SU1318886A1 - Device for measuring thermal diffusivity of materials - Google Patents

Abstract

The invention relates to thermophysical measurements and can be used in thermal non-destructive testing. The purpose of the invention is to improve the accuracy of thermal diffusivity measurements. The device works as follows. A pulsed heat source heats the sample from the front. A temperature meter registers the rise in temperature of the sample's back surface; An electrical signal proportional to the square of the excess temperature is stored in digital form in a random access memory (RAM). During the re-polling of the RAM, the digital code is continuously compared with half the maximum signal value. At the moment of equality of these signals, the indicator displays the address number of the compared digital code proportional to the characteristic time of the heat transfer process, which is used to calculate thermal diffusivity. The invention makes it possible to increase the accuracy of measuring the thermal diffusivity of materials in a pulsed two-way method. 2 Il. with B (L 60 00 00 00 05

Description

The invention relates to thermophysical measurements and can be used in thermal non-destructive testing.

The aim of the invention is to increase the accuracy of measurement of thermal diffusivity.

FIG. 1 shows a structural diagram of the proposed device; FIG. 2 - temperature and its square on the back surface of the sample as a function of time during pulsed heating.

 - A device for measuring the thermal diffusivity of materials contains a pulsed heating source 1 connected in series with a temperature meter 2 and a quadratic amplifier 3, block 4 for determining the maximum temperature value, connected to the output of quadratic amplifier 3, first register 5 connected to the output of block 4 for determining the maximum value temperature, an analog-to-digital converter 6, connected to the output of a quadratic amplifier 3 and connected to the first register 5 by bus data, A device (RAM) 7 connected by a data bus to the first register 5. And an analog-digital converter 6, a comparison device 8, the first input of which is connected to the output of the first register 5 with a shift to the bit, and the second input is connected to the RAM 7 The second register 9, the data input of which is connected by the write / read address bus to the RAM 7, and the write input is connected to the output of the comparator device 8, the controller 10 connected by a pulse source 1 n of the heating unit, analog-digital converter 6, RAM 7 and the second register 8 as well as in series nye a second register 9 vynoda unit 11 and indicator 12.

The object of measurement is the sample of the test material. As a pulsed source of heating, a flashlight can be used, and an infrared pyrometer as a temperature meter.

Characteristic points of the temperature curve are: point

WQKC

at MOmax temperature T, ment time t gij, point when the signal reaches a relative level of 0.721 of the maximum value and ω;

the corresponding point in time, when the scinal reaches relative to the level 0.707 of the maximum value and the corresponding moment 5 of time t.

The characteristic points of curve 2, which is the square of the temperature of the back surface of the sample, are: the point of maximum T and Mo1P / max.

 ment C-IHQKC coincides with the corresponding value for the main temperature point, when the signal reaches a relative level of 0.5 and the corresponding time instant for a quadratic curve o, which coincides with the time instant (, .0 for the main curve, when the temperature reaches level 0.707.

20 When the heating source 1 is turned on, the temperature changes over. specimen surface and aachi- (There is a change in temperature on the back surface.

25 start pulse P of the heating source 1 is fed to the input of the controller 10, which begins to generate the request signals of the analog-to-digital converter (ADC) 6 operating in

30 binary code, as well as the control signals of the RAM 7 and the write / read addresses of the RAM 7. The output signal of the temperature meter 2 is fed through a quadratic amplifier 3 to the inputs of the unit

Hc 4 determine the maximum temperature value and the A / D converter 6. The signal value at the output of amplifier 3 is proportional to the square of the signal value at its input. The digitized signal values are stored in RAM 7.

After the moment of occurrence of the maximum temperature value in block 4, a signal is generated, which is supplied to the recording input of the first register 5, in which the maximum value of the digitized signal is stored, as well as to the first input of the controller 10, which stops generating

5Q control signals and addresses in the mode of recording information in the RAM and begins to generate control signals and addresses in the read mode. The data from the output of the RAM 7 in read mode is sent to the second input of the comparator device 8, the first input of which is connected to the output of the register 5 with a shift by bit, so that the digital value 3 is divided

No code for two, i.e. made a shift by one bit d.

