JP7294517B1 - CONTROL SYSTEM, CONTROL METHOD OF CONTROL SYSTEM, AND NETWORK SWITCH - Google Patents

Abstract

Kind Code: A1 In a field device control system, controller redundancy can be achieved with a simpler configuration.
An IO node to which a field device is connected, a plurality of controllers that perform calculations based on measurement data acquired by the field device, a network switch, and a cache server. A request for the measurement data acquired by the field device is sent to the network switch at each predetermined control timing, and the network switch is connected to the IO node when the cache server does not hold the measurement data. If the measurement data of the field device is transmitted to the controller, and if the cache server holds the measurement data, the cache server is caused to transmit the measurement data of the field device to the controller, and each of the plurality of controllers receives the measurement data A predetermined calculation is performed based on the data.
[Selection drawing] Fig. 11

Description

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

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

JP 2021-157392 A

In the control system as described above, a plurality of controllers are provided, each controller performs the same processing for the input/output of the field device, and the processing results of each controller are compared to improve the reliability of the operation of the controllers. can be considered. In the case of such redundancy of controllers, in the conventional configuration, a plurality of controllers need to operate in synchronization with each other with high precision, which complicates processing and configuration.

An object of the present disclosure is to enable controller redundancy with a simpler configuration in a field device control system.

A control system according to some embodiments includes:
(1) 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;
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 constant period defined in advance at a constant cycle;
The network switch is
if the cache server does not hold the measurement data, causing the IO node to transmit the measurement data obtained by the field device connected to the IO node to the controller via the network switch;
if the cache server holds the measurement data, causing the cache server to transmit the measurement data acquired by the field device to the controller via the network switch;
Each of the plurality of controllers performs a predetermined operation based on the measurement data received from the IO node or cache server.

In this way, each controller can acquire the same measurement data at control timing from an IO node or cache server via a network switch even when operating asynchronously. In other words, when viewed from the controller 30, it appears that the same device is accessed, but in reality, common measurement data is sent from the IO node 20 or the cache server 40 to all the controllers 30 depending on whether or not there is a cache. can be obtained. Therefore, in the field device control system, it is possible to achieve controller redundancy with a simpler configuration.

(2) In the control system of (1),
The network switch is
if the cache server does not hold the measurement data, requesting 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 is transmitted to the controller, and the measurement data is transmitted to the cache server to be stored as a cache of the measurement data. may

Thus, the network switch receives the measurement data from the IO node and transmits it to the controller and the cache server when the cache server does not hold the measurement data. In this way, since the measured data transmitted to the controller that requested the measured data first is stored in the cache server, the other controllers also acquire the same measured data from the cache server and share the same measured data. It is possible to perform calculations based on

(3) In the control system of (1) or (2),
The network switch is
if the cache server holds the measurement data, requesting the cache server to cache the measurement data;
The cache of measurement data may be transmitted to the controller in response to receiving the cache of measurement data from the cache server based on the request.

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

(4) In the control system of any one of (1) to (3),
The network switch is
holding a management table containing information indicating whether or not the cache server holds the measurement data for each of the control timings;
It may be determined whether or not the cache server holds the measurement data by referring to the management table in response to receiving the request for the measurement data from one of the plurality of controllers. .

In this way, the network switch holds a management table containing information indicating whether or not the cache server holds measurement data at each control timing. It can be determined whether or not measurement data is held.

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

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

(6) In the control system of any one of (1) to (5),
each of the plurality of controllers transmits a calculation result, which is a result of performing the calculation, to the IO node at each control timing based on the measurement data received via the network switch;
The IO node is
comparing the calculation results received from each of the plurality of controllers at each control timing to determine whether the operation of the plurality of controllers is normal;
A determination result as to whether the operations of the plurality of controllers are normal may be output.

In this way, the network switch and the control system can detect an abnormality in a controller by comparing the calculation results of a plurality of controllers. In addition, since it is determined whether or not the operation of the controller is normal based on the operation result received within the control timing, the operation result of the controller that could not be transmitted within the control timing is abnormal. It is possible not to use it for determining whether or not.

A network switch according to some embodiments includes:
(7) A network switch used in a field device control system,
Acquiring from the cache server information as to whether the measurement data is held by the cache server in response to a request for the measurement data acquired by the field device being received from the controller;
if the cache server does not hold the measurement data, sending a request for the measurement data to the 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, upon receiving a request for measurement data from the controller, the network switch distributes the request for measurement data to the IO node or cache server according to whether the cache server holds the measurement data. to send. Therefore, each controller can query the same network device to obtain measurement data common to all controllers.

