JP3246860B2 - Thermal characteristic measuring device and soil moisture content measuring device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring thermal characteristics such as volumetric heat capacity and thermal conductivity of an object to be inspected, such as soil, and is particularly suitable for continuous measurement on site because the invasion of the object to be inspected is slight. Regarding improvement.

[0002]

2. Description of the Related Art For example, Japanese Patent Application Laid-Open No.
As disclosed in Japanese Patent Application Laid-Open No. 195443/1992, physical properties are measured by applying heat to an object to be measured. In the field of agriculture, there is an increasing need to measure the soil moisture content and optimally supply precious water in desert agriculture, facility horticulture, and the like.

[0003] As a technique for measuring the soil moisture content, a measurement method for measuring and indirectly determining the thermal conductivity is known (see, for example, "Agriculture of the Month", October 1989). FIG. 7 is a sectional view of the configuration of a conventional probe-type thermal conductivity measuring device. In the figure, a heater wire and a temperature-measuring resistance wire are inserted inside a stainless steel pipe having a diameter of about 1 mmφ.
The stainless steel pipe is pierced into the soil, a heater wire is energized and heated, and the time during which the temperature rises to about 2 to 5 ° C. is measured using a temperature measuring resistance wire. FIG. 8 is a relationship diagram between the thermal conductivity and the moisture content. Depending on whether the soil is a dip or a volcanic ash soil, the thermal conductivity generally increases as the moisture content increases. Therefore, the soil moisture content can be measured indirectly by obtaining the relationship between the moisture content and the thermal conductivity of the soil to be measured in advance.

[0004]

However, the thermal conductivity is a measure of the temperature rise and the time required for the temperature rise. There was a problem that it was difficult to measure the soil moisture content accurately because of the influence of errors. Therefore, as a method of measuring the soil moisture content without much depending on the properties of the soil, measuring the volumetric heat capacity or the specific heat has been performed. However, in the conventional measurement of volumetric heat capacity, since a sample is put in a specific heat measurement container, there is a problem that an operation of collecting soil is required and continuous measurement cannot be performed. An object of the present invention is to solve the above-described problems and to provide a device for measuring thermal characteristics such as volumetric heat capacity, which can perform continuous measurement with minimal invasion to a sample like a probe.

[0005]

According to the present invention for achieving the above object, there is provided a heating element inserted into an object to be inspected, heat generation control means for causing the heating element to generate a pulsed heat of a predetermined heat quantity Qpulse, A temperature measuring means 30 which is held at a predetermined interval ro with the heating element and measures a temperature change occurring in the inspection object due to the pulsed heating of the heating element; and a temperature rising peak in a temperature waveform measured by the temperature measuring means. The temperature change recording means 40 for obtaining the value ΔTpeak and the peak time tpeak, the temperature rise peak value obtained by the temperature change recording means, and the arrangement of the heating element and the temperature measuring means with respect to the test object. Volumetric heat capacity Co
Alternatively, there is provided a thermal characteristic calculating means 50 for calculating the temperature conductivity Do or calculating the thermal conductivity Ko of the inspection object from the peak temperature and the peak time obtained by the temperature change recording means.

According to the configuration of the present invention, the pulse-like heat generated by the heating element diffuses into the object to be inspected, and after a certain transmission delay time, the peak value of the temperature rise is located at the temperature measuring means. Is generated. The temperature change recording means records the time-dependent change of the temperature measurement to facilitate obtaining the temperature rise peak value ΔTpeak and the peak time tpeak. The thermal characteristic calculating means calculates the volumetric heat capacity from the temperature rise peak value and the positional relationship between the heating element and the temperature measuring means with respect to the test object, and calculates the heat rise peak value and peak time of the test object from the temperature change recording means. Calculate the thermal conductivity Ko.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the present invention. In the figure, a heating element 10 is one that can easily control the amount of heat generated by a heater wire or the like, is surrounded by a metal material having high rigidity and good heat conductivity such as a pipe, and an object to be inspected such as soil. Easy to plug into. The heat generation control unit 20
In order to make the heating element 10 generate a pulse-like heat of a predetermined heat quantity Qpulse, the amount of electricity supplied to the heater wire is controlled here for ease of control. However, the supply amount of a heating substance such as gasoline or flammable gas is controlled. It may be controlled. The pulse-shaped heat generation time is set shorter than the peak time tpeak of the temperature fluctuation occurring in the inspection object in the vicinity of the temperature measuring unit 30, and is preferably tpeak.
/ 4 or less is preferable. The temperature measuring unit 30 measures the temperature fluctuation generated in the inspection object by the pulse-like heat generation of the heating element 10. For example, a thermocouple or a thermocouple in which a plurality of thermocouples are connected in series to amplify the thermoelectromotive force is used. Is used.

