JPH09113369A - Temperature distribution measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an economical measuring instrument which can measure the temperature before a sensor is operated and the temperature after operated. SOLUTION: This instrument is constituted so that a pulse is transmitted from one end of a coaxial cable 01 laid in contact with a measured object to detect the reflected wave of the pulse due to the change of the impedance of the coaxial cable 01, thereby measuring a temperature distribution being a measured object. In that case, a high-frequency coaxial cable in which an SiO2 is filled between the core wire and the covering conductor 03 of the coaxial cable 01 is used, thereby being able to measure not only the temperature of the coaxial cable 01 in a specified measuring position but also the temperature of the coaxial cable 01 by itself in an unspecified position, so that the execution of works may be performed at low costs.

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 changes in temperature distribution.

[0002]

2. Description of the Related Art In various types of plants, the number of temperature measuring points and temperature monitoring points for heat management thereof is enormous. Here, as the temperature measuring means,
Conventionally, it is customary to install sensors such as thermocouples, thermistors, and temperature switches 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 the length and number of signal lines will be enormous accordingly, and the number of measurement points is naturally limited in terms of the number of penetrations and costs. Is the current situation. By the way, a means for inputting a pulse signal to a coaxial cable, detecting a signal reflected from a change point of its impedance, and knowing a distance to the change point is a TDR method (Time Domain Refl).
ectmeter), which has been used for a long time to detect disconnection and short circuit of coaxial cables and parallel cables. This measurement principle is based on the fact that the position l _{d of the} reflection point is determined by the following equation, where V is the propagation velocity of the pulse in the coaxial cable and t is the time from the pulse incidence to the reception of the reflected wave. l _d = (1/2) V · t

[0003]

