Thermocouple abnormality detection system and detection method thereof

According to one embodiment, a thermocouple abnormality detection system including: a plurality of thermocouples each including a plurality of thermocouple wires housed in a sheath; a transmission signal conversion unit configured to convert a thermo-electromotive force generated by each of the plurality of the thermocouple wires to a transmission signal and to output the transmission signal; a transmission unit configured to transmit the transmission signal outputted from the transmission signal conversion unit; and an abnormality detection circuit configured to detect an abnormality of each of the plurality of the thermocouples by comparing, with each other, the transmission signals obtained from the plurality of thermocouple wires provided in each of the thermocouples.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2011-162426, filed Jul. 2, 2011; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments of the present invention relates to a thermocouple abnormality detection system and detection method thereof used in an industrial plant.

BACKGROUND

A thermocouple is provided in an industrial plant, and the temperature information obtained from the thermocouple is used as an index for evaluating the performance of the industrial plant. The thermo-electromotive force generated by the thermocouple is inputted into a monitoring and control apparatus so as to be used for temperature monitoring and temperature control.

The thermocouple is gradually deteriorated by being subjected to stress due to repeated expansion and contraction caused by temperature change. The thermocouple is provided with a system for detecting the deterioration thereof. When the deterioration of the thermocouple is detected by the system, a measure, such as exchanging the thermocouple, is taken by plant maintenance personnel.

As an example of the conventional detection system, a detection system provided with two active and standby thermocouples is known. The conventional detection system has such a merit that an abnormality of the standby side thermocouple can be monitored by monitoring the difference between the detection signals of the two thermocouples.

DETAILED DESCRIPTION

Embodiments of a thermocouple abnormality detection system and a detection method thereof according to the present invention will be described with reference to the accompanying drawings.

In some industrial plants, a large number (such as 100 to 300) of thermocouples can be provided. In the case where, in addition to active thermocouples, a large number of standby thermocouples are provided, it is necessary that, in addition to the 100 to 300 thermocouples, 100 to 300 standby thermocouples are further provided.

This significantly increases the construction work and the installation cost which are required for installing the thermocouples. Further, in order to transmit a detection signal to a monitoring and control apparatus from each of the thermocouples, it is necessary to extend the thermocouples or to install cables for transmitting electric signals converted from the thermo-electromotive forces of the thermocouples. Thus, it has been actually impossible to install such large number of thermocouples.

The embodiments according to the present invention have been made in view of the above described circumstances. An object of the embodiments according to the present invention is to provide a thermocouple abnormality detection system and a detection method thereof capable of suitably detecting an abnormality of a thermocouple.

This and other objects can be achieved according to the present invention by providing a thermocouple abnormality detection system including: a plurality of thermocouples each including a plurality of thermocouple wires housed in a sheath; a transmission signal conversion unit configured to convert a thermo-electromotive force generated by each of the plurality of the thermocouple wires to a transmission signal and to output the transmission signal; a transmission unit configured to transmit the transmission signal outputted from the transmission signal conversion unit; and an abnormality detection circuit configured to detect an abnormality of each of the plurality of the thermocouples by comparing, with each other, the transmission signals obtained from the plurality of thermocouple wires provided in each of the thermocouples.

First Embodiment

A first embodiment of a thermocouple abnormality detection system and a detection method thereof according to the present invention will be described with reference to the accompanying drawings.

FIG. 1is a view showing a configuration of a first embodiment of a thermocouple abnormality detection system according to the present invention.

A thermocouple abnormality detection system (abnormality detection system)1according to a first embodiment is provided in an industrial plant, such as a thermal power generation plant, a nuclear power generation plant, a chemical plant, and various factories.

The abnormality detection system1includes a temperature measurement system10mainly provided in an industrial plant2, a monitoring and control apparatus11provided, for example, outside the industrial plant2, and transmission cables12ato12ffor connecting the temperature measurement system10to the monitoring and control apparatus11.

For example, 100 to 300 of thermocouple pairs are provided in the industrial plant2(for example, when 500 instrument sensors are provided as a whole). In the first embodiment, three thermocouple pairs21to23are illustrated for convenience of description. Each of the thermocouple pairs21to23is provided in a predetermined measurement area, such as an apparatus installation site area.

The apparatus installation site area is an area in the industrial plant2, in which area facility apparatuses, such as a pump, a fan, a turbine, and a valve, and pipes are arranged. The apparatus installation site area is also an area in the industrial plant2, in which area main facility apparatuses are particularly intensively arranged. Note that the apparatus installation site area is not clearly separated from the other area, and a part of the facility apparatuses, and the like, are also installed in the other area.

Since the thermocouple pairs21to23have almost the same configuration, only the thermocouple pair21is described, and the description of the other thermocouple pairs22and23is omitted.

The thermocouple pair21includes a thermocouple wire21a(first thermocouple) and a thermocouple wire21b(second thermocouple). The thermocouple pair21(so-called two-wire thermocouple) is housed in a sheath31. The sheath31has a cylindrical shape, and has the outer layer made of a heat-resistant alloy to thereby protect the thermocouple wires21aand21bhoused therein. In the sheath31, each of the thermocouple wires21aand21bis fixed and insulated by a filler, such as magnesium oxide.

Each of the thermocouple wires21aand21bhas, at the tip portion thereof, a hot junction as a measurement place, and also has a cold junction (head portion) at the end portion opposite to the measurement place. The thermocouple wires21aand21brespectively include, at the cold junctions thereof, A/D converters41aand41b, and adapters51aand51bin this order.

