JP3132994B2 - Temperature distribution measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature distribution measuring device for monitoring a change in a temperature distribution.

[0002]

2. Description of the Related Art In various plants, the number of temperature measuring points and temperature monitoring points for thermal management is enormous. Here, as the temperature measuring means,
Conventionally, sensors such as a thermocouple, a thermistor, and a temperature switch are usually installed at a plurality of specific places where the temperature of an object to be measured is desired to be measured and monitored. In this case, it is necessary to install a large number of sensors, and accordingly, the length and the number of signal lines also become enormous, and the number of measurement points is naturally limited from the viewpoint of the number of penetrations and cost. Is the current situation. Means for inputting a pulse signal to a coaxial cable, detecting a signal reflected from a change point of the impedance, and knowing a distance to the change point is a TDR method (Time Domain Refl).
This is conventionally used for detecting disconnection or short circuit of a coaxial cable or a parallel cable for a long time. This measurement principle is based on the following equation: where the propagation speed of a pulse in a coaxial cable is V, and the time from the incidence of the pulse to the reception of the reflected wave is t, the position l _{d of the} reflection point is determined by the following equation. l _d = (1/2) V · t

[0003]

As a conventional temperature distribution measuring device of this kind, an invention applied and made publicly known from Japanese Patent Application No. 2-53106 will be described as a first conventional example. Reference numeral 01 denotes a high-frequency coaxial cable (hereinafter referred to as a coaxial cable) laid along the longitudinal direction of the subject to be subjected to temperature distribution measurement, as shown in the overall circuit diagram of FIG. Is a core wire, and 03 is a jacket conductor.
It is comprised so that it may surround. Reference numeral 05 denotes a ferrite ring which is a point in the configuration of the conventional example, which is an O-ring made of a shape memory alloy, and whose inner diameter is equal to the outer diameter of the coaxial cable 01 at a steady temperature (a temperature not exceeding the transformation point). It is externally fitted to the coaxial cable 01 in a substantially equal or slightly larger shape. Reference numeral 06 denotes a TDR measuring instrument (hereinafter referred to as a measuring instrument) for measuring a temperature change, which will be described in detail later. Next, the main parts will be described with reference to FIGS. 9 and 10. FIGS.
FIG. 10B is a cross-sectional view taken along arrows A and B-B. FIG. 10B shows a distorted ring 05 in which the shape memory alloy ring 05 shown in FIG. 9 is hatched beyond the transformation point due to a change in temperature.
a, indicating a state in which the original shape stored at that temperature has been restored. When the ring 05 returns to the original shape due to a temperature change exceeding the transformation point, the ring 05 is deformed into an oval shape like the ring 05a, and the outer diameter of the cable 01 is tightened, so that the cross-sectional shape of the coaxial cable 01 changes.
FIG. 11 is a cross-sectional view of the second conventional example. Instead of the ring 05 of the first conventional example, a coaxial cable 01 is sandwiched between two rods 066a and 066b, and the left and right ends thereof are made of a spring made of a shape memory alloy. It is fixed by pushing at 055a and 055b. Even in such a configuration, the spring 05
5a and 055b contract the cable 01 and the upper and lower rods 06
6a and 066b can be tightened and deformed at both ends. Here, to supplement a little about the TDR method, the TDR method is a known measurement method, using a pulse wave as a signal source, observing a waveform with an oscilloscope,
This is a method of clarifying the point of failure directly. The pulse waveform to be used is determined based on the type of cable, the resolution in the distance direction, and the like. For example, in the case of a cable having a relatively long distance and a large amount of attenuation, an impulse wave (specifically, a half wave of a sine wave or its square wave) is used. Use pulse waves. In the TDR method, not only can the position of a fault point be determined, but at the same time, the type of the fault can be determined by the waveform displayed on the oscilloscope, and by analyzing the reflected pulse waveform, Can also be estimated. In this first conventional example, a pulse is transmitted to a coaxial cable, and the distance to the discontinuity can be known from the timing of the signal reflected from the discontinuity of the impedance of the line. This is because, assuming that the pulse speed in the coaxial cable is V, the relationship between the time τ from pulse transmission to reception and the position l _{d of the} reflection point (distance from the transmission end) is represented by the following equation. l _d = (１ ／) V · τ (1) In order to observe the reflection from the specific point l _d, only the signal that has elapsed by τ calculated from the equation (1) is received. A gate may be installed on the receiving side. That is, FIG.
In (A), when a transmission pulse 010 is sent out, after a time τ, if there is a temperature change in the ring installed therein, the outer diameter of the ring is deformed, and as shown in FIG. A reflected pulse 011 is generated due to a discontinuity in impedance at that portion. Gate close to time τ
When N is set and a gate pulse 012 slightly wider than the width of the reflected wave is issued, the reflected pulse 011 can be detected. These measurements are performed by the TDR measuring instrument 06 in FIG. To summarize the operation in such a configuration, for example, when there is no temperature change, the impedance of the cable (usually 50Ω or 75Ω) can be reduced even if the ring 05 made of a shape memory alloy is fitted. Therefore, there is no change in impedance regardless of the presence or absence. Therefore, even if the impedance change point of this electric wire is measured, no change appears. However, as shown in FIG. 10, when the temperature at the place where the shape memory alloy ring 05 is fitted rises beyond the transformation point, the ring 05 returns to its original shape and is deformed, for example, as 05a. And tighten the outer diameter of the coaxial cable 01. For this reason, the coaxial cable 01 is locally deformed, and the impedance at that portion changes. Since the installation location of the ring 05, that is, the distance, is known in advance, all the arrival times of the pulses can be set. If this is constantly monitored by an external measuring device 06, the ring 05
It can be seen that the temperature at a certain place has exceeded the temperature previously determined by the material of the ring. That is, FIG.
As shown in (C), when a gate pulse 012 is issued at a known time τ in advance and a reflection pulse 011 at an impedance discontinuity point generated by a change in the shape of the ring installed at that location is measured, the temperature change and If judged and no reflected pulse is measured, there will be no temperature change at that point. The same operation is performed in the second conventional example shown in FIG. That is, when the temperature in the vicinity becomes equal to or higher than the transformation point, the springs 055a and 055b contract, and the outer diameter of the cable 01 is reduced and deformed by the rods 066a and 066b connected by these springs. This action creates a discontinuity in the impedance near the cable,
As in the first conventional example, the reflected pulse is measured, and the temperature change at that location can be detected. According to such a temperature detection device, a mechanical force is applied to a cable in addition to a shape deformation of a shape memory alloy due to a temperature change to cause a local impedance change, which is monitored as an impedance change from a cable end. Thus, the temperature rise can be detected, and the following effects can be obtained. (1) One (one pair) of coaxial cables can monitor temperature rise at an extremely large number of points. (2) If the transformation temperature of the shape memory alloy is adjusted to the temperature to be monitored, multipoint monitoring of a wide range of different temperature limits can be performed simply by measuring the reflected wave at the discontinuity of the impedance of the coaxial cable due to the change. Becomes possible. (3) The reflected pulse can be detected by opening the gate with a pulse propagation time that matches the installation distance of the shape memory alloy, which is structurally simple.