The temperature change recording section 40 records the temperature waveform measured by the temperature measuring section 30 and obtains a temperature rise peak value ΔTpeak and a peak time tpeak in the temperature waveform. The peak time may be the center time of the pulse-like heat generated by the heat generation control unit 20, or a value obtained by correcting a delay time due to the heat transfer of the heating element 10 to the pulse-like heat generation. The thermal characteristic calculation unit 50 multiplies the temperature rise peak value obtained by the temperature change recording unit 40 and a calibration coefficient determined from the positional relationship between the heating element 10 and the temperature measurement unit 30 with respect to the inspection object, and calculates the volume of the inspection object. The heat capacity Co or the temperature conductivity Do is obtained. Further, the thermal characteristic calculating section 50 calculates the thermal conductivity Ko of the inspection object from the peak temperature and the peak time obtained by the temperature change recording section 40. The specific contents of these arithmetic expressions will be described later in detail.

FIG. 2 is an external view of the apparatus shown in FIG. The detection probe holds the two heating elements 10 and a thermometer 30 provided therebetween, and is arranged in a comb shape so as to be easily inserted into the soil. The converter is connected to the detection probe via a signal line, and has the functions of the heat generation control unit 20, the temperature change recording unit 40, and the thermal characteristic calculation unit 50. It has a key input device. Here, the outer dimension of the heating element 10 is a diameter Dhφ, the length from the detection probe is Lh, and the interval between the two heating elements 10 is 2 ro. On the other hand, thermometer 30
Has a diameter Dsφ, and the temperature measurement position O is half the length Lh / 2 of the length of the heating element 10. In the coordinate system, the longitudinal direction of the heating element 10 is the Z axis, the longitudinal direction of the detection probe is the X axis, and the upward direction with respect to the paper surface is the Y axis.

Next, the calculation of the temperature rise peak value ΔTpeak and the peak time tpeak will be described. The temperature difference ΔT in the thermometer 30 is defined by the following equation. ΔT = (ΔQ / Co) (4πDot) ^{-m / 2} exp (−ro ² / 4Dot) (1) Here, m is a coefficient determined by the shape of the heating element 10. M = 2 for a heat source and m = 1 for a plane. ΔQ is the amount of heat generated per unit length of the heating element 10 [Jm ^m−3 ], Co is the volumetric heat capacity of the test object [JK ⁻¹ m ⁻³ ], and Do is the temperature conductivity of the test object [m
² s ⁻¹ ] and t is the elapsed time [s] after the start of heat generation. Note that SI units are used for the above-mentioned unit system. ro is the distance [m] between the heating element 10 and the thermometer 30, and π is the circumference ratio of 3.14.
159 ...

Then, the temperature rise peak value ΔTpeak and the peak time tpeak are as follows. ^{ΔTpeak = (m / 2πe) m} / 2 (ΔQ / Coro m) (2) tpeak = ro 2 / 2mDo (3) ΔTpeak xtpeak = (m / 2πe) m / 2 (ΔQro 2-m / 2mKo) (4) Here, e is the number of napiers, 2.72828..., And Ko is the thermal conductivity [JK ^-1 m ^-1 s ^-1 ]. On the other hand, the following relational expression holds for the volumetric heat capacity Co, the thermal conductivity Do and the thermal conductivity Ko. Ko = CoDo (5)

On the premise of the above, the volumetric heat capacity Co, the thermal conductivity Do and the thermal conductivity Ko have the following relational expressions. ^{Co = (m / 2πe) m} / 2 (ΔQ / ΔTpeakro m) (6) Do = ro 2 / 2mtpeak (7) Ko = (m / 2πe) m / 2 (ΔQro 2-m / 2mΔTpeak xtpeak) (8)

