RU2125258C1 - Method and device for identification of complex of thermophysical properties of solid materials - Google Patents

Abstract

FIELD: technical physics, study of thermophysical properties of substances. SUBSTANCE: method includes action with thermal pulses from line source onto flat surface of examined and standard samples, measurement of excess temperature at moments of feed of thermal pulses at points located at fixed distances from heating line on surface of samples. Measured temperature is approximated with minimal error to calculated temperatures formed by means of program control over parameters of thermophysical characteristics. Sought-for characteristics are determined by identified parameters of samples and by actual values of characteristics of standard. Device for realization of method incorporates demultiplexer, controlled power supply unit, measurement probe, D C amplifier, analog-to-pulse converter, programmed timers, register and address selector connected in series. Output bus of address selector is connected to address inputs of demultiplexer, first and second programmed timers and register linked with first and second inputs correspondingly to synchronizing input and output of first programmed timer. Controlling input of first timer is tied together with like bus to corresponding inputs of second programmed timer, address selector, register and output of microcomputer. Address output of microcomputer is coupled through like bus to proper input of address selector and data input/output of microcomputer is linked through like bus to corresponding input of demultiplexer and output of register. EFFECT: enlarged range and enhanced accuracy of measurement of thermophysical properties of materials. 2 dwg, 4 tbl

Description

 The invention relates to technical physics, and in particular to the field of studies of the thermophysical properties of substances.

 A known method for determining the thermophysical characteristics of materials [ed. St. USSR N 1608535, class G 01 N 25/18, 1990], which consists in exposing the surface of the reference and test samples to the same number of thermal pulses and recording the time interval between the last pulse and the moment the temperature reaches its maximum.

 The disadvantage of this method is the inability to accurately determine the time when the maximum temperature, and the range of the time interval is comparable with this accuracy. Moreover, this method has a relatively low speed, because To reduce the error in determining the maximum, an increase in the number of thermal pulses is required.

There is also known a device for determining the TFH materials [ed. St. USSR N 1236355 USSR, cl. G 01 N 25/18, 1986], which contains a thermal probe in the form of a material with known thermophysical characteristics, a linear wire heater and two thermocouples at a distance of x ₁ and x ₂ from the action line of the heater are mounted on the contact surface of the probe, the third thermocouple is located inside the temperature probe material at a distance of x ₃ from the line of action of the heater, an analog-to-digital converter, a power supply unit, a microprocessor, an input-output unit, controlled frequency dividers, a frequency divider and a 2I-NOT element.

 The disadvantage of this device is the rigid structure, due to the organization of the number of pulse sensor generator with a narrow specialization in the monitoring of the thermal characteristics through three channels. All this does not allow the identification of the TFC with a given degree of accuracy.

 The prototype adopted a method of monitoring the thermophysical characteristics of insulating materials [ed. St. USSR N 1711052, class G 01 N 25/18, 1992], which includes linear heating of the surfaces of the reference and studied samples by pulses with a period equal to the thermal relaxation time of the sample with normalized characteristics, and determining the number of thermal pulses for which a given temperature is reached on the standard and the materials under study, according to which calculate the desired characteristics.

 The device taken as a prototype [ed. St. USSR N 1298713, class G 01 N 25/18, 1987], consists of a measuring probe, a direct current amplifier, an analog-to-pulse converter, a pulse generator, an executive unit, a switching power supply, a command shaper, a channel commutator, a microcomputer, an indication and recording unit, a permanent memory device, reprogrammable read-only memory device, multiplexer.

 The disadvantages of the known method and device is a narrow range of measured values of TFC at one standard. To expand the range with a given accuracy, it is necessary to use a set of reference materials, and this increases the duration of the experiment.

 The disadvantages of this device are the low information content due to the input of information by simulating contact, low performance due to the sequential input of information over three decades and the software normalization of the recorded information, low flexibility due to the use of an electromechanical switch acting as a DAC.

 The aim of the invention is to increase the range and accuracy of measurement of thermophysical properties of materials.

