RU2090872C1 - Device determining coefficient of thermal diffusivity - Google Patents

Abstract

FIELD: measurement of thermophysical characteristics of solid materials, thermal nondestructive testing. SUBSTANCE: pulse source 1 of heating is optically coupled to register 18 of heating pulses and tested sample 2, temperature of back surface of which is measured by temperature transducer 3. Output of this transducer is connected to input of first key 16. Controlling input of first key 16, first inputs of first 9 and second 10 coincidence circuits are connected to first output of RS flip-flop 7. Output of register 18 of heating pulses is connected to input of second key 17. Controlling input of second key 17 and first input of third coincidence circuit 11 are connected to second input of RS flip-flop 7. Outputs of first 16 and second 17 keys are connected to input of first differentiator 4. Output of first differentiator 4 is coupled to input of second differentiator 5. Output of second differentiator 5 is connected to null detector 6. Output of null detector 6 is linked to R input of RS flip- flop 7 and second input of second coincidence circuit 10. Second input of first coincidence circuit 9 is connected through second counter-frequency divider 15 to output of pulse generator 8. Second input of third coincidence circuit 11 is connected through first counter-frequency divider 14 to output of pulse generator 8. Output of first coincidence circuit 9 is connected to first information input of reversible counter 12. Output of third coincidence circuit 11 is linked to second information input of reversible counter 12. Outputs of second coincidence circuit 10 is connected to controlling input of reversible counter 12. Output of reversible counter 12 is linked to input of digital indicator 13. Input of setting of initial state of reversible counter 12, S input of RS flip-flop 7, inputs of pulse generator 8 and pulse source 1 of heating are connected to start terminal 19. EFFECT: enhanced operational efficiency and reliability. 2 cl, 2 dwg

Description

 The device relates to technical means of measuring thermophysical characteristics and can be used in studies of the properties of new materials and in thermal non-destructive testing.

 A device for measuring the characteristic time of the heat transfer process [1] comprising a pulsed heat source, a pulse start recorder, a generator, a thermocouple connected to an amplifier, two differentiators, a zero-organ, two triggers, a matching circuit and an indication board connected to the counter output, an input which is connected to the output of the coincidence circuit, to the first input of which a generator is connected, and to the second output of the first trigger, the first input of which is connected to the output of the second trigger, and between the second input and output m amplifier includes two series-connected differentiator and zero-organ.

 The device [1] has a low accuracy in determining the characteristic time of the heat transfer process, since it does not take into account the final duration of the heating pulse. Since the shape of the heating pulse of known sources is far from ideal, the finite duration of the heating pulse is taken into account by using the calculated ratios for the thermal diffusivity of the time to reach the maximum of the first derivative of the energy source of the heating pulse.

 A device for determining the coefficient of thermal diffusivity [2] containing a pulsed heating source, optically coupled to a recorder of heating pulses and through the test sample with a temperature sensor, which is connected through series-connected first and second differentiators and the first zero-organ to the R-input of the RS-trigger the output of which is connected to the first input of the coincidence circuit, the second input of which is connected to the output of the pulse generator, the output of the coincidence circuit is connected to the output of the pulse counter, the output of the cat It is connected to a digital indicator, the output of the heat pulse recorder is connected through a third and fourth differentiators and a second zero-organ connected to the register entry input, the register data input is connected to the output of the first counter - frequency divider, and the register data output is connected to the first input of the digital comparator , to the second input of which the output of the second counter - the frequency divider is connected, and the output of the digital comparator is connected to the S-input of the RS-trigger, the output of the pulse generator is connected to the inputs of the first and second frequency dividers, counters, pulse generator input coupled to the input of the pulsed heat source and the trigger input terminal.

 Due to the presence in the device [2] of two identical parts, each of which consists of two differentiators and a zero-organ connected in series and performs the same function at different points in time, the device has functional redundancy. The part of the device circuit that is used to determine the point in time corresponding to the beginning of pulse counting by a counter is complex. Since the time points necessary for determining the specified time of the heat transfer process are recorded by two independent measuring channels, the accuracy of calculating the difference in time intervals characterizing the specified time of the heat transfer process is reduced.

