 3, comprising the steps of:

a. the upper computer (1) controls the orthogonal signal generator (4) to output two paths of orthogonal low-frequency voltage signals U with equal amplitude_AAnd U_BThe direct current voltage source (2) outputs a positive direct current voltage signal U_DC+The AC voltage source (11) outputs a low-frequency AC voltage signal U to be measured₁；

b. The upper computer (1) controls the first alternating current-direct current conversion switch (7) and the second alternating current-direct current conversion switch (8) to be switched to an alternating current state;

c.U_Aand U_BRespectively by first followingThe device (5) and the second follower (6) are input into a first alternating current-direct current conversion switch (7) and a second alternating current-direct current conversion switch (8) and are input into a double-heating-wire thermoelectric converter (9) through the first alternating current-direct current conversion switch (7) and the second alternating current-direct current conversion switch (8);

d. reading thermoelectric potential E output by the double-heating-wire thermoelectric converter (9) by the nano-volt meter (10)_a1；

e, the upper computer (1) controls the first alternating current-direct current conversion switch (7) and the second alternating current-direct current conversion switch (8) to be switched to a direct current state;

f. the standard DC voltmeter (3) measures the DC voltage signal U_DC+Amplitude, U_DC+The power is respectively input into a thermoelectric converter (9) with double heating wires after passing through a first alternating current-direct current conversion switch (7) and a second alternating current-direct current conversion switch (8);

g. reading thermoelectric potential E output by the double-heating-wire thermoelectric converter (9) by the nano-volt meter (10)_d+；

h. The upper computer (1) controls the direct current voltage source (2) to output a negative direct current voltage signal U_DC-Wherein U is_DC-＝-U_DC+Measuring a DC voltage signal U by a standard DC voltmeter (3)_DC-Amplitude, U_DC-The power is respectively input into a thermoelectric converter (9) with double heating wires after passing through a first alternating current-direct current conversion switch (7) and a second alternating current-direct current conversion switch (8);

i. reading thermoelectric potential E output by the double-heating-wire thermoelectric converter (9) by the nano-volt meter (10)_d-；

j. The upper computer (1) controls the first alternating current-direct current conversion switch (7) and the second alternating current-direct current conversion switch (8) to be switched to an alternating current state;

k. reading thermoelectric potential E output by the double-heating-wire thermoelectric converter (9) in an alternating current input state by a nano-volt meter (10)_a2；

Comparison E_a1+E_a2And E_d++E_d-When E is large or small_a1+E_a2＝E_d++E_d-Then low frequency voltage signal U_AAnd U_BThe effective value U is obtained by calculation according to the formula (1)

m, when E_a1+E_a2≠E_d++E_d-The dc voltage is adjusted by equations (2) and (3):

and repeating the process a-m until E is guaranteed_a1+E_a2＝E_d++E_d-At this time, the low-frequency voltage signal U_AAnd U_BThe effective value U is obtained by calculation according to the formula (4)

n. the upper computer (1) controls the differential sampling system (12) to sample and measure U_AAnd U₁The difference value delta U of (d) is obtained, the measured voltage U is₁Can be obtained by calculation of the formula (5)

Therefore, the magnitude transmission of the ultralow frequency alternating voltage standard is realized.

The technical field is as follows:

the invention belongs to the field of alternating voltage measurement standards, and particularly relates to a method for establishing an ultralow frequency voltage standard and realizing magnitude transmission.

Background art:

at present, the lower limit of the frequency of national standard of the alternating voltage in China is 10Hz, and in the calibration capability of various national measurement institutes published by the international measurement bureau, the lowest frequency of the alternating voltage calibration capability is only 10Hz, so that the traceability requirement of the alternating voltage with lower frequency cannot be met. For the measurement of the ultralow frequency signal below 10Hz, the method has application in various fields, such as civil engineering, oil exploration, earthquake monitoring, precision machining and manufacturing, national defense industry, aerospace and other fields, the requirement of measuring the low frequency vibration signal below 1Hz exists, and the measurement of the vibration signal is usually realized by converting the vibration signal into an electric signal through a sensing technology, so that the ultralow frequency voltage standard is established, and the measurement of the magnitude transmission has important significance for the measurement of the vibration signal. In addition, with the development of the new energy automobile industry, metering calibration of the lithium ion power battery is also a hot problem in the field of electromagnetic metering, and one of the main tasks is to establish an ultra-low frequency voltage standard. In addition, in some high-voltage tests, the ultralow frequency voltage technology can effectively solve the problem of overlarge volume and weight of equipment and meet the requirement of insulation distribution in a test product. Therefore, the magnitude tracing of ultralow frequency voltage below 10Hz is urgently needed to be solved.