This goal is achieved by the fact that in the method of determining the thermophysical characteristics, including exposure to thermal pulses from a linear source on the flat surface of the test and reference samples, measuring excess temperatures at the moments of heat pulses at points located at fixed distances from the heating line on the surface of the samples, unlike the prototype, the calculated temperatures are brought closer to the measured temperatures with a minimum error due to a program change in t according to the identified parameters of the thermophysical characteristics of the samples and the actual values of the thermophysical characteristics of the standard, find the desired characteristics;
a device containing a serially connected demultiplexer, a controlled power supply, a measuring probe, a DC amplifier, an analog-pulse converter, the first programmable timer, the data input / output of which is connected via the same bus with the inputs / outputs of the second programmable timer and microcomputer, in contrast to the prototype additionally entered the register and address selector, the output bus of which is connected to the address inputs of the demultiplexer, the first and second programmable timers and register, connected first and second inputs, respectively, with a clock input and output of the first programmable timer, the control input of which is connected by the bus of the same name with the corresponding inputs of the second programmable timer, demultiplexer, register address selector and microcomputer output, the address output of the latter via the bus of the same name is connected to the corresponding input of the address selector, and the input / output of the microcomputer data is connected via the bus of the same name to the corresponding register output and the input of the demultiplexer connecting the WTO output programmable timer with a synchronization input of the first programmable timer.

и исследуемого образца

в моменты времени t_i=it₀ после подачи тепловых импульсов (фиг. 1) в точках, расположенных на фиксированном расстоянии x от линии нагрева на поверхности образцов.The essence of the method is as follows: heat pulses with a period of τ ₀ from a linear heat source of power q affect the flat surface of a reference sample with thermophysical characteristics {a ₀ , λ ₀ } and a test sample with thermophysical characteristics {a, λ}, measure the excess temperature of the reference

and test sample

at times t _i = it ₀ after applying thermal pulses (Fig. 1) at points located at a fixed distance x from the heating line on the surface of the samples.

в моменты времени t_i рассчитанные значения температуры

(фиг. 1) посредством программного управления параметрами теплофизических характеристик

по модели

где n - количество тепловых импульсов за время t_j= jτ₀,
t₀ - период измерения температуры, c.Approach the values of the measured temperature of the standard

at times t _{i the} calculated temperature

(Fig. 1) through software control of the parameters of thermophysical characteristics

by model

where n is the number of thermal pulses over time t _j = jτ ₀ ,
t ₀ - period of temperature measurement, c.

включающему относительную погрешность

и математическое ожидание

где
k - количество измеренных температур

Теплофизические характеристики

, соответствующие минимальной погрешности Eps, являются измеренными значениями теплофизических характеристик эталонного образца.The approximation is carried out to a minimum of the error Eps:

including relative error

and expectation

Where
k is the number of measured temperatures

Thermophysical characteristics

corresponding to the minimum error Eps are the measured values of the thermophysical characteristics of the reference sample.

в моменты времени t_i происходит аналогично эталону.The approximation of the calculated temperatures T _i (Fig. 1) to the values of the measured temperatures of the test sample

at times t _i occurs similarly to the standard.

по модели

где n - количество тепловых импульсов за время t_j= jτ₀,
t₀ - период измерения температуры, c.The temperature values T _i are formed by the parameters

by model

where n is the number of thermal pulses over time t _j = jτ ₀ ,
t ₀ - period of temperature measurement, c.

включающему относительную погрешность

и математическое ожидание

где k - количество измеренных температур

В результате находятся значения измеренных теплофизических характеристик исследуемого образца

Так как измерения температур эталона

и исследуемого образца

осуществляются одним прибором и сравнивание происходит по одной модели, то действительные значения исследуемого {a, λ } и эталонного {a₀, λ₀ } образцов с измеренными значениями можно описать системой уравнений

Решение систем уравнений приводит к соотношениям

т. е. отношения действительных и измеренных значений равны, откуда следует расчетное соотношение для искомых характеристик {a, λ }:

Предложенный способ реализован устройством в виде измерительно-вычислительной системы (ИВС) для определения ТФХ твердых материалов импульсными методами. Структурная схема ИВС (фиг. 2) состоит из измерительного зонда (ИЗ) 1, усилителя постоянного тока (УПТ) 2, аналого-импульсного преобразователя (АИП) 3, управляемого блока питания (УБП) 4, регистра 5, первого программируемого таймера (ПТ1) 6, демультиплексора (ДМ) 7, селектора адреса (СА) 8, микроЭВМ 9 и второго программируемого таймера (ПТ2) 10.The approximation is carried out to a minimum of the error Eps:

including relative error

and expectation

where k is the number of measured temperatures

As a result, the values of the measured thermophysical characteristics of the test sample are found

