JP2024093915A - Control system, control method for control system, and network switch - Google Patents

Abstract

To enable a controller to be redundant with a simpler configuration in a control system of a field device.SOLUTION: The control system includes an IO node to which a field device is connected, a plurality of controllers that perform computation on the basis of measurement data acquired by the field device, a network switch, and a cache server. Each of the plurality of controllers transmits, to the network switch, a request for the measurement data acquired by the field device at each predetermined control timing. The network switch causes the IO node to transmit, to the controller, the measurement data of the field device connected to the IO node if the cache server does not hold the measurement data, and causes the cache server to transmit the measurement data of the field device to the controller if the cache server holds the measurement data. Each of the plurality of controllers performs predetermined computation on the basis of the received measurement data.SELECTED DRAWING: Figure 11

Description

The present disclosure relates to a control system, a control method for a control system, and a network switch.

Patent document 1 describes a control system in which a controller controls the operation of field devices via an IO node, which is a device to which the field devices are connected.

JP 2021-157392 A

In the above-mentioned control system, it is possible to improve the reliability of the controller's operation by providing multiple controllers, each of which performs the same processing on the input and output of the field devices and comparing the processing results of each controller. When making the controllers redundant in this way, in the conventional configuration, multiple controllers must operate in time synchronization with high precision, which makes the processing and configuration complicated.

The purpose of this disclosure is to make it possible to achieve controller redundancy with a simpler configuration in a field device control system.

In some embodiments, the control system includes:
(1) an IO node to which a field device for acquiring measurement data is connected;
a plurality of controllers that perform calculations based on the measurement data acquired by the field devices;
A network switch;
A cache server;
Equipped with
each of the plurality of controllers transmits a request for the measurement data acquired by the field device to the network switch at each control timing, which is a fixed period determined in a predetermined cycle;
The network switch includes:
If the cache server does not hold the measurement data, the IO node transmits the measurement data acquired by the field device connected to the IO node to the controller via the network switch;
When the cache server holds the measurement data, the cache server transmits the measurement data acquired by the field device to the controller via the network switch;
Each of the plurality of controllers performs a predetermined calculation based on the measurement data received from the IO node or the cache server.

In this way, even when each controller operates asynchronously, it can obtain the same measurement data at the control timing from the IO node or cache server via the network switch. In other words, from the perspective of the controller 30, it appears as if the same device is being accessed, but in reality, depending on whether or not a cache is present, common measurement data can be obtained from the IO node 20 or the cache server 40 for all controllers 30. Therefore, it is possible to achieve controller redundancy with a simpler configuration in a field device control system.

(2) In the control system of (1),
The network switch includes:
If the cache server does not hold the measurement data, the cache server requests the measurement data from the IO node;
In response to receiving the measurement data from the IO node based on the request, the measurement data may be transmitted to the controller, and the measurement data may also be transmitted to the cache server to be stored as a cache of the measurement data.

In this way, when the cache server does not hold the measurement data, the network switch receives the measurement data from the IO node and transmits it to the controller and cache server. In this way, the measurement data transmitted to the controller that first requested the measurement data is stored in the cache server, so other controllers can also obtain the same measurement data from the cache server and perform calculations based on the common measurement data.

(3) In the control system according to (1) or (2),
The network switch includes:
If the cache server holds the measurement data, a request is made to the cache server to cache the measurement data;
In response to receiving the cached measurement data from the cache server upon the request, the cached measurement data may be transmitted to the controller.

In this way, when the cache server holds measurement data, the network switch receives a cache of the measurement data from the cache server and transmits it to the controller. Therefore, other controllers can also obtain measurement data from the cache server via the network switch and perform calculations based on the common measurement data.

(4) In any one of the control systems (1) to (3),
The network switch includes:
A management table including information indicating whether the cache server holds the measurement data for each of the control timings is held;
In response to receiving the request for the measured data from any one of the plurality of controllers, the management table may be referenced to determine whether or not the cache server holds the measured data.

In this way, the network switch holds a management table that contains information indicating whether or not the cache server holds measurement data for each control timing, so it can determine whether or not the cache server holds measurement data without having to query the cache server at the control timing.

(5) In the control system of (4),
The network switch may hold, for each of the control timings, information including identification information of the controller that received the measurement data as the management table.

In this way, the network switch records the identification information of the controller that sent the cached measurement data, making it possible to identify the controller that sent the cached data by referring to the record.

(6) In any one of the control systems (1) to (5),
each of the plurality of controllers transmits, at each control timing, a calculation result that is a result of performing the calculation based on the measurement data received via the network switch to the IO node;
The IO node includes:
comparing the calculation results received from each of the plurality of controllers at each of the control timings to determine whether or not the operations of the plurality of controllers are normal;
A result of the determination as to whether the operations of the plurality of controllers are normal or not may be output.

In this way, the network switch and control system can detect controller abnormalities by comparing the calculation results of multiple controllers. In addition, because it determines whether the operation of a controller is normal or not based on the calculation results received within the control timing, it is possible to avoid using the calculation results of a controller that was unable to transmit its calculation results within the control timing when determining whether the operation is abnormal or not.

In some embodiments, the network switch comprises:
(7) A network switch for use in a control system for a field device, comprising:
acquiring, from the cache server, information as to whether or not the cache server holds the measurement data in response to receiving a request for the measurement data acquired by the field device from the controller;
If the cache server does not store the measurement data, a request for the measurement data is sent to an IO node to which the field device is connected;
If the cache server holds the measurement data, a request for the measurement data is sent to the cache server.

In this way, when the network switch receives a request for measurement data from a controller, it distributes and sends the request for measurement data to an IO node or a cache server depending on whether the cache server holds the measurement data. Therefore, each controller can query the same network device and obtain measurement data that is common to all controllers.

A control method for a control system according to some embodiments includes:
(8) an IO node to which a field device that acquires measurement data is connected;
a plurality of controllers that perform calculations based on the measurement data acquired by the field devices;
A network switch;
A cache server;
A control method for a control system comprising:
each of the plurality of controllers transmitting a request for the measurement data acquired by the field device to the network switch at each control timing, which is a fixed period determined in a predetermined cycle;
a step of causing the IO node to transmit the measurement data acquired by the field device connected to the IO node to the controller via the network switch when the cache server does not hold the measurement data, and causing the cache server to transmit the measurement data acquired by the field device to the controller via the network switch when the cache server holds the measurement data;
Each of the plurality of controllers performs a predetermined calculation based on the measurement data received from the IO node or the cache server;
including.