At present, the magnitude tracing of alternating voltage is to use a thermocouple as a standard and trace to a direct voltage standard through alternating current-direct current conversion. For a thermocouple, when an AC signal u is input_acAnd a direct current signal u_dcWhen the generated thermoelectric force is equal, the two signals are considered to be equivalent, and further equivalent conversion between alternating current electric quantity and direct current electric quantity is achieved. The relationship between the output thermoelectric voltage of the thermocouple and the input voltage can be expressed as

E＝K*u²

Wherein K is the thermocouple sensitivity coefficient and is determined by the self characteristics of the thermocouple, and u is the input voltage. For a thermocouple, the output thermal potential E is a constant in the dc input state and the ac input state at a frequency higher than 10 Hz. When the frequency is higher than 10Hz, the self AC/DC difference of the thermocouple is small, and the equivalent conversion between the AC voltage and the DC voltage can be realized as a standard. When the frequency is lower than 10Hz, due to the influence of the frequency response characteristic of the thermocouple, the input alternating current signal can be regarded as a changed direct current signal for the thermocouple, the output thermal potential is unstable, the alternating current-direct current difference per se is large, and the alternating current-direct current conversion is not suitable for being used as a standard for alternating current-direct current conversion. Therefore, the lower limit of frequency of the national alternating voltage standards published by the international bureau of measurement at present is generally 10Hz, and no effective means is available for tracing the alternating voltage below 10Hz to the direct voltage standard.

The invention content is as follows:

aiming at the defects of the prior art, the invention provides a method for establishing an ultralow frequency voltage standard below 10Hz, and the ultralow frequency alternating voltage and the direct current voltage standard are established to realize the magnitude traceability of the ultralow frequency alternating voltage;

the invention also aims to realize the magnitude transmission of the ultralow frequency voltage standard, establish the relation between the tested ultralow frequency alternating voltage and the voltage standard and verify the tested ultralow frequency voltage.

The invention is realized by the following technical scheme:

the ultralow frequency voltage standard is established, and the ultralow frequency voltage and the direct current voltage are equivalently converted through an ultralow frequency voltage alternating current-direct current conversion system, so that the ultralow frequency alternating current voltage is traced to the direct current voltage standard. The ultralow-frequency voltage alternating current-direct current conversion system comprises an upper computer 1, a direct current voltage source 2, a standard direct current voltmeter 3, an orthogonal signal generator 4, a follower 5, a follower 6, an alternating current-direct current conversion switch 7, an alternating current-direct current conversion switch 8, a double-heating-wire thermoelectric converter 9 and a nanovoltmeter 10. The upper computer 1 is respectively connected with a direct current voltage source 2, a direct current standard voltmeter 3, an orthogonal signal generator 4, an alternating current-direct current conversion switch 7, an alternating current-direct current conversion switch 8 and a nanovolt meter 10 through an IEEE-488 bus, and system automation control is achieved. The orthogonal signal generator 4 is respectively connected with the alternating current-direct current conversion switch 7 and the alternating current-direct current conversion switch 8 through the follower 5 and the follower 6, the direct current voltage source 2 is respectively connected with the direct current standard voltmeter 3, the alternating current-direct current conversion switch 7 and the alternating current-direct current conversion switch 8 are connected with the double-heating-wire thermoelectric converter 9, and the double-heating-wire thermoelectric converter 9 is connected to the nano-volt meter 10.

The method for establishing the ultra-low frequency voltage standard comprises the following steps:

A. the upper computer 1 controls the orthogonal signal generator 4 to output two paths of orthogonal low-frequency voltage signals U with equal amplitude_AAnd U_BThe DC voltage source 2 outputs a positive DC voltage signal U_DC+；

B. The upper computer 1 controls the AC/DC conversion switch 7 and the AC/DC conversion switch 8 to be switched to an AC state;

C.U_Aand U_BThe signals are respectively input into an alternating current-direct current conversion switch 7 and an alternating current-direct current conversion switch 8 after passing through a follower 5 and a follower 6, and are input into a double-heating-wire thermoelectric converter 9 after passing through the alternating current-direct current conversion switch 7 and the alternating current-direct current conversion switch 8;

D. reading thermoelectric potential E output by the dual-heating-wire thermoelectric converter 9 by the nano-volt meter 10_a1；

E. The upper computer 1 controls the AC/DC conversion switch 7 and the AC/DC conversion switch 8 to be switched to a DC state;

F. measuring a DC voltage signal U by a standard DC voltmeter 3_DC+Amplitude, U_DC+The power is respectively input into a thermoelectric converter 9 with double heating wires after passing through an AC/DC conversion switch 7 and an AC/DC conversion switch 8;

G. reading thermoelectric potential E output by the dual-heating-wire thermoelectric converter 9 by the nano-volt meter 10_d+；

