JP5400691B2 - Programmable display monitoring operation method, monitoring operation program, and programmable display - Google Patents

Description

  The present invention relates to a monitoring operation method, a monitoring operation program, and a programmable display for a programmable display that performs a monitoring operation for water and sewage plant equipment.

  The programmable display device transmits / receives information to / from a host machine such as a programmable controller (hereinafter referred to as PLC), and is a useful device for monitoring and controlling the host machine.

  When the programmable display is connected to a duplexed PLC on the Ethernet (registered trademark) transmission path, information on both the active PLC and the standby PLC can be acquired from the programmable display. However, information monitoring and device operation must be targeted only for active PLCs. For this reason, it is configured to determine which one is in operation, transfer the internal register of the active PLC to the internal register in the programmable display, and display based on the information.

  Similarly, the device operation is configured such that the internal register in the programmable display is transferred to the internal register of the active PLC and the device is operated. That is, the internal register in the programmable display and the internal register of the active PLC are separate registers, and it is necessary to exchange between the registers. A register correspondence table is used for the replacement.

  Further, the PLC duplex switching device of Patent Document 1 discloses a technique for enabling communication with the other PLC even when one PLC becomes abnormal when the duplexed PLC is connected to the Ethernet transmission line. ing.

JP 2000-56817 A

  In Patent Document 1, the host monitoring device can monitor only the operating system (master) of the duplexed PLC and regard it as one device, and can transmit and receive data. The PLC is characterized in that the operating system is switched on the PLC side and the PLC transmits information only on the operating system. The host monitoring device reads the information of the active system allocated to the shared memory, and this becomes the information of the internal register of the monitoring device. Further, the host monitoring device does not read information on the standby system (slave). That is, the host monitoring device refers to the information area of the active system of the shared memory, but the register designation is different from the register designation in the PLC. Furthermore, the status of the standby PLC cannot be monitored because only the active PLC is monitored.

  In the Ethernet transmission path, an IP (Internet Protocol) address is assigned to identify devices connected on the transmission path, and the same program is loaded in both the active PLC and standby PLC. IP address is assigned. However, it is more convenient to recognize only the active PLC as one IP address from the programmable display. However, duplicated PLCs are not allowed to use the same IP address due to the restriction of the IP address.

  When the programmable display is connected to a single PLC, the display location of the corresponding PLC register and the programmable display is fixed at 1: 1, so that the register in the PLC can be directly designated for display on the programmable display.

  On the other hand, when the programmable display is connected to the duplexed PLC, only the information on the active PLC is used for display, so the register designation of the display component of the programmable display cannot be fixed at 1: 1. Therefore, switching is performed so that only the information on the active PLC is monitored and controlled, and the status of the PLC can be monitored as necessary for the standby PLC.

  As already explained in the background art, since the PLC data of the operating system must be transferred to the internal register of the programmable display and used for display, the programmable display is the same as for a single PLC. An application program for the display device could not be created, and it was necessary to replace the register in the PLC and the register in the programmable display (register correspondence table).

  For this reason, even in the case of a duplex PLC composed of a plurality of PLCs, the registers in the PLC can be displayed and operated directly from the programmable display, and the internal registers of the programmable display are not used, just like a single PLC. It has been desired to create an application program for a programmable display that directly uses PLC internal registers.

  The present invention is an invention for solving the above-described problems, and monitors and operates an active PLC when the active PLC is switched when a programmable display is connected to a plurality of PLCs. It is an object of the present invention to provide a programmable display monitoring method, a monitoring operation program, and a programmable display.

In order to achieve the above object, a monitoring operation method for a programmable display according to the present invention includes a duplex PLC having a first PLC (for example, A system PLC 20A) and a second PLC (for example, B system PLC 20B) via a network. Connected to the programmable display (10),
In the programmable display, the first station number associated with the first PLC and the second station number associated with the second PLC are registered in the storage unit as station number management information (for example, the station number table 121). And
The reference station number of each display operation component arranged on the programmable display has a first station number as a setting for monitoring and displaying information of the active PLC or for transmitting an operation command to the active PLC. Is set,
The programmable display monitors the operating state based on the status information of each PLC operating or stopped received from each PLC, and when it is determined that the standby PLC is operating, it is set to each display operation component. The station number of the reference destination is rewritten to the second station number, and after the rewriting, the programmable display is reset and the monitoring operation is continued.

