JPH11248545A - Temperature measuring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce restrictions on laying, to simplify the constitution of a measuring device and to lower a cost. SOLUTION: One end of a 2-core cable 13 is stipulated as an input end and a pulse generation circuit 11 applies electric pulses as input pulses from the input end of the 2-core cable. A reflection pulse measuring circuit 12 receives reflection pulses generated corresponding to the input pulses inside the 2-core cable based on temperature change in a length direction in the 2-core cable at the input end. Then, the reflection pulse measuring circuit 12 detects the polarity of the reflection pulses and delay time from the input pulses and measures the temperature change as temperature distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a temperature measuring system, and more particularly to a temperature measuring system using a two-core cable.

[0002]

2. Description of the Related Art Generally, a so-called point measurement method for measuring a temperature in a limited range (environmental range) using a thermocouple or a temperature-sensitive element such as a platinum resistor is known for temperature measurement.
Further, when measuring the temperature distribution, a so-called distribution type method of measuring the temperature distribution using a stimulated Raman scattering phenomenon of an optical fiber cable is used.

In the distribution type method, a wide range of temperature distribution can be measured by using one optical fiber cable. For this reason, the temperature distribution is used in the area of civil engineering measurement, for example, for controlling concrete placing temperature. .

[0004]

By the way, in the above-mentioned distribution type system, when the optical fiber cable is installed, not only the radius of curvature is limited due to the transmission loss, but also the optical fiber cable is limited.
There are various restrictions on manufacturing and mounting, such as connection of optical fiber cables and mounting of connectors.

In addition, in the method using the Raman scattering phenomenon described above, it is necessary to detect a small signal.
Due to the need to handle small signals, there is a problem that there is a measurement limit in the length direction of the optical fiber cable, and that the measuring device itself becomes expensive.

It is an object of the present invention to provide a temperature measuring system which has no manufacturing and mounting restrictions.

Another object of the present invention is to provide an inexpensive temperature measurement system having a large measurement limit.

[0008]

According to the present invention, there is provided a two-core cable having one end defined as an incident end, a pulse generating circuit for emitting an electric pulse as an incident pulse from the incident end of the two-core cable, A reflected pulse generated in response to the incident pulse in the two-core cable is received at the incident end based on a temperature change in the length direction of the two-core cable, and the polarity of the reflected pulse and a delay time from the incident pulse are detected. And a measuring circuit for measuring the temperature change as a temperature distribution.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

Referring to FIG. 1, the illustrated temperature measuring system includes a pulse generating circuit 11 and a reflected pulse measuring circuit 12, and these pulse generating circuit 11 and reflected pulse measuring circuit 12 are arranged as shown in FIG. It is connected to a two-core cable 13. Now, an electric pulse is input from the pulse generation circuit 11 to the two-core cable 13 as an incident pulse,
The reflected pulse from the core cable 13 is detected by the reflected pulse measuring circuit 12.

The time from the incidence of the incident pulse to the detection of the reflected pulse is t, the speed of the pulse propagating in the two-core cable 13 is v, and the distance of the two-core cable 13 from the incident end to the point where the reflected pulse is generated is L. Then, the distance L is expressed by Equation 1.

[0012]

(Equation 1)

When the time t (that is, the propagation delay time of the reflected pulse) is measured, the reflection position can be obtained from Equation 1.

Incidentally, in a parallel two-core cable,
Assuming that the radius of the core wire is r, the center-to-center distance is d, the magnetic permeability around the conductor is μ, and the dielectric constant around the conductor is ε, the characteristic impedance Zp in the high frequency region is expressed by Equation 2.

[0015]

(Equation 2)

On the other hand, in a coaxial cable, assuming that the outer conductor inner diameter of the coaxial cable is b, the inner conductor outer diameter is a, the magnetic permeability between conductors is μ, and the dielectric constant between conductors is ε, the characteristic impedance Zc Is represented by Equation 3.

[0017]

(Equation 3)

In equations (2) and (3), the temperature change rate of the dielectric constant ε is larger than the inner conductor outer diameter a, the outer conductor inner diameter b, and the magnetic permeability μ.
It will change in proportion to √ε.

Both the parallel two-core cable and the coaxial cable can be used as an electric pulse transmission line. The characteristic impedance of the transmission line at a predetermined temperature (hereinafter referred to as reference characteristic impedance) is defined as Z0, and the characteristic is increased by temperature rise. When the impedance (hereinafter, referred to as changed characteristic impedance) changes to Z, the reflectance R of the reflected wave generated by the change in the characteristic impedance
Is represented by Equation 4.

[0020]

(Equation 4)

Here, the relationship between the change in the characteristic impedance due to the temperature rise of the coaxial cable and the reflectance will be obtained. Assuming that the characteristic impedance in the normal temperature range is Z0, the characteristic impedance in the high temperature range is Z, the temperature coefficient of the dielectric constant is α, and the proportionality constant is k, the reference characteristic impedance Z0 and the changed characteristic impedance Z are represented by Equations 5 and 6, respectively. Can be represented by

[0022]

(Equation 5)

[0023]

(Equation 6) However, the proportionality constant k is represented by Expression 7.

[0024]

(Equation 7) Here, when Equation 6 is transformed using Equation 8 (approximation formula),
Equation 9 is obtained.

[0025]

(Equation 8)

[0026]

(Equation 9)

Substituting Equations 5 and 9 into Equation 4 gives Equation 10
Is obtained.

[0028]

(Equation 10)

Similarly, by substituting Equation 2 representing the characteristic impedance of the parallel two-core cable into Equation 4, and calculating the reflectance R of the parallel two-core cable, Equation 10 is obtained in the same manner as with the coaxial cable.