The A/D converters41aand41b(transmission signal conversion units) respectively A/D-convert thermo-electromotive forces generated in the thermocouple wires21aand21binto transmission signals, so as to output the transmission signals. The adapters51aand51b(transmission units) transmit the transmission signals transmitted from the A/D converters41aand41bto the transmission cables12aand12b, respectively.

Note that each of the thermocouples21to23may be configured such that an apparatus, in which each of the A/D converters41ato43aand41bto43b, and each of adapters51ato53aand51bto53bare integrated, is incorporated in the cold junction, or the like. The transmission signals may be transmitted to the monitoring and control apparatus11via a relay apparatus provided between the monitoring and control apparatus11, and the adapters51ato53aand51bto53b.

The transmission cables12ato12fare, for example, optical cables, and transmit, to the monitoring and control apparatus11, the transmission signals transmitted from the adapters51ato53aand51bto53b, respectively.

The transmission cable12aconnects the adapter51ato the monitoring and control apparatus11. The transmission cable12bconnects between the adapters51aand51bprovided at the thermocouple pair21, that is, connects between the adapters51aand51bof the thermocouple pair21. The transmission cable12cconnects the adapter51bof the thermocouple pair21to the adapter52aof the thermocouple pair22.

Similarly, the transmission cable12dconnects between the adapters52aand52bof the thermocouple pair22, and the transmission cable12fconnects between the adapters53aand53bof the thermocouple pair23. The transmission cable12econnects the adapter52bof the thermocouple pair22to the adapter53aof the thermocouple pair23.

That is, the transmission cable12aas a second connection unit connects the thermocouple wire21a(adapter51a) to the monitoring and control apparatus11(abnormality detection circuit60). The transmission cables12bto12fas first connection units connect between the plurality of mutually adjacent thermocouples21to23(adapters51ato53aand51bto53b).

The transmission cables12ato12fare connected by a wiring system (so-called Daisy Chain system) in which the mutually adjacent thermocouples21to23(adapters51ato53aand51bto53b) are connected in series. The transmission signal transmitted from each of the adapters52a,53a, and51bto53bare successively transmitted through the required transmission cables12bto12f, so as to be transmitted to the adapter51a. Eventually, the respective transmission signals are collected and transmitted as a transmission signal P to the monitoring and control apparatus11through the transmission cable12a.

In the Daisy Chain system, only one cable of the transmission cable12ais used as the transmission cable (second connection unit) which is laid over a long distance (generally, a length of 200 m to 400 m) so as to be connected to the monitoring and control apparatus11. The transmission cables12bto12fother than the transmission cable12aneed only to be capable of connecting between mutually adjacent adapters51ato53aand51bto53b, and hence need only to have a very short length (generally, 10 m to 20 m).

Even in the case where the number of thermocouples is increased, it is only necessary that the transmission cables12bto12fhaving very short lengths are laid between the adapters51ato53aand51bto53b. Thus, from the viewpoint of reducing the amount of cables, the Daisy Chain system is advantageous.

Note that any of one-core cable or two-core cable may also be used as the transmission cables12ato12f. When two-core cables are applied, the transmission cables12ato12fcan also perform power supply from the monitoring and control apparatus11to the A/D converters41ato43aand41bto43band the adapters51ato53aand51bto53b, in addition to the transmission of the transmission signals. Each of the transmission cables12ato12fis configured as a single cable in which one core for supplying a positive voltage and the other core for supplying a negative voltage are paired so as to satisfy the predetermined functions.

The monitoring and control apparatus11monitors measurement values on the basis of the transmission signals which are measured by the thermocouples21to23and transmitted by the on-site transmission. The monitoring and control apparatus11includes the abnormality detection circuit60.

FIG. 2is a view showing an internal configuration of the abnormality detection circuit60provided in the monitoring and control apparatus11.

In the abnormality detection circuit60, transmission signals p1ato p1aand p1bto p3boutputted from the respective thermocouples21to23are taken out from the transmission signal P supplied through the transmission cable12a, and are respectively supplied to subtractors61to63.

Among the set of subtractors61to63, a set of absolute value converters71to73, a set of comparators81to83, and a set of timers91to93, the components in each of the sets have the almost same configuration. Thus, only the subtractor61, the absolute value converter71, and the comparator81, and the timer91will be described, and the description of the other components, that is, the description of the subtractors62and63, the absolute value converters72and73, the comparators82and83, and the timers92and93will be omitted.

The subtractor61calculates a deviation e1by performing subtraction between the transmission signals p1aand p1boutputted from the thermocouple pair21(thermocouple wires21aand21b). The absolute value converter71calculates an absolute deviation f1by converting the absolute value of the deviation e1. The absolute deviation f1becomes a positive value irrespective of the magnitude relationship between the transmission signals p1aand p1b.

The comparator81compares the absolute deviation f1with a threshold value α set beforehand. The comparator81outputs an output g1, when the absolute deviation f1is larger than the threshold value α. In the case where the transmission signal at the time of generation of the maximum thermo-electromotive force is set to 100%, the threshold value α is selected to be, for example, about 5% of the value of the transmission signal.

The timer91issues an abnormality signal h1when the output g1is continuously outputted during a predetermined time period (for example, 15 seconds). The timer91prevents that the abnormality signal h1is frequently generated due to a temporary increase in the deviation e1resulting from the difference in the response speed between the thermocouple wires21aand21b.

Next, the effects of the thermocouple abnormality detection system1according to the first embodiment will be described.