 The proposed device for determining the coefficient of thermal diffusivity increases the accuracy of calculating the specified time of the heat transfer process while simplifying the circuit of the device.

 To solve the problem in a device for determining the coefficient of thermal diffusivity, containing a pulsed heating source, optically coupled to a heat pulse recorder and through a test sample with a temperature sensor, the first and second differentiators are connected in series, the output of the second differentiator is connected to the input of the zero-organ, the output of which is connected to the R-input of the RS-flip-flop, the first output of which is connected to the first input of the first match circuit, the output of which is connected to the first information an ode of a pulse counter, the output of which is connected to a digital indicator, a pulse generator, the input of which is connected to the output of the pulse heating source and the start terminal, and the output is connected to the input of the first counter of the frequency divider and the input of the second counter of the frequency divider, the output of the second counter of the frequency divider is connected to the second the input of the first matching circuit, the first input of which is connected to the first input of the second matching circuit and the control input of the first key, the input of which is connected to the output of the temperature sensor, and the output is is dined with the input of the first differentiator and the output of the second key, the input of which is connected to the output of the heating pulse recorder, and the control input is connected to the second output of the RS-trigger and the first input of the third matching circuit, the second input of which is connected to the output of the first counter of the frequency divider, and the output is connected with the second information input of the pulse counter, the input of the initial state setting of which is connected to the S-input of the RS-trigger and the start terminal, and the control input of the pulse counter is connected to the output of the second circuit the second input of which is connected to the output of the zero-organ. As a pulse counter, a reversible counter is used.

 Compared with the prototype, the third and fourth differentiators, the second zero-organ, register and digital comparator are excluded from the functional structure of the device for determining the thermal diffusivity. Instead of these elements, two matching schemes and two keys were introduced, and the pulse counter was replaced with a reversible counter.

 In FIG. 1 shows a functional diagram of a device; in FIG. 2 is a timing diagram explaining its operation.

 The device contains a pulsed heating source 1, a test sample 2, a temperature sensor 3, a first 4 and a second 5 differentiators, a zero-organ 6, an RS-flip-flop 7, an 8 pulse generator, a first 9, a second 10 and a third 0 11 matching schemes, a counter 12 pulses, digital indicator 13, first 14 and second 15 counters frequency dividers, first 16 and second 17 keys, recorder 18 heating pulses, start terminal 19.

 The pulse source 1 is optically connected to the recorder 18 and the test sample 2, the temperature of the back surface of which is measured by the sensor 3. The output of the sensor 3 is connected to the input of the first key 16. The control input of the first key 16, the first inputs of the first 9 and second 10 matching schemes are connected to the first output RS-flip-flop 7. The output of the recorder 18 is connected to the input of the second key 17. The control input of the second key 17 and the first input of the third matching circuit 11 are connected to the second output of the RS-flip-flop 7. The outputs of the first 16 and second 17 keys are connected to the input of the first differentiator 4. The output of the first differentiator 4 is connected to the input of the second differentiator 5. The output of the second differentiator 5 is connected to the input of the zero-organ 6. The output of the zero-differentiator 6 is connected to the R-input of the RS-flip-flop 7 and the second input of the second matching circuit 10. Second the input of the first matching circuit 9 through the second counter, the frequency divider 15 is connected to the output of the generator 8. The second input of the third matching circuit 11 through the first counter the frequency divider 14 is connected to the output of the generator 8. The output of the first matching circuit 9 is connected to the first information the input of the reversing counter 12. The output of the third matching circuit 11 is connected to the second information input of the reversing counter 12. The output of the second matching circuit 10 is connected to the control input of the reversing counter 12. The output of the reversing counter 12 is connected to a digital indicator 13. The initial state setting input of the reversing counter 12, The S-input of the RS-flip-flop 7, the input of the generator 8 and the input of the pulse source 1 are connected to the start terminal 19.