  According to the present invention, when a programmable display is connected to a plurality of PLCs, the active PLC can be monitored and operated when the active PLC is switched.

It is a block diagram which shows the water and sewage plant monitoring control system containing a programmable display and duplex PLC. It is a block diagram which shows the function of a programmable display and duplex PLC. It is explanatory drawing which shows operation | movement at the time of an active system switching (at the time of switchover). It is explanatory drawing which shows the description of the internal register | resistor for monitoring and controlling the active system PLC which is a comparative example, and its processing method. It is explanatory drawing which shows the definition method of the internal register | resistor of PLC for monitoring and controlling the active system PLC of this embodiment, and its processing method. It is a flowchart which shows a reference destination station number switching process. It is explanatory drawing which shows the relationship between the combination of the operation | movement / stand-by state of duplexed PLC, and the reference destination station number at that time. It is a block diagram which shows the function of a programmable display and a triple PLC. It is explanatory drawing which shows the relationship between the combination of the state of triple PLC, and the reference station number at that time. It is a flowchart which shows the reference destination station number switching process in the case of triple PLC.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. When creating an application program for a programmable display, in the case of Ethernet connection of a programmable display and a single PLC (not shown), the PLC internal register is directly specified for 1: 1 connection, and the programmable display There is no need to use internal registers. In the present embodiment, a method capable of directly designating an internal register of a PLC will be described with reference to FIG. 1 and FIG. 2 even in the case of Ethernet connection of a duplex PLC composed of a programmable display and a plurality of PLCs. To do.

<Embodiment 1>
FIG. 1 is a configuration diagram illustrating a water and sewage plant monitoring and control system including a programmable display and a duplexed PLC. The water and sewage plant monitoring and control system is composed of a programmable display 10, a duplexed PLC 20, an input / output device (I / O) 4 and a water and sewage plant 5. An administrator of the water and sewage plant monitoring and control system is a programmable display. 10, information on the water and sewage plant 5 can be monitored and operated (controlled) via the input / output device 4 and the duplex PLC 20.

  The programmable display 10 has a display / operation unit 14 for monitoring and operating, and is connected to an Ethernet N1 (Ethernet network) via an Ethernet I / F (interface) 15.

  The duplex PLC 20 is composed of an A-system PLC 20A (first PLC) and a B-system PLC 20B (second PLC). The A-system PLC 20A includes a processor 21A, an Ethernet I / F 25A, and a duplex I / F 26A. Further, the B-system PLC 20B includes a processor 21B, an Ethernet I / F 25B, and a duplex I / F 26B.

  The A-system PLC 20A is connected to the Ethernet N1 via the Ethernet I / F 25A, and is connected to the FL net N3 (FL net network) via the duplexed I / F 26A. The B system PLC 20B is connected to the Ethernet N1 via the Ethernet I / F 25B, and is connected to the FL net N3 via the duplexed I / F 26B. The FL net is a FA (Factory Automation) control network, and uses UDP (User Datagram Protocol) / IP and FA link protocols as transmission protocols.

  Here, the A-system PLC 20A is an active PLC when both PLCs are normal. On the other hand, the B-system PLC 20B is a standby PLC when both PLCs are normal, and an active PLC when the A-system PLC 20A becomes abnormal. However, the reverse operation is also possible.

  FIG. 2 is a block diagram illustrating functions of the programmable display and the duplexed PLC. An outline of a method for specifying an internal register of the PLC when creating a program for a programmable display, which is a feature of the present embodiment, will also be described.

  The processor 11 of the programmable display 10 has an application program 12 of the programmable display 10 and an internal register 13. The application program 12 is a station number table 121 (station number management information) (see FIG. 5) in which station numbers and IP addresses for identifying active PLCs and standby PLCs to be described later are associated with each other. A reference destination station number switching processing unit 122 (see FIG. 6) that performs a certain reference destination station number switching process is provided. Details of the station number will be described later. The station number table 121 is stored in the processor 11, but may be stored in a memory (storage unit) (not shown) and loaded into the processor 11 as necessary.

  The processor 21A of the A-system PLC 20A has an application program 22A and an internal register 23A. Similarly, the processor 21B of the B-system PLC 20B has an application program 22B and an internal register 23B.

