UA25389U - Thermal-noise thermometer - Google Patents

Abstract

The proposed thermal-noise thermometer contains a thermal-noise resistive transducer, two band-pass filters, two voltage amplifiers, a low-pass filter, a multiplier, an analog-to-digital converter, a microprocessor computing unit, a digital display unit, and additionally, a thermostat, a reference resistor, which is installed in the thermostat, a reference capacitor, a differential amplifier, two isolating capacitors, an operational amplifier with resistive negative feedback, multiplexers, and a digital-to-analog converter.

Description

Description of the invention

A useful model belongs to noise thermometry and can be used to measure the temperature of 2 thermal noise resistive transducers with degrading resistance, preferably for monitoring an aggressive temperature environment.

To exclude the influence of the instability of the electrical resistance of the thermal noise resistive converter on the temperature value, a noise temperature meter is used | see Savateev A.V. Noise thermometry - L.: Znergoatomizdat. Leningrad otd-nie, 1987, -P.93-95), which contains a thermal noise resistive converter, a voltage preamplifier, a current-to-voltage converter, a band-pass filter, a voltage amplifier, a detector and an integrator, two switches, two memory devices and a multiplying device with registrar

Due to the multiplication of the current of the thermal noise resistive converter with its voltage, the influence of the instability of the resistance of the thermal noise converter on the temperature measurement result is excluded. But the inherent noises of the voltage converter and the current-to-voltage converter, as well as the inevitable voltage drift 19 displacement of the multiplying device do not allow to realize the potential accuracy of the known noise meter.

The famous noise temperature meter (authenticated by the USSR Mo1362951, IPC 501K7/30, 1986), which contains a thermal-noise resistive converter, a sample resistor, two voltage amplifiers, a multiplier, an analog-to-digital converter, an adder, a resistance converter - code, switches, keys , digital divider, recorder and control unit.

Thanks to the digital dividing device, the influence of the instability of the resistance of the thermal noise resistive converter on the temperature measurement result is excluded. But the meter has low accuracy due to the influence of errors in the conversion of the resistance of the thermal noise resistive converter, especially in extreme temperature conditions, into the voltage of the dividing device, as well as due to the difficulty of maintaining the resistance of the sample resistor at a given level. -at

A noise temperature meter is also known (authenticated certificate of the USSR Mo1732186, MPK 01K7/30, 19921, which contains a thermal noise resistive converter, two bandpass filters, two voltage amplifiers, a multiplier whose inputs are connected through voltage amplifiers to the outputs of the bandpass filters, a filter of low frequencies, connected to the output of the multiplier, an analog-to-digital converter, the input of which is connected to a 30 analog-to-digital converter, a micro-computer and a digital indicator connected to the output of a micro-computer.

In addition, the noise temperature meter includes a current-to-voltage converter, a reference DC voltage source, a digital adder, and a control signal generator. at

The simultaneous connection of a voltage amplifier with a high-impedance input and a current-to-voltage converter with a low-impedance input to the thermal-noise resistive converter causes large distortions in the 35 values of the noise current and voltage, which does not allow obtaining high accuracy of temperature measurement. In addition, the c multiplier in the known scheme does not exclude the influence of correlated noises of voltage amplifiers and bandpass filters on the temperature measurement result, which also reduces the reliability of temperature control. The source of the error remains the time and temperature instability of the parameters of the amplifiers and bandpass filters, which determine the steepness of the transformation of the measured temperature into a digital code. C 70 The basis of a useful model is the task of creating such a noise temperature meter, in which, by introducing new elements and connections between them, it would ensure the elimination of errors, which, in turn, would allow to measure the temperature with higher accuracy in conditions of degradation of the thermal noise resistance resistive converter and instability of parameters of amplifiers, filters and the multiplier itself.