The thermocouple wires are gradually deteriorated by being subjected to stress due to repeated expansion and contraction caused by temperature change. For example, when the thermocouple wire21bis deteriorated more rapidly than the thermocouple wire21aand becomes unable to generate a thermo-electromotive force, the transmission signal p1brepresents an abnormal value.

On the other hand, the thermocouple wire21ais normal as compared with the thermocouple wire21b, and hence the transmission signal p1arepresents a normal value. When the transmission signal p1ais compared with the transmission signal p1b, the absolute deviation f1is increased. Eventually, the abnormality detection circuit60issues the abnormality signal h1, so that the abnormality is detected.

A plant operator can know the occurrence of the abnormality by the abnormality detection, and specifies which of the thermocouple wires is abnormal. The abnormality is specified, for example, by referring to the trend graphs of the transmission signal p1aand the transmission signal p1b, and the like.

Here, the superiority of the abnormality detection system1according to the first embodiment will be described by using an abnormality detection system as a comparison example.

FIG. 3is a view showing an abnormality detection system101as a comparison example of the thermocouple abnormality detection system1according to the first embodiment.

An abnormality detection system101includes a temperature measurement system110, and a monitoring and control apparatus111provided, for example, outside the industrial plant2.

The temperature measurement system110includes thermocouple pairs121to123which are two-wire thermocouples. The thermocouple pairs121to123have almost the same configuration, and hence only the thermocouple pair121is described, and the description of the other thermocouple pairs122and123is omitted.

A thermocouple wire121aand a thermocouple wire121bare housed in a sheath131. The thermocouple wires121aand121bincludes a terminal box141at the cold junction. From the terminal box141, the thermo-electromotive force (small thermo-electromotive force) generated in each of the thermocouple wires121aand121bis supplied to a compensation lead wire151.

The compensation lead wire151is connected to one (the thermocouple wire121ainFIG. 3) of the thermocouple wires of the thermocouple pair121.

The monitoring and control apparatus111includes an I/O board160. The thermo-electromotive forces of the thermocouples121to123are inputted into the I/O board160through compensation lead wires151to153, respectively.

Note that the thermocouples121to123may be directly connected to the I/O board160. However, the distance between the I/O board160and the thermocouples121to123is large (for example, 200 m to 400 m), and hence extremely long thermocouples121to123are needed, resulting in high cost. For this reason, the thermocouples121to123are connected to the I/O board160by the compensation lead wires151to153, respectively.

The I/O board160includes a disconnection detection circuit. The disconnection detection circuit includes a power source to apply a voltage to each of thermocouple wires121ato123aand121bto123bat each predetermined period. When one of the thermocouple wires121ato123aand121bto123bis disconnected, a phenomenon (burnout), in which the applied voltage is greatly increased by being charged by the input portion, is caused, and thereby the disconnection detection circuit detects the disconnection.

Temperatures of measurement object portions are transmitted to the hot junctions of the thermocouples121to123via sheaths131to133, respectively. At this time, the thermocouples121to123are repeatedly subjected to rapid temperature changes. The thermocouples121to123are gradually deteriorated by being subjected to stress due to repeated expansion and contraction, and are eventually disconnected (broken).

For example, when the disconnection of the thermocouple wire122ais detected, the connection to the disconnected thermocouple wire122ais removed in a terminal box142by plant maintenance personnel. The thermocouple wire122bwhich is paired with the thermocouple wire122ais connected to the compensation lead wire152in the terminal box142(illustrated by dotted lines inFIG. 3). As a result, the thermo-electromotive force of the exchanged thermocouple wire122bis transmitted to the I/O board160.

In the case where single wire thermocouples, in each of which one thermocouple wire (for example, each of thermocouple wires121ato123a) is housed in each of the sheaths131to133, are used, and where one of the thermocouple wires121ato123ais disconnected, a new thermocouple used as a substitution of the disconnected one of the thermocouple wires121ato123ais needed. Thus, when the single wire thermocouples are used, the replacement work and the cost for the replacement are required at the time of the disconnection.

On the other hand, in the case where the two wire thermocouples121to123are used as shown inFIG. 3, the disconnected thermocouple wire can be easily exchanged by a simple work of changing the connection in the terminal box141to143. That is, in the abnormality detection system101of the thermocouples121to123, the thermocouple pairs121to123(two-wire thermocouples) are provided mainly in view of the disconnection of the thermocouple wire.

Here, in an actual industrial plant, a large number (such as 100 to 300) of two-wire thermocouples121to123are installed. For this reason, in view of the installation work and the cost, it is unrealistic that the thermo-electromotive forces obtained from both of the thermocouple wires121ato123aand of the thermocouple wires121bto123bof the two-wire thermocouples121to123are inputted into the monitoring and control apparatus111.

Specifically, in the case where, in the thermocouple abnormality detection system101as the comparison example, the thermo-electromotive forces of both of the thermocouple wires121ato123aand of the thermocouple wires121bto123bof the two-wire thermocouples121to123are inputted to the I/O board160, each of the compensation lead wire pairs151to153are needed for each of the thermocouple wires121ato123aand121bto123b. That is, the number of the necessary compensation lead wires151to153is doubled, resulting in an increase in the installation work and the cost.

Further, when the number of the compensation lead wires151to153is doubled, the number of input points of the I/O board160is also doubled. Further, in order to input the thermo-electromotive forces into the monitoring and control apparatus111, A/D conversion processing, and the like, for converting the analog voltage signals to digital signals are needed, so that the operation load of the monitoring and control apparatus111is increased.

