JP6299230B2 - Cable soundness evaluation method - Google Patents

Description

  The present invention relates to a cable soundness evaluation method for evaluating the soundness of a cable of a thermocouple circuit that transmits a detection signal detected by a thermocouple to a measuring device via a cable.

  A thermocouple is a temperature sensor that uses the Seebeck effect, which is formed of two different kinds of metals, and generates a thermoelectromotive force due to a temperature difference between contact points of different metals. Thermocouples are required to be able to measure temperature stably even in a poor environment.

  Therefore, in order to determine whether or not the thermocouple has deteriorated, there is one in which a diagnostic current is passed to detect the resistance value of the thermocouple (see, for example, Patent Document 1). In addition, there is one that can detect that the installation state of the thermocouple becomes abnormal (see, for example, Patent Document 2).

Japanese translation of PCT publication No. 2003-510731 JP 2008-254017 A

  However, even if there is no significant change in the resistance value of the thermocouple, the temperature behavior detected by the thermocouple may vary greatly, and even if the temperature behavior varies greatly, It may return to the state. As described above, the abnormal state of the thermocouple circuit cannot be grasped only by the change of the resistance value or the temperature behavior. Therefore, it is difficult to determine a standard for determining a failure of the thermocouple circuit only by changing the resistance value of the thermocouple and the temperature behavior.

  It is considered that the change in the resistance value of the thermocouple and the change in temperature behavior are not the abnormality of the thermocouple itself but the influence of the cable of the thermocouple circuit. For example, when the environment where the cable of the thermocouple circuit is installed is an environment where a wet state and a dry state are repeated, the characteristics of the cable may change and may occur. In particular, when the thermocouple is installed in a place that is difficult to replace and the cable of the thermocouple circuit is long, the temperature behavior detected by the thermocouple is considered to be easily affected by the cable. Therefore, it is desired that the soundness of the cable of the thermocouple circuit can be properly evaluated.

  The objective of this invention is providing the cable soundness evaluation method which can evaluate the soundness of the cable of a thermocouple circuit in detail.

  The cable soundness evaluation method of the present invention is formed of the same metal as the two kinds of metals that are drawn from two different kinds of metals that form a thermocouple and transmit detection signals detected by the thermocouple to a measuring device. In the cable soundness evaluation method for evaluating the soundness of the cable, voltage or current is applied to the cable from the measurement device side, impedance measured from the measurement device side is measured, and characteristics of the measured impedance are determined in advance. It is judged whether it is within the range of the reference value, and the soundness of the cable due to the presence or absence of deterioration of the insulator of the cable is evaluated.

  According to the present invention, the impedance of a cable that may change in an environment where a thermocouple circuit is placed is measured, and it is determined whether or not the characteristic of the impedance is within a predetermined reference value range. Therefore, the soundness of the thermocouple circuit cable can be evaluated in more detail.

The flowchart which shows an example of the cable soundness evaluation method which concerns on embodiment of this invention. The circuit block diagram of an example of the thermocouple circuit to which the cable soundness evaluation method which concerns on embodiment of this invention is applied. Explanatory drawing of an example of the impedance characteristic about the disconnection tendency (increase of line resistance) of the cable of the thermocouple circuit in embodiment of this invention. Explanatory drawing about the influence of the galvanic battery which generate | occur | produced between the cables of the thermocouple circuit in embodiment of this invention. The characteristic view which represented the impedance characteristic of the thermocouple circuit in embodiment of this invention by making a frequency into a variable. Explanatory drawing of an example which determines whether the cable of a thermocouple circuit is normal by the impedance characteristic at the time of expressing the impedance characteristic of a thermocouple circuit as a variable in embodiment of this invention. Explanatory drawing of an example which determines the position of the insulation degradation of a cable at the time of expressing the impedance characteristic of the thermocouple circuit in embodiment of this invention as a variable. Explanatory drawing of another example which determines the position of the insulation deterioration of the cable in embodiment of this invention. The characteristic diagram of the impedance characteristic at the time of expressing the disconnection tendency (increase in wire resistance) of the cable of the thermocouple circuit of the circuit configuration diagram shown in FIG. 3A using a Nyquist diagram. The characteristic view at the time of expressing the impedance characteristic when the galvanic battery of the circuit block diagram shown to Fig.3 (a) generate | occur | produces using a Nyquist diagram. Explanatory drawing about the influence at the time of the disconnection tendency (increase in line resistance), a short circuit tendency (decrease in line resistance), and the galvanic battery between cables as deterioration of the cable of the thermocouple circuit in embodiment of this invention. Explanatory drawing of an example which determines the grade of the insulation deterioration of a cable based on the impedance characteristic at the time of expressing the impedance characteristic of the cable of the thermocouple circuit in embodiment of this invention using a Nyquist diagram. Explanatory drawing of an example which determines the position of the insulation deterioration of a cable based on the impedance characteristic at the time of expressing the impedance characteristic of the cable of the thermocouple circuit in embodiment of this invention using a Nyquist diagram.

