JP3278567B2 - Method and apparatus for setting applied current value in thermal conductivity measurement - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art As shown in FIG. 4, for example, the measurement of the thermal conductivity by a thin wire heating method (also referred to as a hot wire method) is carried out by heating a heater wire 2 attached to the center of a homogeneous sample 1 in a shape that can be regarded as an infinite cylinder.
A current having a predetermined current value is applied from the power supply 4 to the temperature T ₁ of the sample 1 near the heater wire 2 at a predetermined time t ₁ from the start to the end of the application, and a certain time has elapsed. In this method, 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, a thermocouple may be used as the temperature sensor 3, and a configuration may be used in which a platinum wire is used as the heater wire 2 and the resistance change due to the temperature of the platinum wire is detected as a temperature and a hand.

[0003] The measurement principle of this method is as follows.
That is, when a 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 rises exponentially with the passage of time as shown in FIG. As shown in the figure, the temperature rise curve becomes a straight line, and in Sample 1 having a small thermal conductivity, the temperature rises quickly, so that the slope of the straight line becomes large, and conversely, in 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 the slope can be obtained by the thermal conductivity calculating means 7 in accordance with the following equation 1.

[0004]

(Equation 1) Here, q is a heating value per unit time and unit length of the heater wire 2. According to this thin wire heating method, these q, t
₁ , t ₂ , T ₁ , and T ₂ , the thermal conductivity λ can be directly obtained.
Since the measurement can be performed in a short time of 200 seconds, and the temperature rise of the sample 1 during that period remains at about 20 ° C., this is a very effective measurement method for the sample 1 in which the temperature dependence of the thermal conductivity is large. Furthermore, since the measurement time is short and only a relatively small portion of the sample 1 is heated, a value corresponding to the composition and structure near the sample surface can be obtained as the required thermal conductivity.

In FIG. 4, reference numeral 8 denotes an applied current value.
Is a current control means for controlling the current. By the way, in general
Temperature ΔT (= T
_Two-T₁) And the thermal conductivity λ of the sample are shown in FIG.
If the rise temperature ΔT is too large,
Exceeds the dynamic range and prevents deterioration and burning of sample 1.
There is a problem that it may be invited. Conversely, the temperature rise ΔT
In the region where is small, the rate of change of λ becomes too large
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-mentioned problem, for example, 20
It is necessary to carry out the measurement so that the temperature is around ℃. However, it is possible to predict the thermal conductivity λ of the sample 1 within a certain range depending on the material, but it is essentially unknown. Therefore, the applied current value I at which the appropriate temperature rise ΔT is obtained is set in advance. There is a need to.

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

[0008]

According to the method of setting the applied current value I by trial and error among these conventional applied current value setting methods, it takes a lot of time and effort to obtain the applied current value I. In addition, according to the method using the applied current value I guessed by experience, the applied current value I is not always appropriate, exceeding the dynamic range of the measuring instrument, or causing deterioration or burning of the sample 1. May cause a large measurement error.

The present invention has been made in view of the above circumstances, and has been made in consideration of the above circumstances. A method of setting an applied current value in a thermal conductivity measurement, in which an appropriate applied current value at the time of measurement can be automatically set in a short time before measurement. And an apparatus therefor.

[0010]

The present invention employs the following method to achieve the above object. That is,
A small current I ₀ is applied to the heater wire 2, and an applied current value at which an appropriate measurement can be performed 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 increases by a temperature corresponding to the value of the flowing current and time. At this time, the temperature rise ΔT ₀ of the sample 1 and the predetermined time (t ₂ −t) for obtaining the predetermined temperature rise ΔT at the time of actual measurement.
The relationship between ₁ ) and the current I to be applied to the heater wire can be obtained 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 out from the memory 6 based on the temperature rise ΔT _0. decide.

Therefore, there is no need to repeat trial and error,
The applied current value I at the time of measurement is automatically set in a short time,
Further, since the applied current value I is empirically set to the temperature rise ΔT ₀ , there is no possibility that a large error occurs.