Since measuring temperature reference

and test sample

carried out by one device and the comparison is carried out according to one model, then the actual values of the studied {a, λ} and reference {a ₀ , λ ₀ } samples with measured values can be described by a system of equations

The solution of systems of equations leads to the relations

that is, the ratios of real and measured values are equal, whence the calculated relation for the desired characteristics {a, λ} follows:

The proposed method is implemented by a device in the form of a measuring and computing system (IVS) for determining the thermal characteristics of solid materials by pulsed methods. The block diagram of the IVS (Fig. 2) consists of a measuring probe (IZ) 1, a direct current amplifier (DC) 2, an analog-pulse converter (AIP) 3, a controlled power supply unit (UBP) 4, register 5, the first programmable timer (PT1 ) 6, demultiplexer (DM) 7, address selector (CA) 8, microcomputer 9 and the second programmable timer (PT2) 10.

 Microcomputer 9 is a computer built on the basis of a co-pulse microprocessor with a three-bus architecture, including address 11, data bus 12, and control bus 13. Microcomputer 9 is used to program the IVS units, process the results of the experiment using a mathematical model, calculate the TFH, and program-controlled calibration.

Programmable timers 6 and 10 are multifunctional programmable counters in integrated design. PT1 6 converts the input frequency into a measurement code. PT2 10 forms time intervals that determine the measurement duration τ _and , as well as τ _n - the duration of the heat pulses on the material under study.

 The address selector 8 is a decoder that determines the position of the IVS blocks in the address space of the microcomputer 9.

 Demultiplexer 7 is an electronic switch for the spatial and temporal separation of the output signal PT2 10 between the measurement and heating channels.

 Register 5 has outputs with a Z-state and is designed to transmit information from the output of PT1 6 and DM 7 to the data bus, which allows the microcomputer 9 to control the state of the input and output of PT1 6 to register an overflow or complete a measurement cycle.

 UBP 4 generates electrical pulses for heating the investigated material FROM 1.

 FROM 1 consists of a heater that converts electrical pulses of UBP into thermal energy, and a thermocouple that converts the response temperature on the surface of the material into an electrical signal.

 UPT 2 is used to amplify the recorded response signal coming from FM 1 and suppress high-frequency interference.

 AIP 3 converts the measured voltage into frequency.

 The device operates in two modes: measurement and heating. Microcomputer 9, using standard input / output procedures, writes control codes to control registers PT1 6 and PT2 10. In this case, PT2 10 is programmed into the standby multivibrator mode, and PT1 6 - into the mode of a controlled pulse counter.

In the measurement mode, the microcomputer via the demultiplexer 7 connects the output of ПТ2 10 to the input of the resolution of the account ПТ1 6. To measure the temperature of the material under investigation, the microcomputer 9 writes a code in ПТ2 10 that determines the pulse duration τ _{and the} waiting multiplexer, and forms its start via CA 8. The electric signal from the thermocouple of the measuring probe 1 is fed to the input of the CTD 2. The amplified signal is converted by the AIP 3 to the frequency F _i , which is fed to the counting input PT1 6. PT1 6 for the period τ _and counts the number of pulses. As a result of this, a code N is obtained that is directly proportional to the value of the frequency F _i and the duration τ _and : by changing τ _, you can programmatically switch the measuring range. To register a steady-state value in a given range, N is read at the end of τ _and in the absence of overflow of counter PT1 6. For this, the microcomputer through register 5 monitors the states at the output of DM 7 and output PT1 6, where the appearance of logic level 1 indicates overflow of the counter PT1. In case of overflow, the duration τ _and decreases programmatically. The code is read by the microcomputer 9, where it is converted to a temperature value and processed according to the program.

In the heating mode, for programmed control of the heat output to the test material, the microcomputer through the DM 7 connects the output ПТ2 10 to the control input of the control unit 4. When writing the necessary code to ПТ2 10, the microcomputer 9 programmatically controls the heat output due to the change in pulses τ _n . In order to form a heating pulse, the microcomputer via CA 8 starts PT2 10 at the required time. The pulse from the output of PT2 10 through DM7 is supplied to the control unit 4. The control unit generates a powerful pulse of duration τ _n entering the heater FROM 1. The response from the thermal effect on the test material is recorded by the IVS in the measurement mode in accordance with the proposed method.