  Embodiments of the present invention will be described below. FIG. 1 is a flowchart showing an example of a cable soundness evaluation method according to an embodiment of the present invention, and FIG. 2 is a circuit configuration diagram of an example of a thermocouple circuit to which the cable soundness evaluation method according to an embodiment of the present invention is applied. is there.

  In FIG. 2, the thermocouple circuit of the embodiment of the present invention has a thermocouple 11 installed in a reactor containment vessel PCV (Primary Containment Vessel) of a nuclear power plant, and a detection signal (temperature) detected by the thermocouple 11 is The data is transmitted to the measuring device 13 through the cables 12a and 12b. The cables 12a and 12b are connected to the penet inner terminal block 15 installed inside the penetration portion of the reactor containment vessel PCV via the relay terminal block 14, and the penetration portion (PCV penetration) 16 of the reactor containment vessel PCV is connected. It is connected to the penet outer terminal block 17 of the reactor building R / B (Reactor Building) outside the through-reactor containment vessel PCV, and further connected to the measuring device 13 in the central operation room.

  The thermocouple 11 detects the internal temperature of the reactor containment vessel PCV. For example, a T-type thermocouple in which two different types of metals are copper and constantan is adopted. The cables 12a and 12b are made of the same metal as the two kinds of metals of the thermocouple 11, and for example, the cable 12a is copper and the cable 12b is constantan.

  As described above, the thermocouple circuit according to the embodiment of the present invention is installed in the reactor containment vessel PCV, that is, a place where replacement is difficult, and the cables 12a and 12b of the thermocouple circuit are long. Further, since the cables 12a and 12b are different kinds of metals (copper and constantan) and are installed in a humid environment, there is a possibility that the electrical characteristics of the cables 12a and 12b change due to the influence of the humid environment. is there.

  Therefore, in the embodiment of the present invention, the impedance of the thermocouple circuit is measured, it is determined whether or not the characteristic of the measured impedance is within the range of the predetermined reference value, and it is caused by the presence or absence of deterioration of the cable insulator. I tried to evaluate the soundness of the cable.

  In FIG. 1, in the cable soundness evaluation method according to the embodiment of the present invention, first, voltage or current is applied to the cables 12a and 12b of the thermocouple circuit (S1). That is, a test voltage or a test current is applied to the cables 12a and 12b of the thermocouple circuit from the measuring device 13 side. When a voltage is applied, the current flowing through the cables 12a and 12b is measured. When a current is applied, the voltage between the cables 12a and 12b is measured.

  Next, the impedance of the thermocouple circuit is measured (S2). The impedance Z of the thermocouple circuit is obtained as Z = Vr / I using the measured current I flowing through the cables 12a and 12b when the test voltage Vr is applied. On the other hand, when the test current Ir is applied, the measured voltage V between the cables 12a and 12b is used to obtain Z = V / Ir.

