JPH09210933A - Method and apparatus for setting applied current value in thermal conductivity measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make automatic setting of the proper value of applied current by feeding in a short time a minute current to a heater wire which is set on a sample, measuring the temp. rise of the sample during this period, and reading out of the memory the proper amperage value corresponding to the temp. rise. SOLUTION: A temp. rise calculating means 5 measures the temp. rise of a sample 1 using a temp. sensor 3 when a minute current flows in a heater wire 2 for a short period of time, while a memory 6 outputs a proper value of feed current at measuring corresponding to the temp. rise on the basis of the result from measurement. From a power supply 4 a minute current is fed to the heater wire 2 for the specified short time, and the temp. rise ΔT0 of the sample 1 at this time is measured by a temp. rise calculating means 5. The relation of the obtained ΔT0 value to the feed amperage I measurable properly is stored in the memory 6, wherefrom the feed amperage I corresponding to the applicable temp. rise ΔT0 is read, and the applied amperage at the time of measuring is set. This enables automatic setting of the proper applied amperage I in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an applied current value setting method and apparatus for a thin wire heating method, and more particularly to a fine wire capable of automatically setting an appropriate current value applied to a heater wire in a short time before measurement. The present invention relates to an applied current value setting method for a heating method and an apparatus thereof.

[0002]

2. Description of the Related Art For example, as shown in FIG. 4, the measurement of the thermal conductivity by a thin wire heating method (also referred to as a hot wire method) is performed with a heater wire 2 stretched around the center of a homogeneous sample 1 having a shape that can be regarded as an infinite cylinder.
A current having a predetermined current value is applied from the power source 4 to the temperature of the sample 1 in the vicinity of the heater wire 2 at a predetermined time t ₁ from the start to the end of the application, and a certain time elapses further than this temperature T _1. The temperature T _{2 of the} sample 1 at the time t ₂ is measured by the temperature sensor 3, and the thermal conductivity λ is measured based on the _two temperatures T ₁ and T ₂ . In this case, as the temperature sensor 3, a thermocouple is used, and as the heater wire 2, a platinum wire is used, and a structure in which the resistance change due to the temperature of the platinum wire is detected by the temperature and the finisher is also used.

The measuring principle of this method is as follows.
That is, when constant power is continuously supplied from the power source 4 to the heater wire 2, the sample temperature in the vicinity of the heater wire 2 exponentially rises with the passage of time as shown in FIG. 5, and when the time axis is set to a logarithmic scale, FIG. As shown in, the temperature rising curve becomes a straight line, and in the sample 1 having a small thermal conductivity, the temperature rising is fast, and therefore the slope of this straight line becomes large, and conversely, in the sample 1 having a large thermal conductivity, the slope of this straight line becomes small. . Therefore, the thermal conductivity λ corresponds to the slope of the temperature rise graph in logarithmic time, and this slope can be obtained by the thermal conductivity calculation means 7 according to the following mathematical formula 1.

[0004]

[Equation 1] Here, q is the amount of heat generation of the heater wire 2 per unit time and unit length. According to this thin wire heating method, these q, t
_The thermal conductivity λ can be directly obtained from ₁ , t ₂ , T ₁ and T _2, and after applying a current to the heater wire 2, 10 to 10 can be obtained.
Since the measurement can be performed in a short time of 200 seconds and the temperature rise of the sample 1 stops at about 20 ° C. during that time, it is a very effective measurement method for the sample 1 having a large temperature dependence of thermal conductivity. Further, since the measurement time is short and only a relatively small portion of the sample 1 is heated, the required thermal conductivity can be a value corresponding to the composition and structure near the sample surface.

In FIG. 4, reference numeral 8 is an applied current value.
It is a current control means for controlling. By the way, generally
Rise temperature ΔT (= T
_Two-T₁) And the thermal conductivity λ of the sample are shown in Fig. 7.
There is such a relationship, and if the temperature rise ΔT is too large,
Exceeding the dynamic range, and deterioration or burning of sample 1
There is a problem that it may invite. Conversely, the temperature rise ΔT
In the region where is small, the rate of change of λ becomes too large and the measurement
There is a problem that the degree decreases.