The task is achieved by the fact that in a noise temperature meter containing a thermal noise 45 resistive converter, two bandpass filters, two voltage amplifiers, a multiplier whose inputs are connected through voltage amplifiers with the outputs of bandpass filters, a low-pass filter connected to output 4 ! multiplier, an analog-to-digital converter, a micro-EBOM, the input of which is connected to an analog-to-digital converter and a digital indicator connected to the output of a micro-computer, according to a useful model, a thermostat is introduced into it, a sample resistor placed in the thermostat, a sample capacitor, a differential amplifier by 20, two distribution capacitors, a decoupling unit on the operational amplifier and with a resistor in the negative feedback circuit, three-channel and two-channel multiplexers and a digital-to-analog converter, the input of which is connected to the second output of the micro- Computer, the output is connected to the terminals of the thermal noise resistive converter, the sample resistor, the sample capacitor, which in turn are connected together, and to one of the inputs of the differential amplifier through one distribution capacitor, the other outputs of the thermal noise resistive converter, the sample resistor and the sample capacitor , each connected separately to the inputs of a three-channel multiplexer, the output of which is connected with the second input of the differential amplifier through the second sharing capacitor and directly with the input of the decoupling unit, the output of which is connected to one of the inputs of the two-channel multiplexer, the second input of which is connected to the output of the low-pass filter, and the output is connected to the analog input -differential converter, the control inputs of the three-channel and 60 two-channel multiplexers are connected to the third and fourth outputs of the micro-computer, and the output of the differential amplifier is connected to the inputs of the bandpass filters.

Introduction to the scheme of the noise temperature meter of a sample resistor placed in the thermostat, a sample capacitor, a differential amplifier, two distribution capacitors, a decoupling block on the operational amplifier and a resistor in the negative feedback circuit, three-channel and two-channel multiplexers, a digital-to-analog converter , connected in the specified manner, allows additional voltages to be generated at the output of the multiplier in different cycles of operation, the alternate supply of which to the resolving unit through a thermal noise resistive converter, a sample resistor, a sample capacitor and further mathematical processing in a micro-BEOM allows to obtain the temperature value, which is measured, in digital form, corrected for the effect of noises and interferences that act in the amplifier-converter path, as well as the effect of the instability of the parameters of amplifiers, filters, multipliers and the instability of the resistance of both the thermal noise converter itself and the model, which allows with higher accurately measure the temperature in conditions of degradation of the parameters of the thermal noise resistive converter and instability of the parameters of the measuring circuit. 70 The drawing shows the functional diagram of the noise temperature meter.

The noise temperature meter contains a thermal noise resistive converter 1, a sample resistor 2 placed in the thermostat C, a three-channel multiplexer 4, a sample capacitor 5, two distribution capacitors 6 and 7, a differential amplifier 8, a resolving unit 9 on an operational amplifier 10 with a resistor 11 in negative feedback circuits, two bandpass filters 12 and 13, two voltage amplifiers 7/5 14 and 15, multiplier 16, low-pass filter 17, two-channel multiplexer 18, analog-to-digital converter 19, digital-to-analog converter 20, micro- Computer 21 and digital indicator 22.

The outputs of the thermal noise resistive converter 1, the sample resistor 2 and the sample capacitor 5 are connected together and through the distribution capacitor 6 are connected to one of the inputs of the differential amplifier 8.

The second outputs of the thermal noise resistive converter 1, the sample resistor 2 and the sample capacitor 5 are each connected separately to the inputs of the three-channel multiplexer 4.

The output of the multiplexer 4 is connected to the second input of the differential amplifier 8 through the distribution capacitor 7 and directly to the input of the decoupling unit 9 on the operational amplifier 10 with a resistor 11 in the negative feedback circuit. The output of the differential amplifier 8 is connected to the inputs of the bandpass filters 12 and 13, the outputs of which are connected through the voltage amplifiers 14 and 15 to the inputs of the multiplier 16. The output of the multiplier 16 is connected through the low-pass filter 17 to one input of the two-channel multiplexer 18, the second input of which is connected to the output of the resolving unit 9. -

The output of the two-channel multiplexer 18 is connected through the analog-to-digital converter 19 to the input of the micro-computer 21, the first output of which is connected to the digital indicator 22. The second output of the micro-computer 21 is connected to the input of the digital-to-analog converter 20, the output of which is connected to connected together conclusions Ge! from the thermal noise resistive converter 1, the sample resistor 2 and the sample capacitor 5. The third and fourth outputs of the micro-BOM 21 are connected to the control inputs of the two-channel multiplexer 18 and the three-channel multiplexer 4.