H. The upper computer 1 controls the direct current voltage source 2 to output a negative direct current voltage signal U_DC-Wherein U is_DC-＝-U_DC+Measuring a DC voltage signal U by a standard DC voltmeter 3_DC-Amplitude, U_DC-The power is respectively input into a thermoelectric converter 9 with double heating wires after passing through an AC/DC conversion switch 7 and an AC/DC conversion switch 8;

I. reading thermoelectric potential E output by the dual-heating-wire thermoelectric converter 9 by the nano-volt meter 10_d-；

J. The upper computer 1 controls the AC-DC change-over switch 7 and the AC-DC change-over switch 8 to be switched to an AC state;

K. reading out the AC input state of the dual-heating-wire thermoelectric converter 9 by the nano-volt meter 10Thermoelectric potential E of lower output_a2；

L. comparison E_a1+E_a2And E_d++E_d-When E is large or small_a1+E_a2＝E_d++E_d-Then low frequency voltage signal U_AAnd U_BThe effective value U is obtained by calculation according to the formula (1)

M, when E_a1+E_a2≠E_d++E_d-The dc voltage is adjusted by equations (2) and (3):

and repeating the processes A to M until E is guaranteed_a1+E_a2＝E_d++E_d-At this time, the low-frequency voltage signal U_AAnd U_BThe effective value U is obtained by calculation according to the formula (4)

Therefore, equivalent conversion between the ultralow frequency alternating voltage and the direct current voltage is realized, the alternating current voltage is traced to the direct current voltage standard, and the ultralow frequency alternating current voltage standard is established.

The method realizes the magnitude transmission of the ultralow frequency voltage standard, takes the ultralow frequency voltage standard as a reference, and measures the difference value between the measured low frequency voltage and the low frequency voltage standard through a differential sampling system to realize the verification of the measured voltage. The ultralow-frequency voltage standard magnitude transmission system comprises an upper computer 1, a direct-current voltage source 2, a standard direct-current voltmeter 3, an orthogonal signal generator 4, a follower 5, a follower 6, an alternating-current and direct-current conversion switch 7, an alternating-current and direct-current conversion switch 8, a double-heating-wire thermoelectric converter 9, a nano-volt meter 10, an alternating-current voltage source 11 and a differential sampling system 12. The upper computer 1 is respectively connected with a direct current voltage source 2, a direct current standard voltmeter 3, an orthogonal signal generator 4, an alternating current-direct current conversion switch 7, an alternating current-direct current conversion switch 8, a nanovolt meter 10, an alternating current voltage source 11 and a differential sampling system 12 through an IEEE-488 bus, and automatic control of the system is achieved. The orthogonal signal generator 4 is respectively connected with the alternating current-direct current conversion switch 7 and the alternating current-direct current conversion switch 8 through the follower 5 and the follower 6, meanwhile, one channel of the orthogonal signal generator 4 is connected with one channel of the differential sampling system 12, the alternating current voltage source 11 is connected with the other channel of the differential sampling system 12, the direct current voltage source 2 is respectively connected with the standard direct current voltmeter 3, the alternating current-direct current conversion switch 7 and the alternating current-direct current conversion switch 8 are connected with the double-heating-wire thermoelectric converter 9, and the double-heating-wire thermoelectric converter 9 is connected.

The method for realizing the standard magnitude transmission of the ultralow frequency voltage comprises the following steps:

a. the upper computer 1 controls the orthogonal signal generator 4 to output two paths of orthogonal low-frequency voltage signals U with equal amplitude_AAnd U_BThe DC voltage source 2 outputs a positive DC voltage signal U_DC+The AC voltage source 11 outputs a low-frequency AC voltage signal U to be measured₁；

b. The upper computer 1 controls the AC/DC conversion switch 7 and the AC/DC conversion switch 8 to be switched to an AC state;

c.U_Aand U_BThe alternating current and direct current are respectively input into an alternating current and direct current conversion switch 7 and an alternating current and direct current conversion switch 8 through a follower 5 and a follower 6, and are input into a double-heating-wire thermoelectric converter 9 through the alternating current and direct current conversion switch 7 and the alternating current and direct current conversion switch 8;

d. reading thermoelectric potential E output by the dual-heating-wire thermoelectric converter 9 by the nano-volt meter 10_a1；

e, the upper computer 1 controls the alternating current-direct current conversion switch 7 and the alternating current-direct current conversion switch 8 to be switched to a direct current state;

f. measuring a DC voltage signal U by a standard DC voltmeter 3_DC+Amplitude, U_DC+Respectively passes through an AC/DC conversion switch 7 and an AC/DC conversion switch 8 and then is input into the double heating wires for thermoelectricityA converter 9;

g. reading thermoelectric potential E output by the dual-heating-wire thermoelectric converter 9 by the nano-volt meter 10_d+；