A description will now be given of a heat transfer state in the measuring apparatus thus configured. FIG. 3 shows XY near the temperature measurement point.
In the distribution diagram of the temperature rise peak value ΔTpeak on the plane, the inspection object is calculated as an isotropic body. Each coordinate X, Y is normalized by the interval ro between the heating element 10 and the thermometer 30. X = ±
The heating element 10 exists at a position of 1.00 ro, Y = 0.00 ro, and X
The center O of the thermometer 30 is at the position of = 0.00 ro, Y = 0.00 ro. With reference to the temperature rising peak value ΔTpeak at the center O, the distribution of the temperature rising peak value at each coordinate point is represented by an equal temperature rising peak value line in increments of 0.01ΔTpeak. For example, 1.05ΔTpe
The isothermal heating peak value line of ak passes through X = ± 0.20 ro, Y = 0.00ro, and the isothermal heating peak value line of 1.10ΔTpeak is X = ± 0.26
ro, Y = 0.00ro. Also, 0.95ΔTpeak
The isothermal heating peak value line passes through X = 0.00ro, Y = ± 0.20ro, and the isothermal heating peak value line of 0.90ΔTpeak is X = 0.00r.
o, Y = ± 0.30 ro. Thus, the center O
Is equivalent to the saddle point of the isothermal temperature peak value line. There is.

FIG. 4 is a calculation diagram of the influence of the heating element diameter Dh and the thermometer diameter Ds on the measured value of the temperature rise peak value ΔTpeak. When the heating element 10 is formed in a cylindrical shape, the area in contact with the inspection object can be increased, so that even when the same amount of heat is transferred to the inspection object in a short time, the temperature rise on the cylindrical surface can be suppressed low. The thermal stress on the inspection object in contact with the cylindrical surface can be reduced. In addition, when the thermometer 30 is formed in a cylindrical shape, even when the number of detection ends is increased as in the case of heat transfer, the thermometer 30 can be uniformly arranged on the circumference, and can be easily installed, and the sensitivity of temperature detection can be improved. It has the effect of increasing. Here, the heating element diameter Dh and the thermometer diameter Ds are normalized by the interval ro between the heating element 10 and the thermometer 30. The heating element 10
The distribution of the heating peak value at each coordinate point is represented by an isothermal heating peak value line in increments of 0.0005 ΔTpeak with reference to the heating peak value ΔTpeak in an ideal state where the diameter of the thermometer 30 is zero.

As shown in the figure, in a region where the heating element diameter Dh and the thermometer diameter Ds are 0.40 ro or less, the peak temperature rise value is 0.00
It is almost constant in the range of 05ΔTpeak. Further, even in a region where the heating element diameter Dh and the thermometer diameter Ds are 0.60 ro or less,
The peak temperature rise is substantially constant in the range of about 0.002ΔTpeak. Therefore, the heating element diameter Dh and the thermometer diameter Ds
Even a shape of about 0.40 ro has almost no effect on the measured temperature rise peak value.

FIG. 5 is a calculation diagram of the influence of the heating element diameter Dh and the thermometer diameter Ds on the measured value of the peak time tpeak.
As in FIG. 4, the heating element diameter Dh and the thermometer diameter Ds are normalized by the distance ro between the heating element 10 and the thermometer 30. Also,
With reference to the peak time tpeak in the ideal state where the diameter of the heating element 10 and the thermometer 30 is zero, the distribution of the peak time at each coordinate point is represented by an isopeak time line in increments of 0.02 tpeak. Heating element diameter Dh and thermometer diameter Ds are 0.20 ro
In the following fan-shaped area, the peak time is almost constant within a range of 0.02 tpeak. However, the isopeak time line of 0.90 tpeak, which causes a 10% error in the measured value, is represented by the heating element diameter D
The isopeak time line of 0.80 tpeak, which spreads in a quarter circle with h and thermometer diameter Ds of 0.44 ro and gives a 20% error to the measured value, is a quarter circle with heating element diameter Dh and thermometer diameter Ds of 0.62 ro. Has spread. Therefore, a shape having a heating element diameter Dh and a thermometer diameter Ds of about 0.20 ro has almost no effect on the peak time to be measured, but an increase in the size beyond that causes an error in the peak time to be measured.