A method of controlling 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
a step in which 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 constant period defined in advance at a constant cycle;
When the cache server does not hold the measurement data, the network switch transmits the measurement data obtained by the field device connected to the IO node to the IO node via the network switch. and if the cache server holds the measurement data, causing the cache server to transmit the measurement data acquired by the field device to the controller via the network switch;
each of the plurality of controllers performing a predetermined calculation based on the measurement data received from the IO node or the cache server;
including.

In this way, each controller can acquire the same measurement data at control timing from an IO node or cache server via a network switch even when operating asynchronously. In other words, when viewed from the controller 30, it appears that the same device is accessed, but in reality, common measurement data is sent from the IO node 20 or the cache server 40 to all the controllers 30 depending on whether or not there is a cache. can be obtained. Therefore, in the field device control system, it is possible to achieve controller redundancy with a simpler configuration.

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

It is a figure which shows the structure of the control system which concerns on a comparative example. 1 is a diagram showing a schematic configuration example of a control system according to an embodiment; FIG. 3 is a block diagram showing a functional configuration example of the control system of FIG. 2; FIG. 4 is a diagram showing an example of a management table in FIG. 3; FIG. 4 is a diagram showing an example of a management table in FIG. 3; FIG. 3 is a block diagram showing a hardware configuration example of an IO node in FIG. 2; FIG. 3 is a block diagram showing a hardware configuration example of a controller in FIG. 2; FIG. 3 is a block diagram showing a hardware configuration example of a cache server in FIG. 2; FIG. 4 is a sequence chart showing an operation example of the control system according to one embodiment; 4 is a sequence chart showing an operation example of the control system according to one embodiment; 1 is a diagram showing a schematic configuration example of a control system according to an embodiment; FIG. 12 is a block diagram showing a hardware configuration example of the network switch of FIG. 11; FIG. 4 is a sequence chart showing an operation example of the control system according to one embodiment; 4 is a sequence chart showing an operation example of the control system according to one embodiment;

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

The field devices 91 (91a, 91b) are devices that perform at least one of acquisition of measurement data for plant control and plant operation. The IO node 92 is a device to which the field devices 91 (91a, 91b) are connected and functions as an interface with the controllers 93 (93a, 93b). The controller 93 (93a, 93b) is a device that performs computation on the measurement data of the field device 91 (91a, 91b) and controls the field device 91 (91a, 91b) based on the computation result.

In the control system 9, the IO node 92 collects measurement data from the field devices 91 (91a, 91b) at regular intervals (for example, every second). Each of the controllers 93a and 93b acquires measurement data of the field devices 91 (91a and 91b) from the IO node 92 at regular intervals (for example, every second). The controllers 93 ( 93 a and 93 b ) 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 result from the controller 93 (93a, 93b), it outputs the received calculation result to the field device.

In the example of FIG. 1, the control system 9 includes a plurality of controllers 93a and 93b and compares the calculation results of the controllers 93a and 93b in order to improve the reliability of the calculations of the controllers 93 (93a and 93b). Specifically, each of the controllers 93 a and 93 b performs the same calculation on the same measurement data of the field device 91 ( 91 a and 91 b ) and outputs the calculation result to the IO node 92 . The IO node 92 compares the calculation results received from the controllers 93a and 93b. If the calculation results received from the controllers 93a and 93b match, the IO node 92 determines that the results are normal. In order to improve the reliability of computation by making the controllers 93 (93a, 93b) redundant, the controllers 93 (93a, 93b) acquire measurement data at the same timing from the IO node 92, and perform the same computation. It is necessary to

Generally, the timing at which the IO node 92 collects measurement data from the field devices 91 (91a, 91b) and the timing at which the controller 93 (93a, 93b) collects measurement data from the IO node 92 are not synchronized. Therefore, if the controller 93a and the controller 93b acquire the measurement data from the IO node 92 at different timings, the same measurement data may not be acquired. However, in order to match the operation timings of the controllers 93a and 93b, highly accurate time synchronization is required, which complicates processing and configuration. In order to synchronize the data acquisition timings of the IO node 92 and the controllers 93a and 93b, the controllers 93 (93a and 93b) require highly accurate time synchronization.

As described above, in the control system 9 according to the comparative example, the plurality of controllers 93 (93a, 93b) need to operate in synchronization with each other with high accuracy, which complicates the processing and configuration. An object of the present disclosure is to enable a plurality of controllers to acquire measurement data at the same timing without high-precision time synchronization.

<Embodiment 1>
An embodiment of the present disclosure will be described below with reference to the drawings. In each drawing, parts having the same configuration or function are given the same reference numerals. In the description of the present embodiment, overlapping descriptions of the same parts may be appropriately omitted or simplified.

