SU1221624A1 - Method of measuring frequency errors of thermoelectric temperature transducers - Google Patents

Abstract

The invention can be used to estimate the frequency properties of thermal ac transducers in the CONSTANT in a wide frequency range. The purpose of the invention is to precisely equalize the effective values of heating currents, the first and second frequencies, which allows to improve the measurement accuracy by the relative difference of thermo-emf. AC current of the first fixed frequency. and the second tunable frequency from sources 1 and 2 are alternately passed through the heater of the thermoelectric converter 6. After its heating, the corresponding values of the thermo-emf are measured. The signals corresponding to the currents of the first and second frequencies are alternately transferred to a third frequency, equal to the sum of these frequencies. To do this, use an auxiliary signal corresponding to the current of the fourth frequency, equal to the half-difference of the first and second frequencies. In the description of the device that implements this method. The device contains sources 1 and 2 of the alternating current fixed and ree ke ke o tho 4

Description

frequency, resistors 3 and 4, switches 5 and 15, converters 6 and 12, the signal frequency transfer unit 7, made, for example, on the basis of galvanomagnetic

Hall sensor, current source 8, tunable selective amplifier

The invention relates to electrical measuring equipment and can be used to evaluate frequency properties of thermoelectric converters of alternating current to a constant in a wide frequency range.

The purpose of the invention is to improve the accuracy of measuring the frequency errors of thermoelectric converters by precisely equalizing the effective values of the heating currents of the first and second frequencies, which makes it possible to increase the measurement accuracy by the relative difference of the thermo-emf.

The drawing shows a device that implements the proposed method.

The device contains sources 1 and 2 of alternating currents of the first fixed and second tunable frequencies, which through alternating resistors 3 and 4 and switching element 5 are alternately connected to the heater of the controlled thermoelectric converter 6. Signal frequency transfer unit 7 is turned on in series with the heater of the converter 6 , which is made, for example, on the basis of galvanmagnetic Hall sensor. Unit 7 is connected to the auxiliary current source 8 of the fourth tunable frequency. The output of block 7 is connected through a tunable selective amplifier 9 and a rectifier 10 connected to a DC compressor 11. Source 1 is also connected to the reference thermoelectric converter 12, the heating element of which is shunted by a variable resistor 13 Between counter-connected thermoelectrodes of converters 6 and 12

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9, the rectifier 10, the DC compensator II, the resistor 13, and the digital millivoltmeter 14. The description shows the calculations for obtaining am-. Pounds of dedicated signals corresponding to currents of different frequencies. 1 il.

A digital millivoltmeter 14 is switched on, which is connected by a switch 15 only to the output of a controlled thermoelectric transducer;

In the proposed method, alternating current of the first fixed frequency; (tj and alternating current of the second tunable frequency ij

10., ImjCos (alternately nponycKatoT through the heater of the controlled thermoelectric converter. After the thermoelectric converter is heated by the currents of the first and second frequencies, the corresponding EMF values are measured;

E, 51

Where

,, (UrJll

g iU fn

S is the sensitivity of the controlled thermoelectric a SO / converter;

the relative frequency error of sensitivity of the thermoelectric converter at the second frequency relative to the first. Signals corresponding to the currents of the first and second frequencies and alternately flowing through the heater of a thermoelectric converter are transferred to one frequency — the third; equal to the half sum of the first and second frequencies Ljj (uJa + "jJi / i. For this, an auxiliary signal is used corresponding to the current of the fourth frequency equal to the half difference of the first and second frequencies" jJt, () | l

As a result of the transfer of the signal corresponding to the current of the first frequency, a signal is formed

 Im .., cos ((,) ImjCosyt- M j)

-2Mm, (,, - 4 3) +. -.

cos (.

V,)

where K. is the conversion factor.

From the received signal 11, a signal is extracted, for example, by filtering. third frequency

, Im3Cos (

where Kg is the filtration coefficient.

As a result of the transfer of the signal corresponding to the current of the second frequency,. a signal is generated (I U3 K, Im:, Cos (,) InijCosHt j)

 - | -l- ..

.Co. (T, VvfJJ

From the received signal, Ug also isolates the voltage of the third frequency.

t v.

U, .- Kilniilni3cos (

and) -t-uJi

The amplitudes of the selected signals -U and and /, one frequency are compared with each other. Then the amplitude of the alternating current of the second frequency is changed to ensure that the amplitudes of the compared signals of the third frequency are equal. The achievement of equality of the amplitudes of the currents of the compared signals (,) means the equality of the amplitudes of the heating currents (). ,

Comparison of the amplitudes of signals of one frequency excludes the error in establishing the equality of the currents of the first and second frequencies heating the controlled thermoelectric converter.