Equation 10 indicates that the temperature coefficient α of the dielectric constant is the reflectance R
In this case, it is shown that the reflectance R changes in proportion to 1/4 of the temperature coefficient α of the dielectric constant. Note that, in Expression 10, the sign “−” indicates the polarity of the reflected wave.

For example, in a 3C-2V high-frequency coaxial cable, its reference characteristic impedance Z0 is 75Ω at room temperature, and polyethylene having a temperature coefficient of a dielectric constant of −1500 (ppm / ° C.) as a dielectric used between the inner and outer conductors. (Source: IEICE / Electronic Communications Handbook, 402 pages / 1997). In this 3C-2V high-frequency coaxial cable, the reflectance is about 375 ppm / ° C.
The 3C-2V high-frequency coaxial cable can be used as a temperature distribution sensor cable having a temperature coefficient having a reflectance of about 375 ppm / ° C.

In the parallel two-core cable, the characteristic impedance changes in proportion to 1 / √ε, as in the case of the coaxial cable. become. Therefore, a parallel two-core cable can also be used as a temperature distribution sensor cable.

Here, referring also to FIG.
3 is laid in a straight line. At this time, FIG.
As shown in (a), there is a region where the cable temperature is high (temperature rising region) in the length direction of the cable. When an incident pulse is applied from the pulse generation circuit 11 in such a state, as shown in FIG. A pulse is generated (hereinafter, the reflection pulse at the start point is called a start point pulse, and the reflection pulse at the end point is called an end point pulse). Further, a reflected pulse is also generated at the end of the cable (hereinafter referred to as an end pulse).

In the example shown in FIG. 2A, there is a temperature rise region, and at the start point, the characteristic impedance changes from a low region to a high region. It has the same polarity.

On the other hand, at the end point, since the characteristic impedance changes from a high region to a low region, the reflected pulse at the end point has a polarity opposite to that of the incident pulse.

The reflected pulse generated as described above is supplied to the reflected pulse measuring circuit 12. Then, the pulse generation circuit 11 and the reflected pulse measurement circuit 12 are linked to each other,
When the pulse generation circuit 11 receives an incident pulse, the reflection pulse measurement circuit 12 starts counting (time measurement), and measures the count value when the reflection pulse (start point pulse) is first received (hereinafter referred to as a first pulse). Count value). The reflected pulse measuring circuit 12 obtains the distance to the starting point based on Equation 1. Further, the reflected pulse measuring circuit 12 continues counting time and measures the count value at the time when the reflected pulse (end point pulse) is received for the second time (referred to as a second count value). The reflected pulse measuring circuit 12 obtains the distance to the end point based on Equation 1.

The reflected pulse measuring circuit 12 obtains a temperature change area from the distance to the start point and the distance to the end point. Further, since the start point pulse has the same polarity as the incident pulse and the end point pulse has the opposite polarity to the incident pulse, the reflected pulse measurement circuit 12 determines that the temperature change region is the temperature rise region, and, for example, The temperature distribution display shown in FIG.

In the example shown in the figure, the terminal pulse is further received. However, since no further reflected pulse is received thereafter, the pulse measuring circuit 12 determines that it is the terminal pulse.

When the temperature change area is a temperature drop area, a reflected pulse having a polarity opposite to that of the incident pulse is generated at the start point and a reflected pulse having the same polarity as the incident pulse is generated at the end point. The pulse measurement circuit 12 first receives a start point pulse of the opposite polarity, and then receives an end point pulse of the same polarity, whereby it is possible to determine that the temperature change region is a temperature decrease region.

Furthermore, even if there are a plurality of temperature change regions, the polarity of the reflected pulse received at the odd number and the polarity of the reflected pulse received at the even number become opposite to each other, considering the pair of the start point pulse and the end point pulse. Therefore, similarly, it can be determined whether a plurality of temperature change regions are a temperature rise region or a temperature fall region.

[0041]

As described above, in the present invention, since the two-core cable is used as the temperature distribution sensor cable, there is an advantage that there is less restriction on the laying as compared with the optical fiber cable. In addition, according to the present invention, since it is not necessary to use an optical component, there is an effect that the configuration of the measuring device is simplified and the measuring range (distance) can be expanded.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a temperature measurement system according to the present invention.

FIGS. 2A and 2B are diagrams for explaining the operation of the temperature measurement system shown in FIG. 1; FIG. 2A is a diagram showing a temperature rising region existing in a cable laying direction; FIG. It is a figure for explaining a pulse.

[Explanation of symbols]

 11 pulse generation circuit 12 reflected pulse measurement circuit 13 two-core cable

Claims (3)

[Claims] 1. A two-core cable having one end defined as an input end, a pulse generating circuit for inputting an electric pulse as an input pulse from the input end of the two-core cable, and a temperature change in the length direction of the two-core cable. Receiving a reflected pulse generated in accordance with the incident pulse in the two-core cable at the incident end based on the detection of the polarity of the reflected pulse and a delay time from the incident pulse, and measuring the temperature change as a temperature distribution. A temperature measurement system comprising: 2. The temperature measurement system according to claim 1, wherein the reflected pulse is generated by a change in a characteristic impedance of the two-core cable generated according to the temperature change, and the measurement circuit is configured to perform the measurement based on the polarity. A temperature measurement system for measuring whether the temperature change is a temperature rise change or a temperature fall change, and measuring the magnitude of the temperature change based on the delay time. 3. The temperature measurement system according to claim 1, wherein the two-core cable is a coaxial cable.