(control system)
FIG. 2 is a diagram showing a schematic configuration example of the control system 1a according to one embodiment. The control system 1 a includes field devices 10 ( 10 a, 10 b ), IO nodes 20 , controllers 30 ( 30 a, 30 b ), cache servers 40 and a network 50 .

The field devices 10 (10a, 10b) are devices that perform at least one of acquisition of measurement data for plant control and plant operation. 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 device 10". The field device 10 outputs measurement data to the IO node 20 and controls 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 functions as an interface between the field device 10 and the controllers 30 (30a, 30b). The IO node 20 is connected to the network 50 and can communicate with the controller 30 (30a, 30b) via the network 50. FIG. In the example of FIG. 2, the control system 1a has 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 computation on the measurement data of the field device 10 and controls the field device 10 based on the computation result. Hereinafter, the controllers 30a and 30b may be collectively referred to as "controller 30". The controller 30 is configured 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 and 30b, but the number of controllers 30 is arbitrary.

The cache server 40 is a device that caches the measurement data acquired from the IO node 20 by whichever of the controllers 30a and 30b accesses the cache server 40 first. 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 that can connect information devices such as the IO node 20, the controller 30, and the cache server 40 in the plant. The network 50 may include a wired or wireless local area network (LAN). Wired local area networks include, for example, Ethernet. The wireless local communication network includes wireless networks complying with wireless communication standards such as Wi-Fi (registered trademark) and WiMAX (registered trademark). Additionally, communication networks using standardized protocols 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, and the like.

In the control system 1a, the IO node 20 collects measurement data from the field device 10 at regular intervals (for example, every second). The IO node 20 stores the collected measurement data in the storage unit 202 (see FIG. 6). Each of the controllers 30a and 30b accesses the cache server 40 at regular intervals (for example, every second) and performs processing for acquiring measurement data of the field devices 91 (91a and 91b). Here, the operations of the IO node 20 and the controllers 30a and 30b are not completely synchronized with each other in terms of time, and they operate separately at regular intervals.

In such a configuration, only one of the plurality of controllers 30 (30a, 30b) that first accesses the cache server 40 accesses the IO node 20 and acquires measurement data. For example, when the controller 30 a first accesses the cache server 40 , the controller 30 a accesses the IO node 20 and acquires 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 cache the measurement data. On the other hand, the controller 30b that accessed the cache server 40 later obtains the cached measurement data from the cache server 40 . Thus, in the control system 1 a , only the controller 30 (for example, the controller 30 a ) that first accessed the cache server 40 acquires the measurement data of the field device 10 from the IO node 20 . Other controllers 30 (for example, the controller 30 b ) acquire cached measurement data from the cache server 40 . Therefore, the control system 1a can ensure that the plurality of controllers 30 (30a, 30b) acquire the same measurement data even if the operations of the controllers are not synchronized with high accuracy. be.

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

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

The control application unit 21 controls the field device 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 necessary for process control. For example, the control application unit 21 collects measurement data from the field devices 10, transmits control data to the field devices 10, and the like.

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

The communication control unit 23 communicates with 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 necessary communication processing according to the connection form with the field device 10, the type of the network 50, and the like.

The controller 30 (30a, 30b) includes a control application unit 31 (31a, 31b), an access route control unit 32 (32a, 32b), and a communication control unit 33 (33a, 33b). Like the IO node 20, the controllers 30 (30a, 30b) may include virtualization units 34 (34a, 34b). The control application unit 31a, the access route control unit 32a, the communication control unit 33a, and the virtualization unit 34a of the controller 30a are connected to the control application unit 31b, the access route control unit 32b, the communication control unit 33b, and the virtualization unit 34a of the controller 30b. It is the same as the part 34b. Therefore, the control application units 31a and 31b, the access route control units 32a and 32b, the communication control units 33a and 33b, and the virtualization units 34a and 34b are hereinafter collectively referred to as "control application unit 31" and "access route control unit 32". , “communication control unit 33”, and “virtualization unit 34”. The control application unit 31, the access route control unit 32, the communication control unit 33, and the virtualization unit 34 of the controller 30 are the control application unit 21, the access route control unit 22, the communication control unit 23, and the virtualization unit 24 of the IO node 20. Since they have the same or similar functions, detailed description is omitted.