A noise temperature meter works like this.

In the thermal noise resistive converter 1, placed in the temperature zone Tu, which is measured, about

Зз5 There is an electric voltage of thermal noise proportional to this temperature. In the sample resistor 2, s placed in the thermostat Z, there is also an electric voltage of thermal noise proportional to the fixed temperature To of the thermostat 3. The temperature T is measured during six cycles of operation of the micro-computer 21.

During the first cycle of operation, the micro-BOM 21 is connected by a three-channel multiplexer 4 to the inputs of the differential amplifier 8 through the first channel of the thermal noise resistive converter 1 with resistance K.. with s Amplified voltage, which consists of thermal noises ОО (0 and interference ХУ, including inherent noises of the differential of the amplifier 8, enters the inputs of the bandpass filters 12 and 13. Filtered from low-frequency and high-frequency interference, the noise voltage components are amplified by the voltage amplifiers 14, 15 and multiplied in the multiplier 16. The constant component of the multiplied voltages, taking into account the averaging in the low-pass filter 17, is determined by the expression: name) -k2 ng. that, "sl. Also Yuk ztyshch issue (95) p. . not where they are the gain coefficient of the differential amplifier 8; (ee) K» and Kz - gain coefficients of voltage amplifiers 14 and 15; с т - scale factor of transformation of the multiplier 16 taking into account the filter 17 of lower frequencies;

C - thermal noise dispersion of the thermal noise resistive converter 1; pe: dispersion of interference and inherent noise of the differential amplifier 8; p s She is the zero offset voltage multiplied by taking into account the correlated noises of voltage amplifiers 14 and 15.

The DC voltage is converted into a digital code using an analog-to-digital converter 19. The code of the first conversion cycle --- 2 50 schi. ka kokzti kiy)" o 9 CHA where 41 is the unit of the junior digit of the analog-to-digital converter 19. 65 Code M, is memorized and stored in the memory of the micro-computer 21.

During the second cycle of operation of the micro-BOM 21, a three-channel multiplexer 4 connects to the differential amplifier 8 through the second channel an exemplary resistor 2 with a Ko-K resistance, the thermal noise voltage of which is Od(O. As a result of performing similar operations at the output of the low-frequency filter 17, a second constant voltage of the coke zone Y

Sha - ЮЛ at ил where it is the dispersion of thermal noises of the sample resistor 2. The code of the second cycle of conversion cat? but 9 mtsa LOTY code is 7 -8K- - 5353 - - I - - ---tl -yalsh-nlshshu

CHI CHI

The M" code is also memorized and stored in the memory of the micro-computer 21.

During the third cycle of operation of the micro-GOM 21, a three-channel multiplexer 4 connects to the differential amplifier 8 through the third channel, an exemplary capacitor 5, which has practically no dissipative losses. The value of the capacity of the sample capacitor is selected under the condition 1.95)

Са - -- - 2. where и is the central frequency of bandpass filters 12 and 13.

Due to the fact that the sample capacitor 5 has no losses, it itself does not create thermal noise, and in terms of total resistance (impedance) in the band of thermal noise frequencies used, the sample capacitor 5 is equivalent to the resistance of the thermal noise resistive converter 1 and the sample resistor 2 1 (6 ) ---e»E:N.,-th from the extract of 15 g (o) p

Therefore, during the third cycle of operation of the micro-computer 21, when the three-channel multiplexer 4 is connected to the differential amplifier 8 through the third channel, the sample capacitor 5 is the noiseless equivalent of the sample resistor at the output of the differential amplifier 8, the level of interference and noise does not change, and the useful signal (I) from 5 is absent . The constant component of the multiplied noise voltages, taking into account the averaging in the filter 17 of the low frequencies in the third cycle of operation of the micro-ENBOM 21 is determined only by its own noises and interferences (y - 0 2 What (7 y - KKok that Or v s "z Code of the third conversion cycle n zatv tya ya ma - 53 - BIT about the name) in CHI i-y ' aka still