где L толщина исследуемого образца;
τ₂-mτ₁= τ_т интервал времени процесса теплопередачи, скорректированный с учетом конечной длительности импульса нагрева;
m постоянный коэффициент;
τ₂, τ₁ интервалы времени от момента запуска устройства до моментов достижения первыми производными хронологической термограммы T′(τ) и плотности потока энергии импульса нагрева φ′(τ) соответственно максимальных значений (фиг. 2).The device allows to determine the value of thermal diffusivity coefficient a in accordance with the ratio

where L is the thickness of the test sample;
τ ₂ -mτ ₁ = τ _t the time interval of the heat transfer process, adjusted for the finite duration of the heating pulse;
m constant coefficient;
τ ₂ , τ ₁ time intervals from the moment the device is started up to the moments when the first derivatives of the chronological thermogram T ′ (τ) and the energy flux density of the heating pulse φ ′ (τ) respectively reach the maximum values (Fig. 2).

 The coefficient m depends on the type of source of heating pulses used. Its value is determined by processing a thermogram for a sample with known thickness L and thermal diffusivity a. In particular, for a xenon flash lamp m 1.7.

где m₀ целая часть m, поэтому частота f₂ импульсов на втором информационном входе реверсивного счетчика 12 равна

где f₀ частота импульсов на выходе генератора 8.The device operates as follows. When the START button is pressed, the generator 8 is started, as well as the installation of the RS-trigger 7 and the reverse counter 12 in the initial state. The initial state of the RS-trigger 7 corresponds to a state in which there is no signal at its first output. The initial state of the reverse counter 12 corresponds to its zeroing ("zero" state) and recording mode. After the signal from the start terminal 19 to the input of the pulse source 1 arrives, the light stream of the pulse source 1 heats the flat sample 2. The part of the light stream illuminates the recorder 18, the signal from the output of which is closed due to the signal from the second output of the RS-trigger 7 at the control input the second key 7 is fed to the input of the first differentiator 4, differentiated by the first 4 and second 5 differentiators, and fed to the input of the zero-organ 6. The pulses from the output of the generator 8 through the first counter divider 14 and opened by a signal from the second output of the RS-flip-flop 7 coincidence circuit 11 is fed to the second information input of the reverse counter 12. The division coefficient K _{1 of the} first counter-divider 14 is

where m _{0 is the} integer part m, therefore, the frequency f ₂ pulses at the second information input of the reverse counter 12 is

where f ₀ is the pulse frequency at the output of the generator 8.

В результате переброса RS-триггера 7 на его первом выходе появляется сигнал, который поступает на управляющий вход первого ключа 16. Первый ключ 16 замыкается и выход датчика 3 подключается к выходу первого дифференциатора 4. Сигнал с первого выхода RS-триггера 7 отрывает первую 9 и вторую 10 схемы совпадения, поступая на их первые входы. Импульсы с выхода генератора 8 через второй счетчик-делитель 15 и открытую первую схему совпадения 9 поступает на первый информационный вход реверсивного счетчика 12. Коэффициент деления K₂ второго счетчика-делителя 15 равен K₂ m₀, поэтому частота импульсов f₁ на первом информационном входе реверсивного счетчика 12 равна

Тепловой поток от тыльной поверхности плоского исследуемого образца 2 поступает на датчик 3 температуры, выходной сигнал которого, пропорциональный измеряемой температуре тыльной поверхности образца 2, через замкнутый первый ключ 16 поступает на вход дифференциатора 4, дифференцируется первым 4 и вторым 5 дифференциаторами и поступает на вход нуль-органа 6.After a time interval τ ₁ after pressing the START button, the zero-organ 6 is triggered due to a change in the polarity of the signal at the output of the second differentiator 5. The signal from the output of the zero-organ 6 is fed to the R-input of the RS-trigger 7, transferring it to a state in which the second output of the RS-flip-flop 7 signal is missing. The second key 17 opens and the input of the first differentiator 4 is disconnected from the output of the recorder 18. The third matching circuit 11 is closed and the pulses from the output of the first counter-divider 14 do not pass to the second information input of the reverse counter 12, which will record the number of pulses N ₂ equal to