On the other hand, the thermocouple abnormality detection system1according to the first embodiment uses the on-site transmission in which the thermo-electromotive forces generated by the thermocouples21to23are converted into transmission signals, and in which the transmission signals are then transmitted to the monitoring and control apparatus11. Thus, the abnormality detection system1of the thermocouples21to23can suitably detect an abnormality of the thermocouples21to23while efficiently utilizing merits of the two-wire thermocouples21to23. That is, from the measurement results of each of the two-wire thermocouples21to23, it is possible to surely detect the deterioration of each of the thermocouples at an early stage in the process before each of the thermocouples is disconnected.

In the thermocouple abnormality detection system1, only the transmission cable12ais used as the transmission cable connected to the abnormality detection circuit60(monitoring and control apparatus11), and the transmission signal P is transmitted via the transmission cable12a. Thereby, the labor, time and cost required for laying the cables can be reduced as compared with the case where long cables (compensation lead wires151to153) are required in correspondence with the number of the thermocouple wires121ato123aand121bto123bas in the comparison example of the abnormality detection system101.

In the abnormality detection system1, the transmission signal P, which is a digital signal, is transmitted to the monitoring and control apparatus11by using a on-site transmission technique. Thereby, the load of the arithmetic operation, such as A/D conversion processing performed by the monitoring and control apparatus11, is reduced.

The transmission cables12bto12ffor connecting between the thermocouple wires21ato23aand21bto23bof each of the thermocouple pairs21to23, and for connecting between the thermocouple wires21ato23aand21bto23bof the mutually adjacent thermocouple pairs21to23are very short cables as compared with the transmission cable12a. For this reason, the abnormality detection system1is also effective in that the load of the cable installation and the cost are reduced.

That is, the thermocouple abnormality detection system1according to the first embodiment can reduce the installation work and the cost of the temperature measurement system as compared with the conventional thermocouple abnormality detection system.

Further, measurement results of temperatures at very near positions can be obtained by a pair of thermocouple wires (two-wire thermocouple) housed in the same sheath. For this reason, as compared with the case where two temperature measurement results are obtained separately from two single wire thermocouples, the abnormality detection system1has no temperature measurement error depending on the positions of the thermocouple wires. Therefore, the abnormality detection system1can perform abnormality detection with sufficient accuracy.

Note that as shown inFIG. 4, each of A/D converters241to243and each of adapters251to253may be provided in each of the thermocouple pairs21to23. Further, the thermocouple23may be connected to the A/D converter243via a relay unit263. Further, an abnormality detection circuit260(monitoring and control apparatus211) may receive the transmission signals through two transmission cables212aand212d(second connection unit). Further, transmission cables212band212cmay be housed in a housing280from the viewpoint of protection from the surrounding environment. In the following, the details will be described with reference to the drawings.

FIG. 4is a view showing a configuration of a modification of the thermocouple abnormality detection system according to the first embodiment.

The portions corresponding to those of the thermocouple abnormality detection system1according to the first embodiment are denoted by the same reference numerals and characters, and the description thereof will be omitted.

An abnormality detection system201includes a temperature measurement system210mainly provided in the industrial plant2, the monitoring and control apparatus211provided, for example, outside the industrial plant2, and the transmission cables212ato212dfor connecting the temperature measurement system210to the monitoring and control apparatus211.

Since the A/D converters241to243have almost the same configuration, and since the adapters251to253have almost the same configuration, only the A/D converter241and the adapter251are described, and the description of the other A/D converters242and243and the other adapters252and253is omitted.

The A/D converter241is provided in common to the thermocouple wires21aand21b. The A/D converter241AD-converts thermo-electromotive forces generated by the thermocouple wires21aand21bto transmission signals and outputs the transmission signals. The adapter251(transmission unit) transmits the transmission signals transmitted from the A/D converter241to the transmission cables212aand212b, respectively.

The thermocouple wires23aand23bof the thermocouple23are connected to the terminal box263serving as a relay unit and provided at the cold junction. The terminal box263is configured so that it can be installed in a high temperature environment. The terminal box263connects the thermocouple23to the compensation lead wires273aand273b. The terminal box263supplies the thermo-electromotive forces (small thermo-electromotive forces) generated by the thermocouple23to the compensation lead wires273aand273b(third connection unit). The compensation lead wires273aand273bsupply the thermo-electromotive forces to the A/D converter243.

The transmission cables212ato212dare, for example, optical cables, and transmit the transmission signals transmitted from the adapters251to253to the monitoring and control apparatus211.

The transmission cable212aconnects the adapter251provided at the thermocouple21to the monitoring and control apparatus211. The transmission cable212bconnects the adapter251provided at the thermocouple21to the adapter252provided at the thermocouple22. The transmission cable212cconnects the adapter252provided at the thermocouple22to the adapter253provided at the thermocouple23. The transmission cable212dconnects the adapter253provided at the thermocouple23to the monitoring and control apparatus211.

That is, the transmission cables212aand212das the second connection units connect the thermocouples21and23(adapters251and253) to the monitoring and control apparatus211(abnormality detection circuit260), respectively. The transmission cables212band212c, as the first connection units, connect between the plurality of mutually adjacent thermocouples21to23(adapters251to253), respectively.

The transmission cables212ato212dare connected by a wiring system (so-called Daisy Chain system) in which the mutually adjacent thermocouples21to23(adapters251to253) are connected in series. The adapters251to253respectively transmit transmission signals to the transmission cables212ato212dwhich are respectively connected to the adapters251to253. The respective transmission signals are successively transmitted through the required transmission cables212band212c, and are eventually collected and transmitted, as transmission signals P and P′, to the monitoring and control apparatus211through the transmission cables212aand212d.