  Then, it is determined whether or not the impedance characteristic is within the range of the reference value (S3). Since the impedance obtained in step S2 is represented by a function of frequency (angular frequency ω), it is determined whether or not the impedance characteristic when the frequency is changed is within a predetermined reference value range. The predetermined reference value range will be described later.

  If it is determined in step S3 that the impedance characteristic is within a predetermined reference value range, it is evaluated that the cable is normal (S4). On the other hand, when the impedance characteristic is not within the predetermined reference value range, it is evaluated that the cable is deteriorated (S4). When it is evaluated that the cable is deteriorated, the detection signal (temperature) detected from the thermocouple of the thermocouple circuit is not used for monitoring control, or replacement of the thermocouple circuit is considered.

  Next, the predetermined reference value range of the impedance characteristic will be described. As the deterioration of the cables 12a and 12b of the thermocouple circuit, the cable 12a and 12b tend to be disconnected (increase in wire resistance) and the influence of the galvanic cell generated between the cables 12a and 12b, which are different metals.

  First, the disconnection tendency (increase in wire resistance) of thermocouple circuit cables will be examined. FIG. 3 is an explanatory diagram of an example of impedance characteristics regarding the disconnection tendency (increase in line resistance) of the cable of the thermocouple circuit, and FIG. 3A shows that a part of the cable 12a of the thermocouple circuit tends to be disconnected. FIG. 3B is a characteristic diagram of impedance characteristics with a tendency to disconnection. FIG. 3B shows a case where the impedance characteristic has a frequency as a variable.

  For example, as shown in FIG. 3A, the length of the cables 12a and 12b is 300 m, the resistance at the position of 295 m from the measuring device 13 and 5 m from the thermocouple side is Ra, and the value of the resistance Ra is changed. Then, the impedance Z viewed from the measuring device side is measured, and the characteristics of the impedance Z when the cable 12a tends to be broken are examined. When the resistance Ra is 0, there is no disconnection tendency, and when the resistance Ra is ∞, it is a disconnection. FIG. 3B shows the impedance characteristics viewed from the measuring device side when the resistance Ra is changed from 0Ω to 10 kΩ.

Now, it is assumed that the impedance Z viewed from the measuring device side is Z = Re−jIm. In the following description, the vertical axis represents the absolute value | Z | of the impedance Z, the horizontal axis represents the frequency, and the frequency ω is changed from a certain value to a smaller value to represent the impedance characteristics. When the resistance Ra is 0Ω, the characteristic of the impedance Z viewed from the measuring device side is almost equal to the conductor resistance R _{1 of the} cable, as shown by the curve S1 in FIG. When the resistance Ra is generated due to the disconnection tendency, the absolute value | Z | of the characteristic of the impedance Z increases as shown by the curve S2 in FIG. Further, when the disconnection tendency proceeds, the absolute value | Z | of the characteristic of the impedance Z further increases as shown by the curve S3 in FIG. As described above, as the resistance Ra indicating the disconnection tendency of the cables 12a and 12b increases, the absolute value | Z | of the characteristic of the impedance Z viewed from the measuring device side increases.

  Next, the influence of the galvanic battery generated between the cables 12a and 12b, which are different metals of the thermocouple circuit, will be examined. FIG. 4 is an explanatory view of the influence of the galvanic cell generated between the cables of the thermocouple circuit, and FIG. 4A is a circuit configuration showing a case where the galvanic cell is generated between the cables 12a and 12b of the thermocouple circuit. FIG. 4B is a circuit diagram showing an example of an equivalent circuit of the internal impedance of the galvanic cell, FIG. 4C is an explanatory diagram of a calculation formula for the impedance of the cable generated by the galvanic cell, and FIG. It is a characteristic view of the impedance characteristic when a galvanic battery generate | occur | produces. FIG. 4D shows a case where the impedance characteristic has a frequency as a variable.