In this way, even when each controller operates asynchronously, it can obtain the same measurement data at the control timing from the IO node or cache server via the network switch. In other words, from the perspective of the controller 30, it appears as if the same device is being accessed, but in reality, depending on whether or not a cache is present, common measurement data can be obtained from the IO node 20 or the cache server 40 for all controllers 30. Therefore, it is possible to achieve controller redundancy with a simpler configuration in a field device control system.

According to one embodiment of the present disclosure, controller redundancy can be achieved with a simpler configuration in a field device control system.

FIG. 1 is a diagram showing a configuration of a control system according to a comparative example. FIG. 1 is a diagram illustrating an example of a schematic configuration of a control system according to an embodiment. 3 is a block diagram showing an example of a functional configuration of the control system shown in FIG. 2 . FIG. 4 is a diagram illustrating an example of a management table of FIG. 3 . FIG. 4 is a diagram illustrating an example of a management table of FIG. 3 . 3 is a block diagram showing an example of a hardware configuration of the IO node shown in FIG. 2. 3 is a block diagram showing an example of a hardware configuration of a controller shown in FIG. 2. 3 is a block diagram showing an example of a hardware configuration of the cache server shown in FIG. 2. 4 is a sequence chart showing an example of an operation of a control system according to an embodiment. 4 is a sequence chart showing an example of an operation of a control system according to an embodiment. FIG. 1 is a diagram illustrating an example of a schematic configuration of a control system according to an embodiment. 12 is a block diagram showing an example of a hardware configuration of the network switch of FIG. 11. 4 is a sequence chart showing an example of an operation of a control system according to an embodiment. 4 is a sequence chart showing an example of an operation of a control system according to an embodiment.

Comparative Example
1 is a diagram showing a configuration of a control system 9 according to a comparative example. The control system 9 includes field devices 91 (91a, 91b), an IO (Input/Output) node 92, and controllers 93 (93a, 93b). The IO node 92 and the controllers 93 (93a, 93b) are connected to each other via a network 95 so as to be able to communicate with each other.

The field devices 91 (91a, 91b) are devices that acquire measurement data for controlling the plant and/or operate the plant. The IO node 92 is a device to which the field devices 91 (91a, 91b) are connected and that functions as an interface with the controller 93 (93a, 93b). The controller 93 (93a, 93b) is a device that performs calculations on the measurement data of the field devices 91 (91a, 91b) and controls the field devices 91 (91a, 91b) based on the calculation results.

In the control system 9, the IO node 92 collects measurement data from the field devices 91 (91a, 91b) at regular intervals (e.g., every second). Each of the controllers 93a, 93b acquires the measurement data of the field devices 91 (91a, 91b) from the IO node 92 at regular intervals (e.g., every second). The controllers 93 (93a, 93b) perform calculations based on the acquired measurement data and transmit the calculation results to the IO node 92. When the IO node receives the calculation results from the controllers 93 (93a, 93b), it outputs the received calculation results to the field devices.

In the example of FIG. 1, in order to improve the reliability of the calculations of the controllers 93 (93a, 93b), the control system 9 includes multiple controllers 93a, 93b, and compares the calculation results of the controllers 93a, 93b. Specifically, each of the controllers 93a, 93b performs the same calculation on the same measurement data of the field devices 91 (91a, 91b) and outputs the calculation results to the IO node 92. The IO node 92 compares the calculation results received from the controllers 93a, 93b. If the calculation results received from the multiple controllers 93a, 93b match, the IO node 92 judges them to be normal, and if they do not match, it judges that the calculation was not performed correctly due to a failure of the controllers 93a, 93b, etc. In order to improve the reliability of the calculations by making the controllers 93 (93a, 93b) redundant in this way, it is necessary for the controllers 93 (93a, 93b) to obtain measurement data at the same timing from the IO node 92 and perform the same calculation.

In general, the timing at which the IO node 92 collects measurement data from the field devices 91 (91a, 91b) is not synchronized with the timing at which the controller 93 (93a, 93b) collects measurement data from the IO node 92. Therefore, if the timing at which the controller 93a and the controller 93b acquire measurement data from the IO node 92 differs, it may not be possible to acquire the same measurement data. However, in order to match the calculation operation timing of the controllers 93a and 93b, highly accurate time synchronization is required, which complicates the processing and configuration. In order to synchronize the data acquisition timing of the IO node 92 and the controllers 93a and 93b, highly accurate time synchronization is also required in the controllers 93 (93a, 93b).

As such, in the control system 9 according to the comparative example, multiple controllers 93 (93a, 93b) need to operate in highly accurate time synchronization, which complicates the processing and configuration. The present disclosure aims to enable multiple controllers to acquire measurement data at the same timing without highly accurate time synchronization.

<Embodiment 1>
Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, parts having the same configuration or function are denoted by the same reference numerals. In the description of this embodiment, duplicated descriptions of the same parts may be omitted or simplified as appropriate.

(Control System)
2 is a diagram showing an example of a schematic configuration of a control system 1a according to an embodiment. The control system 1a includes field devices 10 (10a, 10b), an IO node 20, controllers 30 (30a, 30b), a cache server 40, and a network 50.

The field devices 10 (10a, 10b) are devices that acquire measurement data for controlling the plant and/or operate the plant. The field devices 10 (10a, 10b) may be, for example, sensors 10a such as temperature sensors or flow meters, and actuators 10b such as valve devices, fans, or motors. Hereinafter, the field devices 10a and 10b may be collectively referred to as "field devices 10." The field devices 10 output measurement data to the IO node 20 and control operations based on control signals received from the IO node 20. In the example of FIG. 2, the control system 1a includes two field devices 10a and 10b, but the number of field devices 10 is arbitrary.

The IO node 20 is a device to which the field device 10 is connected and which functions as an interface between the field device 10 and the controller 30 (30a, 30b). The IO node 20 is connected to a network 50 and can communicate with the controller 30 (30a, 30b) via the network 50. In the example of FIG. 2, the control system 1a includes one IO node 20, but the number of IO nodes 20 is arbitrary. Also, the number of field devices 10 connected to each IO node 20 is arbitrary.

The controller 30 (30a, 30b) is a device that performs calculations on the measurement data of the field device 10 and controls the field device 10 based on the calculation results. Hereinafter, the controllers 30a, 30b may be collectively referred to as "controller 30". The controller 30 is configured to be able to communicate with the IO node 20 and the cache server 40 via the network 50. The controller 30 can access the field device 10 via the IO node 20. The control system 1a includes two controllers 30a, 30b, but the number of controllers 30 may be any number.

The cache server 40 is a device that caches and stores the measurement data acquired from the IO node 20 by the controller 30a or 30b that first accesses the cache server 40. The control system 1a includes one cache server 40, but the number of cache servers 40 is arbitrary.