The housing280(housing unit) is a housing which is made of, for example, iron or FRP (Fiber Reinforced Plastic) and has a closing property. In such a case where the housing280is installed at a high place, it is preferred that the housing280is made of FRP so as to be lightened in weight. The housing280has a size corresponding to the number of the thermocouples21to23housed in the housing280.

The housing280houses the transmission cables212ato212d(a part of the transmission cables212aand212d), the A/D converters241to243, the adapters251to253, the cold junctions at which the thermocouples21and22are connected to the A/D converters241and242, and connection points at which the A/D converter243is connected to the compensation lead wires273aand273b.

The transmission cables212aand212d, the thermocouples21and22, and the compensation lead wires273aand273bare provided so as to pass through the housing280. The housing280has required protective properties which can protect the apparatuses installed in the housing280, for example, from hot water, steam and gas generated in the surrounding environment of the temperature measurement area, and from human activities.

Note that the housing280is provided to protect the transmission cables from the surrounding environment and hence is required only to house at least the transmission cables212ato212d.

The monitoring and control apparatus211includes the abnormality detection circuit260. The configuration of the abnormality detection circuit260is substantially the same as the configuration of the abnormality detection circuit60shown inFIG. 2except that the respective transmission signals p1ato p3aand p1bto p3bare taken out from the two transmission signals P and P′, and hence the description and the illustration of the abnormality detection circuit260are omitted here.

In the thermocouple abnormality detection system201, each of the thermocouple pairs21to23is provided with each of the A/D converters241to243and each of the adapters251to253. The thermocouple abnormality detection system201can reduce the number of the A/D converters241to243and the number of the adapters251to253, and can improve the efficiency of installation work and the economic efficiency.

Further, in the thermocouple abnormality detection system201, the transmission route of the transmission signal is duplicated by the transmission cables212aand212d. For example, even when the transmission cable212ais disconnected, the transmission signal P′ is transmitted to the monitoring and control apparatus211via the transmission cable212d. Therefore, the reliability of the thermocouple abnormality detection system201can be improved.

Further, the environment in the vicinity of the installation places of the thermocouples is high temperature and severe environment. Depending on the surrounding environment, there is a case where the electronic devices that are the A/D converter and the adapter cannot be arranged at the cold junction of the thermocouple.

In the thermocouple abnormality detection system201under such environment, the terminal box263and compensation lead wires273aand273b, which can be installed in the high temperature environment, are installed at the hot junction of the thermocouple. The thermocouple23is connected to the A/D converter243and the adapter253via the terminal box263and the compensation lead wires273aand273b. The A/D converter243and the adapter253can be installed in the place (site) away from the high temperature environment, and hence the temperature measurement and the abnormality detection of the thermocouple can be suitably performed without being influenced by the installation environment of the thermocouple.

Further, the thermocouple abnormality detection system201includes the housing280, and thereby can suitably protect the A/D converters241to243, the adapters251to253, and the transmission cables212ato212dfrom the severe surrounding environment and from human activities. As a result, the thermocouple abnormality detection system201can further improve the reliability.

Note that each of the A/D converters241to243also has a software program having the calculation function for performing the A/D conversion processing, and hence may be provided with a function equivalent to the function of the abnormality detection circuit260by extending and utilizing the calculation function. That is, a circuit, which determines the detection of an abnormality of each of the thermocouple pairs21to23by comparing, with each other, the transmission signals obtained from each of the thermocouple pairs21to23, may be provided in each of the A/D converters241to243.

However, the abnormality detection method in which the abnormality detection function is provided in the A/D converters241to243, cannot detect, for example, that the transmission signal cannot be correctly distributed and transmitted due to a failure or a malfunction caused in the adapters251to253, or due to a failure caused in the transmission cables212ato212d. That is, since the transmission signals are supplied for the monitoring and control performed in the monitoring and control apparatus211, it is preferred that the abnormality detection is performed by using the transmission signals received by the monitoring and control apparatus211. From such a viewpoint, it is further preferred that the abnormality detection circuit is provided in the monitoring and control apparatus211.

Second Embodiment

A thermocouple abnormality detection system and a detection method thereof of a second embodiment according to the present invention will be described with reference to the accompanying drawings.

FIG. 5is a view showing a second embodiment of a thermocouple abnormality detection system according to the present invention.

The same configurations and portions as those of the thermocouple abnormality detection system1of the first embodiment are denoted by the same reference numerals and characters, and the description thereof is omitted.

A thermocouple abnormality detection system301of the second embodiment is different from the first embodiment in that each of the transmission signals generated in each of the thermocouple pairs21to23is transmitted to the monitoring and control apparatus311via a different transmission route.

The abnormality detection system301includes a temperature measurement system310mainly provided in the industrial plant2, a monitoring and control apparatus311provided, for example, outside the industrial plant2, and transmission cables312ato312ffor connecting the temperature measurement system310to the monitoring and control apparatus311.

The transmission cables312ato312fare, for example, optical cables, and transmit the transmission signals transmitted from adapters351ato353aand351bto353bto the monitoring and control apparatus311, respectively.

The transmission cables312band312c(first connection unit) respectively connect between the thermocouple wires21ato23aas first thermocouple wires which are respectively provided in the thermocouple pairs21to23(between one set of the adapters351ato353aconnected to the first thermocouple wires). The transmission cable312a(second connection unit) connects the thermocouple wire21a(adapter351a) to the monitoring and control apparatus311(abnormality detection circuit360). The adapter351ais one of the one set of the adapter351ato353aconnected to the first thermocouple wires.