  Now, as shown to Fig.4 (a), the length of cable 12a, 12b is 300 m, and it was made to immerse with tap water over 3 m in the meantime. As a result, the galvanic battery 18 was generated. A galvanic cell is a cell caused by a difference in the equilibrium potential (standard oxidation-reduction potential) of the electrochemical reaction that occurs on the surface of each electrode. When the electrode is conducted through an electrolyte such as an aqueous solution or water film, It is formed. It is different from the thermoelectromotive force in the thermocouple. That is, a galvanic cell is an electrochemical cell in which phases of different types of electrical conductors are connected in series, at least one of which is an ionic conductor phase, and both end phases are electronic conductors of the same chemical composition. It is considered to occur between copper and constantan conductors. Every Kalbani battery has an internal impedance.

As shown in FIG. 4B, the internal impedance of the galvanic cell is shown as the conductor resistance R ₁ connected in series to the parallel circuit of the line resistance Rx and the galvanic cell capacity component C of the cables 12a and 12b. Then, as shown in FIG. 4C, the impedance Z viewed from the measuring device side is expressed by the following equation (1).

Z = Z'-jZ "
= R ₁ + Rx / (1 + ω ² Rx ² C ² ) {ωRx ² C / (1 + ω ² Rx ² C ² )} (1)
Then, when the frequency ω is changed from a certain value to become smaller, the characteristic of the impedance Z seen from the measuring device side is as shown in FIG. 4D, as the frequency becomes smaller, the absolute value | Z of the impedance Z | Is an increasing characteristic.

  FIG. 5 is a characteristic diagram showing the impedance characteristics of the thermocouple circuit with the frequency as a variable. In FIG. 5, the vertical axis represents the real part Re of the impedance, and the horizontal axis represents the frequency. In FIG. 5, curves G1 and G2 show examples of impedance characteristics when the cable is insulation-degraded, and curves G3 show examples of impedance characteristics when the cable is normal.

  When the impedance characteristics of the thermocouple circuit are expressed using the frequency as a variable, whether or not the cable of the thermocouple circuit is normal is determined by paying attention to the locus of the real part Re of the impedance when the frequency is changed. To do. This is because when the carbani battery is generated in the cables 12a and 12b, as shown in FIG. 4 (c), the real part Re (Z ′) of the impedance increases as the frequency decreases. Pay attention to its characteristics.

  FIG. 6 is an explanatory diagram of an example of determining whether or not the cable of the thermocouple circuit is normal based on the impedance characteristic when the impedance characteristic of the thermocouple circuit is expressed as a variable. The impedance characteristics shown in FIG. 6 are impedance characteristics in the low frequency region (0.1 to 40 Hz) of the curve G2 in FIG. The cable of the thermocouple circuit depends on whether or not the fluctuation ΔRe of the real part Re of the impedance accompanying the frequency fluctuation is within a predetermined reference value ΔRref within a predetermined low frequency region (0.1 to 40 Hz). It is determined whether or not it is normal. This is because the real part Re (Z ′) of the impedance exhibits a characteristic that increases as the frequency decreases.

  As shown in FIG. 6, for example, the determination is made based on whether or not the fluctuation ΔRe of the real part Re of the impedance in the low frequency region (0.1 to 40 Hz) is within the range of the reference value ΔRref. In this case, since the variation ΔRe of the real part Re of the impedance of the curve G2 in FIG. 5 deviates from the reference value ΔRref in the low frequency region (0.1 to 40 Hz), it is determined that the cable is deteriorated in insulation. . The impedance characteristics of the curves G1 and G3 in FIG. In the case of the curve G3 in which the cable is normal, the real part Re (Z ′) of the impedance is constant even when the frequency is reduced. It is within the range of the reference value ΔRref at (0.1 to 40 Hz).

  In the above description, the predetermined low frequency region is 0.1 to 40 Hz, but may be a frequency of 100 Hz or less excluding 0 Hz. If the frequency is lowered, the reference value ΔRref can be set large, so that the accuracy of the determination is improved, but the determination takes time. Practically, a range of 0.1 to 100 Hz excluding commercial frequencies (50 Hz and 60 Hz) is desirable.