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

The management table 41 is a table for managing the access status of the controller 30 to the cache server 40 . 4 and 5 are diagrams showing an example of the management table of FIG. 3. FIG. The cache server 40 retains the identification information of the controller 30 that first accessed the cache server 40 at regular intervals (for example, every second). In the initial state, the management table 41 holds values 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 predetermined period of time for the controller 30 to periodically acquire measurement data. The control timing T001 corresponds to, for example, a period from 0:00:00 to 0:00:01. The control timing T002 corresponds to, for example, a period from 0:00:01 to 0:00:02. The control timing T003 corresponds to, for example, a 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 in length defined by a cycle of 1 second. Note that the period and length of the control timing may be different. For example, the control timing may be a period of 1 second in length determined by a period of 10 seconds. The control timing is determined based on the time measured by the clock unit of the cache server 40, but is determined based on the time measured by a time server such as an NTP (Network Time Protocol) server or another device such as the controller 30. may When the control timing is determined based on the time measured by the time server, it is possible to acquire the control timing that reflects the correct time and maintain the reliability of the control timing. 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 another device such as a time server, thereby maintaining availability.

Although the number of IO nodes 20 is one in the example of FIG. 2, the management table 41 of FIG. holds the identification information of the controller 30 that has accessed the cache server 40 . The management table 41 of FIG. 5 holds identification information of the controller 30 that first accessed the cache server 40 in the control system 1a having two IO nodes 20 (IO-5, IO-6).

For example, in FIG. 4, at the control timing "T001", for the IO nodes 20 with the identification information "IO-1" and "IO-2", the controller 30 (for example, the controller 30a) with the identification information "CNT-1" is the first. , the cache server 40 is accessed. As for the IO node 20 of “IO-3”, the controller 30 (for example, the controller 30b) of the identification information “CNT-2” first accesses the cache server 40 . At the control timing “T002”, for each IO node 20 with identification information “IO-1”, “IO-2” and “IO-3”, the controller 30 (for example, controller 30a) with identification information “CNT-1” first The cache server 40 is accessed. At the control timing “T003”, the controller 30 (for example, the controller 30b) with the identification information “CNT-2” first accesses the cache server 40 for the IO nodes 20 with the identification information “IO-1” and “IO-2”. ing. None of the controllers 30 has accessed the cache server 40 for the IO node 20 with the identification information "IO-3". In the example of FIG. 5, the controller 30 has not yet accessed the cache server 40 for any IO node 20 at any control timing.

When managing accesses to multiple IO nodes 20 by 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 a plurality of controllers 30 to be redundant. For example, the cache server 40 may classify the controllers 30 and the IO nodes 20 into a plurality of control groups according to which controller 30 performs calculation of the measurement data of the field device 10 connected to which IO node 20. good. For example, the management table 41 of FIG. It may indicate the access management of control group 1 to be performed. For example, the management table 41 of FIG. May indicate access control. Controllers 30 included in the same control group perform the same control calculation.

Returning to the description of FIG. The access route 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 route control unit 22, the communication control unit 23, and the virtualization unit 24 of the IO node 20. , detailed description is omitted.

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

(IO node)
FIG. 6 is a block diagram showing a hardware configuration example of the IO node 20 of FIG. The IO node 20 is one or more computer devices that can communicate with each other. The IO node 20 is realized by, for example, a general-purpose computer such as a PC (Personal Computer) or WS (Workstation). may be As shown in FIG. 6 , the IO node 20 includes a control section 201 , a storage section 202 and a communication section 203 .

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

The storage unit 202 includes arbitrary storage modules such as HDD (Hard Disk Drive), SSD (Solid State Drive), ROM (Read-Only Memory), and RAM (Random Access Memory). The storage unit 202 may function, for example, as a main storage device, an auxiliary storage device, or a cache memory. The storage unit 202 stores arbitrary information used for the operation of the IO node 20 . For example, the storage unit 202 may store a system program (operating system), an application program, various information received by the communication unit 203, and the like. The storage unit 202 is not limited to being built in 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 be communicatively connected with other devices such as the field device 10 and the controller 30 by 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 implemented by executing a computer program (program) according to the present embodiment with 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 the computer to execute the processing of steps included in the operation of the IO node 20, thereby causing the computer to implement 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. The program includes information that is used for processing by a computer and that conforms to the program. For example, data that is not a direct instruction to a computer but that has the property of prescribing the processing of the computer corresponds to "things equivalent to a program."

A part or all of the functions of the IO node 20 may be realized by a dedicated circuit included in the control unit 201. FIG. That is, part or all of the functions of the IO node 20 may be realized by hardware. Also, the IO node 20 may be realized by a single computer device, or may be realized by cooperation of a plurality of computer devices.

(controller)
FIG. 7 is a block diagram showing an example hardware configuration of the controller 30 of FIG. Controller 30 is one or more computing devices that can communicate with each other. The controller 30 is implemented by, for example, a general-purpose computer such as a PC or WS, but may also be implemented by a dedicated computer designed for control of an FPGA, plant, or the like. As shown in FIG. 7 , the controller 30 includes a control section 301 , a storage section 302 and a communication section 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 thereof will be omitted. Also, similarly to the IO node 20 , the functions of the controller 30 can be realized by executing the program according to the present embodiment with the processor included in the control unit 301 .