As a conventional temperature distribution measuring device of this type, first, the invention filed and made public by 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 in contact with an object to be subjected to temperature distribution measurement, as shown in the overall circuit diagram of FIG. Is a core wire of the core wire, and 03 is an outer conductor, and is made of, for example, a braided conductor,
It is configured to be surrounded by. Reference numeral 05 denotes a ferrite ring, which is a key point in the configuration of this conventional example, and is an O-ring shape made of a shape memory alloy, and its inner diameter is equal to the outer diameter of the coaxial cable 01 at a steady temperature (temperature not exceeding the transformation point) It is fitted onto the coaxial cable 01 in a shape that is substantially equal or slightly larger. Reference numeral 06 denotes a TDR type measuring instrument (hereinafter referred to as a measuring instrument) for measuring a temperature change whose details will be described later. Next, in FIG. 9 to FIG. 10, the main part will be described. FIGS. 9 (A) and 9 (B) are A- of FIGS. 9 and 10, respectively.
FIG. 10B is a cross-sectional view taken along arrows A, B-B, and FIG. 10B is a ring 05 having a distorted shape in which the ring 05 made of the shape memory alloy shown in FIG. 9 is hatched beyond the transformation point due to a change in temperature.
It is a, and the state is restored to the original shape that was stored at that temperature. When the ring 05 returns to its original shape due to a temperature change exceeding the transformation point, the ring 05 is deformed into an elliptical 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, two coaxial rods 066a and 066b sandwich the coaxial cable 01, and the left and right ends of the coaxial cable 01 are made of a shape memory alloy spring. It is fixed by pushing with 055a and 055b. Even with such a configuration, the spring 05 is heated at a temperature above the transformation point.
5a and 055b contract to connect the cable 01 to the upper and lower bars 06
Both ends of 6a and 066b can be tightened and deformed. Here, a little supplement to the TDR method, the TDR method is a known measurement method, a pulse wave is used as a signal source, and the waveform is observed with an oscilloscope.
This is a method of directly identifying the point of failure. The pulse waveform to be used is determined by the type of cable and the disassembly ability in the distance direction. For example, use impulse waves (specifically, half-waves of sine waves or their square waves) for cables with a relatively long distance and high attenuation, and use steps for relatively short distances and high resolution. Use pulse wave. In the TDR method, not only the position of the failure point can be obtained, but at the same time, the type of the failure can be determined by the waveform displayed on the oscilloscope, and by analyzing the waveform of the reflected pulse, what kind of failure point It is also possible to estimate whether or not is loaded. In the first conventional example, it is possible to know the distance from the timing of the signal reflected from the impedance discontinuity of the line to the discontinuity by sending a pulse to the coaxial cable. This is because when the pulse speed in the coaxial cable is V, the relationship between the time τ from pulse transmission to reception and the reflection point position l _d (distance from the transmission end) is expressed by the following equation. l _d = (1/2) V · τ (1) In order to observe the reflection from the specific point l _d, only the signal after τ calculated from equation (1) has been received. The gate should be installed on the receiving side. That is, FIG.
In (A), when the transmission pulse 010 is sent, if the temperature of the ring installed there changes after a time τ, the outer diameter of the ring is deformed, and as shown in FIG. An impedance discontinuity occurs at that portion, and a reflected pulse 011 is generated. Gate O near 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 system measuring device 06 shown in FIG. The operation of such a configuration will be summarized as follows. For example, when there is no temperature change, the impedance of the cable (usually 50Ω or 75Ω) is measured even if the ring 05 made of the shape memory alloy is fitted. Therefore, there is no change in impedance regardless of the presence or absence of it. Therefore, measuring the impedance change point of this wire does not show any change. However, as shown in FIG. 10, when the temperature of the place where the shape memory alloy ring 05 is fitted rises above the transformation point, the ring 05 returns to its original shape and is deformed, for example, like 05a. Shrink and tighten the outer diameter of the coaxial cable 01. Therefore, the coaxial cable 01 is locally deformed, and the impedance of 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, ring 05
It can be seen that the temperature at a certain location has exceeded the temperature preset by the material of the ring. That is, FIG.
As shown in (C), if a gate pulse 012 is issued at a known time τ in advance and the reflected pulse 011 at the impedance discontinuity point caused by the shape change of the ring installed at that location is measured, it is found that there is a temperature change. If so, and if the reflected pulse is not measured, then there is 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 thereof becomes equal to or higher than the transformation point, the springs 055a and 055b contract, and the rod-shaped bodies 066a and 066b connected by these springs contract and deform the outer diameter of the cable 01. This action creates a discontinuity in the impedance near the cable,
Similar to the first conventional example, the reflected pulse can be measured and the temperature change at that location can be detected. According to such a temperature detecting device, a mechanical force is applied to the cable in addition to the shape deformation of the shape memory alloy due to the temperature change to cause a local impedance change, which is monitored from the cable end as an impedance change. As a result, the temperature rise can be detected, so that the following effects can be obtained. (1) With one (one pair) coaxial cable, it is possible to monitor the 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, the multi-point monitoring of a wide range of different temperature limits can be performed only by measuring the reflected wave at the discontinuity point of the impedance of the coaxial cable due to the change. Will be possible. (3) It is structurally simple as long as the gate is opened and the reflected pulse is detected at a pulse propagation time that matches the installation distance of the shape memory alloy.

Next, as another conventional example, Japanese Patent Application No. 2-86
The invention applied and publicized in No. 343 is described as a third conventional example, and has the following structure. That is, in the overall wiring diagram of FIG. 13, the same reference numerals as those in the first conventional example indicate the same members as those in the conventional example, and 034 is a measuring instrument 06.
036 is a temperature switch which is inserted at a position of a distance l ₁ from the contact and turns on a contact when the temperature reaches T ₁ , 035 is a temperature switch which is inserted at a position of a distance l ₂ from the measuring instrument 06 and turns on a contact at a temperature T ₂ , 036 Is a temperature switch that is inserted at a position of a distance l ₃ from the measuring device 06 and turns on the contact when the temperature reaches T ₃ . In such a device, the coaxial cable 01 is arranged at an appropriate position of the subject, that is, at a position where temperature monitoring is desired. Now, when none of the temperature switches is operating, the pulse signal emitted from the measuring instrument 06 propagates through the coaxial cable to the end thereof, and if the terminating resistance 07 is selected to be equal to the characteristic resistance of the line, for example. , The reflected signal becomes 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. The time from the transmission pulse to the reflection pulse at this time is a value t ₀ obtained by dividing twice the distance l ₄ by the signal speed v. If this t ₀ is a reasonable value for l ₄ , it can be said that this line is sound up to the termination resistance. Note that, for convenience of explanation, the terminating resistor 07
Is written in the drawing, but this value may be infinity or short circuit. Next, if the temperature of the place where the temperature switch T ₂ is installed rises and the temperature switch is activated and the line is short-circuited at that position, as shown in FIG. 14B, the position corresponding to time t ₂ is reached. Is reflected. If this point is completely short-circuited, then the condition of T ₃ or termination is ignored and does not appear in the output of TDR. Here, as the temperature switch, there are many known commercial products 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 its set temperature, the line is opened so that all the temperature switches are inserted in series in the cable, and when the set temperature is reached, the line is apparently disconnected at that point. Even with this structure, the same operational effect as the third conventional example can be achieved. According to such a temperature detecting device, the following effects can be obtained. (1) A large number of sensors can be monitored with a single coaxial cable. (2) Therefore, the cost of the electric wire material and the laying are greatly reduced. (3) The soundness of the electric wire can be confirmed by selecting a suitable terminating resistance. (4) The reached temperature and the position can be obtained with a relatively simple configuration.

