JPS6351499B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal constant measuring device for measuring the thermal constant of a solid by a laser flash method.

According to the laser flash method, a disk-shaped specimen is instantaneously irradiated and heated from the front side with a laser flash, and the temperature change on the back side is detected by a thermocouple or an infrared temperature detector, and the temperature change is measured. Then, the thermal diffusivity (α) and specific heat (Cp) of the sample can be determined. FIG. 1 is a graph showing the temperature change ΔT of a certain substance after instantaneous irradiation. The thermal diffusivity α is given by the following equation by knowing the instant t(1/2) until ΔT reaches 1/2 of the maximum value ΔTm shown in the figure.

α=1.37L ² /π ²・t(1/2) ...(1) However, L: Thickness of the sample Also, specific heat (Cp) is calculated using ΔTm ₀ calculated from the above graph or measured value. It is given by the following formula.

Cp = ΔQ/M・ΔTmo ...(2) where, M: Mass of the sample ΔQ; Thermal energy received by the irradiation of the sample As mentioned above, (α) can be calculated by knowing the temperature change with respect to ΔTm. 1/2) can be obtained from equation (1).

Since ΔTmo, which is necessary to determine (Cp), cannot be measured, a method is used that estimates it from the change in sample temperature after tm.

Attempting to achieve the above-mentioned thermal constant using digital processing technology in the same device causes the following problems.

The time to tm is extremely short, but it varies depending on the sample. During that time, temperature changes must be sampled and stored at short time intervals. In order to obtain ΔTmo, it is necessary to obtain data on temperature changes over a considerable period of time after tm.
If such data are obtained at the same sampling interval, a large capacity memory will be required, making it difficult to implement the apparatus.

The main object of the present invention is to provide a thermal constant measuring device that can measure both constants simultaneously with the same device by changing the sampling interval depending on the purpose of measurement.

A first aspect of the present invention to achieve the above object.
The configuration of the is to rationally store the necessary data of the sample temperature change (ΔT) in the same memory by first storing it at a high sampling frequency and then at a low frequency, and then using the laser data obtained separately from these data. This is an attempt to obtain various thermal constants from the energy ΔQ data.

The second configuration is to change the sampling frequency of the separately prepared memories, one to obtain data to obtain t(1/2), and the other to obtain data to obtain ΔTmo, and use the data for ΔQ obtained separately in the same way as above. Similarly, it is configured to obtain a thermal constant.

The third configuration is to control the switch and sampling frequency so that one of the separately prepared memories obtains data for ΔQ and data for obtaining ΔTmo, and the other obtains data for t(1/2). , the thermal constant and the laser beam pulse width can be corrected.

The thermal constant measuring device according to the present invention will be explained in more detail below with reference to the drawings and the like.

FIG. 2 is a block diagram showing an embodiment of the first configuration of the apparatus according to the invention, and FIG. 3 is a graph schematically showing the sampling state.

The output of the ruby laser oscillator forming the laser light source 1 is transmitted to the sample 4 in the sample chamber 3 by 1 m via a divider.
Irradiate with a light pulse of s position.

A portion of this optical pulse is divided by a splitter 2 such as a half mirror and supplied to the optical sensor 8.

The sample chamber 3 is maintained at a constant temperature at fixed times by a temperature controller 6. A platinum-platinum-rhodium thermocouple 5 is brought into contact with the back surface of the sample 4. Further, the temperature of this back surface is measured without contact by an indium antimony infrared detector 7. These detectors 5, 7 are used for one-sided correction or selectively. The respective outputs are amplified by preamplifiers 9 and 10 and selectively connected to amplifier 18 via switch 20. A portion of the laser light split by the splitter 2 is photoelectrically converted by an optical sensor 8 made of a silicon diode detector. The output of this optical sensor 8 is amplified by an amplifier 11, and an integrator 13 and a rise detector 1
Connected to 2. The integrator 13 is a circuit for determining ΔQ shown in the above-mentioned equation (2).

When the detector 12 detects laser emission, the output of high frequency sampling is sent out for a time preset by the setting device 35, and after the elapse of that time, the output of low frequency sampling is sent out.

The set period is a period preset to slightly exceed t _n shown in Figure 1, and sample 4
Generally set between 0.05 and 5s, taking into consideration the shape and material of the.