(cache server)
FIG. 8 is a block diagram showing a hardware configuration example of the cache server 40 of FIG. The cache server 40 is one or more computer devices that can communicate with each other. The cache server 40 is realized by, for example, a general-purpose computer such as a PC or WS, but may be realized by an FPGA, a dedicated computer designed for controlling a plant, or the like. As shown in FIG. 8 , the cache server 40 includes a control section 401 , a storage section 402 and a communication section 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 thereof will be omitted. . Also, similarly to the IO node 20 , the functions of the cache server 40 can be realized by executing the program according to the present embodiment with the processor included in the control unit 401 .

(Operation of control system)
9 and 10 are sequence charts showing an operation example of the control system 1a according to one embodiment. The operation of the control system 1a described with reference to FIGS. 9 and 10 may correspond to one control method of the control system 1a. 9 and 10 may be executed under the control of 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. FIG. The processing in FIGS. 9 and 10 is executed at each control timing, for example, every second. 9 and 10 show examples in which the controller 30a first accesses the cache server 40 and then the controller 30b accesses the cache server 40 at certain control timings. FIG. 9 shows processing in which the controller 30a obtains measurement data and performs calculation. FIG. 10 shows processing in which the controller 30b obtains measurement data and performs calculation. An example in which the control system 1a includes one IO node 20 as shown in FIG. 2 will be described below.

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 route 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 the cache of the measurement data inquired in step S1 is stored. For example, the control unit 401 may refer to the management table 41 to determine whether or not access by the controller 30 is recorded for the corresponding control timing and IO node 20, thereby determining whether or not there is a cache. Since the example of FIG. 9 shows the case where the controller 30a accesses for the first time at a certain control timing, 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.

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

Upon receiving the measurement data request from the controller 30a, the control unit 201 of the IO node 20 acquires the measurement data of the field device 10 in step S5. As described above, the IO node 20 collects measurement data from the field device 10 at regular intervals (for example, every second) and stores the collected measurement data in the storage unit 202 . Therefore, the control unit 201 reads the measurement data from the storage unit 202 and acquires the measurement data. Note that the control unit 201 may acquire 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, the control unit 301 of the controller 30a stores the received measurement data in the storage unit 302 and transmits the measurement data to the cache server 40 in step S7.

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

On the other hand, in step S9, the control section 301 of the controller 30a performs predetermined calculation based on the measurement data acquired in step S7. For example, the control application unit 21a of the controller 30a may perform the calculation. The calculation content is set in advance according to the type of the field device 10 or the like.

In step S<b>10 , the control unit 301 of the controller 30 a transmits to the IO node 20 the calculation result obtained by the process of step S<b>9 . Note that the control system 1a may execute the processes of steps S9 and S10 before steps S7 and S8.

Upon receiving the calculation result from the controller 30a, in step S11, the control unit 201 of the IO node 20 causes the storage unit 202 to store and hold the calculation result received from the controller 30a.

Next, in step S21 of FIG. 10, the control unit 301 of the controller 30b asks 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. inquire whether For example, the inquiry may be made by the virtualization unit 34b of the controller 30b.

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

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

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

In step S<b>26 , the control unit 301 of the controller 30 b transmits to the IO node 20 the calculation result obtained by the process of step S<b>25 .

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

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

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

Note that the control unit 301 of each of the plurality of controllers 30a and 30b performs calculation based on the measurement data received from the IO node 20 or the cache server 40, and sends the calculation result to the IO node 20 at each control timing. You may send. The control unit 201 of the IO node 20 compares the calculation results received from each of the plurality of controllers 30a and 30b at each control timing to determine whether the operations of the plurality of controllers 30a and 30b are normal. may The control unit 201 may output a determination result as to whether the operations of the plurality of controllers 30a and 30b are normal. Thus, the control system 1a can detect an abnormality in the controller 30 by comparing the calculation results of the controllers 30a and 30b. In addition, the control system 1a can avoid using the calculation results of the controllers 30a and 30b that have failed to transmit the calculation results within the control timing for determining whether or not the operation is abnormal.

Further, when the control unit 301 of each of the plurality of controllers 30a and 30b acquires the measurement data acquired by the field device 10 connected to the IO node 20 from the IO node 20, the acquired measurement data is transferred to the cache server 40. You may send. When receiving measurement data from the controllers 30 included in the plurality of controllers 30a and 30b, the control unit 401 of the cache server 40 may cause the storage unit 402 to hold the received measurement data. Therefore, the control system 1a caches and holds the measurement data of the controller 30 that first accessed the cache server 40, thereby enabling other controllers 30 to perform calculations based on this measurement data.