The following apparatus is used to implement the above method. That is, a rising temperature measuring means 5 for measuring a rising temperature of the sample 1 detected by the temperature sensor when a predetermined short-time minute current I ₀ is supplied to the heater wire 2,
A memory for outputting an appropriate applied current value at the time of measurement corresponding to the temperature rise based on the measurement result of the temperature rise measurement means;
Are provided.

As a result, a predetermined short-time minute current I ₀ is applied from the power supply 4 to the heater wire 2, and the temperature rise ΔT ₀ of the sample 1 at this time is measured by the temperature rise measurement means 5. In the device of the present invention, the memory 6 further stores the relationship between the temperature increase ΔT ₀ and the applied current value I that enables proper measurement.
Is provided. Thus, the applied current value I corresponding to the rise temperature ΔT ₀ measured by the rise temperature measurement means 5 is read, 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 above-described method of the present invention, and an appropriate applied current value I at the time of measurement is automatically set in a short time.

[0017]

FIG. 1 is a block diagram showing an embodiment of the apparatus according to the present invention. As with the thermal conductivity measuring device in the conventional thin wire heating method, a heater wire 2 stretched at the center of a homogeneous sample 1 having a shape that can be regarded as an infinite cylinder, and a temperature detecting device arranged near the heater wire 2 A temperature sensor 3 comprising a thermocouple,
A current is applied to the heater wire 2 from a power supply 4.

Further, the current applied from the power supply 4 is controlled by a current control means 8 so that a current corresponding to the sample 1 is generated. Control is exercised.

In the above apparatus, first, the above power supply 4
The small current I by the current control circuit 8 ₀, For example, 0.5A
Is applied to the heater wire 2 for a predetermined short time (preheat
G). In the present invention, further, a rising temperature measuring means 5 is provided.
The above-mentioned current application is opened by the rising temperature measuring means 5.
Time after the start of the predetermined time (for example, after the start of current application)
1 second) and the time after a predetermined short time has elapsed
(Eg, 10 seconds after the start of current application) near heater wire 2
Temperature difference of the sample 1, ie, the minute current I₀Application of
In a predetermined short time from a predetermined time after the start (for example, application start
1 second to 10 seconds after) the temperature rise ΔT of sample 1₀Is measured
You.

In the above description, the first second is excluded from the measurement target in order to eliminate unstable personnel. However, if there is no unstable personnel, the first second may be included in the predetermined short time. No problem.

Further, in the present invention, the above-mentioned temperature rise ΔT ₀ ,
A memory 6 for storing a relationship between the current value I and an appropriate applied current value at the time of measurement, which is empirically recognized to correspond thereto, and a reading means 9 are provided. As a result, the temperature increase ΔT ₀
Is applied to the reading means 9, the applied current value I corresponding to the temperature increase 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 "relationship between the temperature rise 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 to obtain a predetermined temperature rise ΔT (for example, 20 ° C.) in the sample 1 during a predetermined time (t ₂ −t ₁ ) at the time of measuring the thermal conductivity corresponds to the thermal conductivity. I'm doing On the other hand, the temperature rise ΔT ₀ of the sample 1 due to the minute current I ₀ applied in the predetermined short time also corresponds to the thermal conductivity. However, if the thermal conductivity is directly calculated from the temperature rise ΔT ₀ of the sample 1 due to the minute current I ₀ , the error increases, 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 appropriate applied current I is obtained. The relationship between the temperature rise ΔT ₀ stored in the memory 6 and the applied current value I at which proper measurement can be performed at the time of measurement is as shown in Table 1, for example.

[0023]

[Table 1] In Table 1 above, the rise temperature ΔT ₀ is taken step by step.
Needless to say, the continuous relationship between the temperature increase ΔT ₀ and the applied current value I may be stored in the memory 6.