[0004] Next, as another conventional example, Japanese Utility Model Application No. 2-86 is proposed.
The following is the structure of the invention disclosed and disclosed in Japanese Patent No. 343 as a third conventional example. That is, in the overall wiring diagram of FIG. 13, the same reference numerals as those in the first conventional example denote the same members as those in the first conventional example, and 034 denotes a measuring device 06.
A temperature switch 035 is inserted at a distance l ₁ from the sensor and turns on when the temperature reaches T _1. A temperature switch 035 is inserted at a distance l ₂ from the measuring instrument 06 and turns on when the temperature reaches T _2. Is a temperature switch which is inserted at a distance l ₃ from the measuring instrument 06 and turns on the contact when the temperature reaches T ₃ . In such an apparatus, the coaxial cable 01 is disposed at an appropriate position of the subject, that is, at a position where the temperature is desired to be monitored. Now, when none of the temperature switches are operated, the pulse signal emitted from the measuring instrument 06 travels through the coaxial cable to the end thereof, and if the terminating resistor 07 is selected, for example, to be equal to the characteristic resistance of the line. , The reflected signal goes to zero. However, if an appropriate value different from this is selected, a reflected signal from the terminating resistor can be obtained as shown in FIG. At this time, the time from the transmission pulse to the reflection pulse is a value t ₀ obtained by dividing twice the distance l ₄ by the signal speed v. If t ₀ is a reasonable value for l ₄ , it can be said that the line is sound up to the terminating resistor. Note that, for convenience of explanation, the terminating resistor 07 is used.
Is written in the drawing, but this value may be infinite or short-circuited. Then, if elevated temperature of the installation location of the temperature switch T ₂ is the temperature switch is activated, if short-circuited line at that position, as shown in FIG. 14 (B), the position corresponding to the time t ₂ Reflection occurs. If this point is completely short-circuited, then T ₃ or termination conditions are ignored and will not appear at the output of the TDR. Here, there are many known commercially available temperature switches such as a bimetal type, a temperature fuse type, and a sound-sensitive ferrite type, and any of them can be used. When each temperature switch reaches the set temperature, the line is opened, that is, all the temperature switches are inserted in series with the cable, and when the set temperature is reached, the line is apparently broken at that point. With this structure, the same operation and effect as those of the third conventional example can be achieved. According to such a temperature detecting device, the following effects can be obtained. (1) Many sensors can be monitored by one coaxial cable. (2) Therefore, the cost of the electric wire material and installation is greatly reduced. (3) The soundness of the wire can be confirmed by selecting an appropriate value for the terminating resistance. (4) The attained temperature and position can be obtained with a relatively simple configuration.