However, as in the above-mentioned first, second, and third conventional examples, the conventional temperature measurement or monitoring requires a large number of sensors to be installed at the specified required measurement points, so that the installation work is also large-scale. And will incur a considerable cost. Also in the measurement using the TDR method, it works when the temperature reaches a specific temperature, and it is not clear how much the temperature before the sensor works and the temperature after the sensor works. Further, in the means using the shape memory alloy, since the external force is applied to the cable, the cable stress remains even after the force from the shape memory alloy is released, so that it is judged as if the temperature had risen. There is a point.

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 of only the coaxial cable at an unspecified position to be measured, 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 cost and that can know the temperature until the sensor acts and the temperature after the sensor acts.

[0007]

In order to achieve such an object, the invention of claim 1 transmits a high frequency pulse from one end of a coaxial cable laid in contact with an object to be measured,
In a temperature measuring device for measuring a temperature distribution of a measuring object by detecting a reflected wave of the pulse due to a change in impedance of the coaxial cable at a temperature changing portion, SiO ₂ is provided between a core wire of the coaxial cable and a jacket conductor. It is characterized in that a high frequency coaxial cable filled with is used.

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

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to the detection of temperature distribution in a branch pipe of a pipe to be measured will be described with reference to the drawings. FIG. , Its reflected wave waveform and temperature distribution diagram along the pipe to be measured, Fig. 3 is a wiring procedure diagram of a coaxial cable showing a modified example different from Fig. 1, and Fig. 4 is a temperature difference in the coaxial cable of Figs. Fig. 5 is a comparative longitudinal sectional view of the coaxial cable of Fig. 1 and a conventional coaxial cable, and Fig. 6 is a coaxial cable of Fig. 1 and a conventional coaxial cable. FIG. 7 is a comparison diagram of noise waveforms in a high temperature portion and a low temperature portion of the pipe to be measured by the cable, and FIG. 7 is a diagram showing noise generated in the cable at the temperature boundary portion 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 in the same drawing, respectively, 1 is a mother pipe, 2 is a branch pipe, and high temperature water is retained therein. Reference numeral 3 is a pipe on the low temperature side, and 4 is a valve for shutting off cold water.

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

At that time, it is known from the experimental result 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, it is possible to improve the measurement accuracy of the position of the boundary and the temperature difference from the following relationship.

In the above embodiment, the change in impedance due to the temperature change in the coaxial cable is expressed by the equation (2). ε _T = ε _R × {[(π / 4) (D ² −d ² )]} / {[(π / 4) [D (1 + ε _C ) ² } -d (1 + ε _C ) ² ] Z = (60 / √ε _T ) 1n (D / d) (2) Where, ε: Dielectric constant of insulator D: Outer diameter of high frequency cable d: Outer diameter of high frequency cable outer conductor Temperature difference and reflected wave Since the result obtained by the experiment for the relationship with the level is as shown in FIG. 4, it is possible to obtain the temperature difference ΔT by detecting the level of the reflected wave.