Also, the control unit 401 of the cache server 40 may record the identification information of the controller 30 that has received the measurement data in the management table 41 at each control timing. In this way, by recording the identification information of the controller 30 that has sent the measurement data cache, the controller 30 that has sent the cache data can be specified.

Further, the control unit 401 of the cache server 40 holds measurement data acquired by the field device 10 from one of the controllers 30 (for example, the controller 30a) included in the plurality of controllers 30a and 30b at each control timing. A reply to an inquiry from another controller 30 (for example, the controller 30b) may be withheld from the first inquiry as to whether or not the controller 30a is received until measurement data is received from the controller 30a. Specifically, for example, even if an inquiry is received from the controller 30b (S21) from the time the inquiry is received from the controller 30a in step S1 of FIG. You may do so. As a result, when an inquiry is received from another controller 30b while a certain controller 30a is acquiring measurement data from the IO node 20, all the controllers can access the IO node 20 without the other controller 30b Acquisition of the same measurement data can be guaranteed.

In the above embodiment, the cache server 40 holds the management table 41, but each controller 30 also synchronizes with the management table 41 (first management table) of the cache server 40. A management table (second management table) managed in this manner may be held. According to such a configuration, the controller 30 can determine whether the acquisition destination of the measurement data is the IO node 20 or the cache server 40 without inquiring of the cache server 40 . Also, although an example in which the IO node 20 periodically acquires measurement data from the field device 10 has been described, the processing is not limited to such processing. For example, the field devices 10 a and 10 b may independently transmit measurement data to the IO node 20 .

<Embodiment 2>
In the first embodiment, an example in which the virtualization unit 34 of the controller 30 controls the acquisition destination of the measurement data has been described. good.

(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 1 b includes field devices 10 ( 10 a, 10 b ), IO nodes 20 , controllers 30 ( 30 a, 30 b ), cache servers 40 , networks 50 and network switches 60 . Since the functions and configurations of the field devices 10 (10a, 10b), IO nodes 20, controllers 30 (30a, 30b), cache servers 40, and networks 50 are the same as those of the control system 1a of FIG. Only the content different from the configuration of is explained.

In the control system 1b, the network switch 60 holds a management table 61 instead of the cache server 40 or together with the cache server 40. FIG. The management table 61 of the network switch 60 is similar to the management table 41 of the cache server 40, and may contain the same information as the contents illustrated in FIGS. 4 and 5, for example. In the control system 1b, the plurality of controllers 30a and 30b transmit a request to the IO node 20 for measurement data acquired by the field device 10 to the network switch 60 at each control timing. The network switch 60 refers to the management table 61 to determine whether the cache server 40 holds measurement data. When the cache server 40 does not hold the measurement data, the network switch 60 transmits the measurement data acquired by the field device 10 connected to the IO node 20 to the controller 30 via the network switch 60. Let The network switch 60 transmits the measurement data received from the IO node 20 to the cache server 40 to hold it. On the other hand, when the cache server 40 holds 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 plurality of controllers 30 performs predetermined calculations based on measurement data received from the IO nodes 20 or cache servers 40 . Specifically, the network switch 60 may switch the communication destination by rewriting the IP address or the like of the packet received from the controller 30, the IO node 20, and the cache server 40, for example.

According to such a configuration, when viewed from the controller 30, it appears that the same device is being accessed. to acquire common measurement data. Note that even in a configuration including the network switch 60 , the access destination switching may be performed by the access route control section 32 of each controller 30 instead of the network switch 60 .

(network switch)
FIG. 12 is a block diagram showing a hardware configuration example of the network switch 60 of FIG. 11. As shown in FIG. Network switch 60 is one or more computer devices that can communicate with each other. The network switch 60 is implemented by, for example, an FPGA or a dedicated computer designed for control of a plant or the like, but may be implemented by a general-purpose device such as a PC. As shown in FIG. 12 , the network switch 60 includes a control section 601 , a storage section 602 and a communication section 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, so detailed description thereof will be omitted. . Also, like the IO node 20 , the functions of the network switch 60 can be realized by executing the program according to the present embodiment by the processor included in the control unit 601 .

(Operation of control system)
13 and 14 are sequence charts showing an operation example of the control system 1b according to one embodiment. The operation of the control system 11b described with reference to FIGS. 13 and 14 may correspond to one control method of the control system 1b. 13 and 14 are executed under the control of 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. may The processing in FIGS. 13 and 14 is executed at each control timing, for example, every second. 13 and 14 show examples in which the controller 30a first accesses the network switch 60 and then the controller 30b accesses the network switch 60 at certain control timings. FIG. 13 shows processing in which the controller 30a obtains measurement data and performs calculation. FIG. 14 shows processing in which the controller 30b obtains measurement data and performs calculation. An example in which the control system 1b includes one IO node 20 as shown in FIG. 11 will be described below.