However, as in the first, second, and third conventional examples described above, the conventional temperature measurement or monitoring involves a large-scale laying work because a plurality of sensors are installed at specified locations where the measurement is required. And a considerable cost is required. The measurement using the TDR method also operates when a specific temperature is reached, and it is not possible to determine the temperature until the sensor operates and the temperature after the operation. Also, in the means using a shape memory alloy, since an external force is applied to the cable , stress remains in the cable even after the force from the shape memory alloy is released, so that it is determined that the temperature has risen, etc. There is a problem.

The present invention has been proposed in view of the above circumstances, and enables not only the temperature at a specific measurement position of a coaxial cable but also the temperature measurement using only the coaxial cable at an unspecified position, thereby reducing construction work. It is an object of the present invention to provide an economical temperature distribution measuring device that can be performed at a low cost, and can also know the temperature before the sensor operates and the temperature after the sensor operates.

[0007]

In order to achieve the above object, according to the present invention, a high-frequency pulse is transmitted from one end of a coaxial cable laid in contact with an object to be measured.
In a temperature measuring device for detecting a reflected wave of the pulse due to a change in impedance of a coaxial cable at a temperature change portion and measuring a temperature distribution of an object to be measured, an SiO ₂ is provided between a core wire of the coaxial cable and a jacket conductor. Characterized in that a high-frequency coaxial cable filled with is used.

The invention according to claim 2 is characterized in that, in claim 1, the high-perimeter coaxial cable is laid in the longitudinal direction while meandering left and right along the surface of the object to be measured.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to the detection of the temperature distribution of a branch pipe of a pipe to be measured will be described with reference to the drawings. FIG. FIG. 3 is a diagram showing the distribution waveform of the reflected wave and the temperature distribution along the pipe to be measured, FIG. 3 is a wiring diagram of a coaxial cable showing a modification example different from FIG. 1, and FIG. 4 is a temperature difference in the coaxial cable of FIGS. FIG. 5 is a diagram showing the relationship between the reflection wave level of the temperature boundary portion and the noise, FIG. 5 is a longitudinal sectional view comparing the coaxial cable of FIG. 1 with a conventional coaxial cable, and FIG. FIG. 7 is a comparison diagram of noise waveforms at a high temperature part and a low temperature part of a pipe to be measured by a cable, and FIG. 7 is a diagram showing noise generated in a cable at a temperature boundary part of the pipe to be measured in FIG.

First, in FIG. 1, the same reference numerals as those in FIG. 8 denote the same members as those in FIG. 1, 1 is a mother pipe, 2 is a branch pipe, and high-temperature water is retained inside. Reference numeral 3 denotes a low-temperature side pipe, and reference numeral 4 denotes a valve for shutting off cold water.

In such a line to be measured and a coaxial cable circuit, as shown in FIG. 2, the branch pipe 2 has a temperature gradient at a certain position in the axial direction. The temperature boundary fluctuates in the pipe axis direction, and the branch pipe 2 causes thermal fatigue loss. At this time, in order to measure the heat cycle, the coaxial cable 2 is fixed to the surface of the branch pipe 2 along the same branch pipe 2 with a metal tape or the like, and the impedance change of the coaxial cable at the temperature boundary portion (for the insulator). By measuring the time until the reflected wave due to the change in the dielectric constant and the level of the reflected wave, the position of the temperature boundary and the temperature difference can be obtained. Assuming that the pulse speed V in the cable and the time from the pulse incidence to the reflected wave signal are t, the position l _d of the temperature boundary is obtained by the following equation as described above. l _d = (1/2) V · t

At this time, it is known from the experimental results that the level of the reflected wave has a correlation with the temperature difference, and the temperature difference at the temperature boundary can be obtained by measuring the level. Further, as shown in FIG. 3, by laying the coaxial cable in a meandering shape, the measurement accuracy of the position of the boundary and the temperature difference can be improved from the following relationship.