The network 50 is a dedicated communication network to which information devices such as the IO nodes 20, controllers 30, and cache servers 40 in the plant can be connected. The network 50 may include a wired or wireless local area network (LAN). The wired local area network includes, for example, Ethernet. The wireless local area network includes, for example, a wireless network conforming to wireless communication standards such as Wi-Fi (registered trademark) and WiMAX (registered trademark). Furthermore, a communication network using a standardized protocol such as OPC UA or PROFINET may be used. Furthermore, the network 50 may include, for example, the Internet, an intranet, a mobile communication network, etc.

In the control system 1a, the IO node 20 collects measurement data from the field devices 10 at regular intervals (e.g., every second). The IO node 20 stores the collected measurement data in the memory unit 202 (see FIG. 6). Each of the controllers 30a, 30b accesses the cache server 40 at regular intervals (e.g., every second) and performs processing to acquire the measurement data of the field devices 91 (91a, 91b). Here, the operations of the IO node 20 and the controllers 30a, 30b are not completely synchronized in time, and each operates at a regular interval independently.

In such a configuration, only the controller 30 (30a, 30b) that first accesses the cache server 40 accesses the IO node 20 to acquire the measurement data. For example, when the controller 30a first accesses the cache server 40, the controller 30a accesses the IO node 20 and acquires the measurement data of the field device 10 from the IO node 20. The controller 30a transmits the acquired measurement data to the cache server 40 and causes the cache server 40 to hold the cache of the measurement data. On the other hand, the controller 30b that accesses the cache server 40 later acquires the cache of the measurement data from the cache server 40. In this way, in the control system 1a, only the controller 30 (e.g., the controller 30a) that first accesses the cache server 40 acquires the measurement data of the field device 10 from the IO node 20. The other controllers 30 (e.g., the controller 30b) acquire the cache of the measurement data from the cache server 40. Therefore, the control system 1a can ensure that multiple controllers 30 (30a, 30b) acquire the same measurement data even if the operations of each controller are not synchronized with high precision.

Each of the controllers 30 (30a, 30b) performs calculations based on the acquired measurement data and transmits the calculation results to the IO node 20. When the IO node 20 receives the calculation results from each of the controllers 30 (30a, 30b), it compares the received calculation results and determines whether the operation of each of the controllers 30 (30a, 30b) is normal. The IO node 20 outputs the determination results as log information to the memory unit 302 (see FIG. 5) or a display device (display), etc. The IO node 20 may transmit the determination results to another device such as the controller 30 or the cache server 40.

Figure 3 is a block diagram showing an example of the functional configuration of the control system 1a in Figure 2. The IO node 20 includes a control application unit 21, an access path control unit 22, and a communication control unit 23.

The control application unit 21 controls the field devices 10 connected to the IO node 20. The control application unit 21 may run on an operating system. The control application unit 21 controls the field devices 10 as required for process control. For example, the control application unit 21 collects measurement data from the field devices 10 and transmits control data to the field devices 10.

The access path control unit 22 provides an abstracted IO access method for the control application unit 21. The access path control unit 22 adaptively changes the access method in accordance with the physical relationship between the IO node 20 on which the access path control unit 22 is mounted and the field device 10. To abstract the hardware, the access path control unit 22 may be included in the virtualization unit 24 in the IO node 20. The virtualization unit 24 operates virtually on the hardware of the IO node 20 as a substitute for the hardware. The virtualization unit 24 is provided to enable replacement of the hardware of the IO node 20 without changing the control application unit 21. However, the virtualization unit 24 is not essential to provide the functions of the access path control unit 22. It is possible to implement the access path control unit 22 without the virtualization unit 24.

The communication control unit 23 communicates between the field device 10 connected to the IO node 20 and the controller 30 connected to the network 50. The communication control unit 23 performs the necessary communication processing depending on the connection form with the field device 10 and the type of the network 50, etc.

The controller 30 (30a, 30b) includes a control application unit 31 (31a, 31b), an access path control unit 32 (32a, 32b), and a communication control unit 33 (33a, 33b). The controller 30 (30a, 30b) may include a virtualization unit 34 (34a, 34b) like the IO node 20. The control application unit 31a, access path control unit 32a, communication control unit 33a, and virtualization unit 34a of the controller 30a are the same as the control application unit 31b, access path control unit 32b, communication control unit 33b, and virtualization unit 34b of the controller 30b. Therefore, hereinafter, the control application units 31a and 31b, the access path control units 32a and 32b, the communication control units 33a and 33b, and the virtualization units 34a and 34b may be collectively referred to as the "control application unit 31," the "access path control unit 32," the "communication control unit 33," and the "virtualization unit 34." The control application unit 31, the access path control unit 32, the communication control unit 33, and the virtualization unit 34 of the controller 30 have the same or similar functions as the control application unit 21, the access path control unit 22, the communication control unit 23, and the virtualization unit 24 of the IO node 20, and therefore detailed description thereof will be omitted.

The cache server 40 includes a management table 41, an access route control unit 42, a communication control unit 43, and a cache database 45.

The management table 41 is a table for managing the status of the controller 30's access to the cache server 40. FIGS. 4 and 5 are diagrams showing an example of the management table in FIG. 3. The cache server 40 holds the identification information of the controller 30 that first accessed the cache server 40 at a fixed period (for example, every second). In the initial state, the management table 41 holds a value such as blank, "0", or "-" ("-" in the examples of FIGS. 4 and 5). In the examples of FIGS. 4 and 5, the control timing indicates a fixed period determined in advance at a fixed period for the controller 30 to periodically acquire measurement data. The control timing T001 corresponds, for example, to the period from 0:00:00 to 0:00:01. The control timing T002 corresponds, for example, to the period from 0:00:01 to 0:00:02. The control timing T003 corresponds, for example, to the period from 0:00:02 to 0:00:03. In these examples, the control timings T001 to T003 correspond to a period of 1 second, with a length determined in a 1-second cycle. The cycle and length of the control timing may be different; for example, the control timing may be a period of 1 second with a length determined in a 10-second cycle. The control timing is determined based on the time measured by the clock unit of the cache server 40, but may also be determined based on the time measured by a time server such as an NTP (Network Time Protocol) server or other device such as the controller 30. When the control timing is determined based on the time measured by the time server, it is possible to obtain control timing that reflects the correct time, and the reliability of the control timing can be maintained. When the control timing is determined based on the time measured by each controller 30, each controller 30 can determine the control timing without accessing other devices such as a time server, and availability can be maintained.

In the example of FIG. 2, there is one IO node 20, but the management table 41 in FIG. 4 holds the identification information of the controller 30 that first accessed the cache server 40 in a control system 1a that has three IO nodes 20 (IO-1, IO-2, IO-3). The management table 41 in FIG. 5 holds the identification information of the controller 30 that first accessed the cache server 40 in a control system 1a that has two IO nodes 20 (IO-5, IO-6).