The M" code is also memorized and stored in the memory of the micro-computer 21. (95) During the fourth cycle of the micro-computer 21, the three-channel multiplexer 4 again connects to the so 50 inputs of the differential amplifier 8 through the first channel of the thermal noise resistive converter 1 with resistance

Ku. At the same time, the two-channel multiplexer 18 connects the input of the analog-to-digital converter 19 to the output of the decoding block 9.

A constant voltage from the output of the digital-to-analog converter 20 is supplied to the input of the resolving unit 9 through the thermal-noise resistive converter 1. The value of this voltage is determined by the difference code M.4-M", which is produced in the micro-computer processor 21:

KK kat is 0-3; --- --- I am 505

From 60 where to is the unit of the lower order of the digital-to-analog converter 20.

The transmission coefficient of the resolving unit 9, as is known, is determined by the ratio of the resistance of the resistor 11 in the negative feedback circuit of the operational amplifier 10 and the series resistance of the resistor at the input of the operational amplifier 10. The resistance of the resistor 11 has a fixed value Ko, while the gain factor is 65 of the yazing block 9 K) becomes inversely proportional to the resistance of the thermal noise resistive converter 1:

on)

Ka - V

Kia de AK uncontrolled changes in the resistance of the thermal noise resistive converter 1 during operation.

The output voltage of the resolving unit 9, taking into account expressions (9) and (10), reaches the value:

In fi pog -KaiEV-- i - "KK in - ka Visa Z zy

Voltage О5 is converted into a digital code using analog-to-digital converter 19. The code of the fourth cycle of conversion that Ko fi pola в--Е- 5656 - ( 656 Kt КК. m o ВИТАВ Е ПОЗ is also memorized and stored in the memory of the micro -EBEOM 21. During the fifth cycle of operation of the micro-computer 21, the three-channel multiplexer 4 connects to the output of the digital-to-analog converter 20 through the second channel, the exemplary resistor 2. The two-channel multiplexer 18 remains in its previous state. To the input of the solving unit 9 through the exemplary resistor 2 receives a constant voltage from the output of the digital-to-analog converter 20. The value of this voltage is determined by the difference code Mo-Mz, which is produced by the micro-EOM 21: --o- (13) cat 5 - fo - kokh - ZT no) 1

The transmission coefficient of the resolving unit 9 when connected to the input of a sample resistor 2 with resistance Ко» Ф зо is determined by the expression: с

Ka 19

Kk --8 5 sia so

IS)

The output voltage of the solving unit 9, taking into account the expressions (13) and (14), will take the value: sch in - (15)

Shk - Kotsv - 20. fkokati

Ka fi

The SHO voltage is converted into a digital code using an analog-to-digital converter 19. The code is from the fifth conversion cycle. » 7 in - (6) " Fo from 2

M - nn sh-5 KTKOKa ti fo de is also memorized and stored in the memory of the micro-EOM 21. During the sixth cycle of work in the micro-EOM 21 s, the ratio of codes M, and Mo (95) - at is determined

Because 92.2 2 - is: - KO KO ZI -- so VI AVdY 2 me v --B2 M

Mk Meoz, 75 Ivano vu koka tO sht

Z, 55. oh and

According to the Nyquist formula, the mean square voltage of the thermal noise of the thermal noise resistive converter is determined by the expression: - 18 и -акАпваКУУС 60 where К is Boltzmann's constant;

AG - frequency band in which thermal noise is measured;

Ku i AK - the real resistance of the thermal noise resistive converter;

Tu is the temperature of the thermal noise resistive converter on the thermodynamic scale in degrees Kelvin.

Similarly, the dispersion of the thermal noise of the sample resistor at the thermodynamic temperature To

Fsh - akavota OO

Substituting (18) and (19) into expression (17), we obtain

Ma 02 aAKACHEYAAVIKH Tu 20)

Me o RYAAKO 0 AKATOTO That is where the temperature that is measured in degrees Kelvin comes from: ti-et (27).