Specifically, the transmission cable312bconnects between the thermocouple wire21aof the thermocouple pair21and the thermocouple wire22aof the thermocouple pair22(between the adapters351aand352a). The transmission cable312cconnects between the thermocouple wire22aof the thermocouple pair22and the thermocouple wire23aof the thermocouple pair23(between the adapters352aand353a).

The transmission cables312eand312f(first connection units) respectively connect between the thermocouple wires21bto23bas second thermocouple wires which are respectively provided in the thermocouple pairs21to23(between one set of the adapters351bto353bconnected to the second thermocouple wires). The transmission cable312d(second connection unit) connects the thermocouple wire23b(adapter353b) to the monitoring and control apparatus311(abnormality detection circuit360). The adapter353bis one of the one set of the adapter351bto353bconnected to the second thermocouple wires.

Specifically, the transmission cable312econnects between the thermocouple wire22bof the thermocouple pair22and the thermocouple wire23bof the thermocouple pair23(between the adapters352band353b). The transmission cable312fconnects between the thermocouple wire21bof the thermocouple pair21and the thermocouple wire22bof the thermocouple pair22(between the adapters351band352b).

The transmission cables312ato312fare connected by a wiring system (so-called Daisy Chain system) in which the mutually adjacent thermocouples21to23(adapters351ato353aand351bto353b) are connected in series. The transmission signal transmitted from each of the adapters352aand353aare successively transmitted through the required transmission cables312band312c, so as to be transmitted to the adapter351a. Eventually, the respective transmission signals are collected and transmitted as a transmission signal P1to the monitoring and control apparatus311through the transmission cable312a.

The transmission signal transmitted from each of the adapters351band352bis successively transmitted through the required transmission cables312fand312e, so as to be transmitted to the adapter353b. Eventually, the respective transmission signals are collected and transmitted as a transmission signal P2to the monitoring and control apparatus311through the transmission cable312d.

FIG. 6is a view showing an internal configuration of the abnormality detection circuit360provided in the monitoring and control apparatus311.

Note that the circuit, into which the set of the signals p1aand p1bare inputted, is almost the same as the circuits into which the set of the other signals p2aand p2b, and the set of the other signals p3aand p3bare respectively inputted. Thus, the illustration and description of the circuits, into which the set of the other signals p2aand p2b, and the set of the other signals p3aand p3bare respectively inputted, are omitted.

In the abnormality detection circuit360, the transmission signals p1ato p3arespectively outputted from the thermocouple wires21ato23a(first thermocouple wires) are taken out from the transmission signal P1supplied through the transmission cable312a, and are supplied to the subtractors61, respectively. In the abnormality detection circuit360, the transmission signals p1bto p3brespectively outputted from the thermocouple wires21bto21b(second thermocouple wires) are taken out from the transmission signal P2supplied through the transmission cable312d, and are supplied to the subtractors61, respectively.

Since the processing applied to the transmission signals inputted into each of the subtractors61is almost the same as that in the first embodiment, the description of the processing is omitted here.

The transmission signals p1aand p1bare supplied to the subtractor61and at the same time are supplied to a switching selector361. In the switching selector361, the transmission signal inputted into a PID control calculator381is switched between the transmission signal p1aobtained from the thermocouple wire21a(first thermocouple wire) and the transmission signals p1bobtained from the thermocouple wire21b(second thermocouple wire). The switching selector361outputs the selected transmission signal as a PV value k1. The switching selector361is, for example, operated by the plant maintenance personnel.

A setting device371holds an SV value j1set beforehand. The setting device371inputs the SV value j1into the PID control calculator381.

The PID control calculator381(control unit) is a PID controller for performing drive and control of a temperature regulation valve as a control object provided in the industrial plant2. The PID control calculator381acquires an MV value n1used for the control of the temperature regulation valve on the basis of the PV value k1and the SV value j1.

Next, the effects of the thermocouple abnormality detection system301will be described.

The temperature information obtained from the thermocouples21to23during normal operation is used to detect an abnormality of the thermocouples21to23, and at the same time, is used for the control of the temperature regulation valve.

For example, when a certain abnormality is caused in the thermocouple21, and when the abnormality signal h1is issued by the abnormality detection circuit360, the plant maintenance personnel performs such an operation as referring to the trend graphs of the transmission signals p1aand the transmission signal p1b, and thereby determines the thermocouple in which the abnormality is caused.

For example, On the basis of the operation of the plant maintenance personnel, the switching selector361switches between the transmission signals so that the transmission signal obtained from the thermocouple wire determined as normal is selected as the PV value k1.

In the thermocouple abnormality detection system301according to the second embodiment, two transmission cables are provided to be connected to the monitoring and control apparatus311. Thus, even when one of the transmission cables is disconnected, the transmission signal can be surely acquired via the other transmission cable.

That is, in the thermocouple abnormality detection system301, the on-site transmission route (including the A/D converters341ato343a, the adapters351ato353a, and the transmission cables312ato312c), through which the transmission signals of the thermocouple wires21ato23a(first thermocouple wires) are transmitted, and the on-site transmission route (including the A/D converters341bto343b, the adapters351bto353b, and the transmission cables312dto312f), through which the transmission signals of the thermocouple wires21bto23b(second thermocouple wires) are transmitted, are made completely separated and independent from each other. Thereby, the thermocouple abnormality detection system301can surely detect not only the abnormality of the thermocouples21to23themselves, but also the abnormality of the on-site transmission routes.

For example, in the abnormality detection system101shown inFIG. 3, after one of the thermocouples121to123is deteriorated and finally disconnected, the abnormality of the one of the thermocouples121to123is detected.