For example, in FIG. 4, at control timing "T001", for the IO nodes 20 with identification information "IO-1" and "IO-2", the controller 30 with identification information "CNT-1" (e.g., controller 30a) first accesses the cache server 40. For the IO node 20 with identification information "IO-3", the controller 30 with identification information "CNT-2" (e.g., controller 30b) first accesses the cache server 40. At control timing "T002", for each of the IO nodes 20 with identification information "IO-1", "IO-2", and "IO-3", the controller 30 with identification information "CNT-1" (e.g., controller 30a) first accesses the cache server 40. At control timing "T003", for the IO nodes 20 with identification information "IO-1" and "IO-2", the controller 30 with identification information "CNT-2" (e.g., controller 30b) first accesses the cache server 40. For the IO node 20 with the identification information "IO-3", none of the controllers 30 have yet accessed the cache server 40. In the example of FIG. 5, at any control timing, none of the controllers 30 have yet accessed the cache server 40 for any of the IO nodes 20.

When managing access to multiple IO nodes 20 from multiple controllers 30, the cache server 40 may classify the controllers 30 and IO nodes 20 into multiple control groups and hold a management table 41 for each control group. For example, a control group such as "C001" may be set for multiple controllers 30 to be made redundant. For example, the cache server 40 may classify the controllers 30 and IO nodes 20 into multiple control groups depending on which controller 30 performs calculations on the measurement data of the field device 10 connected to which IO node 20. For example, the management table 41 in FIG. 4 may show access management for control group 1 in which the controllers 30 with identification information "CNT-1" and "CNT-2" control the IO nodes 20 with identification information "IO-1", "IO-2", and "IO-3". For example, the management table 41 in FIG. 5 may show access management for control group 2 in which the controllers 30 with identification information "CNT-X" and "CNT-Y" control the IO nodes 20 with identification information "IO-5" and "IO-6". Controllers 30 in the same control group perform the same control calculations.

Returning to the explanation of FIG. 3, the access path control unit 42, the communication control unit 43, and the virtualization unit 44 of the cache server 40 have the same or similar functions as the access path control unit 22, the communication control unit 23, and the virtualization unit 24 of the IO node 20, so detailed explanations are omitted.

At each control timing, the cache database 45 stores as a cache the measurement data acquired from the IO node 20 by the controller 30 that accessed the cache server 40 earliest. As shown in FIG. 1, when multiple field devices 10a and 10b are connected to the IO node 20, the cache database 45 may store the measurement data of each field device 10. As described above, when the control system 1a includes multiple IO nodes 20, the cache database 45 may store the measurement data acquired from each IO node 20 for each IO node 20. As described above, when the control system 1a manages access to multiple IO nodes 20 by a number of controllers 30 classified into multiple control groups, the cache database 45 may store the measurement data acquired from each IO node 20 for each control group.

(IO node)
Fig. 6 is a block diagram showing an example of a hardware configuration of the IO node 20 in Fig. 2. The IO node 20 is one or a plurality of computer devices capable of communicating with each other. The IO node 20 is realized by a general-purpose computer such as a personal computer (PC) or a workstation (WS), but may also be realized by a field programmable gate array (FPGA) or a dedicated computer designed for controlling a plant or the like. As shown in Fig. 6, the IO node 20 includes a control unit 201, a storage unit 202, and a communication unit 203.

The control unit 201 includes one or more processors. In one embodiment, the "processor" is, but is not limited to, a general-purpose processor or a dedicated processor specialized for a particular process. The control unit 201 is communicatively connected to each component that constitutes the IO node 20, and controls the operation of the entire IO node 20.

The storage unit 202 includes any storage module, such as a hard disk drive (HDD), a solid state drive (SSD), a read-only memory (ROM), and a random access memory (RAM). The storage unit 202 may function as a main storage device, an auxiliary storage device, or a cache memory, for example. The storage unit 202 stores any information used in the operation of the IO node 20. For example, the storage unit 202 may store a system program (operating system), an application program, and various information received by the communication unit 203. The storage unit 202 is not limited to being built into the IO node 20, and may be an external database or an external storage module.

The communication unit 203 includes any communication module that can communicate with other devices such as the field device 10 and the controller 30 using any communication technology. The communication unit 203 may further include a communication control module for controlling communication with other devices, and a storage module for storing communication data such as identification information required for communication with other devices.

The functions of the IO node 20 can be realized by executing a computer program (program) according to this embodiment on a processor included in the control unit 201. That is, the functions of the IO node 20 can be realized by software. The computer program causes a computer to execute the processing of steps included in the operation of the IO node 20, thereby causing the computer to realize the functions corresponding to the processing of each step. That is, the computer program is a program for causing a computer to function as the IO node 20 according to this embodiment. The computer program may be recorded on a computer-readable recording medium. Programs include information used for processing by an electronic computer and equivalent to a program. For example, data that is not a direct command to a computer but has properties that dictate computer processing falls under "something equivalent to a program."

Some or all of the functions of the IO node 20 may be realized by a dedicated circuit included in the control unit 201. In other words, some or all of the functions of the IO node 20 may be realized by hardware. In addition, the IO node 20 may be realized by a single computer device, or may be realized by the cooperation of multiple computer devices.

(controller)
7 is a block diagram showing an example of a hardware configuration of the controller 30 in FIG. 2. The controller 30 is one or a plurality of computer devices capable of communicating with each other. The controller 30 is realized by a general-purpose computer such as a PC or a WS, but may be realized by a dedicated computer designed for controlling an FPGA or a plant. As shown in FIG. 7, the controller 30 includes a control unit 301, a storage unit 302, and a communication unit 303. The control unit 301, the storage unit 302, and the communication unit 303 of the controller 30 are realized in the same manner as the control unit 201, the storage unit 202, and the communication unit 203 of the IO node 20, so detailed description will be omitted. In addition, like the IO node 20, the function of the controller 30 can be realized by executing the program according to this embodiment in a processor included in the control unit 301.

(cache server)
FIG. 8 is a block diagram showing an example of a hardware configuration of the cache server 40 in FIG. 2. The cache server 40 is one or a plurality of computer devices capable of communicating with each other. The cache server 40 is realized by a general-purpose computer such as a PC or a WS, but may be realized by a dedicated computer designed for controlling an FPGA or a plant. As shown in FIG. 8, the cache server 40 includes a control unit 401, a storage unit 402, and a communication unit 403. The control unit 401, the storage unit 402, and the communication unit 403 of the cache server 40 are realized in the same manner as the control unit 201, the storage unit 202, and the communication unit 203 of the IO node 20, so detailed description will be omitted. In addition, like the IO node 20, the function of the cache server 40 can be realized by executing the program according to this embodiment by a processor included in the control unit 401.