Therefore, in this thin wire heating method, the temperature rise ΔT is set to an appropriate value which does not cause the above problem, for example, 20.
It is necessary to measure the temperature around ℃. However, the thermal conductivity λ of the sample 1 can be predicted within a certain range depending on the material, but it is essentially unknown. Therefore, the applied current value I that can obtain the appropriate increased temperature ΔT is set in advance. There is a need to.

Conventionally, as a method of setting the applied current value I, prior to the measurement of the thermal conductivity, the applied current value I is changed and trial and error are repeated several times to increase the temperature ΔT by, for example, 2.
There are a method of selecting a value that is around 0 ° C. and a method of selecting a value at which the temperature rise ΔT estimated by experience is likely to be around 20 ° C.

[0008]

Among these conventional applied current value setting methods, the method of setting the applied current value I by trial and error requires a great deal of time and effort before the applied current value I is obtained. However, according to the method of using the applied current value I estimated by experience, the applied current value I is not always appropriate and may exceed the dynamic range of the measuring instrument, or cause deterioration or burning of the sample 1. There is a possibility that a large measurement error will occur.

The present invention has been made in view of the above circumstances, and is a method for setting an applied current value in a thermal conductivity measurement which enables automatic setting of an appropriate applied current value at the time of measurement before measurement. And its device.

[0010]

The present invention employs the following method in order to achieve the above object. That is,
A minute current I ₀ is applied to the heater wire 2, and an applied current value that allows proper measurement is set based on the temperature rise ΔT ₀ of the sample 1 near the heater wire 2 in a predetermined short time. .

As described above, when the minute current I ₀ is applied to the heater wire 2 for a predetermined short time, the temperature of the sample 1 near the heater wire rises by a temperature corresponding to the value of the flowing current and the time. The rising temperature ΔT ₀ of the sample 1 at this time and the predetermined time (t ₂ −t) in order to obtain the predetermined rising temperature ΔT at the time of actual measurement.
The relationship between ₁ ) and the current I to be applied to the heater wire can be found empirically.

Therefore, the relationship between the temperature rise ΔT ₀ and the applied current I is stored in the memory 6, and the current value I to be applied at the time of actual measurement is read from the memory 6 from the temperature rise ΔT _0. decide.

Therefore, it is not necessary to repeat trial and error,
The applied current value I at the time of measurement is automatically set in a short time,
Further, the applied current value I is empirically set to the above-mentioned raised temperature ΔT ₀ , so that there is no possibility of causing a large error.

The following devices are used to implement the above method: That is, the temperature rise measuring means 5 for measuring the temperature rise of the sample 1 detected by the temperature sensor when a minute current I ₀ is passed through the heater wire 2 for a predetermined time,
A memory 6 which outputs an appropriate applied current value at the time of measurement corresponding to the temperature rise based on the measurement result of the temperature rise measuring means 5.
And is configured to include.

As a result, a minute current I ₀ is applied from the power source 4 to the heater wire 2 for a predetermined short time, and the temperature rise ΔT ₀ of the sample 1 at this time is measured by the temperature rise measuring means 5. In the device of the present invention, the memory 6 further stores the relationship between the increased temperature ΔT ₀ and the applied current value I that enables proper measurement.
Is provided. As a result, the applied current value I corresponding to the increased temperature ΔT ₀ measured by the increased temperature measuring means 5 is read out, and the applied current value I at the time of measurement is set to the read applied current value I.

Thus, the apparatus of the present invention implements the method of the present invention, and automatically sets an appropriate applied current value I at the time of measurement in a short time.

[0017]

1 is a block diagram of an embodiment of the device of the present invention. Similar to the thermal conductivity measuring device in the conventional thin wire heating method, a heater wire 2 stretched around the center of a homogeneous sample 1 having a shape that can be regarded as an infinite cylinder, and a temperature detecting element arranged near the heater wire 2 for temperature detection. A temperature sensor 3 including a thermocouple,
A current is applied to the heater wire 2 from a power supply 4.

Further, the current applied from the power source 4 is controlled by the current control means 8 so that the current corresponding to the sample 1 is applied, and the current at the time of preheating with the minute current of the present invention described below is also used. Control is made.