[0014] In addition, regarding the impedance sensitivity of only the coaxial cable, the permittivity of the insulator of the coaxial cable which is usually commercially available largely changes depending on the temperature. Further, since it has drawbacks such as a large coefficient of thermal expansion, the 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 the signal and the noise cannot be distinguished. However, the coaxial cable described in the embodiments of the present invention is a special cable having good high frequency characteristics, and its insertion loss is very small.
In addition, the normal coaxial cable causes noise to increase and is indistinguishable depending on the frequency applied to the high-frequency coaxial cable. 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. In this way, with the above-mentioned special cable, it is possible to remarkably change the temperature at the boundary portion even if the change in impedance is small. By the way, from the equation (2), as described below, the first derivative of the impedance Z of the coaxial cable by the inner diameter D is the equation (3), and the second derivative is 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 amount of the diameter of the coaxial cable based on the local temperature variation ΔT, the first derivative dZ / dD of the impedance due to the thermal deformation amount ΔD of the outer diameter D is proportional to 1 / D. It changes drastically and its second derivative d ² Z /
dD ² changes further in proportion to 1 / D ² . Therefore, the impedance change due to the temperature change can be detected only by the coaxial cable, because the geometrical electromagnetic relationship according to the equations (3) and (4) and the above-mentioned SiO ₂
It is considered that this is due to the synergistic effect of the noise reduction effect of.
By the way, the outer diameter of the coaxial cable used for carrying out 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 formed between the core wire and the outer 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 changes,
Compared to E-cable, it has a large shielding effect, high reliability, and easy wiring. On the other hand, a conventional coaxial cable has an ethylene tetrafluoride insulator around a core wire, an aluminum shield wire is braided on the outside thereof, and a tetrafluoroethylene wire is provided on the outside thereof, as shown in FIG. 5 (B). Ethylene oxide is applied as the jacket. Due to such a difference in structure, there are the following differences in action and effect, as shown in FIG. 7. (1) Since the insulator and the jacket of the conventional coaxial cable are made of ethylene tetrafluoride resin, the loss of the incident power is large with respect to the temperature and the phase is changed, so that the noise component is greatly affected. . (2) Since the cable used in this embodiment uses SiO ₂ as an insulator, it has better thermal characteristics with respect to temperature than a conventional cable. (3) As the temperature of the part where the cable is laid becomes higher with the conventional cable, noise is increased and it is difficult to determine even if a temperature boundary occurs, but the coaxial cable used in this example is Since the noise is very small even at high temperatures, it becomes easy to determine the boundary portion.

[0016]

According to the temperature distribution measuring device of the present invention, the temperature boundary portion and the temperature difference in the axial direction can be measured by measuring the impedance change at the point where the temperature difference occurs only in the measuring cable. 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 in a wide range only by measuring the reflected wave due to the impedance change. (3) The thermal fatigue loss of the pipe can be easily evaluated. (4) The cost can be significantly reduced. (5) The present invention can also be applied to stress measurement of cables.

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

According to the invention of claim 2, in claim 1, the coaxial cable of high circumference is laid in the longitudinal direction while meandering to the left and right along the surface of the object to be measured. Not only the temperature at a specific measurement position,
Economical temperature that enables temperature measurement using only coaxial cables at unspecified positions, allows construction work to be performed at low cost, and knows the temperature up to and after the sensor is activated. The present invention is extremely useful industrially because a distribution measuring device is obtained.

[Brief description of the drawings]

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

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

FIG. 4 is a diagram showing a relationship between a temperature difference due to the temperature measuring coaxial cable of FIG. 1 and respective reflected wave levels of a temperature boundary portion and noise.

FIG. 5 is a longitudinal sectional view of the temperature measuring coaxial cable of FIG. 1 and a comparative diagram with a vertical sectional view of a conventional coaxial cable.

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

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

FIG. 8 is a conduit diagram showing a conventional temperature-sensing 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 a BB transverse sectional view thereof.

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 thereof.

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

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

FIG. 13: T filed for a patent in Japanese Patent Application No. 2-86343
It is a whole circuit diagram of a DR temperature measuring device.

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

[Explanation of symbols]

 1 Mother 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 Outer conductor 04 Insulator 05 Ferrite ring 05a Ferrite ring 06 TDR measuring instrument (measuring instrument) 07 Terminating resistance

Claims (2)

[Claims] 1. An object to be measured by transmitting a high-frequency pulse from one end of a coaxial cable laid in contact with the object to be measured and detecting a reflected wave of the pulse due to a change in impedance of the coaxial cable at a temperature changing portion. A temperature distribution measuring device for measuring temperature distribution, characterized by using a high frequency coaxial cable in which SiO ₂ is filled between a core wire of the coaxial cable and an outer conductor. 2. The high-perimeter coaxial cable according to claim 1, meandering to the left and right along the surface of the object to be measured,
A temperature distribution measuring device, which is laid in the longitudinal direction.