  The application program 12 of the programmable display 10 and the application programs 22A and 22B for the PLC created here are created by using a programming tool 32 executed by a processor 31 of a personal computer (personal computer) 30, and via the Ethernet N1. Loaded. The application program 12 and the PLC application programs 22A and 22B are stored in the programmable display 10 and the memory (not shown) of each PLC, loaded as necessary, and executed by the processors 11, 21A and 22B. Needless to say.

  In FIG. 2, an IP address for identifying each of the A system PLC 20A, the B system PLC 20B, and the programmable display 10 is assigned. The IP address of the A system PLC 20A is “0” (normal IP address is expressed in dotted decimal notation, but in the figure, it is expressed as IP address 0), and the IP address of the B system PLC 20B is “1” is set, the IP address of the programmable display 10 is set to “2”, and the network of the Ethernet N1 is configured. In order to make the internal data of the PLC consistent, the internal data is transferred from the active PLC to the standby PLC via the FL net N3.

  In the station number table 121 of the programmable display 10, the A system PLC 20A is associated with the station number 0 (first station number), and the B system PLC 20B is associated with the station number 1 (second station number). The programmable display 10 is associated with station number 2.

  In this embodiment, when creating the application program 12 of the programmable display 10, the display component, operation component, and setting component used for the display / operation unit 14 are not the internal register 13 of the programmable display 10, for example, The internal register 23A of the A-system PLC 20A, that is, the PLC with the station number 0 can be directly designated.

  That is, when the duplexed PLC 20 is monitored and operated (controlled) by a single programmable display 10, it is determined which PLC is active by the macro processing of the application program 12 of the programmable display 10, and the information is displayed and operated. Although used in the unit 14, when the application program 12 is created, the internal register 23A or the internal register 23B of the PLC is referred to instead of referring to the internal register 13 of the programmable display 10.

  An example of an internal register designation method will be described with reference to FIG. Reference numeral 40 indicates an example of the internal register 13 of the programmable display 10. On the other hand, reference numeral 41 shows an example of the internal register 23A of the A-system PLC 20A and the internal register 23B of the B-system PLC 20B. Conventionally, the internal register 13 of the programmable display device 10 has been referred to for monitoring the parts and setting the operation registers as indicated by reference numeral 42. On the other hand, in this embodiment, as indicated by reference numeral 43, the internal register 23A of the A system PLC 20A and the internal register 23B of the B system PLC 20B can be directly referred to. The internal register 23A of the A system PLC 20A and the internal register 23B of the B system PLC 20B are identified by the station number.

  In this embodiment, when the A-system PLC 20A that is the active system becomes abnormal, the standby B-system PLC 20B becomes the active system, and therefore, all display / operation units are executed by the macro processing of the application program 12 of the programmable display 10. The link destination of 14 display components, operation components, and setting components is switched to the B-type PLC 20B. As the switching method, all the PLC internal registers directly designated by the station number 0 (stored in the Ethernet I / F 25A) can be rewritten to the station number 1 (Ethernet I / F 25B).

  FIG. 3 is an explanatory diagram showing an operation when the operating system is switched (at the time of switchover). If the A-system PLC 20A is in the active system and fails, the active system switches over to the B-system PLC 20B. The programmable display 10 monitors and controls the A system PLC 20A because the A system PLC 20A is the active system, but determines that the operating system has switched over to the B system PLC 20B, and changes the monitoring control target to the B system PLC 20B. Switch. The contents of the internal processing (macro processing) of the programmable display 10 at the time of this switchover will be described with reference to FIG. 4 (comparative example) and FIG. 5 (this embodiment).

  FIG. 4 is an explanatory diagram illustrating an internal register for monitoring and controlling an active PLC, and a processing method thereof, as a comparative example. Please refer to FIG. 2 as appropriate. In the case of the comparative example, the internal register of the active PLC (internal register 23A or internal register 23B) is determined, and the macro processing of the application program 12 of the programmable display 10 is used, and the internal registers and programmable display of the active PLC are used. Data transfer processing is performed with the internal register 13 of the container 10 to realize monitoring control. For this reason, the creator of the application program 12 needs to create the correspondence table 13R between the internal registers 23A and 23B of the PLC and the internal register 13 of the programmable display 10 and be aware of the register allocation.