In the above device, the above power source 4
From the current control circuit 8 ₀, For example, 0.5A
Is applied to the heater wire 2 for a predetermined time (preheat
G). The present invention further includes a temperature rise measuring means 5.
Then, the rising temperature measuring means 5 opens the above-mentioned current application.
The time when a predetermined time has passed since the start (for example, after starting the current application)
1 second) and the time when a predetermined short time has passed
(For example, 10 seconds after starting the current application) near the heater wire 2
Temperature difference of the sample 1, that is, the minute current I₀Application of
From a predetermined time after the start for a predetermined short time (for example, application start
1 second to 10 seconds later) rise temperature ΔT of sample 1₀Is measured
You.

In the above, the first second is excluded from the object of measurement in order to eliminate unstable personnel. However, if there are no unstable personnel, the first second may be included in the predetermined short time. It doesn't matter.

Further, in the present invention, the above-mentioned temperature increase ΔT ₀ ,
A memory 6 storing a relationship with an appropriate applied current value I at the time of measurement, which is empirically determined to correspond to this, and a reading means 9 are provided. As a result, the temperature rise ΔT ₀
Is applied to the reading means 9, the applied current value I corresponding to the increased temperature ΔT ₀ is read from the memory 6 and given to the current control means 8 as the applied current value I at the time of measurement.

The above "relationship between the rising temperature ΔT ₀ and the applied current value I" can be considered as follows. That is, the current I to be passed through the heater wire 2 in order to obtain a predetermined temperature rise ΔT (for example, 20 ° C.) in the sample 1 during a predetermined time (t ₂ −t ₁ ) when measuring the thermal conductivity corresponds to the thermal conductivity. I'm doing it. On the other hand, the temperature rise ΔT ₀ of the sample 1 due to the minute current I ₀ applied for the predetermined short time also corresponds to the thermal conductivity. However, if the thermal conductivity is calculated directly from the temperature rise ΔT ₀ of the sample 1 due to this minute current I ₀ , the error becomes large, which is inconvenient. Therefore, as shown in FIG. 3, predict thermal conductivity lambda ₀ of the sample than the elevated temperature [Delta] T ₀ of the sample 1 by the minute current I _0, the current value obtained through the predictive heat conductivity lambda ₀ is, The applied current I becomes appropriate. Table 1 shows the relationship between the temperature rise ΔT ₀ stored in the memory 6 and the applied current value I that enables proper measurement at the time of measurement.

[0023]

[Table 1] In Table 1 above, the temperature rise ΔT ₀ is taken stepwise,
Of course, the continuous relationship between the temperature rise ΔT ₀ and the applied current value I may be stored in the memory 6.

In this apparatus, the thermal conductivity calculating means 7 is selectively connected to the temperature sensor 3 and the rising temperature measuring means 5.
The heater wire 2 and the temperature sensor 3 can be used also as a thermal conductivity measuring device for measuring the thermal conductivity of the sample 1 after this. At the time of measurement, the thermal conductivity calculating means 7 is used for the temperature sensor 3 After the connection to the heater wire 2, a measurement current having the applied current value I set as described above is applied to the heater wire 2, and at a time t when a predetermined time has elapsed after the start of the application.
The sample temperatures T ₁ and T ₂ in the vicinity of the heater wire 2 at ₁ and the time t ₂ after a certain time has elapsed are measured, and the thermal conductivity calculating means 7 measures these temperatures T ₁ and T ₂ and time. Based on t ₁ and t ₂ , the thermal conductivity λ is calculated according to the above-mentioned formula 1.

That is, as shown in the flow chart of FIG. 2, the applied current value setting method of the thin wire heating method according to one embodiment of the method of the present invention carried out using this apparatus is as follows. The heater wire 2 and the temperature sensor 3 are carried out prior to the measurement.
Is set on the sample 1, the temperature sensor 3 is connected to the rising temperature measuring means 5, and after the start, a minute current I ₀ of, for example, 0.5 A is applied from the power source 4 to the heater wire 2 (S
1) After 1 second has passed from the start of the application (S2), the temperature of the sample 1 is measured using the temperature sensor 3 (S3), and 10 seconds after the start of the application (S4), the temperature sensor is turned on again. 3 is used to measure the temperature of the sample 1 and the minute current I ₀ is stopped (S5).