(Control system operation)
9 and 10 are sequence charts showing an example of the operation of the control system 1a according to an embodiment. The operation of the control system 1a described with reference to FIG. 9 and FIG. 10 may correspond to one of the control methods of the control system 1a. The operation of each step in FIG. 9 and FIG. 10 may be executed based on the control by the control unit 201 of the IO node 20, the control unit 301 of the controller 30, or the control unit 401 of the cache server 40. The process in FIG. 9 and FIG. 10 is executed for each control timing, for example, every second. FIG. 9 and FIG. 10 show an example in which the controller 30a first accesses the cache server 40 at a certain control timing, and then the controller 30b accesses the cache server 40. FIG. 9 shows a process in which the controller 30a acquires measurement data and performs calculations. FIG. 10 shows a process in which the controller 30b acquires measurement data and performs calculations. Hereinafter, an example in which the control system 1a includes one IO node 20 as shown in FIG. 2 will be described.

In step S1 of FIG. 9, the control unit 301 of the controller 30a inquires of the cache server 40 whether or not the cache of the measurement data of the field device 10 connected to the IO node 20 is stored in the cache database 45. For example, the access path control unit 32a of the controller 30a may make the inquiry.

In step S2, the control unit 401 of the cache server 40 determines whether or not a cache of the measurement data queried in step S1 is stored. For example, the control unit 401 may refer to the management table 41 and determine whether or not an access by the controller 30 is recorded for the relevant control timing and IO node 20, thereby determining whether or not a cache exists. The example in FIG. 9 shows a case where the controller 30a has accessed for the first time at a certain control timing, so the control unit 401 determines that there is no cache.

In step S3, the control unit 401 of the cache server 40 notifies the controller 30a that there is no cache.

When a notification of no cache is received from the cache server 40, in step S4, the control unit 301 of the controller 30a requests the measurement data of the field device 10 from the IO node 20. For example, the control application unit 31a of the controller 30a may request data acquisition.

When a request for measurement data is received from the controller 30a, in step S5, the control unit 201 of the IO node 20 acquires the measurement data of the field device 10. As described above, the IO node 20 collects measurement data from the field device 10 at regular intervals (e.g., every second) and stores the collected measurement data in the memory unit 202. The control unit 201 then reads out the measurement data from the memory unit 202 to acquire the measurement data. Note that the control unit 201 may acquire the measurement data from the field device 10 in response to receiving a request for measurement data from the controller 30.

In step S6, the control unit 201 of the IO node 20 transmits the measurement data of the field device 10 acquired in step S5 to the controller 30a.

When the measurement data of the field device 10 is received from the IO node 20, in step S7, the control unit 301 of the controller 30a stores the received measurement data in the memory unit 302 and transmits the measurement data to the cache server 40.

When the measurement data of the field device 10 is received from the controller 30a, in step S8, the control unit 401 of the cache server 40 stores the received measurement data in the cache database 45 and updates the management table 41. For example, the control unit 401 may update the item corresponding to the IO node 20 of the relevant control timing in the management table 41 of the corresponding control group with the identification information of the controller 30a.

Meanwhile, in step S9, the control unit 301 of the controller 30a performs a predetermined calculation based on the measurement data acquired in step S7. For example, the calculation may be performed by the control application unit 21a of the controller 30a. The content of the calculation is preset according to the type of the field device 10, etc.

In step S10, the control unit 301 of the controller 30a transmits the calculation result of the process of step S9 to the IO node 20. Note that the control system 1a may execute the processes of steps S9 and S10 before steps S7 and S8.

When the calculation result is received from the controller 30a, in step S11, the control unit 201 of the IO node 20 stores and retains the calculation result received from the controller 30a in the memory unit 202.

Next, in step S21 of FIG. 10, the control unit 301 of the controller 30b inquires of the cache server 40 whether or not the cache of the measurement data of the field device 10 connected to the IO node 20 is stored in the cache database 45. For example, the virtualization unit 34b of the controller 30b may make the inquiry.

In step S22, the control unit 401 of the cache server 40 determines whether or not a cache of the measurement data queried in step S21 is stored. For example, the control unit 401 may refer to the management table 41 and determine whether or not an access by the controller 30 is recorded for the corresponding control timing and IO node 20, thereby determining whether or not a cache exists. The example in FIG. 10 shows a case where the controller 30a has already accessed at the corresponding control timing, so the control unit 401 determines that a cache exists.

Therefore, in step S23, the control unit 401 of the cache server 40 reads and acquires the cache of the measurement data stored in the cache database 45 in step S8 of FIG. 9. Specifically, the control unit 401 may acquire the measurement data of the corresponding control timing that is stored in association with the identification information of the IO node 20 of the corresponding control group.

In step S24, the control unit 401 of the cache server 40 transmits the cache of the measurement data acquired in step S23 to the controller 30b.

When the cache of the measurement data is received from the cache server 40, in step S25, the control unit 301 of the controller 30b performs a predetermined calculation based on the acquired cache of the measurement data. For example, the calculation may be performed by the control application unit 21b of the controller 30b. The content of the calculation is the same as the calculation executed by the controller 30a.

In step S26, the control unit 301 of the controller 30b transmits the calculation result obtained by the processing in step S25 to the IO node 20.

When the calculation result is received from controller 30b, in step S27, the control unit 201 of the IO node 20 compares it with the calculation result by controller 30a held in step S11 of FIG. 9, and determines whether the controllers 30a, 30b are operating normally. For example, the control unit 201 may determine that each controller 30a, 30b is operating normally if the calculation results by controllers 30a, 30b match, and that each controller is not operating normally if they are not. Similarly, when the control system 1a includes three or more controllers 30, the control unit 201 may determine that each controller 30 is operating normally if the calculation results by all controllers 30 match, and that each controller is not operating normally if they are not.

In step S28, the control unit 201 of the IO node 20 outputs the result of the determination made in step S27. For example, the control unit 201 may output the determination result to the memory unit 202 as a log file. Alternatively, the control unit 201 may display the determination result on a display device or the like, or transmit the determination result to another device such as the controller 30 or cache server 40. The control unit 201 may perform such output if it is determined in step S27 that the state is not normal.