 Efficiency over the measuring range.

If there are n control sub-ranges for measurements, it is necessary for known solutions at least 2 standards per sub-range, i.e. the number of standards m ₁ ≥2n, and for the proposed solution - 1 or more, i.e. the number of standards m ₂ ≥1.

 Evaluate the effectiveness of the minimum number of standards.

т.е. в предлагаемых решениях диапазон расширяется в 2n раз.The efficiency η _d in the measuring range for the proposed solution is the ratio of m ₁ to m ₂

those. in the proposed solutions, the range is expanded by 2n times.

 Efficiency for accuracy.

Measurements are taken in the subrange d _{0 of the} range d.

To control by known methods with a given error ε _back m standards are necessary. However, k standards are used for measurements.

а для предлагаемого решения

Эффективность по точности η_T/ есть отношение погрешностей, т.е.When controlling by known methods with k standards, the error

and for the proposed solution

The accuracy efficiency η _{T /} is the ratio of errors, i.e.

Следовательно, предлагаемое техническое решение обеспечивает точность измерения в 2n раз выше, чем прототип.

Therefore, the proposed solution provides a measurement accuracy of 2n times higher than the prototype.

The measurements were carried out on the following materials: polymethylmethacrylate (PMM) (Table 1), FT-4 fluoroplast (Table 2), TF quartz (Table 3), ripor foam (NK) (table 4). The heat pulse power is 5 W from a linear source with a diameter of 0.1 mm from chromel, point thermocouples of chrome-droplets with a diameter of 0.1 mm are located at a distance of 1.5 mm from the linear heater, the periods of supply of thermal pulses τ ₀ and measurements t ₀ are equal and are 5 s, the duration of thermal pulses varied from 0.125 to 1.25 s.

 The studies were carried out on the measuring and computing system "Temp - 075". UPT 2 is made on the OU of the K140UD14 series; AIP 3 - on chips of the K544, K590 series; UBP 4 - on the chip K142EN3; Register 5 - on the 1533IR22 chip; PT1 and PT2 - on the chip K580VI53; DM 7 - on the chips 1533TM2, 1533LL1; CA 8 - on the K555ID7 chip. Microcomputer 9 is a PC based on the microprocessor Z80.

 From a comparison of the experimental results (Table 1-4), it can be seen that the proposed technical solutions allow one to identify in a wide range the studied TPS with errors of a not more than 1%, by λ - 1.3% relative to measures with normalized characteristics.

 The method of identifying thermophysical characteristics, in contrast to the known solutions, extends the measurement range by 2n times or reduces the measurement error by 2n times on a fixed subband.

Claims (2)

 1. A method for determining thermophysical characteristics, including exposure to thermal pulses from a linear source on a flat surface of the investigated and reference samples, measuring excess temperatures at the moments of heat pulses at points located at fixed distances from the heating line on the surface of the samples, characterized in that to the measured the temperatures are approximated with minimal error by the calculated temperature values due to a program change in the parameters of thermophysical characteristics, the identified parameters are found from the identified parameters of the thermophysical characteristics of the samples and the actual values of the thermophysical characteristics of the standard.  2. A device containing a series-connected demultiplexer, a controlled power supply, a measuring probe, a DC amplifier, an analog-pulse converter, the first programmable timer, the data input / output of which is connected via the same bus with the inputs / outputs of the second programmable timer and microcomputer, characterized in that the register and address selector are additionally introduced, the output bus of which is connected to the address inputs of the demultiplexer, the first and second programmable timers and the register connected first and second inputs, respectively, with a clock input and output of the first programmable timer, the control input of which is connected by the bus of the same name with the corresponding inputs of the second programmable timer, demultiplexer, register address selector and microcomputer output, the address output of the latter via the bus of the same name is connected to the corresponding selector input addresses, and the input / output of microcomputer data is connected via the bus of the same name to the corresponding register output and input of the demultiplexer connecting the WTO output programmable timer with a synchronization input of the first programmable timer.

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