Then, the rising temperature measuring means 5 measures the rising temperature ΔT _{0 for the} predetermined short time (1 to 10 seconds) (S6), and the applied current value I corresponding to this rising temperature ΔT _0.
Is read from the memory 6 to the reading means 9 and the read applied current value I is given to the current control means 8 to set the measured current value to the applied current value I (S7).

In this embodiment, after the applied current value I at the time of measurement is set as described above, the temperature sensor 3 is connected and switched to the thermal conductivity calculating means 7 to stabilize the temperature of the sample 1 (for example, as shown in FIG. Wait until it returns to the initial temperature T _{0 of} 5 (S8).
The order of steps S7 and S8 may be reversed.

After that, the thermal conductivity λ of the sample 1 is measured by the following procedure. That is, the measurement current of the applied current value I set from the power source 4 is applied to the heater wire 2 (S9),
At a predetermined time t ₁ after the start of the application (S10),
The temperature T _{1 of} the sample is measured using the temperature sensor 3 (S1
1) After that, at time t ₂ when a certain time has elapsed (S12), the temperature T of the sample 1 is again measured using the temperature sensor 3.
₂ is measured and the measurement current is stopped (S13),
The thermal conductivity λ is calculated by the thermal conductivity calculating means 7 according to the mathematical formula 1 (S14).

The heat generation amount q per unit time and unit length of the heater wire 2 in this calculation is calculated based on the applied current value I. After that, when an end command is given (S15), the program ends, and in other cases, the state returns to the state before the start of application of the minute current I ₀ .

Furthermore, the procedure of measurement (S9 to S13) with the set applied current value I can be repeated a plurality of times, and the average value of the measured values of each time can be finally used as the measured value.

[0031]

As described above, according to the method of the present invention, a minute current is applied (preheated) to the heater wire set on the sample for a predetermined short time, and the temperature rise of the sample during this period is measured, and the temperature rise is measured. By reading the proper applied current value corresponding to the temperature from the memory, the proper applied current value at the time of measurement can be automatically set within a short time, and the preheating and the next main measurement can be performed continuously.

Further, when the thermal conductivity is measured by changing the measurement temperature of a substance having a large temperature dependence of the thermal conductivity, the appropriate applied current value varies depending on the measured temperature, but this method automatically The applied current value corresponding to the measured temperature can be automatically set.

[Brief description of drawings]

FIG. 1 is a configuration diagram of the device of the present invention.

FIG. 2 is a flow chart of the method of the present invention.

FIG. 3 is a graph showing a relationship between a temperature difference due to a minute current and an appropriate current.

FIG. 4 is a configuration diagram of an apparatus for performing a conventional thin wire heating method.

FIG. 5 is a graph showing a temperature change of a sample due to application of a current.

FIG. 6 is a graph showing a temperature change of a heater wire due to application of a current on a logarithmic time axis.

FIG. 7 is a graph showing the relationship between the rising temperature and the thermal conductivity.

[Explanation of symbols]

 1 sample 2 heater wire 3 temperature sensor 4 power supply 5 rising temperature calculation means 6 memory

Claims (2)

[Claims] 1. A method for measuring thermal conductivity using a thin wire heating method, in which a minute current is applied to a heater wire for heating, and an appropriate measurement is performed based on the temperature rise of a sample near the heater wire in a predetermined short time. A method for setting an applied current value in thermal conductivity measurement, which comprises setting an applied current value capable of controlling. 2. A heater wire for heating, a temperature sensor for detecting a temperature in the vicinity of the heater wire, and a thermal conductivity measuring device using a thin wire heating method, wherein a minute current is applied to the heater wire for a predetermined predetermined short time. A rising temperature measuring means for measuring the rising temperature of the sample detected by the temperature sensor when flowing, and an appropriate applied current value at the time of measurement corresponding to the rising temperature based on the measurement result of the rising temperature measuring means. An applied current value setting device for thermal conductivity measurement, comprising: an output memory.