  Further, although the variation ΔRe of the real part Re of the impedance accompanying the frequency variation is used, it may be the absolute value | Z | of the impedance. This is because the real part Re of impedance and the absolute value | Z | of impedance are substantially equal in the low frequency region.

  Next, a description will be given of a case where the position of cable insulation deterioration is determined when the impedance characteristics of the thermocouple circuit are expressed as a variable. FIG. 7 is an explanatory diagram of an example of determining the position of insulation deterioration of the cable when the impedance characteristic of the thermocouple circuit in the embodiment of the present invention is expressed as a variable. In FIG. 7, a galvanic cell is generated. The characteristic figure of the impedance characteristic when changing a position is shown.

  As in the case shown in FIG. 4, the length of the cables 12a and 12b is 300 m, the thermocouple 11 between the cables 12a and 12b is extended from the thermocouple 11 to the position of X by 3 m, and immersed in tap water to install the galvanic cell 18. The impedance was measured when the distance X from the tip of the thermocouple 11 to the position of the galvanic cell 18 was 200 m, 100 m, or 15 m.

  In FIG. 7, a curve H1 is a locus of impedance characteristics when the distance X from the tip of the thermocouple to the galvanic cell position is 15 m, and a curve H2 is a distance X from the tip of the thermocouple to the galvanic cell position is 100 m. The locus of the impedance characteristic at the time of, and the curve H3 is the locus of the impedance characteristic when the distance X from the tip of the thermocouple to the position of the galvanic cell is 200 m.

When the distance from the tip of the thermocouple 11 to the galvanic cell 18 is increased, the distance from the measuring device 13 is decreased, so that the real part Re of the impedance is decreased. That is, the real part Re of the impedance when the distance X to the position of the galvanic cell is 15 m is large, and the real part Re of the impedance becomes small as the distance X becomes 100 m and 200 m. Thus, by determining the size and locus of the real part Re of the impedance Z , the position of cable insulation deterioration can be determined.

  The distance X from the tip of the thermocouple 11 to the galvanic battery 18 can also be estimated from the temperature error T-T0 between the temperature indication value T measured by the measuring device 13 and the ambient temperature T0 around the thermocouple 11. FIG. 8 is an explanatory diagram of another example for determining the position of cable insulation deterioration in the embodiment of the present invention.

  In FIG. 8, curve I1 is a locus of temperature error T-T0 when the distance X from the tip of the thermocouple to the position of the galvanic cell is 15 m, and curve I2 is the distance from the tip of the thermocouple to the position of the galvanic cell. The locus of the temperature error T-T0 when X is 100 m, and the curve I3 is the locus of the temperature error T-T0 when the distance X from the tip of the thermocouple to the position of the galvanic cell is 200 m.

  As shown in FIG. 8, when the distance from the tip of the thermocouple 11 to the galvanic cell 18 increases, the temperature error T-T0 increases regardless of the ambient temperature T0 around the thermocouple 11. When the distance X from the tip of the thermocouple to the position of the galvanic cell is 15 m, the temperature error T-T0 is about 5 ° C even if the ambient temperature T0 around the thermocouple 11 changes from 50 ° C to 200 ° C. is there. Similarly, when the distance X from the tip of the thermocouple to the position of the galvanic cell is 100 m, even if the ambient temperature T0 around the thermocouple 11 changes from 50 ° C to 200 ° C, the temperature error T-T0 is about When the distance X from the tip of the thermocouple to the position of the galvanic cell is 200 m when the ambient temperature T0 around the thermocouple 11 changes from 50 ° C to 200 ° C, the temperature error T-T0 Is about 80 ° C.

  Thus, by determining the temperature error T-T0 between the temperature instruction value T measured by the measuring device 13 and the ambient temperature T0 around the thermocouple 11, the position of cable insulation deterioration can be determined.