  FIG. 5 is an explanatory diagram showing a method of defining an internal register of the PLC for monitoring and controlling the active PLC according to the present embodiment and a processing method thereof. In the present embodiment, in the station number table 121, the A system PLC 20A is defined as the station number 0, the B system PLC 20B is defined as the station number 1, and the programmable display 10 is defined as the station number 2, and the application program 12 is created. In the macro process of the application program 12 of the programmable display 10, the operation status of the PLC is determined, and the reference destination station number switching process (see FIG. 6, specifically, the station number 0 → 1, the station number 1 → 0) is performed.

  In this embodiment, the macro process of the application program 12 monitors and controls the state of the active PLC. Further, it is possible to directly set information (refer to reference numerals 80A1, 80A2 or 80B1, reference numeral 80B2) of the PLC internal registers 23A and 23B for each display operation component of the programmable display 10. When the programmable display 10 is connected to the duplex PLC connection, the application program 12 of the programmable display 10 can be created in the same manner as the connection to the single PLC connection. This also eliminates the need for the register correspondence table 13R, thereby reducing the burden on the application program creator. Further, by referring to the station number opposite to the active system at the stage of creating the application program 12 of the programmable display 10 (reference numerals 83 and 84), it is possible to monitor the register information of the standby PLC.

Next, reference destination station number switching processing will be described.
FIG. 6 is a flowchart showing the reference station number switching process. FIG. 6A shows the initial process S1 after loading of the application program 12 of the programmable display 10, and FIG. 6B shows a fixed period process for every predetermined time (for example, 1 second period). In the present embodiment, immediately after loading of the application program 12, the reference destination station number of each display operation component arranged in the programmable display 10 is assumed to be 0 (A PLC is an active system).

  When executing the initial process S1 shown in FIG. 6A (step S11), the processor 11 sets the current station number as the initial value in the work data (step S12), and ends the process. Specifically, the station number 0 of the A system PLC 20A, which is the active PLC, is set as the work W1, and the station number 1 of the B system PLC 20B, which is the standby PLC, is set as the work W2. For the work, a temporary storage area of the internal register 13 may be used.

  When the processor 11 starts the periodic processing shown in FIG. 6B (step S21), the processor 11 performs processing from step S22 to step S27, for example, every one second cycle. The processor 11 sets the RUN (operation) or STOP (stop) status information of the A-system PLC 20A in the work W11 (step S22), and sets the RUN or STOP status information of the B-system PLC 20B in the work W12. (Step S23). Then, the processor 11 determines the condition “whether the standby PLC has been operated” from the workpieces W11 and W12 (step S24), and determines that the standby PLC has been operated (step S24, Yes). The values of the workpiece W1 and the workpiece W2 are exchanged (step S25).

  The processor 11 executes a switching process for the reference station number for each display operation component of the programmable display 81 (step S26). Specifically, the station number of the reference destination for each display operation component of the programmable display 81 is switched (rewritten) as the value of the work W1. And reset is performed to the screen of the display and operation part 14 of the programmable display 10 (step S27), and a process is complete | finished. When there is a reset request for the programmable display 10 in step S27, the processor 11 executes the initial process S1 shown in FIG. 6A (step S11), and sets the current station number as work data (step S12). . Specifically, the station number 1 of the active PLC is set to the work W1, and the station number 0 of the standby PLC is set to the work W2.

  If it is not determined in step S24 that the standby PLC has been activated (No in step S24), the process ends.

  In the initial process S1, the station number is read and set in the work data, so that it is not necessary to read the station number every time in the regular cycle process, so a method of reducing the processing load on the processor 11 is adopted.

  In the present embodiment, the station number of the active PLC is always referred to by replacing the station number of the reference destination for each display operation component of the programmable display 81. Furthermore, if the opposite station number is referred to here, it is the standby PLC.

  FIG. 7 is an explanatory diagram showing the relationship between the combination of operating / standby states of the duplexed PLC and the reference station number at that time. There are four combinations depending on the operating / standby state of the A system PLC 20A and the operating / standby state of the B system PLC 20B. The reference destination station number switching process shown in FIG. 6 is based on the hardware circuit, so that only one of the operating systems is necessarily used, and the A system PLC 20A and the B system PLC 20B are not simultaneously operating systems (see reference numeral 71). The destination station number switching process is established. Normally, one is an active system and the other is a standby system (see reference numeral 72 or 73). In the case of reference numeral 72, the reference station number is 1, and in the case of reference numeral 73, the reference station number is 0. . If both systems are out of order and both systems are standby systems (see reference numeral 74), the station number is not rewritten and the previous value is held. Note that the standby state includes a failure state.