A memory 15 connected to the output of the amplifier 18 stores sampled data which is sampled at the preset sampling interval and A/D converted. After the above period has elapsed, data is sampled at 25 ms and similarly A/D converted and stored. The arithmetic circuit 16 calculates the t(1/2) based on the data sampled at the initial sampling interval, and calculates the input L.
Thermal diffusivity (α) is calculated using the algorithm shown in equation (1).
Calculate. In addition, ΔTmo is calculated by extrapolation using the 25 ms sampling data, and from the data regarding ΔQ from the integrator 13 and the input M, formula (2) is used.
Calculate specific heat (Cp) using the algorithm shown below.
This calculation result is displayed or outputted by the output means 17, a Braun Kandy display, a printer, or the like.

FIG. 3 is a graph showing the sampling state. The sampling ratio is kept small for presentation purposes.

FIG. 4 is a block diagram showing a second embodiment of the apparatus according to the invention. The same parts as those described in connection with the first embodiment are given the same reference numerals, and include a laser light source 1, a splitter 2, a sample chamber 3, an optical sensor 8, temperature sensors 5 and 7, and an integrator. Vessel 1
3, etc. are common.

In this embodiment, the first memory 21 samples and stores the output of the temperature sensor at a high frequency (25 ms pulse interval), and the first memory 21 samples and stores the output of the temperature sensor at a low frequency (25 ms pulse interval).
A second memory 22 for sampling and storing data at a pulse interval of ms is provided.

When the laser 1 is activated, the surface of the sample 4 is irradiated, and a portion of the divided light is sent to the integrator 13.
The above-mentioned integration of ΔQ is then started.

On the other hand, when a rising edge is detected by the rising edge detector 12, the control circuit 25 activates the first and second memories. Note that the setting device 27 is used to set the sampling interval, the amount of preliminary memory before laser emission, and the like. In this embodiment, the rising edge detector 1
2. The control circuit 25 and the setting device 27 form a starting circuit, which operates each memory after detecting the rise of the laser beam. The first memory 21 continues sampling and stores data at the set sampling interval from the time of startup as long as the memory capacity allows. This capacity is large enough to store at least data up to the time tm shown in FIG.

The second memory 22 performs sampling at a lower frequency. FIG. 5A schematically shows the sampling state of the first memory 21, and FIG. 5B schematically shows the sampling state of the second memory 22.

The data stored in this manner is used by the arithmetic circuit 29 to calculate the thermal diffusion constant (α) from the contents of the first memory 21 and the specific heat (Cp) from the outputs of the second memory 22 and the integrator 13. . This calculation result is outputted by the output device 17 as described above.

FIG. 6 is a block diagram showing an embodiment of the third configuration. In this embodiment as well, the same reference numerals are given to the parts common to those previously explained in FIGS. 2 and 4.

This embodiment does not use the integrator shown in FIGS. 2 and 4, but is configured so that the sampling data of the laser output is taken into an area of a small address in the first memory 23. Therefore, the first memory 23 is provided with a changeover switch 39 for initially taking in the output from the optical sensor 8 and then taking in the output from the temperature sensor 5 or 7, and the operation of this switch is controlled by the control circuit 26. It is configured. The setting device 28 is a setting device for inputting the designation of the sampling frequency, the switching timing, and the like.

FIG. 7A schematically shows sampling positions of data stored in the first memory 23, and FIG. 7B shows sampling positions of data stored in the second memory 24. In order to facilitate understanding, the width of the laser pulse that first appears in FIG.

As shown in Fig. 7, the rise of the laser beam is at the sixth
When detected by the rising edge detector 12 shown in the figure, the control circuit 26 controls the first and second memories 23, 2.
4 at the same time with a high sampling frequency.

Note that since the changeover switch 39 is initially connected to the amplifier 11 side, that is, to the side receiving the output of the optical sensor 8, the laser beam data is sampled and stored. The second memory 24 similarly samples and stores the temperature change of the sample at high speed. The changeover switch 39 is switched to the position shown in FIG. 6 after the laser beam disappears (Tc), and thereafter switched to a lower sampling frequency to store temperature change data.

When storage is performed in this way, the first memory 23 stores data regarding ΔQ and the data necessary to calculate ΔTmo, and the second memory stores data related to ΔQ and data necessary to calculate ΔTmo. The necessary data is stored. Based on these, the arithmetic circuit 30 calculates (α) and (Cp) as described above, and the output device 17 outputs the result of this calculation.