As described above, the control system 1a includes an IO node 20 to which a field device 10 that acquires measurement data is connected, a plurality of controllers 30a, 30b that perform calculations based on the measurement data acquired by the field device 10, and a cache server 40. The control unit 301 of each of the plurality of controllers 30a, 30b determines whether or not the field device 10 holds the measurement data acquired by the field device 10 at each control timing that is a fixed period determined in advance by a fixed cycle, for example, by inquiring of the cache server 40. If the cache server 40 does not hold the measurement data, the control unit 301 acquires the measurement data acquired by the field device 10 connected to the IO node 20 from the IO node 20. If the cache server 40 holds the measurement data, the control unit 301 acquires the measurement data acquired by the field device 10 from the cache server 40. The control unit 301 performs a predetermined calculation based on the measurement data received from the IO node 20 or the cache server 40. Therefore, even if the operation timing of the controllers 30 is shifted, all controllers 30 can perform calculations based on the same measurement data at the control timing.

The control unit 301 of each of the multiple controllers 30a, 30b may transmit to the IO node 20 a calculation result, which is a result of performing calculations based on the measurement data received from the IO node 20 or the cache server 40, at each control timing. The control unit 201 of the IO node 20 may compare the calculation results received from each of the multiple controllers 30a, 30b at each control timing to determine whether the operation of the multiple controllers 30a, 30b is normal or not. The control unit 201 may output a determination result of whether the operation of the multiple controllers 30a, 30b is normal or not. In this way, the control system 1a can detect an abnormality in the controller 30 by comparing the calculation results of the multiple controllers 30a, 30b. Furthermore, the control system 1a may not use the calculation results of the controllers 30a, 30b that were not able to transmit the calculation results within the control timing to determine whether the operation is abnormal or not.

In addition, when the control unit 301 of each of the multiple controllers 30a, 30b acquires measurement data acquired by a field device 10 connected to the IO node 20 from the IO node 20, the control unit 301 may transmit the acquired measurement data to the cache server 40. When the control unit 401 of the cache server 40 receives measurement data from a controller 30 included in the multiple controllers 30a, 30b, the control unit 401 may store the received measurement data in the memory unit 402. Therefore, the control system 1a caches and stores the measurement data of the controller 30 that first accessed the cache server 40, thereby enabling the other controllers 30 to perform calculations based on this measurement data.

The control unit 401 of the cache server 40 may also record, for each control timing, in the management table 41, the identification information of the controller 30 that received the measurement data. In this way, by recording the identification information of the controller 30 that sent the cached measurement data, it is possible to identify the controller 30 that sent the cached data.

The control unit 401 of the cache server 40 may also withhold responses to inquiries from other controllers 30 (e.g., controller 30b) from the time when it first receives an inquiry from one of the controllers 30 (e.g., controller 30a) included in the multiple controllers 30a, 30b as to whether the field device 10 holds the acquired measurement data, until it receives the measurement data from the controller 30a. Specifically, for example, after receiving an inquiry from the controller 30a in step S1 of FIG. 9, even if it receives an inquiry from the controller 30b (S21), it may not immediately respond until the measurement data is held in the cache in step S8. This makes it possible to guarantee that, when a certain controller 30a receives an inquiry from the other controller 30b while the other controller 30b is acquiring measurement data from the IO node 20, all the controllers acquire the same measurement data without the other controller 30b also accessing the IO node 20.

In the above embodiment, the cache server 40 holds the management table 41, but each controller 30 may hold a management table (second management table) that is managed in synchronization with the management table 41 (first management table) of the cache server 40. With this configuration, the controller 30 can determine whether the measurement data is obtained from the IO node 20 or the cache server 40 without inquiring of the cache server 40. In addition, the IO node 20 periodically obtains measurement data from the field device 10, but the present invention is not limited to this process. For example, the field devices 10a and 10b may each independently transmit measurement data to the IO node 20.

<Embodiment 2>
In the first embodiment, an example has been described in which the virtualization unit 34 of the controller 30 controls the acquisition destination of the measured data. However, other devices such as a network (NW) switch may also control the acquisition destination of the measured data.

(Control System)
Fig. 11 is a diagram showing a schematic configuration example of a control system 1b according to the second embodiment. The control system 1b includes field devices 10 (10a, 10b), an IO node 20, a controller 30 (30a, 30b), a cache server 40, a network 50, and a network switch 60. The functions and configurations of the field devices 10 (10a, 10b), the IO node 20, the controller 30 (30a, 30b), the cache server 40, and the network 50 are similar to those of the control system 1a in Fig. 2, so only the differences from the configuration of the first embodiment will be described.

In the control system 1b, instead of or together with the cache server 40, the network switch 60 holds a management table 61. The management table 61 of the network switch 60 is similar to the management table 41 of the cache server 40, and may include, for example, the same information as the contents exemplified in FIG. 4 and FIG. 5. In the control system 1b, the multiple controllers 30a, 30b transmit requests to the IO node 20 for measurement data acquired by the field device 10 at each control timing to the network switch 60. The network switch 60 refers to the management table 61 to determine whether the cache server 40 holds the measurement data. If the cache server 40 does not hold the measurement data, the network switch 60 causes the IO node 20 to transmit the measurement data acquired by the field device 10 connected to the IO node 20 to the controller 30 via the network switch 60. The network switch 60 transmits the measurement data received from the IO node 20 to the cache server 40 and causes it to hold. On the other hand, if the cache server 40 holds the measurement data, the network switch 60 causes the cache server 40 to transmit the measurement data acquired by the field device 10 to the controller 30. Each of the multiple controllers 30 performs a predetermined calculation based on the measurement data received from the IO node 20 or the cache server 40. Specifically, the network switch 60 may switch the communication destination by, for example, rewriting the IP addresses of packets received from the controller 30, the IO node 20, and the cache server 40.

With this configuration, from the perspective of the controller 30, it appears as if the same device is being accessed, but in reality, common measurement data can be obtained from the IO node 20 or the cache server 40 to all controllers 30 depending on whether or not a cache is present. Note that even in a configuration with a network switch 60, the access destination may be switched by the access path control unit 32 of each controller 30, rather than by the network switch 60.

(Network Switch)
FIG. 12 is a block diagram showing an example of a hardware configuration of the network switch 60 in FIG. 11. The network switch 60 is one or a plurality of computer devices capable of communicating with each other. The network switch 60 is realized, for example, by a dedicated computer designed for controlling an FPGA or a plant, but may be realized by a general-purpose device such as a PC. As shown in FIG. 12, the network switch 60 includes a control unit 601, a storage unit 602, and a communication unit 603. The control unit 601, the storage unit 602, and the communication unit 603 of the network switch 60 are realized in the same manner as the control unit 201, the storage unit 202, and the communication unit 203 of the IO node 20, and therefore detailed description thereof will be omitted. In addition, similar to the IO node 20, the function of the network switch 60 can be realized by executing a program according to this embodiment in a processor included in the control unit 601.