  In the above description, the impedance characteristic of the thermocouple circuit is described with the frequency as a variable. However, the impedance characteristic may be expressed by a Nyquist diagram.

  FIG. 9 is a characteristic diagram of impedance characteristics when the cable disconnection tendency (increase in line resistance) of the thermocouple circuit in the circuit configuration diagram shown in FIG. 3A is represented using a Nyquist diagram.

  Now, it is assumed that the impedance Z viewed from the measuring device side is Z = Re−jIm. In the following description, the ordinate represents the imaginary axis Im, the abscissa represents the real axis Re, and the frequency ω is changed in the range of 0 to ∞, and the impedance characteristics are represented by a Nyquist diagram. When the resistance Ra is 0Ω, the characteristic of the impedance Z viewed from the measuring device side is almost 0 as shown by a curve C1 in FIG. When the resistance Ra is 100Ω, the characteristic of the impedance Z draws a very small semicircular arc in the first quadrant as shown by a curve C2 in FIG. When the resistance Ra is 1 kΩ, the impedance Z draws a small semicircular arc in the first quadrant, as shown by a curve C3 in FIG. When the resistance Ra is 10 kΩ, the impedance Z draws a large semicircular arc in the first quadrant as shown by a curve C4 in FIG. As described above, as the resistance Ra indicating the disconnection tendency of the cables 12a and 12b increases, the characteristic of the impedance Z viewed from the measuring device side draws a large semicircular arc in the first quadrant.

  Next, the influence of the galvanic battery generated between the cables 12a and 12b, which are different metals of the thermocouple circuit, will be examined. FIG. 10 is a characteristic diagram in the case where the impedance characteristic when the galvanic battery of the circuit configuration diagram shown in FIG. 3A is generated is represented using a Nyquist diagram. When a galvanic battery is generated, the impedance Z viewed from the measuring device side is expressed by the above-described equation (1). Therefore, when the frequency ω is changed in the range of 0 to ∞, the impedance viewed from the measuring device side. The characteristic of Z draws a semicircular arc in the first quadrant as shown in FIG.

  FIG. 11 is an explanatory view of the influence when a disconnection tendency (increase in line resistance), a tendency toward short circuit (decrease in line resistance), and a galvanic cell between cables occur as deterioration of the cable of the thermocouple circuit. In FIG. 11, in addition to the occurrence of galvanic cells and the tendency of the cables 12a and 12b to be disconnected (increase in wire resistance), the influence of the short-circuit tendency between the cables 12a and 12b is also considered.

  That is, FIG. 11A is a circuit showing a case where a part of the cable 12a of the thermocouple circuit tends to be disconnected and the cable 12a, 12b tends to be short-circuited, and a galvanic battery is generated between the cables 12a, 12b of the thermocouple circuit. FIG. 11B is a characteristic diagram when impedance characteristics when a galvanic battery is generated and a galvanic battery is generated are expressed using a Nyquist diagram.

  As shown in FIG. 11A, in addition to the resistance Ra indicating the disconnection tendency of the cables 12a and 12b and the galvanic battery 18 generated between the cables 12a and 12b of the thermocouple circuit, the resistance indicating the short-circuit tendency of the cables 12a and 12b. Rb is also considered. The impedance characteristic in that case is as shown in FIG.

  For example, at a low load (a high resistance load in which current does not easily flow), a high voltage of the galvanic battery is maintained, so that the galvanic battery capacity component C increases. On the other hand, since the voltage of the galvanic battery decreases at a high load (a low load circuit through which a large amount of current flows), the galvanic battery capacity component C becomes small.

  As described above, in a high load circuit having a small resistance Ra indicating the disconnection tendency of the cables 12a and 12b and a resistance Rb indicating a short-circuit tendency of the cables 12a and 12b, the impedance characteristic is a semicircular arc shape as shown by the curve E1. In a low resistance load with a small resistance (capacitance component C small) and a large resistance Ra or resistance Rb, the impedance characteristic has a large semicircular arc shape (capacitance component C is large) as shown by a curve E2.