In the above embodiment, a change in impedance of the coaxial cable due to a change in temperature is expressed by equation (2) . Z = (60 / √ε _T ) 1n (D / d) (2) where ε: dielectric constant of the insulator D: outer diameter of the high-frequency cable d: outer diameter of the high-frequency cable jacket conductor Temperature difference FIG. 4 shows the result of an experiment that determines the relationship between the reflected wave level and the reflected wave level. Thus, the temperature difference ΔT can be obtained by detecting the level of the reflected wave.

Here, as for the impedance sensitivity of only the coaxial cable, the dielectric constant of the insulator of a commercially available coaxial cable greatly changes depending on the temperature. In addition, there are disadvantages such as a large coefficient of thermal expansion, so that thermal characteristics are poor, and there is no faithful reproducibility of a signal waveform generated based on a local change in impedance. Therefore, the signal level increases as noise (see the broken line in FIG. 4). Further, since the insertion loss of the high-frequency power is large, there is a high possibility that it is impossible to distinguish between a signal and noise. However, the coaxial cable described in the embodiment of the present invention is a special cable having good high-frequency characteristics, and has a very small insertion loss.
In addition, depending on the frequency applied to the high-frequency coaxial cable, noise is increased in a normal coaxial cable, and the coaxial cable cannot be identified. FIG. 6A shows an example of a signal waveform of the special cable, and FIG. 6B shows a signal waveform of a conventional coaxial cable. As described above, with the special cable, even when the impedance change is small, the temperature change at the boundary can be significantly obtained. Incidentally, from the above equation (2), as described below, the first derivative by the inner diameter D of the impedance Z of the coaxial cable becomes the equation (3), and the second derivative becomes the equation (4). dZ / dD = (K / d) · (1 / D) (3) d ² Z / dD ² = − (K / d) · (1 / D ² ) (4) Considering that ΔD is the variation of the diameter of the coaxial cable based on the local temperature variation ΔT, the primary differential dZ / dD of the impedance due to the thermal deformation ΔD of the outer diameter D is proportional to 1 / D. It changes greatly, and its second derivative d ² Z /
dD ² changes more greatly in proportion to 1 / D ² . Therefore, the impedance change due to the temperature change can be detected only by the coaxial cable because of the geometrical electromagnetic relationship according to the equations (3) and (4) and the above-mentioned SiO _2.
This is considered to be due to a synergistic effect of the noise reduction effect.
Incidentally, the outer diameter of the coaxial cable used in the embodiment of the present invention is about 3.6 mmφ.

The measuring cable used in this embodiment is shown in FIG.
As shown in (A), SiO is provided between the core wire and the jacket conductor.
₂ is a SiO ₂ -filled coaxial cable filled as an insulator, and this coaxial cable has very little change in phase and insertion loss due to temperature change.
As compared with the E cable, the shielding effect is large, the reliability is high, and the wiring is easy. On the other hand, in a conventional coaxial cable, as shown in FIG. 5 (B), there is a tetrafluoroethylene insulator around the core wire, an aluminum shield wire is braided on the outside thereof, and a tetrafluoroethylene wire is braided thereon. Ethylene chloride is applied as a jacket. Due to such differences in structure, as shown in FIG. (1) A conventional coaxial cable has a large influence such as an increase in a noise component because the loss of incident power and the phase change with respect to temperature because the insulator and the jacket are made of tetrafluoroethylene resin. . (2) Since the cable used in this embodiment uses SiO ₂ as an insulator, it has better thermal characteristics with respect to temperature than conventional cables. (3) As the temperature at which the cable is laid becomes higher, noise increases in a conventional cable, and it becomes difficult to determine even when a temperature boundary occurs. However, the coaxial cable used in this embodiment is Since the noise is very small even at high temperatures, it is easy to determine the boundary.

[0016]

According to the temperature distribution measuring device of the present invention, by measuring the impedance change at the point where the temperature difference occurs only in the measuring cable, the temperature boundary portion and the temperature difference in the axial direction can be measured. it can. Therefore, the following effects can be expected. (1) The temperature boundary can be arbitrarily measured with one coaxial cable. (2) Since no external force is applied to the coaxial cable, the point where the temperature difference occurs can be monitored over a wide range only by measuring the reflected wave due to the impedance change. (3) Thermal fatigue loss of piping can be easily evaluated. (4) Cost can be significantly reduced. (5) The present invention can also be applied to cable stress measurement.