This device has a thermal conductivity calculating means 7 selectively connected to the temperature sensor 3 and the rising temperature measuring means 5.
The heat conductivity measuring device for measuring the heat conductivity of the sample 1 and the heater wire 2 and the temperature sensor 3 are also used. Is applied to the heater wire 2, a measurement current of the applied current value I set as described above is applied, and at a time t after a predetermined time has elapsed after the start of the application.
The sample temperatures T ₁ , T ₂ near the heater wire 2 at ₁ and at a time t ₂ after a certain time has elapsed are measured, and the thermal conductivity calculating means 7 calculates the temperatures T ₁ , T ₂ and the time. Based on t ₁ and t ₂ , the thermal conductivity λ is calculated in accordance with the above equation (1).

That is, as shown in the flow chart of FIG. 2, the method for setting the applied current value of the thin wire heating method according to one embodiment of the method of the present invention, which is carried out using this apparatus, is based on the thermal conductivity of the sample 1. The measurement is performed prior to the measurement, and the heater wire 2 and the temperature sensor 3
Is set on the sample 1, the temperature sensor 3 is connected to the rising temperature measuring means 5, and after starting, a small current I ₀ of, for example, 0.5 A is applied from the power source 4 to the heater wire 2 (S
1) When one second elapses after the start of the application (S2), the temperature of the sample 1 is measured using the temperature sensor 3 (S3). When ten seconds elapse after the start of the application (S4), the temperature sensor is again activated. temperature of the sample 1 with 3 minute current I ₀ is stopped while being measured (S5).

[0026] Then, the temperature rise [Delta] T ₀ of the predetermined short time (1-10 seconds) is measured by the temperature rise measurement section 5 (S6), the applied current value I corresponding to the temperature increase [Delta] T 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 current value of the measured current 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 connection of the temperature sensor 3 to the thermal conductivity calculating means 7 is switched to stabilize the temperature of the sample 1 (for example, FIG. Wait for the temperature to return to the initial temperature T ₀ of Step 5 (S8).
Note that the order of steps S7 and S8 may be reversed.

Thereafter, the measurement of the thermal conductivity λ of the sample 1 is performed according to the following procedure. That is, the measurement current of the applied current value I set from the power supply 4 is applied to the heater wire 2 (S9),
When a predetermined time t ₁ after the application start (S10),
Temperature T ₁ of the sample using a temperature sensor 3 is measured (S1
1), this then becomes a time t ₂ has elapsed further predetermined time (S12), the temperature T of the sample 1 using the temperature sensor 3 again
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 above equation (S14).

The calorific value q per unit time and unit length of the heater wire 2 in this calculation is calculated based on the applied current value I. Further, thereafter, given a termination command (S15), the program is terminated, and otherwise return to the application start state before the minute current I _0.

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

[0031]

As described above, according to the method of the present invention, a minute current is applied to the heater wire set on the sample for a predetermined short time (preheating), and the temperature of the sample is measured during this time. By reading the appropriate applied current value corresponding to the temperature from the memory, the appropriate 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 continuously performed.

When the thermal conductivity is measured by changing the measurement temperature of a substance having a large temperature dependence of the thermal conductivity, an appropriate applied current value differs depending on the measurement temperature. The applied current value corresponding to the measurement temperature can be automatically set.

[Brief description of the drawings]

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

FIG. 2 is a flowchart of the method of the present invention.

FIG. 3 is a graph showing a relationship between a temperature difference caused by 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 change in temperature of a sample due to current application.

FIG. 6 is a graph showing a change in temperature 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 temperature rise and the thermal conductivity.

[Explanation of symbols]

 Reference Signs List 1 sample 2 heater wire 3 temperature sensor 4 power supply 5 rising temperature calculating means 6 memory

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 25/18 G01N 25/00

Claims (2)

(57) [Claims] In a thermal conductivity measuring method using a thin wire heating method, a minute current is applied to a heater wire for heating, and an appropriate measurement is performed based on a temperature rise of a sample near the heater wire in a predetermined short time. A method for setting an applied current value in the measurement of thermal conductivity, characterized by setting an applied current value capable of performing the following. 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 for a predetermined short time is applied to the heater wire. A rising temperature measuring means for measuring a 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 in thermal conductivity measurement, comprising a memory for outputting.