  Due to the presence or absence of deterioration of the insulation of the cable from the above-mentioned disconnection tendency (increase in wire resistance), short-circuit tendency between cables (decrease in line resistance), and impedance characteristics when a galvanic battery is generated between cables Evaluate the soundness of the cable.

  FIG. 12 is an explanatory diagram of an example in which the degree of insulation deterioration of the cable is determined based on the impedance characteristic when the impedance characteristic of the cable of the thermocouple circuit in the embodiment of the present invention is expressed using a Nyquist diagram. 12 (a) is a characteristic diagram showing an example of the impedance characteristic when the cable is normal, FIG. 12 (b) is a characteristic chart showing an example of the impedance characteristic when the cable is insulated, and FIG. 12 (c). These are explanatory drawings of an example for determining whether or not the impedance characteristic is within a predetermined reference value ΔRref.

  Whether or not the cable of the thermocouple circuit is normal is determined by paying attention to the impedance locus in the first quadrant of the impedance characteristic. As described above, the resistance Ra indicating the disconnection tendency of the cables 12a and 12b is viewed from the measuring device side as the resistance Ra indicating the disconnection tendency of the cables 12a and 12b increases as shown in FIG. This is because the characteristic of the impedance Z draws a large semicircular arc in the first quadrant. Also, when a galvanic cell is generated, a semicircular arc is drawn in the first quadrant as shown in FIG.

  For the impedance characteristics of the thermocouple circuit shown in FIG. 12 (a) and the impedance characteristics of the thermocouple circuit shown in FIG. 12 (b), the locus portions X1 and X2 of the impedance in the first quadrant are extracted, It is determined whether or not the impedance locus portions X1 and X2 are within a predetermined reference value ΔRref. That is, it is determined whether or not the impedance characteristic (the locus portion X1 and X2 of the impedance in the first quadrant) that has changed with the change in frequency is within a predetermined reference value ΔRref.

  As shown in FIG. 12C, it is determined whether or not the real part Re of the impedance Z is within a predetermined reference value ΔRref with respect to the locus X of the impedance in the first quadrant. This is almost semicircular in the first quadrant, regardless of whether the cables 12a, 12b show a disconnection tendency, the cables 12a, 12b show a short-circuit tendency, or a galvanic battery is generated. This is because an arc is drawn so that it can be determined. In the impedance characteristics of the thermocouple circuit shown in FIG. 12A, the cable is determined to be normal because the impedance locus in the first quadrant is small and the real part Re of the impedance Z is within the predetermined reference value ΔRref. To do. On the other hand, in the impedance characteristic of the thermocouple circuit shown in FIG. 12 (b), since the locus of the impedance in the first quadrant is large and the real part Re of the impedance Z is not within the predetermined reference value ΔRref, the cable is deteriorated in insulation. It is determined that FIG. 12C shows the impedance characteristics of the thermocouple circuit shown in FIG. 12A in which the locus of the impedance in the first quadrant is small and the real part Re of the impedance Z is within the predetermined reference value ΔRref. Yes.

  The reference value ΔRref is determined so as to satisfy the allowable range of the influence (temperature error) that the insulation deterioration generated in the cable has on the detection signal (temperature) detected by the thermocouple. For example, when the thermocouple circuit (thermocouple 11 or cables 12a, 12b) is placed in a humid environment, the cables 12a, 12b not only show a tendency to break or a short circuit, but a galvanic cell may be generated in the cable. Since it is expected, the allowable range of the influence of the galvanic battery generated in the cable on the detection signal detected by the thermocouple is determined.

  Thereby, for example, when the thermocouple circuit (thermocouple 11 or cables 12a, 12b) is placed in a wet environment and the cables 12a, 12b show a disconnection tendency or a short-circuit tendency, or when a galvanic battery is generated. Even in this case, it is possible to evaluate the soundness of the cable due to the presence or absence of deterioration of the cable insulator.