(Control system operation)
13 and 14 are sequence charts showing an example of the operation of the control system 1b according to an embodiment. The operation of the control system 11b described with reference to FIG. 13 and FIG. 14 may correspond to one of the control methods of the control system 1b. The operation of each step in FIG. 13 and FIG. 14 may be executed based on the control by the control unit 201 of the IO node 20, the control unit 301 of the controller 30, the control unit 401 of the cache server 40, or the control unit 601 of the network switch 60. The processing in FIG. 13 and FIG. 14 is executed for each control timing, for example, every second. FIG. 13 and FIG. 14 show an example in which the controller 30a first accesses the network switch 60 at a certain control timing, and then the controller 30b accesses the network switch 60. FIG. 13 shows a process in which the controller 30a acquires measurement data and performs calculations. FIG. 14 shows a process in which the controller 30b acquires measurement data and performs calculations. Hereinafter, an example in which the control system 1b includes one IO node 20 as shown in FIG. 11 will be described.

In step S31 of FIG. 13, the control unit 301 of the controller 30a requests the network switch 60 for measurement data of the field device 10 connected to the IO node 20. For example, the access path control unit 32a of the controller 30a may make the request.

In step S32, the control unit 601 of the network switch 60 determines whether or not a cache of the measurement data requested in step S31 is stored in the cache server 40. For example, the control unit 601 may refer to the management table 61 held by the device itself and determine whether or not an access by the controller 30 is recorded for the relevant control timing and IO node 20, thereby determining whether or not there is a cache. The example in FIG. 13 shows a case where the controller 30a has accessed for the first time at a certain control timing, so the control unit 601 determines that there is no cache (step S33).

In step S34, the control unit 601 of the network switch 60 requests the IO node 20 for the measurement data of the field device 10. For example, the control unit 601 may rewrite the IP address, etc. of the packet received from the controller 30a in step S31 and send a request for the measurement data to the IO node 20.

When a request for measurement data is received from the network switch 60, in step S35, the control unit 201 of the IO node 20 acquires the measurement data of the field device 10. As described above, the IO node 20 collects measurement data from the field device 10 at regular intervals (e.g., every second) and stores the collected measurement data in the memory unit 202. The control unit 201 then reads out the measurement data from the memory unit 202 to acquire the measurement data. Note that the control unit 201 may acquire the measurement data from the field device 10 in response to receiving a request for measurement data from the network switch 60.

In step S36, the control unit 201 of the IO node 20 transmits the measurement data of the field device 10 acquired in step S35 to the network switch 60.

In step S37, the control unit 601 of the network switch 60 receives and acquires the measurement data of the field device 10 from the IO node 20.

In step S38, the control unit 601 of the network switch 60 transmits the measurement data acquired in step S37 to the controller 30a. For example, the control unit 601 may rewrite the IP address, etc. of the packet received from the IO node 20 in step S36 and transmit the measurement data to the controller 30a.

In step S39, the control unit 601 of the network switch 60 transmits the measurement data acquired in step S37 to the cache server 40.

In step S40, the control unit 601 of the network switch 60 updates the management table 61. For example, the control unit 401 may update the item corresponding to the IO node 20 of the relevant control timing in the management table 61 of the corresponding control group with the identification information of the controller 30a.

Meanwhile, in step S41, the control unit 301 of the controller 30a performs a predetermined calculation based on the measurement data acquired in step S38. For example, the calculation may be performed by the control application unit 21a of the controller 30a. The content of the calculation is preset according to the type of the field device 10, etc.

In step S42, the control unit 301 of the controller 30a transmits the calculation result of the process of step S41 to the IO node 20. Note that the control system 1b may execute the processes of steps S41 and S42 before steps S39 and S40.

When the calculation result is received from the controller 30a, in step S43, the control unit 201 of the IO node 20 stores and retains the calculation result received from the controller 30a in the memory unit 202.

On the other hand, when the control unit 401 of the cache server 40 receives the measurement data of the field device 10 from the network switch 60, in step S44, it stores the received measurement data in the cache database 45 and updates the management table 41. For example, the control unit 401 may update the item corresponding to the IO node 20 of the relevant control timing in the management table 41 of the corresponding control group with the identification information of the controller 30a.

Next, in step S51 of FIG. 14, the control unit 301 of the controller 30b requests the network switch 60 for measurement data of the field device 10 connected to the IO node 20. For example, the virtualization unit 34b of the controller 30b may make the request.

In step S52, the control unit 601 of the network switch 60 determines whether a cache of the measurement data requested in step S51 is stored in the cache server 40. For example, the control unit 601 may refer to the management table 61 and determine whether an access by the controller 30 has been recorded for the relevant control timing and IO node 20, thereby determining whether a cache exists. The example in FIG. 14 shows a case where the controller 30a has already accessed at the relevant control timing, so the control unit 601 determines that a cache exists (step S53).

Therefore, in step S54, the control unit 601 of the network switch 60 requests the cache server 40 to cache the measurement data stored in the cache database 45 in step S44 of FIG. 13. For example, the control unit 601 may rewrite the IP address, etc. of the packet received from the controller 30b in step S51 and send a request for the measurement data to the cache server 40. Specifically, the control unit 601 may request the caching of the measurement data of the corresponding control timing that is stored in association with the identification information of the IO node 20 of the corresponding control group.

In step S55, the control unit 401 of the cache server 40 obtains the cache of the measurement data requested by the network switch 60 from the cache database 45.

In step S56, the control unit 401 of the cache server 40 transmits the cache of the measurement data acquired in step S55 to the network switch 60.

In step S57, the control unit 601 of the network switch 60 receives and acquires the cache of the measurement data of the field device 10 from the cache server 40.

In step S58, the control unit 601 of the network switch 60 transmits the cache of the measurement data acquired in step S57 to the controller 30b. For example, the control unit 601 may rewrite the IP address of the packet received from the cache server 40 in step S56 and transmit the cache of the measurement data to the controller 30b.

When the cache of measurement data is acquired, in step S59, the control unit 301 of the controller 30b performs a predetermined calculation based on the acquired cache of measurement data. For example, the calculation may be performed by the control application unit 21b of the controller 30b. The content of the calculation is the same as the calculation executed by the controller 30a.

In step S60, the control unit 301 of the controller 30b transmits the calculation result obtained by the processing in step S59 to the IO node 20.

When the calculation result is received from controller 30b, in step S61, the control unit 201 of the IO node 20 compares it with the calculation result by controller 30a held in step S43 of FIG. 13, and determines whether the controllers 30a, 30b are operating normally. For example, the control unit 201 may determine that each controller 30a, 30b is operating normally if the calculation results by controllers 30a, 30b match, and that each controller is not operating normally if they are not. Similarly, when the control system 1b includes three or more controllers 30, the control unit 201 may determine that each controller 30 is operating normally if the calculation results by all controllers 30 match, and that each controller is not operating normally if they are not.