Thus, the relative difference of thermo-EMF, corresponding to heating currents of different frequency and of equal amplitudes, is the measured frequency error

Eg. - EI ASM

-Y; - ---

The device works as follows.

Controlled converter 6 is connected to a current source 1 and a variable resistor 3 digitally. Millvoltmeter 14 is set to its rated heating current. (Position a of switch 15) and the corresponding thermo-emf is measured. Then according to the zero reading of a millivoltmeter 14 variable resistor 13

 .

25

thirty

five

0

0

equalize thermo-EMF converters 6 and 12 (the position of the S switch 15). On the scale of source 2, a new frequency value is set, 5 on which the frequency error of the controlled converter 6 is to be determined, Auxiliary current source 8 is adjusted to half the first and second frequency of sources 1 and 2, and selective amplifier 9 to half the sum of these frequencies.

Source I current flows through the converter heater 6 in series with the Hall sensor semiconductor plate. : As a result of the interaction of the current and the magnetic field of the excitation winding, through which the current of source 8 flows, a signal proportional to the product of these currents is generated at the Hall electrodes of the sensor. Since the semiconductor plate. The gauge with dimensions mm has no residuals. Reactivities and processes in the plate are almost free of radiations, the conversion of the heating current to the corresponding product signal occurs without frequency errors in a wide frequency range (up to 10-30 MHz). The voltage of the third frequency inscribed and amplified by the selective amplifier 9 is converted by the rectifier 10 into a constant voltage measured by the compensator 11. After the switching element 5, the heater of the controlled converter 6 is connected to the source 2 of the frequency to be tuned. And the variable resistor 4 again obtains the initial reading of the compensator 11. Since the compensating voltages are the result of the division, amplification, and rectification of harmonic signals of one third frequency, the resulting signals The conversion efficiencies for heating currents of the first and second frequencies will be the same for any value of the auxiliary current of the fourth frequency of source B. Therefore, the frequency distortions arising in the inertia excitation winding of the Hall sensor do not affect the accuracy of setting 5 the equality of heating currents. A millivoltmeter 14 measures the resulting difference in thermo-emf of converters 6 and 12. After that, the value of 5 is determined.

the frequency error of the controlled converter 6 from the ratio

oJ

1l.

-

E,

where LE is the difference of thermo-EMF converters 6 and 12; thermo-emf converter 6, corresponding to the rated current of its heater. Then, on the scale of current source 2, a higher value of its frequency is set, and the measurements are repeated. Based on the measured values of frequency errors, they determine the flow-. with frequency characteristics of the monitored converter. .

The proposed method provides the accuracy of measuring the frequency errors of thermo-electric converters by eliminating the frequency error comparing the amplitudes of the currents of different frequencies. Therefore, it is possible to reduce the error of comparing alternating currents in a wide frequency range (up to 100 kHz) and measuring small frequency errors of the order of thousand fractions of a percent.

1221624

Formula

image

A method of measuring the frequency errors of thermoelectric converters, which involves alternately heating the controlled formation with alternating currents of the first and second frequencies, maintaining the equality of the effective values of these currents, measuring the thermo-EMF corresponding to these currents, and determining the error based on the relative difference of thermo-EMF, that, in order to increase the accuracy, they form an additional electrical signal with a frequency equal to the half-difference of the first and second frequencies; chasing, protsortsio-,-functional currents heat the first swarm vtog and frequency, and then these signals via additional electric signal alternately mixed. with the signal of the third frequency equal to the half-sum of the first and second frequencies, while comparing the amplitude of the signals obtained by mixing. signal of the first frequency and, accordingly, the second frequency, and change the heating current of the second frequency to obtain equality of the amplitudes of the compared signals.

Claims (2)

Claim A method for measuring the frequency errors of thermoelectric converters, which involves alternately heating the controlled converter with alternating currents of the first and second * frequencies, maintaining the equality of the effective values of these 10 currents, measuring the thermo-EMF corresponding to these currents, and determining the error from the relative difference of thermo-EMF, characterized in that, in order to increase accuracy * 5, they form an additional electric signal with a frequency equal to the half-difference of the first and second frequencies, form an electric s signals protsortsio-. 2 ° to the heating currents of the first and second frequencies, and then these signals with: using an additional electric signal are alternately mixed. ₂₅ with a signal of the third frequency equal to the half-sum of the first and second frequencies, and the amplitude of the signals obtained by mixing is compared. signal of the first frequency and, accordingly, of the second frequency, and the heating current of the second frequency is changed until equal-amplitudes of the compared signals are obtained.