  As described above, according to the present embodiment, when the application program 12 for monitoring and controlling a duplicated PLC with the programmable display 10 is created, the active PLC is automatically determined and the station number is used. By switching the reference destination, it becomes possible to always monitor and control the active PLC. Further, by using the station number, the PLC internal registers (for example, the internal registers 23A and 23B) can be set directly on the programmable display 10. In other words, the application program creation method is the same as that for monitoring and controlling by connecting to a single PLC, and the program creator creates an application program without being aware of whether it is a single PLC or a duplexed PLC. There is an advantage that you can. Furthermore, it is only necessary to specify a station number opposite to that of the active system for the status monitoring of the standby PLC, and the status of the standby PLC is directly monitored by the programmable display 10 instead of via the active PLC. Can do.

  Specifically, the duplexed PLC 20 of this embodiment includes an A-system PLC 20A and a B-system PLC 20B, and an active PLC station number 0 and a standby PLC station number 1 are set in each PLC. In order to monitor and display information only for the active PLC and to send a control command only to the active PLC, the reference station number 0, which is the active PLC, is set to each display operation component of the programmable display 10. Set. The programmable display 10 monitors RUN (operation) and STOP (stop) status information of each PLC at a predetermined cycle. When the B-system PLC 20B is switched from the standby system to the active system, the programmable display 10 determines that the active PLC has been switched, rewrites the reference station number (0 → 1), and performs the monitoring operation only for the active system. continue. As a result, in the Ethernet connection of the programmable display 10 for monitoring operation of the water and sewage plant and the duplex PLC 20, the application program of the programmable display equivalent to that for the single PLC connection is used to automatically display the information of the operating PLC. , Can be operable.

<Embodiment 2>
Although the case where the programmable display device 10 is applied to the duplex PLC has been described in the first embodiment, the present invention is not limited to this. In the second embodiment, a case where the programmable display 10 is applied to a triple PLC will be described.

  FIG. 8 is a block diagram showing the functions of the programmable display and the triple PLC. The triple PLC is composed of an A system PLC 20A (PLC 1), a B system PLC 20B (PLC 2), and a C system PLC 20C (PLC 3). In FIG. 8, the same components as those shown in FIG. Referring to FIG. 8, a system that does not perform data matching of three units in the simultaneous RUN system of three PLCs, which is practical as a water and sewage plant monitoring control system, considers the priority order to be referred to as PLC1, PLC2, PLC3. And

  At this time, if PLC 1 is normally RUN (operating), refer to PLC 1, if PLC 1 is faulty and PLC 2 is normal RUN, refer to PLC 2. Similarly, if PLC 2 is also faulty, normal RUN of PLC 3 The reference destination station number processing shown in the first embodiment is also effective when considering a system that performs switching and ensures redundancy, such as referring to the PLC 3 (see FIG. 9 for the combination).

  FIG. 9 is an explanatory diagram showing the relationship between the combination of states of the triple PLC and the reference station number at that time. When the PLC 1 is normally RUN, the reference destination station number is 0. When the PLC 1 is faulty and the PLC 2 is normally RUN, the reference destination station number is 1. When PLC1 and PLC2 fail and PLC3 is normally RUN, the reference station number is 2. If all of PLC1, PLC2, and PLC3 are faulty, the reference station number is set to hold the previous value.

  FIG. 10 is a flowchart showing reference destination station number switching processing in the case of triple PLC. FIG. 10A shows the initial process S2 after loading of the application program 12 of the programmable display 10, and FIG. 10B shows the failure process when the PLC with station number 0 fails. Note that, immediately after loading the application program 12, the reference station number is assumed to be 0 (corresponding to PLC1).

  When executing the initial process S2 shown in FIG. 10A (step S41), the processor 11 sets a station number for each PLC as an initial value (step S42), and ends the process. Specifically, the station number of PLC1 is set to 0, the station number of PLC2 is set to 1, and the station number of PLC3 is set to 2.

  If the processor 11 determines that the PLC with the station number 0 is faulty, it starts the fault processing shown in FIG. 10B (step S51). The processor 11 determines whether or not the PLC of the station number 1 (priority number 2) is RUN (step S52). If the PLC is RUN (step S52, Yes), the station number 0 and the station number 1 are exchanged (step S52). Step S57), the station number rewriting process is executed (step S55), and finally the programmable display 10 is reset (step S56), and the process ends.