h. The upper computer 1 controls the direct current voltage source 2 to output a negative direct current voltage signal U_DC-Wherein U is_DC-＝-U_DC+Measuring a DC voltage signal U by a standard DC voltmeter 3_DC-Amplitude, U_DC-The power is respectively input into a thermoelectric converter 9 with double heating wires after passing through an AC/DC conversion switch 7 and an AC/DC conversion switch 8;

i. reading thermoelectric potential E output by the dual-heating-wire thermoelectric converter 9 by the nano-volt meter 10_d-；

j. The upper computer 1 controls the AC-DC change-over switch 7 and the AC-DC change-over switch 8 to be switched to an AC state;

k. reading thermoelectric potential E output by the double-heating-wire thermoelectric converter 9 in an alternating current input state by the nanovolt meter 10_a2；

Comparison E_a1+E_a2And E_d++E_d-When E is large or small_a1+E_a2＝E_d++E_d-Then low frequency voltage signal U_AAnd U_BThe effective value U is obtained by calculation according to the formula (1)

m, when E_a1+E_a2≠E_d++E_d-The dc voltage is adjusted by equations (2) and (3):

and repeating the process a-m until E is guaranteed_a1+E_a2＝E_d++E_d-At this time, the low-frequency voltage signal U_AAnd U_BThe effective value U is obtained by calculation according to the formula (4)

n. upper computer 1 controls differential sampling system 12 to sample and measure U_AAnd U₁The difference value delta U of (d) is obtained, the measured voltage U is₁Can be obtained by calculation of the formula (5)

Therefore, the magnitude transmission of the ultralow frequency alternating voltage standard is realized.

Has the advantages that: compared with the prior art, the invention provides a method for establishing an ultralow frequency voltage standard, solves the problem that a single thermocouple cannot meet low-frequency voltage alternating current-direct current conversion, realizes equivalent conversion of ultralow frequency voltage below 10Hz and direct current voltage standard based on a double-heating-wire thermoelectric converter, traces the ultralow frequency alternating current voltage to the direct current voltage standard, establishes the ultralow frequency voltage standard, and simultaneously provides a magnitude transmission method of the ultralow frequency voltage standard, realizes magnitude transmission of the ultralow frequency voltage standard and realizes accurate measurement of the ultralow frequency alternating current voltage.

Description of the drawings:

FIG. 1 is a block diagram of an ultra-low frequency voltage AC/DC conversion system

FIG. 2 is a block diagram of an ultra-low frequency AC voltage standard magnitude transfer system

The specific implementation mode is as follows:

the invention is described in further detail below with reference to the following figures and examples:

the ultralow-frequency voltage alternating current-direct current conversion system comprises an upper computer 1, a direct current voltage source 2, a direct current standard voltmeter 3, an orthogonal signal generator 4, a follower 5, a follower 6, an alternating current-direct current conversion switch 7, an alternating current-direct current conversion switch 8, a double-heating-wire thermoelectric converter 9 and a nanovoltmeter 10. The upper computer 1 is respectively connected with a direct current voltage source 2, a direct current standard voltmeter 3, an orthogonal signal generator 4, an alternating current-direct current conversion switch 7, an alternating current-direct current conversion switch 8 and a nanovolt meter 10 through an IEEE-488 bus, and system automation control is achieved. The orthogonal signal generator 4 is respectively connected with the alternating current-direct current conversion switch 7 and the alternating current-direct current conversion switch 8 through the follower 5 and the follower 6, the direct current voltage source 2 is respectively connected with the direct current standard voltmeter 3, the alternating current-direct current conversion switch 7 and the alternating current-direct current conversion switch 8 are connected with the double-heating-wire thermoelectric converter 9, and the double-heating-wire thermoelectric converter 9 is connected to the nano-volt meter 10.

The upper computer 1 is used for controlling the whole system to realize automatic measurement;

the direct current voltage source 2 is used for outputting a direct current voltage signal;

the direct current standard voltmeter 3 is used for accurately measuring the amplitude of the direct current voltage signal and providing a reference standard;

the orthogonal signal generator 4 is used for outputting two paths of orthogonal low-frequency voltage signals with equal amplitude;

the follower 5 and the follower 6 are used for reducing the output impedance of the orthogonal signal generator and improving the loading capacity;

the AC-DC conversion switch 7 and the AC-DC conversion switch 8 are used for controlling the switching between the AC voltage and the DC voltage at the input end of the double-heating-wire thermoelectric converter;

the double-heating-wire thermoelectric converter 9 is used for realizing equivalent conversion between two paths of orthogonal low-frequency alternating-current voltage and direct-current voltage;

the nano-volt meter 10 is used for reading thermoelectric potentials output by the dual-heating-wire thermoelectric converter in an alternating current state and a direct current state.