WITH

The digital indicator 22 displays the measured temperature in degrees Celsius: и (22). i- 0-0 - 213

M

From expressions (21) and (22), we can see that the measurement result does not depend on the degree of degradation of the thermal noise resistive converter (AK), on the actual inequality of the resistances of the thermal noise resistive converter and sample resistors (KK), as well as the instability of the resistance of the sample resistor itself. In addition, the measurement result is not affected by the instability of the gain of the differential amplifier (K 4), from both voltage amplifiers (K/, and Kz), the scaling factor of the multiplier (t), as well as the level of their own noise and interference. The instability of the bandwidth of band-pass filters (Ai), as well as the limited resolving power of analog-to-digital (a) and digital-to-analog (to) converters, is also not affected.

The measurement result is determined only by the stability of the temperature of the sample resistor (T o) and Me) by the discharge of the micro-computer. co

Thus, the proposed schematic and technical solution of the noise temperature meter ensures high measurement accuracy and ensures a reduction in requirements for the stability of the thermal noise resistive converter, "9 sample resistor and electronic elements of the measuring circuit. yu

Simulation of the proposed structure of the noise temperature meter on a computer confirmed the exclusion of the progressive measurement error from uncontrolled changes in the resistance of the thermal noise resistive converter in the range of up to 43095 at the nominal resistance value in uOhm.

Similar consequences were obtained from the instability of the amplification factor at 42595. At the same time, the central frequency of the bandpass filter was assumed equal to 75kHz with a thermal noise bandwidth of 425kHz. The range of measured temperatures during modeling was taken from 300 to 1500K. 7 70 To reduce the random component error from the statistical properties of thermal noise, the averaging time at the output of the multiplier was chosen to 3 seconds, which reduced the indicated error to -0.1K. :z» Invariance to inherent noises allows to implement the measuring scheme on inexpensive broadband operational amplifiers of the 140 UD1 type, and to implement the multiplier on the KM525 PSZA microcircuit.

An increase in immunity is provided by analog-digital converters of the integrating type on the 15 KR572PV2 microcircuit. Processing of the results of intermediate transformations and obtaining a digital temperature reading were carried out on a personal computer in the "Mag SAYU" program package.

Claims (1)

(95) Formula of the invention at 50 A noise temperature meter containing a thermal noise resistive converter, two band-pass filters, two voltage amplifiers, a multiplier whose inputs are connected through voltage amplifiers to the outputs of band-pass filters, a low-pass filter connected to the output of the multiplier, an analog-to-differential converter, a micro- A computer whose input is connected to an analog-to-digital converter and a digital indicator, connected to the output of a micro-computer, which differs in that a thermostat, a sample resistor, c placed in the thermostat, a sample capacitor, a differential amplifier, two distribution capacitors, a decoupling unit on the operational amplifier and with a resistor in the negative feedback circuit, three-channel and two-channel multiplexers and a digital-to-analog converter, the input of which is connected to the second the output of the micro-EEOM, the output is connected to the outputs of the thermal noise resistive converter, exemplary 60 resistor, sample capacitor, which in turn are connected together, and to one of the inputs of the differential amplifier through one distribution capacitor, the other terminals of the thermal noise resistive converter, sample resistor and sample capacitor are connected each separately to the inputs of the three-channel multiplexer, the output of which is connected to the second input of the differential amplifier through the second distribution capacitor and directly to the input of the decoupling unit, the output of which is connected to one of the inputs of the two-channel multiplexer, the second input of which is connected to the output of the low-pass filter, and the output connected to the input of the analog-to-digital converter, the control inputs of the three-channel and two-channel multiplexers are connected to the third and fourth outputs of the micro-GOM, and the output of the differential amplifier is connected to the inputs of the bandpass filters. - Ge) (ee) Ge) yuyu s - with . a ko 1 (95) so 7 (Che) s bo b5