Generally speaking, in the laser flash method, the above formula (1) holds when the duration τ of the laser pulse is sufficiently small compared to t(1/2).
When this cannot be ignored, it is necessary to make some corrections, and proposals have been made for corrections in such cases. In the case of this third embodiment, since the data of the laser pulse waveform is stored, it can be corrected when calculating (α).

As explained in detail above, according to the present invention, since data is obtained by changing the sampling frequency, memory can be used effectively and thermal constants can be measured without using a huge memory. Summer. Moreover, it has become possible to obtain data on both thermal diffusivity and specific heat with a single laser emission.

In the first configuration, data on t(1/2) and ΔTmo can be obtained using the same memory. Second
With this configuration, each data is stored separately, so processing is easy.

It is also convenient for measuring samples whose tm is difficult to estimate.

In the third configuration, data regarding the laser pulse waveform is obtained, thereby eliminating the need for an integrator.

Furthermore, corrections related to pulse waveforms become possible.

[Brief explanation of the drawing]

FIG. 1 is a graph for explaining the principle of flash method thermal constant measurement, and FIG. 2, FIG. 4, and FIG.
Block diagram showing the second and third embodiments, No. 3
5 and 7 are graphs for explaining the sampling timing of the first, second and third embodiment devices, respectively. 1... Laser, 2... Divider, 3... Sample chamber,
4... Sample, 5... Thermocouple, 6... Temperature controller,
7... Infrared temperature detector, 8... Laser light detector (optical sensor), 9, 10... Preamplifier, 11...
Amplifier, 12... Rise detector, 13... Integrator, 14... Control circuit, 15... Memory, 16...
... Arithmetic circuit, 17... Output device, 18, 19...
Main amplifier, 20...Switch, 21, 22, 2
3, 24... memory, 25, 26... control circuit,
27, 28... Setting device, 29, 30, 31... Arithmetic unit, 39... Changeover switch.

Claims (1)

[Scope of Claims] 1. A laser light source, a splitter that takes out a part of the light from the light source, a sample whose one side is irradiated with the light that has passed through the splitter, and an electrical system that measures the temperature of the other side of the sample. a temperature sensor that converts the light into a quantity, and a light sensor that photoelectrically converts a portion of the light extracted from the splitter;
specifying a high frequency sampling period for a certain period of time set in advance so that the temperature of the other surface exceeds the maximum temperature from the time when the optical sensor output is generated;
Subsequently, a period designator generates a signal specifying a low frequency sampling period, a memory that samples and stores the temperature sensor output at the frequency designated by the period designator, and an integrator that integrates the optical sensor output. A thermal constant measuring device comprising: a calculation circuit that calculates a thermal constant from the contents of the memory or the contents and an integrator output; and an output device that outputs the calculation result of the calculation circuit. 2. A laser light source, a splitter that takes out a portion of the light from the light source, a sample whose one side is irradiated with the light that has passed through the splitter, and a temperature sensor that converts the temperature of the other side of the sample into an electrical quantity. and an optical sensor that photoelectrically converts a portion of the light extracted from the splitter;
an integrator that integrates the optical sensor output; a first memory that samples and stores the temperature sensor output at a high frequency; a second memory that samples and stores the temperature sensor output at a low frequency; a startup circuit that activates the first and second memories based on the optical sensor output; and an arithmetic circuit that calculates the thermal diffusivity from the contents of the first memory and the specific heat from the contents of the second memory and the output of the integrator. , and an output device that outputs the calculation results of the calculation circuit. 3. A laser light source, a splitter that extracts a portion of the light from the light source, a sample whose one side is irradiated with the light that has passed through the splitter, and a temperature sensor that converts the temperature of the other side of the sample into an electrical quantity. and an optical sensor that photoelectrically converts a portion of the light extracted from the splitter;
a rise detector that detects a rise upon receiving the optical sensor output; a changeover switch that initially switches and connects the optical sensor output and then the temperature sensor output; and a first memory to which a sampling input is connected via the switch. , a second memory connected to the optical sensor output and the respective memories are activated by the output of the rise detector, sampled at a high frequency and stored, and after the output of the laser light source disappears, the switch is switched; a control circuit that samples and stores a first memory at a low frequency; an arithmetic circuit that calculates a specific heat from the contents of the first memory and a thermal diffusivity from the contents of a second memory; and outputs the arithmetic results of the arithmetic circuit. A device for measuring thermal constants.