FIG. 6 shows the relationship between the heating element length Lh and the temperature rise peak value Δ.
It is a calculation figure of the influence which has a measured value of Tpeak and peak time tpeak. Here, the heating element half length Lh / 2 is set to the heating element 10.
And the interval ro of the thermometer 30 is normalized. Further, a change in the peak temperature and the peak time at each heating element length Lh is represented by a curve based on the peak temperature ΔTpeak and the peak time tpeak in the ideal state in which the heating element half length Lh is infinite. . For example, assuming that 2% is the allowable value of the measurement error, the heating element half length Lh
If / 2 is 1.6 ro or more, the effect of the finite heating element length Lh is eliminated. If the heating element half length Lh / 2 is 2.0 ro or more at the peak time tpeak, the effect of the finite heating element length Lh is eliminated. Therefore, if the heating element length Lh is four times the interval ro between the heating element 10 and the thermometer 30, it may be regarded as an ideal state. However, even if the heating element length Lh is about the same as the distance ro between the heating element 10 and the thermometer 30, it is practically possible to obtain a measured value suitable for an ideal state by obtaining a geometric calibration coefficient.

In the above-described embodiment, the case where the number of the heating elements 10 provided on the detection probe is two has been described. However, the present invention is not limited to this. Place the thermometer evenly on the top
The same effect can be obtained even if 0 is set.

[0019]

As described above, according to the present invention, the heating element 10 is inserted into the object to be inspected while the distance ro between the heating element 10 and the thermometer 30 is kept constant, and the heating element 10 is pulsed. And the temperature rise peak value ΔTpeak measured by the thermometer 30
Since the volume heat capacity and the thermal conductivity are calculated using the peak time tpeak and the peak time tpeak, there is an effect that the thermal characteristics of the test object can be measured in a mode in which the test object is less invasive. In addition, in applications where the test object is soil and the soil moisture content is measured, continuous measurement can be easily performed by previously measuring the correspondence relationship between the volumetric heat capacity or thermal conductivity and the moisture content of the soil. This has the effect.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is an external view of the apparatus of FIG.

FIG. 3 is a distribution diagram of a temperature rise peak value ΔTpeak on an XY plane near a temperature measurement point.

FIG. 4 is a calculation diagram of an influence of a heating element diameter Dh and a thermometer diameter Ds on a measured value of a temperature rise peak value ΔTpeak.

FIG. 5 shows the peak time t of the heating element diameter Dh and the thermometer diameter Ds.
It is a calculation figure of the influence which acts on the measured value of peak.

FIG. 6 is a calculation diagram of an influence of a heating element length Lh on a measured value of a temperature rise peak value ΔTpeak and a peak time tpeak.

FIG. 7 is a configuration sectional view of a conventional probe-type thermal conductivity measuring device.

FIG. 8 is a relationship diagram between thermal conductivity and moisture content.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Heating body 20 Heat generation control part 30 Thermometer 40 Temperature change recording part 50 Volume heat capacity etc. calculation part

Continued on the front page (72) Inventor Fumio Masuda 1-5-13 Shinkawa, Chuo-ku, Tokyo Inside Yokogawa Wezac Corporation (72) Inventor Takao Hirose 1-5-13, Shinkawa, Chuo-ku, Tokyo Yokogawa Wezak Stock In-house examiner Jun Koriyama (56) References JP-A-63-47644 (JP, A) JP-A-3-191852 (JP, A) JP-A-5-52783 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 25/18

Claims (3)

(57) [Claims] A heating element inserted into an object to be inspected.
A heating control means (20) for causing the heating element to generate a pulsed heat of a predetermined amount of heat (Qpulse); and the inspection target being held at a predetermined interval (ro) from the heating element and being pulsed by the heating element. Temperature measuring means (30) for measuring a temperature change occurring in an object; temperature change recording means (40) for obtaining a temperature rise peak value (ΔTpeak) and a peak time (tpeak) in a temperature waveform measured by the temperature measuring means. The volumetric heat capacity (Co) or the temperature conductivity (Do) of the object to be inspected is obtained from the temperature rise peak value obtained by the temperature change recording means and the positional relationship between the heating element and the temperature measuring means with respect to the object to be inspected. And a thermal characteristic calculating means (50) for calculating the thermal conductivity (Ko) of the inspection object from the peak temperature and the peak time obtained by the temperature change recording means. Hot features Measuring device. 2. The heating element is in the form of a rod, and a plurality of heating elements are circumferentially symmetrically arranged around the temperature measuring means as a geometric center, and each heating element generates uniform heat. The thermal characteristic measuring device according to claim 1. 3. The object to be inspected is soil, and the volume determined by the thermal characteristic calculating means is referred to calibration data means for describing the relationship between the moisture content of the soil and the volumetric heat capacity or thermal conductivity. The soil moisture content measuring device according to claim 1, wherein the moisture content of the soil is continuously measured from heat capacity or thermal conductivity.