On the other hand, in the thermocouple abnormality detection system301, the abnormality of one of the thermocouples21to23can be detected in a stage before the one of the thermocouples21to23is completely disconnected, and hence the more normal and reliable temperature information can be obtained. Therefore, in the thermocouple abnormality detection system301, the temperature information obtained from the thermocouples21to23can be used for the control of the temperature regulation valve, and the like.

Further, for example, after the disconnection is detected in the abnormality detection system101shown inFIG. 3, the plant maintenance personnel goes to the measurement area and performs the work of changing the connections in the terminal boxes141to143. Further, the normal control of the temperature regulation valve is interrupted during the work.

On the other hand, in the thermocouple abnormality detection system301, as soon as the deterioration of the thermocouples21to23is recognized at a stage prior to the occurrence of the disconnection, the transmission signal is switched in the monitoring and control apparatus311. As a result, the thermocouple abnormality detection system301can realize high operation efficiency.

Note that one transmission cable312dconnected to the monitoring and control apparatus311is added, which results in an increase in the cost. However, when a large number of thermocouples are installed, the increase of the cost can be canceled, and hence the thermocouple abnormality detection system301can have the superiority that it can surely detect the abnormality.

Here, the effects of applying the connection technique of the transmission cables according to the second embodiment to the case where a large number of thermocouples are provided will be described with reference to the accompanying drawings.

FIG. 7Ais a view showing a configuration of a thermocouple abnormality detection system401according to the second embodiment in the case where a large number of thermocouples are provided.

FIG. 7Bis a view showing a configuration of a thermocouple abnormality detection system501as a comparison example of the thermocouple abnormality detection system shown inFIG. 7A.

The abnormality detection system401mainly includes a temperature measurement system410, a monitoring and control apparatus411, and transmission cables412aand412bfor connecting the temperature measurement system410to the monitoring and control apparatus411.

The abnormality detection system501mainly includes a temperature measurement system510, a monitoring and control apparatus511, and transmission cables512aand512bfor connecting the temperature measurement system510to the monitoring and control apparatus511.

In the Daisy Chain system, the transmission capacity permitted by the transmission cable is limited by a technical factor. The transmission cable has a maximum number of the connectable thermocouple pairs (thermocouples). The maximum number of the thermocouples is, for example, about several tens to several hundreds.

InFIG. 7AandFIG. 7B, the maximum number of the connectable thermocouples is assumed to be six (twelve thermocouple wires) for convenience of description. In the case where six or more thermocouples are connected by the Daisy Chain system, one set of the transmission cable can not connect the thermocouples more than the maximum number of the connectable thermocouples and the monitoring and control apparatus. That is, where the mutually adjacent thermocouple wires are simply connected, it is necessary to further add one set of the transmission cables as shown inFIG. 7B.

On the other hand, when the connection configuration of the transmission cables312ato312f, which configuration is described in the second embodiment inFIG. 5, is used, the number of short transmission cables for connecting the mutually adjacent thermocouple wires is increased, but the required number of the long transmission cables412aand412bfor connecting the adapters (the thermocouples) to the monitoring and control apparatus411is the same.

Thus, in the case where the thermocouples more than the maximum number of connectable thermocouples are provided, the thermocouple abnormality detection system301according to the second embodiment can have high reliability without causing an increase in the facility cost.

Third Embodiment

A third embodiment of a thermocouple abnormality detection system and a detection method thereof according to the present invention will be described with reference to the accompanying drawings.

FIG. 8is a view showing a third embodiment of a thermocouple abnormality detection system according to the present invention.

The configurations and portions corresponding to those of the thermocouple abnormality detection systems according to the first and second embodiments are denoted by the same reference numerals and characters, and the description thereof will be omitted.

The thermocouple abnormality detection system601according to the third embodiment is different from the first and second embodiments in that each of thermocouples621to623is a so-called three-wire thermocouple having each of thermocouple wires621ato623a, each of thermocouple wires621bto623b, and each of thermocouple wires621cto623c.

The abnormality detection system601includes a temperature measurement system610mainly provided in the industrial plant2, a monitoring and control apparatus611provided, for example, outside the industrial plant2, and transmission cables612ato612cfor connecting the temperature measurement system610to the monitoring and control apparatus611.

The thermocouples621to623, the number of which is, for example, 100 to 300, are provided in the industrial plant2(for example, when 500 instrument sensors are provided as a whole). In the third embodiment, three thermocouples621to623are illustrated for convenience of description. Each of the thermocouples621to623is provided in a predetermined measurement area, such as an apparatus installation site area.

Since the thermocouples621and622have almost the same configuration, only the thermocouple621is described, and the description of the thermocouples622is omitted.

The thermocouple621includes the thermocouple wire621a(first thermocouple), the thermocouple wire621b(second thermocouple), and the thermocouple wire621c(third thermocouple). The thermocouple621is housed in a sheath631. The sheath (sheath)631has a cylindrical shape, and has the outer layer made of a heat-resistant alloy to thereby protect the thermocouple wires621ato621choused therein. In the sheath631, each of the thermocouple wires621ato621cis fixed and insulated by a filler, such as magnesium oxide.

Each of the thermocouple wires621ato621chas, at the tip portion thereof, a hot junction as a measurement place, and has a cold junction (head portion) at the end portion opposite to the measurement place. At the cold junctions of the thermocouple wires621ato621c, an A/D converter641and an adapter651are provided in this order.

The A/D converter641is provided in common to the thermocouple wires621ato621c. The A/D converter641A/D-converts thermo-electromotive forces generated by the thermocouple wires621ato621cto transmission signals, and outputs the transmission signals. The adapter651(transmission unit) transmits the transmission signals transmitted from the A/D converter641to the transmission cable612a.