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. FIG. For example, the access route 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 the cache server 40 stores the measurement data requested in step S31. For example, the control unit 601 refers to the management table 61 held by its own device, and determines whether or not access by the controller 30 is recorded for the corresponding control timing and IO node 20, and determines whether or not there is a cache. You may Since the example of FIG. 13 shows the case where the controller 30a accesses for the first time at a certain control timing, the control unit 601 determines that there is no cache (step S33).

In step S<b>34 , the control unit 601 of the network switch 60 requests the IO node 20 for measurement data of the field device 10 . For example, the control unit 601 may rewrite the IP address or the like of the packet received from the controller 30a in step S31 and transmit the measurement data request to the IO node 20 .

Upon receiving the measurement data request from the network switch 60, the control unit 201 of the IO node 20 acquires the measurement data of the field device 10 in step S35. As described above, the IO node 20 collects measurement data from the field device 10 at regular intervals (for example, every second) and stores the collected measurement data in the storage unit 202 . Therefore, the control unit 201 reads the measurement data from the storage unit 202 and acquires the measurement data. Note that the control unit 201 may acquire measurement data from the field device 10 in response to receiving a request for measurement data from the network switch 60 .

At step S<b>36 , the control unit 201 of the IO node 20 transmits the measurement data of the field device 10 acquired at step S<b>35 to the network switch 60 .

In step S<b>37 , 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 .

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

In step S<b>39 , the control unit 601 of the network switch 60 transmits the measurement data acquired in step S<b>37 to the cache server 40 .

At step S<b>40 , 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 at the corresponding control timing with the identification information of the controller 30a in the management table 61 of the corresponding control group.

On the other hand, in step S41, the control unit 301 of the controller 30a performs predetermined calculation based on the measurement data acquired in step S38. For example, the control application unit 21a of the controller 30a may perform the calculation. The calculation content is set in advance according to the type of the field device 10 or the like.

In step S<b>42 , the control unit 301 of the controller 30 a transmits to the IO node 20 the computation result obtained by the process of step S<b>41 . Note that the control system 1b may execute the processes of steps S41 and S42 before steps S39 and S40.

Upon receiving the calculation result from the controller 30a, in step S43, the control unit 201 of the IO node 20 causes the storage unit 202 to store and hold the calculation result received from the controller 30a.

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, it stores the received measurement data in the cache database 45 and updates the management table 41 in step S44. For example, the control unit 401 may update the item corresponding to the IO node 20 at the corresponding control timing with the identification information of the controller 30a in the management table 41 of the corresponding control group.

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

In step S52, the control unit 601 of the network switch 60 determines whether or not the cache server 40 stores the measurement data requested in step S51. For example, the control unit 601 may refer to the management table 61 to determine whether or not access by the controller 30 is recorded for the corresponding control timing and IO node 20, thereby determining whether or not there is a cache. Since the example of FIG. 14 shows the case where the controller 30a has already accessed at the corresponding control timing, the control unit 601 determines that there is a cache (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 held in the cache database 45 in step S44 of FIG. For example, the control unit 601 may rewrite the IP address or the like of the packet received from the controller 30b in step S51 and transmit the measurement data request to the cache server 40 . Specifically, the control unit 601 may request caching of measurement data of the relevant control timing stored in association with the identification information of the IO node 20 of the relevant control group.

In step S<b>55 , the control unit 401 of the cache server 40 acquires the cache of the measurement data requested by the network switch 60 from the cache database 45 .

In step S<b>56 , the control unit 401 of the cache server 40 transmits the cache of the measurement data acquired in step S<b>55 to the network switch 60 .

In step S<b>57 , 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 cached measurement data acquired in step S57 to the controller 30b. For example, the control unit 601 may rewrite the IP address or the like of the packet received from the cache server 40 in step S56 and transmit the cached measurement data to the controller 30b.

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

In step S<b>60 , the control unit 301 of the controller 30 b transmits to the IO node 20 the calculation result obtained by the process of step S<b>59 .

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

In step S62, the control unit 201 of the IO node 20 outputs the result determined in step S61. For example, the control unit 201 may output the determination result to the storage unit 202 as a log file. Alternatively, the control unit 201 may display the determination result on a display device (display) 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 make such an output when it is determined in step S61 that it is not normal.

As described above, according to the control systems 1a and 1b according to the present disclosure, it is possible to acquire data at the same timing among the plurality of controllers 30 that operate asynchronously. Therefore, even if the operation of each controller 30 is not synchronized with high accuracy, it is possible to detect an abnormality in the controller 30 by comparing the calculation results of each controller 30 .