  In step S52, when the PLC of the station number 1 is not RUN (No in step S52), the processor 11 determines whether or not the PLC of the station number 2 (priority order is 3) is RUN (step S53). (Yes in step S53), station number 0 and station number 2 are interchanged (step S54), and the process proceeds to step S55. In step S53, when the PLC of the station number 2 (priority order is 3) is not RUN (step S53, No), the process is terminated.

  In the second embodiment, it is assumed that the station number rewriting process is applied when the PLC fails. However, the station number rewriting process is effective even when the operator performs manual switching.

  Although this embodiment demonstrated as a water-sewage-plant control system, it is not limited to this. Any control system including a programmable display and a duplex PLC or triple PLC can be applied to various control systems such as a transport system control system.

4 Input / output devices (I / O)
5 Water and Sewage Plant 10 Programmable Display 11 Processor 12 Application Program (Macro Processing)
13 Internal Register 14 Display / Operation Unit 15 Ethernet I / F
20 Duplex PLC
20A A-system PLC (first PLC)
20B B PLC (second PLC)
21A, 21B Processor 22A, 22B Application program (ladder)
23A, 23B Internal register 25A, 25B Ethernet I / F
26A, 26B Duplex I / F
121 Station number table (Station number management information)
122 Reference station number rewriting processing part N1 Ethernet (Ethernet network)
N3 FL Net (FL Net network)

Claims (6)

A programmable display monitoring operation method connected via a network to a duplexed PLC having a first PLC and a second PLC,
The programmable display is
The first station number associated with the IP address identifying the first PLC and the second station number associated with the IP address identifying the second PLC are registered in the storage unit as station number management information. And
In the station number of the reference destination of each display operation component arranged on the programmable display, the first PLC is set as a setting for monitoring and displaying information on the active PLC or for transmitting an operation command to the active PLC. Is set,
The programmable display is
The operating state is monitored based on the status information on the operation or stop of each PLC received from each PLC, and when it is determined that the standby PLC has been operated, Rewrite the reference station number to the second station number,
After the rewriting, the programmable display device is reset and the monitoring operation is continued. The programmable display is
After resetting the program display, the operating state is monitored based on the status information of the operation or stop of each PLC received from each PLC, and when it is determined that the standby PLC is operating, Rewrite the reference station number set in the display operation component to the first station number,
The programmable operation monitoring operation method according to claim 1, wherein after the rewriting to the first station number, the programmable display is reset and monitoring operation is continued. The programmable display is
An address of an internal register of each PLC is designated as an address for setting to monitor and display information of the active PLC or to send an operation command to the active PLC. Item 8. A monitoring operation method using the programmable display according to Item 1. A programmable display monitoring operation method connected to a triple PLC having a first PLC, a second PLC, and a third PLC via a network,
The programmable display is
A first code associated with the IP address identifying the first PLC, and a second code associated with the IP address identifying the second PLC, IP address identifying the third PLC The third station number associated with is registered in the storage unit,
The station number of the reference destination of each display operation component arranged on the programmable display includes the first PLC as a setting for monitoring and displaying the information on the first PLC or transmitting an operation command to the first PLC. 1 station number is associated and set,
The programmable display is
The operating status of each PLC is monitored based on the status information on the operation or stop of each PLC received from each PLC, and when it is determined that the first PLC has stopped, Rewrite the set station number to the second station number,
When it is determined that the first PLC and the second PLC are stopped, the station number set in each display operation component is rewritten to the third station number,
After the rewriting, the programmable display device is reset and the monitoring operation is continued.   The monitoring operation program for making a computer perform the monitoring operation method of the programmable display of any one of Claims 1-4. A programmable display connected via a network to a duplexed PLC having a first PLC and a second PLC,
A first code associated with the IP address identifying the first PLC, a storage unit and a second code associated with the IP address identifying the second PLC is stored as code management information ,
Each arranged in the programmable display in which the first station number is set as the setting of the reference station number for monitoring and displaying the information of the active PLC or transmitting the operation command to the active PLC Display operation parts,
The status of each PLC is monitored based on the status information on the operation or stop of each PLC received from each PLC, and when it is determined that the standby PLC has been operated, it is set in each display operation component. A reference station number switching processing unit that rewrites the reference destination station number to the second station number, resets the programmable display after the rewriting, and continues the monitoring operation. Programmable display.

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