As a result of the flip of the RS-flip-flop 7, a signal appears on its first output, which is fed to the control input of the first key 16. The first key 16 is closed and the output of the sensor 3 is connected to the output of the first differentiator 4. The signal from the first output of the RS-flip-flop 7 opens the first 9 and second 10 matching patterns, arriving at their first inputs. The pulses from the output of the generator 8 through the second counter-divider 15 and the open first matching circuit 9 are supplied to the first information input of the reverse counter 12. The division coefficient K _{2 of the} second counter-divider 15 is K ₂ m ₀ , therefore, the pulse frequency f ₁ at the first information input reverse counter 12 is equal

The heat flux from the back surface of the flat sample 2 is fed to a temperature sensor 3, the output signal of which, proportional to the measured temperature of the back surface of sample 2, through a closed first key 16 is fed to the input of differentiator 4, differentiated by the first 4 and second 5 differentiators, and fed to the input zero organ 6.

Реверсивный счетчик 12 в момент второго срабатывания нуль-органа 6 зафиксирует разность N N₁ N₂ количества импульсов, поступивших на информационные входы реверсивного счетчика 12 за интервал времени, равный τ₂

Скорректированный с учетом конечной длительности импульса нагрева интервал времени процесса теплопередачи τ_т= τ₂-mτ₁, необходимый для определения коэффициента температуропроводности, отображается цифровым индикатором 13.After a time interval τ ₂ after pressing the START button, the zero-organ 6 is triggered due to a change in the polarity of the signal at the output of the second differentiator 5. The signal from the output of the zero-organ 6 through the open second coincidence circuit 10 is fed to the control input of the reversible counter 12, bringing it into prohibition mode records. Since the first coincidence circuit 9 is open during the time interval τ ₃ equal to τ ₃ = τ ₂ -τ ₁ , then the number of pulses N ₁ equal to

The reverse counter 12 at the time of the second operation of the null-organ 6 will fix the difference NN ₁ N _{2 the} number of pulses received at the information inputs of the reverse counter 12 for a time interval equal to τ ₂

Adjusted for the final duration of the heating pulse, the time interval of the heat transfer process τ _t = τ ₂ −mτ ₁ necessary to determine the thermal diffusivity is displayed by a digital indicator 13.

 In the time diagrams (Fig. 2), the state of the outputs of the first differentiator 4, null-organ 6, RS-trigger 7, and the second coincidence circuit 10 is reflected from top to bottom.

 Thus, due to changes in the functional diagram of the device and its functioning algorithm, the accuracy of determining the thermal diffusivity is increased and the structure of the device is simplified.

Claims (2)

 1. A device for determining the coefficient of thermal diffusivity, containing a pulsed heating source, optically coupled to a heat pulse recorder and through a test sample with a temperature sensor, the first and second differentiators connected in series, the output of the second differentiator is connected to the input of the zero-organ, the output of which is connected to R- RS trigger input, the first output of which is connected to the first input of the first matching circuit, the output of which is connected to the first information input of the pulse counter, the output to which is connected to a digital indicator, a pulse generator, the input of which is connected to the input of the pulse heating source and the start terminal, and the output is connected to the input of the first counter-frequency divider and the input of the second counter-frequency divider, characterized in that the output of the second counter-frequency divider is connected to the second input of the first matching circuit, the first input of which is connected to the first input of the second matching circuit and the control input of the first key, the input of which is connected to the output of the temperature sensor, and the output is connected to the input m of the first differentiator and the output of the second key, the input of which is connected to the output of the heating pulse recorder, and the control input is connected to the second output of the RS-trigger and the first input of the third matching circuit, the second input of which is connected to the output of the first counter-frequency divider, and the output is connected to the second information input of the pulse counter, the input of the initial state setting of which is connected to the S-input of the RS-trigger and the trigger terminal, and the control input of the pulse counter is connected to the output of the second matching circuit, the second the course of which is connected to the output of the zero-organ.  2. The device according to claim 1, characterized in that a reverse counter is used as a pulse counter.

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