SU1594402A1 - Apparatus for measuring thermal diffusity of solid bodies - Google Patents

Abstract

The invention relates to a technique of thermophysical instrumentation. The purpose of the invention is to improve the measurement accuracy by reducing the effect of fluctuations in heating power, as well as reducing the effect of high-frequency interference. A diaphragm is introduced into the device, which limits the power of the light pulse arriving at the photodetector, the high-pass filter, the controlled amplifier, the integrator, the storage unit and the subtractive device. The invention makes it possible to reduce the scatter of the measurement of the time interval between the start of the heating pulse and the moment when the maximum of the first derivative of the temperature is reached with time. 1 il.

Description

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WITH

The invention relates to a technique of thermophysical instrumentation and can be used to measure the thermal diffusivity of solids.

The purpose of the invention is to improve the accuracy of measuring the thermal diffusivity of solids by reducing the effect of fluctuations in heating power, as well as the effect of high-frequency noise.

The drawing shows a block diagram of the device.

The device contains an optical pulse source of heat 1, sample 2 of the study, the meter 3 temp; pans, second differentiator 4, first differentiator 5, null-organ 6, photodetector 7, shaper 8 imt pulse start of heating, meter 9 time interval, integrator 10, storage unit 11, controlled

amplifier 12, filter 13 frequencies, subtractive device 14 and diaphragm 15.; The device works. The following ob-.

at once. i

After pressing the Start button, the | A clear heating source 1 emits a light pulse of power F, and heats the sample 2. The thermal radiation J from the opposite surface of the treatment 2 is recorded by the temperature meter 3. At the same time part of the light. the first flow F, enters the photodetector 7. Through the diaphragm 15. this flow is limited in power in order to avoid saturation of the photo- and receiver 7. The signal of the photodetector 7 is fed to the input of the imaging unit 8 of the heating start pulse, at which code the start pulse of meter 9 of the time interval appears,

ABOUT

at the same time, the signal of the photodetector 7 is fed to the integrator 10, at which pstengenal appears, the power projection φ of the light pulse. This potential value is stored at the time of registration of thermal radiation I zapo fflnaya unit 11, which can be used as a peak detector. The potential level from the output of the storage unit 11 is fed / 1et to the control input of the controlled amplifier 12, the gain is inversely proportional to this potential.

Thus, from the signal corresponding to the change in the temperature of sample 2, the influence of the change in flash energy caused by external factors is excluded. The signal from the output of the temperate meter 3, the tours through the controlled amplifier 12 is fed to the inputs of the second differentiator 4 and high pass filter 13. The noise signal from the output of the filter 13 is fed to the input of the detractors and 14, the second input of which receives a signal from the output of the second differentiator 4. A signal proportional to the difference of input signals, from the output of the detractor 14. Through the first differentiator 5 it enters the input zero- organ 6. The impulse from the output of the zero-organ 6 is fed to the input of the meter 9 time interval. The output signal of the device is the time interval between the beginning of the heating pulse and the moment of maximum of the first derivative of the temperature with time f „, then according to the formula 0.0.09T.2 / ()

. - M.P.

thermal diffusivity is calculated, where L is the thickness of the test specimen; “.-Thermal diffusivity.

The diaphragm 15 is made in the form of a cartridge with a hole with a diameter of 0.1 mm, worn on the photodetector (photodiode), and restricts the flow in the photo - diode. The integrator 10 is made on the operational amplifier and the signal at its output is proportional to the total energy of the heating pulse. The storage unit 1 (peak detector) stores the value of the total energy of the heating pulse during the measurement time. The control amplifier 12 is made on an operational amplifier with a field-effect transistor in the transmission control circuit and is designed to automatically correct the signal by the heating energy. The high-pass filter 13 is made on an operational amplifier and is designed to transmit frequencies f (3-5) / f, the minimum measured time.

The output device 14 is made on resistors. Signals to the subtractive device 14 from the outputs of the differentiator 4 and the filter 13 are supplied in antiphase, which ensures frequency interference suppression.

The advantage of the device is to reduce the dispersion of the measured parameter - a time of 1 „, which ensures an increase in the measurement accuracy for a fixed number of measurements.

Claims (1)

Invention Formula A device for measuring the thermal diffusivity of solids, containing an optical pulse heat source, a temperature meter, two differentiators, a photodetector, a shaper of the start of heating pulse, a time interval meter, the output of the first differentiator being connected via a zero-organ to the first. A time slot meter input, to the second input of which the output of the impulse booster of the heating start impulse is connected, the input of which is connected to the photoreceiver, characterized in that, in order to improve the measurement accuracy by reducing the effect of fluctuation of the heating power and reducing the effect of high-frequency interference, diaphragms of a nagrevy flux, installed in front of the photoreceiver, a high-pass filter, a controlled amplifier, an integrator, a storage unit and a subtractive device, are additionally inserted into the device; the torus is connected to the flota receiver, the integrator output is connected to the control input of the controlled amplifier through the storage unit, the input of which is connected to the output of the temperature meter, and the output to the input of the second differentiator and input of the high-pass filter, outputs of the second differentiator and high-pass filter connected to the first and second inputs of the subtracting device, respectively, and its output is connected to the input of the first differentiator.