  In the above description, the variation ΔRe of the real part Re of the impedance due to the frequency variation is used, but it may be the absolute value | Z | of the impedance. This is because the real part Re of impedance and the absolute value | Z | of impedance are substantially equal in the low frequency region.

  Next, a description will be given of a case where the position of cable insulation deterioration is determined based on the impedance characteristics when the measured impedance characteristics are expressed using a Nyquist diagram. FIG. 13 is an explanatory diagram of an example of determining the position of cable insulation deterioration based on the impedance characteristics when the impedance characteristics of the cable of the thermocouple circuit are expressed using a Nyquist diagram.

  In FIG. 13, a curve F1 is a locus of impedance characteristics when the distance X from the tip of the thermocouple 11 to the position of the galvanic battery 18 is 200 m, and the DC resistance (corresponding to the line resistance Ra) from the measuring device 13 side is 302Ω. A curve F2 is a locus of impedance characteristics when the distance X from the tip of the thermocouple 11 to the position of the galvanic cell 18 is 100 m, and the DC resistance (corresponding to the line resistance Ra) from the measuring device 13 side is 318Ω. A curve F3 is a locus of impedance characteristics when the distance X from the tip of the thermocouple 11 to the position of the galvanic cell 18 is 15 m, and the DC resistance (corresponding to the line resistance Ra) from the measuring device 13 side is 324Ω. The curves F2 'and F3' of the curves F2 and F3 are impedance loci generated by the LCR portion of the cable from the measuring device 13 to the galvanic battery 18.

  When the distance from the tip of the thermocouple 11 to the galvanic cell 18 is increased, as described above, the resistance Ra indicating the disconnection tendency of the cables 12a and 12b is increased, and the galvanic cell capacity component C is increased. Thus, as shown in FIG. 11B, the semicircular arc becomes larger. Further, as the position of the galvanic battery 18 is farther from the tip of the thermocouple 11, the temperature indication value increases as the semicircular arc becomes larger. This is because when the semicircular arc is large, the galvanic battery capacity component C is large and maintains a high voltage, and the detection signal at the measuring device 13 shows a large value. For example, when the room temperature at the time of measurement is 22 ° C., the distance X from the tip of the thermocouple 11 to the position of the galvanic cell 18 is about 80 ° C. when the distance X is 200 m, and about 50 ° C. when the distance X is 100 m. When the distance X was 15 m, about 30 ° C. was indicated.

  Thus, by determining the real part Re of the impedance Z of the cables 12a and 12b of the thermocouple circuit and the size of the semicircular arc, the position of the insulation deterioration of the cable can be determined.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 11 ... Thermocouple, 12 ... Cable, 13 ... Measuring device, 14 ... Relay terminal block, 15 ... Penet inner terminal block, 16 ... PCV penetr, 17 ... Penet outer terminal block, 18 ... Galvanic cell

Claims (4)

Cable soundness that evaluates the soundness of a cable that is drawn from two different types of metal that forms a thermocouple and that transmits a detection signal detected by the thermocouple to a measuring device, the same metal as the two types of metal In the evaluation method,
Apply voltage or current to the cable from the measuring device side,
Measure the impedance viewed from the measuring device side,
Determining whether the measured impedance characteristic is within a predetermined reference value range;
A cable soundness evaluation method characterized by evaluating the soundness of the cable due to the presence or absence of deterioration of the insulator of the cable.   The thermocouple and the cable are placed in a humid environment, and the range of the predetermined reference value is an allowable range of the influence of the galvanic battery generated in the cable on the detection signal detected by the thermocouple. The cable soundness evaluation method according to claim 1, wherein:   The cable soundness evaluation method according to claim 1, wherein the degree of insulation deterioration of the cable is determined based on the measured impedance characteristic.   The cable soundness evaluation method according to claim 1, wherein a position of insulation deterioration of the cable is determined based on the measured impedance characteristic.

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