Also, the technique of the control systems 1a and 1b may be applied to packet arrival assurance in pub/sub communication such as multicast or broadcast. When performing pub/sub communication using multicast or broadcast, UDP (User Datagram Protocol) is used as a communication protocol. Unlike TCP (Transmission Control Protocol), UDP does not have a delivery confirmation mechanism, and there is no guarantee that transmitted data can be reliably received. Therefore, it is necessary to perform processing when reception is not possible.

For example, in the control system 1a of FIG. 2, the IO node 20 acquires measurement data from the field device 10 at arbitrary timing, and sends control timing information (T001) and measurement data to each node including the controller 30 and the cache server 40. Consider the case of publishing. In this case, each node (controllers 30 a and 30 b and cache server 40 ) waits for data from the IO node 20 and subscribes. When the controller 30 can receive the measurement data of the node to be used at the control timing T001, the data is used to perform the calculation. Also, the controller 30 causes the cache server 40 to hold the received measurement data. When the controllers 30a and 30b cannot receive the measurement data to be used, they transmit a data acquisition request to the cache server 40 and acquire the data.

In this way, when the controller 30 can receive the measurement data at the control timing, the controller 30 performs the calculation based on the measurement data and causes the cache server 40 to hold the measurement data. When the controller 30 fails to receive the measured data at the control timing, it accesses the cache server 40 to acquire necessary measured data and performs a predetermined calculation. Therefore, even when the measurement data of the field device 10 is multicast or broadcast from the IO node 20 instead of 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 an abnormality in the controller 30 by comparing the calculation results of each controller 30 .

The disclosure is not limited to the embodiments described above. For example, multiple blocks shown in the block diagrams may be combined, or a single block may be divided. Instead of being performed in chronological order according to the description, multiple steps described in the flowcharts may be performed in parallel or in a different order depending on the processing power of the device performing each step or as required. . Other modifications are possible without departing from the scope 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 route 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 route 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 route 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 (7)

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;
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 constant period defined in advance at a constant cycle;
The network switch is
based on a management table including information indicating whether or not the cache server holds the measurement data for each control timing in response to receiving the request for the measurement data from any one of the plurality of controllers; , determining whether the cache server holds the measurement data;
if the cache server does not hold the measurement data, causing the IO node to transmit the measurement data obtained by the field device connected to the IO node to the controller via the network switch;
if the cache server holds the measurement data, causing the cache server to transmit the measurement data acquired by the field device to the controller via the network switch;
each of the plurality of controllers performs a predetermined operation based on the measurement data received from the IO node or the cache server;
control system. The network switch is
if the cache server does not hold the measurement data, requesting 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 is transmitted to the controller, and the measurement data is transmitted to the cache server to be stored as a cache of the measurement data. ,
A control system according to claim 1 . The network switch is
if the cache server holds the measurement data, requesting the cache server to cache the measurement data;
transmitting the cache of the measurement data to the controller in response to receiving the cache of the measurement data from the cache server based on the request;
A control system according to claim 1 . 4. The control system according to claim 3 , wherein said network switch holds, as said management table, information including identification information of said controller that has received said measurement data for each of said control timings. each of the plurality of controllers transmits a calculation result, which is a result of performing the calculation, to the IO node at each control timing based on the measurement data received via the network switch;
The IO node is
comparing the calculation results received from each of the plurality of controllers at each control timing to determine whether the operation of the plurality of controllers is normal;
outputting a determination result as to whether the operation of the plurality of controllers is normal;
A control system according to claim 1 . A network switch used in a field device control system,
In response to receiving from a controller a request for the measurement data acquired by the field device , the cache server receives the measurement data based on a management table containing information indicating whether the cache server holds the measurement data. is held ,
if the cache server does not hold the measurement data, sending a request for the measurement data to the IO node to which the field device is connected;
if the cache server holds the measurement data, sending a request for the measurement data to the cache server;
network switch. 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
a step in which 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 constant period defined in advance at a constant cycle;
Information indicating whether or not the cache server holds the measurement data at each control timing in response to the network switch receiving the request for the measurement data from one of the plurality of controllers. Based on the management table included, it is determined whether or not the cache server holds the measurement data, and if the cache server does not hold the measurement data, the IO node via the network switch, When the measurement data acquired by the field device connected to the IO node is transmitted to the controller, and the cache server holds the measurement data, the cache server receives the causing the field device to transmit the acquired measurement data to the controller;
each of the plurality of controllers performing a predetermined operation based on the measurement data received from the IO node or the cache server;
A method of controlling a control system, including

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