The thermocouple623includes the thermocouple wire623a(first thermocouple), the thermocouple wire623b(second thermocouple), and the thermocouple wire623c(third thermocouple). The thermocouple623is housed in a sheath633.

At the cold junctions of the thermocouple wires623ato623c, a converter673, hard cables683ato683c, an A/D converter643, and an adapters653are provided in this order.

The converter673is connected to the A/D converter643by the hard cables683ato683c. The converter673(current signal conversion unit) converts thermo-electromotive forces (small thermo-electromotive forces) generated by the thermocouple623to current signals of 4 to 20 mA (or voltage signals of 1 to 5 V) and outputs the signals. The current signals (voltage signals) are respectively transmitted to the A/D converter643via the hard cables683ato683c. The hard cables688ato683chave required rigidity and/or elasticity.

The A/D converter643(transmission signal conversion unit) A/D-converts the transmitted thermo-electromotive forces to transmission signals and outputs the transmission signals. The adapter653(transmission signal conversion unit) transmits the transmission signals transmitted from the A/D converter643to the transmission cable612c.

The transmission cables612ato612care, for example, optical cables, and transmit the transmission signals transmitted from the adapters651to653to the monitoring and control apparatus611.

The transmission cable612aconnects the thermocouple621(adapter651) to the monitoring and control apparatus611. The transmission cable612bconnects the thermocouple621(adapter651) to the thermocouple622(adapter652). The transmission cable612cconnects the thermocouple622(adapter652) to the thermocouple623(adapter653).

That is, the transmission cable612aas the second connection unit connects the thermocouple621(adapter651) to the monitoring and control apparatus611(abnormality detection circuit660). The transmission cables612band612cas first connection units connect between the plurality of mutually adjacent thermocouples621to623(adapters651to653), respectively.

The transmission cables612ato612care connected by a wiring system (so-called Daisy Chain system) in which the mutually adjacent thermocouples621to623(adapters651to653) are connected in series. The transmission signals transmitted from each of the adapters652and653are successively transmitted through required transmission cables612band612c, so as to be transmitted to the adapter651. Eventually, the respective transmission signals are collected and transmitted as transmission signal P to the monitoring and control apparatus611through the transmission cable612a.

The monitoring and control apparatus611monitors the measurement values on the basis of the transmission signals which are measured by the thermocouples621to623and are transmitted by the on-site transmission. The monitoring and control apparatus611includes the abnormality detection circuit660.

FIG. 9is a view showing an internal configuration of the abnormality detection circuit660provided in the monitoring and control apparatus611.

Note that a circuit into which signals p1ato p1care inputted is substantially the same as the circuits into which the other signals p2ato p2care inputted, and into which the other signals p3ato p3care inputted. Thus, the description and illustration of the circuits, into which the other signals p2ato p2cand p3ato p3care inputted, are omitted.

In the abnormality detection circuit660, the transmission signals p1ato p3aoutputted from the thermocouple wires621ato621care taken out from the transmission signal P supplied through the transmission cable612a, and are supplied to a maximum value selector661, a minimum value selector671, and an intermediate value selector681.

The maximum value selector661selects the maximum value of the transmission signals p1ato p1c, and outputs the maximum value r1. The minimum value selector671selects the minimum of the transmission signals p1ato p1c, and outputs the minimum value s1.

The subtractor61calculates a deviation e1by performing subtraction processing between the maximum value r1and the minimum value s1. The absolute value converter71calculates an absolute deviation f1by converting the absolute value of the deviation e1. The comparator81compares the absolute deviation f1with the threshold value α set beforehand. The comparator81outputs the output g1, when the absolute deviation f1is larger than the threshold value α. The timer91issues the abnormality signal h1when the output g1is continuously outputted during a predetermined time period (for example, 15 seconds).

That is, the abnormality detection circuit660compares, with each other, the transmission signals obtained from the thermocouple wire621a(first thermocouple wire) to the thermocouple wire6216(third thermocouple wire), and detects an abnormality of the thermocouple621at the time when the difference between the respective transmission signals is larger than the predetermined value.

The intermediate value selector681(intermediate value selection unit) selects the intermediate value k1of the transmission signals p1ato p1c. The intermediate value k1is inputted into the PID control calculator381. The setting device371holds the SV value j1set beforehand. The setting device371inputs the SV value j1into the PID control calculator381. The PID control calculator381controls the temperature regulation valve on the basis of the PV value k1and the SV value j1.

That is, the PID control calculator381acquires the MV value n1used for the control of the temperature regulation valve, by using the intermediate value of the transmission signals, which intermediate value is selected by the intermediate value selector681.

The thermocouple abnormality detection system601according to the third embodiment can acquire three transmission signals from each of the thermocouples621to623which are respectively provided with the set of the three thermocouple wires621ato623a, the set of the three thermocouple wires621bto623b, and the set of the three thermocouple wires621cto623c, and can use the acquired transmission signals for detection of an abnormality of the thermocouples621to623. The abnormality detection system601compares, with each other, the three transmission signals of each of the thermocouples. Thereby, on the basis of the difference between the three transmission signals, the abnormality detection system601can surely detect the deterioration of each of the thermocouples at a stage prior to the occurrence of the disconnection.

The abnormality detection system601selects an intermediate value from the values of the three transmission signals, and uses the intermediate value for the control of the temperature regulation valve, and the like. Thereby, the abnormality detection system601can select and provide a normal value as the temperature information used for the control.