In short, according to the first aspect of the present invention, a high-frequency pulse is transmitted from one end of a coaxial cable laid in contact with an object to be measured, and a reflected wave of the pulse is generated due to a change in impedance of the coaxial cable in a temperature change section. In a temperature measuring device for detecting the temperature distribution of an object to be measured by detecting a high-frequency coaxial cable filled with SiO ₂ between a core wire of the coaxial cable and a jacket conductor, specific measurement of the coaxial cable is performed. Not only the temperature at the position, but also the temperature measurement using only the coaxial cable at the unspecified position can be performed at low cost, and the temperature before the sensor works and the temperature after it works can be known. The present invention is industrially very useful because it provides an economical temperature distribution measuring device that can be used.

According to the second aspect of the present invention, in the first aspect, the high-perimeter coaxial cable is laid in the longitudinal direction while meandering left and right along the surface of the object to be measured. Not only the temperature at the specific measurement position,
Economical temperature that enables temperature measurement using only coaxial cables at unspecified positions, enabling low-cost construction work and knowing the temperature before and after the sensor operates. The present invention is extremely useful in industry because a distribution measuring device is obtained.

[Brief description of the drawings]

FIG. 1 is a piping diagram showing an embodiment in which the present invention is applied to measurement of a temperature distribution of a test pipe.

FIG. 2 is a diagram showing an incident pulse, a reflected wave, and a temperature distribution of a branch pipe obtained by the TDR measuring device in the test line of FIG.

FIG. 3 is a wiring diagram showing an embodiment of a wiring procedure different from that of FIG. 1 of the temperature measuring cable of FIG. 1;

FIG. 4 is a diagram showing a relationship between a temperature difference caused by the coaxial cable for temperature measurement of FIG. 1 and a reflected wave level of a temperature boundary portion and noise.

5 is a longitudinal sectional view of the coaxial cable for temperature measurement of FIG. 1 and a comparison diagram with a longitudinal sectional view of a conventional coaxial cable.

6 is a comparison diagram of noise waveforms at a high temperature part and a low temperature part of a test tube using the coaxial cable for temperature measurement of FIG. 1 and a conventional coaxial cable of the related art.

FIG. 7 is a diagram showing noise generated in a temperature measuring cable at a temperature boundary portion of a pipe to be measured in FIG. 6;

FIG. 8 is a pipeline diagram showing a conventional temperature-sensitive ferrite ring type temperature measuring device.

FIG. 9 is a side view showing a first conventional example of a temperature measuring device filed in Japanese Patent Application No. 2-53106 and its BB transverse sectional view.

10 is a side view showing a case where the ring is contracted in FIG. 9 and a cross-sectional view taken along the line BB of FIG.

11 is a longitudinal sectional view showing a second conventional example of FIG. 9 and FIG.
FIG.

12A and 12B are pulse waveform diagrams showing the operation of the temperature measuring device of FIG. 9; FIG. 12A is a transmission pulse waveform, FIG. 12B is a reflection pulse waveform, and FIG. It is.

FIG. 13 shows a T filed in Japanese Patent Application No. 2-86343.
It is an entire circuit diagram of a DR temperature measuring device.

FIG. 14 is an explanatory diagram showing a relationship between a reflected pulse and time in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main pipe 2 Branch pipe 3 Low temperature side pipe 4 Valve 5 Temperature boundary part 01 Coaxial cable 01a Coaxial cable 02 Core wire 03 Jacket conductor 04 Insulator 05 Ferrite ring 05a Ferrite ring 06 TDR measuring instrument (measuring instrument) 07 Terminating resistance

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-255324 (JP, A) JP-A-58-169041 (JP, A) JP-A-57-10429 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01K 7/00

Claims (2)

(57) [Claims] 1. A high-frequency pulse is transmitted from one end of a coaxial cable laid in contact with an object to be measured, and a reflected wave of the pulse is detected due to a change in impedance of the coaxial cable in a temperature change unit, and a reflected wave of the pulse is detected. A temperature distribution measuring device for measuring a temperature distribution, wherein a high-frequency coaxial cable filled with SiO ₂ is used between a core wire of the coaxial cable and a jacket conductor. 2. The method according to claim 1, wherein the high-perimeter coaxial cable meanders left and right along the surface of the object to be measured.
A temperature distribution measuring device laid in the longitudinal direction.