In step S62, the control unit 201 of the IO node 20 outputs the result of the determination made in step S61. For example, the control unit 201 may output the determination result to the memory unit 202 as a log file. Alternatively, the control unit 201 may display the determination result on a display device or the like, or transmit the determination result to another device such as the controller 30, the cache server 40, or the network switch 60. The control unit 201 may perform such output if it is determined in step S61 that the state is not normal.

As described above, according to the control systems 1a and 1b disclosed herein, data at the same timing can be acquired between multiple controllers 30 that operate asynchronously. Therefore, even if the operation of each controller 30 is not synchronized with high precision, it is possible to detect an abnormality in the controller 30 by comparing the calculation results of each controller 30.

The techniques of the control systems 1a and 1b may also be applied to guarantee the arrival of packets in pub/sub communication in multicast or broadcast. When pub/sub communication is performed using multicast or broadcast, UDP (User Datagram Protocol) is used as the communication protocol. Unlike TCP (Transmission Control Protocol), UDP does not have a mechanism for confirming delivery, and there is no guarantee that transmitted data can be reliably received. Therefore, processing is required in the event that data cannot be received.

For example, in the control system 1a of FIG. 2, consider a case where the IO node 20 acquires measurement data from the field device 10 at any timing and distributes (publishes) the control timing information (T001) and the measurement data to each node including the controller 30 and the cache server 40. In this case, each node (controllers 30a, 30b, and cache server 40) waits for and receives (subscribes) data from the IO node 20. If the controller 30 is able to receive the measurement data of the node to be used at the control timing T001, it uses the data to perform calculations. In addition, the controller 30 causes the cache server 40 to hold the received measurement data. If the controllers 30a and 30b are unable to receive the measurement data to be used, they send a data acquisition request to the cache server 40 and acquire the data.

In this way, if the controller 30 receives measurement data at the control timing, it performs calculations based on the measurement data and stores the measurement data in the cache server 40. If the controller 30 does not receive measurement data at the control timing, it accesses the cache server 40 to obtain the necessary measurement data and performs the specified calculations. Therefore, even if the IO node 20 multicasts or broadcasts the measurement data of the field device 10 rather than accessing the IO node 20 from the controller 30, each controller 30 can perform calculations based on the same measurement data. Therefore, it is possible to detect abnormalities in the controller 30 by comparing the calculation results of each controller 30.

The present disclosure is not limited to the above-described embodiments. For example, multiple blocks shown in the block diagram may be integrated, or one block may be divided. Multiple steps shown in the flowchart may be executed in parallel or in a different order depending on the processing capacity of the device executing each step, or as needed, instead of being executed chronologically as described. Other modifications are possible without departing from the spirit of the present disclosure.

1, 1a Control system 10 Field device 20 IO node 21 Control application unit 22 Virtualization unit 23 Communication control unit 24 Access path control unit 201 Control unit 202 Storage unit 203 Communication unit 30 Controller 31 Control application unit 32 Virtualization unit 33 Communication control unit 34 Access path control unit 301 Control unit 302 Storage unit 303 Communication unit 40 Cache server 41 Management table 42 Virtualization unit 43 Communication control unit 44 Access path control unit 45 Cache database 401 Control unit 402 Storage unit 403 Communication unit 50 Network 60 Network switch 61 Management table 601 Control unit 602 Storage unit 603 Communication unit

Claims (8)

an IO node to which a field device for acquiring measurement data is connected;
a plurality of controllers that perform calculations based on the measurement data acquired by the field devices;
A network switch;
A cache server;
Equipped with
each of the plurality of controllers transmits a request for the measurement data acquired by the field device to the network switch at each control timing, which is a fixed period determined in a predetermined cycle;
The network switch includes:
If the cache server does not hold the measurement data, the IO node transmits the measurement data acquired by the field device connected to the IO node to the controller via the network switch;
When the cache server holds the measurement data, the cache server transmits the measurement data acquired by the field device to the controller via the network switch;
Each of the plurality of controllers performs a predetermined calculation based on the measurement data received from the IO node or the cache server.
Control system. The network switch includes:
If the cache server does not hold the measurement data, the cache server requests the measurement data from the IO node;
In response to receiving the sensed data from the IO node based on the request, transmit the sensed data to the controller, and also transmit the sensed data to the cache server to store the sensed data as a cache.
The control system of claim 1 . The network switch includes:
If the cache server holds the measurement data, a request is made to the cache server to cache the measurement data;
In response to receiving the cached measurement data from the cache server based on the request, transmitting the cached measurement data to the controller.
The control system of claim 1 . The network switch includes:
A management table including information indicating whether the cache server holds the measurement data for each of the control timings is held;
in response to receiving the request for the measured data from any one of the plurality of controllers, referring to the management table to determine whether the cache server holds the measured data;
The control system of claim 1 . The control system according to claim 4, wherein the network switch holds information including identification information of the controller that received the measurement data as the management table for each control timing. each of the plurality of controllers transmits, at each control timing, a calculation result that is a result of performing the calculation based on the measurement data received via the network switch to the IO node;
The IO node includes:
comparing the calculation results received from each of the plurality of controllers at each of the control timings to determine whether or not the operations of the plurality of controllers are normal;
outputting a determination result as to whether the operation of the plurality of controllers is normal;
The control system of claim 1 . A network switch for use in a control system for a field device, comprising:
acquiring, from the cache server, information as to whether or not the cache server holds the measurement data in response to receiving a request for the measurement data acquired by the field device from the controller;
If the cache server does not store the measurement data, a request for the measurement data is sent to an IO node to which the field device is connected;
If the cache server holds the measurement data, a request for the measurement data is sent to the cache server.
Network switch. an IO node to which a field device for acquiring measurement data is connected;
a plurality of controllers that perform calculations based on the measurement data acquired by the field devices;
A network switch;
A cache server;
A control method for a control system comprising:
each of the plurality of controllers transmitting a request for the measurement data acquired by the field device to the network switch at each control timing, which is a fixed period determined in a predetermined cycle;
a step of causing the IO node to transmit the measurement data acquired by the field device connected to the IO node to the controller via the network switch when the cache server does not hold the measurement data, and causing the cache server to transmit the measurement data acquired by the field device to the controller via the network switch when the cache server holds the measurement data;
Each of the plurality of controllers performs a predetermined calculation based on the measurement data received from the IO node or the cache server;
A control method for a control system comprising:

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