The division into two is as follows. The most senior Nth bit of the output of register 5 is connected to the N-1th input bit of the first input of the comparison device 8, the N-1th bit of the register 5 to the N-2nd input bit of circuit 8, and so on. D. And nth input bit

Comparison device is connected to the main terminal. A pulsed heating source, a gigantic O. If the value of a digital temperature meter, a block of a certain signal from the output of RAM 7 becomes equal to or greater than the value of the signal at the first input of the comparison circuit 8, then the comparator produces 5 the signal arriving at the input of the record of the second register 9, the data input of which receives the code of the read address. This value is proportional to the characteristic time of the heat transfer process 20, which is output to the indicator 12 by means of an output unit 11. The proportionality factor is the duration of the write cycle in RAM. At the same time, the signal from the output 25 of the controller, the first input of the analog-to-digital comparison circuit 8, is fed to the second transducer connected to the input of the controller 10, which stops the formation of all signals and enters the input of the unit 4 to set 30

13188864

Claims (1)

The device provides a measurement of thermal diffusivity at near-optimal time, which allows an increase in the accuracy of thermal diffusivity measurement by approximately 60%. Invention Formula A device for measuring the thermal diffusivity of materials, the maximum temperature content, the output unit and. Indicator, characterized in that, in order to improve measurement accuracy, a quadratic amplifier, an analog-to-digital converter, a first register, a random access memory; 8 °; a controller, a comparison device, a second register, are inserted into the device; the quadratic amplifier is connected between the output of the temperature meter and the first input of the block for determining the maximum value of its thread to its initial state. Thus, the device registers the square of the temperature change on the back surface of the sample subjected to pulsed heating, and determines the point in time when the quadratic signal reaches half the maximum value. For the initial curve, this moment of time corresponds to the point when the temperature the quad input amplifier, and the second input - with the first output of the controller, the random access memory is connected by control and recording / reading buses to the controller and the data bus - with an analog-digital converter, the data input of the first register is connected to the data bus, and the input records - to the output of the block for determining the maximum temperature and to the first input of the controller j the first input of the comparator device is connected to the output of the first register ra reaches 0.707 from max-40 stra with a shift to discharge, and the second maximum value. Indeed, we have the original function for T (tr), the quadratic function has the form for T2 (r). AT 2   MO KS point, and we have t  ON poppy g , at the level of 0.5, the value of 0 ,, (Cd J.). This value Corresponds to the relative level of the original function v0, 0, (, (since CH0.5 0.707. The obtained value of 0.707 relative level is close to the optimal value 0.721, which is recommended for measuring thermal diffusivity t - 13188864 The device provides a measurement of thermal diffusivity at near-optimal time, which allows an increase in the accuracy of thermal diffusivity measurement by approximately 60%. Invention Formula A device for measuring the thermal diffusivity of materials, containing a pulsed heating source, a temperature meter, a measuring unit, the first input of an analog-to-digital converter, is connected to maximum temperature, output unit, and. An indicator, characterized in that, in order to improve measurement accuracy, a quadratic amplifier, an analog-to-digital converter, a first register, a random access memory; 8 °, a controller, a comparison device, a second register are inserted into the device, and a quadratic amplifier is connected between the output of the temperature meter and the first input of the block for determining the maximum value of a dark pulsed heating source, a temperature meter, a detecting unit, the first input of the analog-to-digital converter is connected to the quad input of the amplifier and the second input to the first controller output, the random access memory is connected by control buses and the write / read addresses to the controller and data bus to the analog-digital converter, the data input of the first register is connected to the data bus, and the write input to the output of the block for determining the maximum temperature and to the first input of the controller j the first input of the comparator device is connected to the output of the first register 45 50 the input is to the output of the random access memory, the data input of the second register is connected to the write / read address bus, the write input is connected to the output of the comparison device, and the output is connected to the input of the output unit, the output of the comparison circuit is connected to the second input of the maximum temperature value detection unit and the second input of the controller, the third input of the controller is connected to the input of the pulse heating source and the start button. 7 jp max f --- 7Z1 0. 707 f..7 0.721 mc№ Compiled by V. Guseva Editor A. Shandor Tehred A. Kravchuk Proofreader G. Reshetnik Order 2502/36 Edition 776 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, st. Project, 4 FIG. 2