Abstract: This paper mainly discusses the Modbus communication interface mode, communication protocol format, and communication capabilities of the NETWORK6000 decentralized control system T103 controller, and the connection scheme of the data communication between the NETWORKWORK6000 decentralized control system and the Modbus communication interface, temperature patrol meter, and SOE meter.
One of the most important ideas for the design of decentralized control systems is centralized information and decentralized control. From its birth, development, and to the present, data networks are an important part of it. It is the "centralization" and "decentralization" of DCS. This kind of thinking is one of the key components.In the early stages of its development, major DCS manufacturers have developed high-performance network products for their own DCS, but with the further increase in the integration of industrial process control system requirements for network products It is no longer just the performance of reliable and excellent data transmission capabilities, the network's open performance has increasingly become an important indicator of the quality of its control system.
The NETWORK6000 decentralized control system (UK EUROTHERM products) complies with this trend, from the highest to the lowest Ethemet network, LIN network, and ALIN network. The Ethernet network can be connected to external devices that conform to the Ethernet communication protocol. Communication; LIN network connects the operator station of the decentralized control system with the T103 controller; the ALIN network completes the communication between the T103 controller and the process I/O modules. On the T103 controller, there is an RS/485 serial communication port (the Modicon Modbus protocol is fixed on the T103 controller). It is easy to communicate with an external real-time control device that supports the Modbus communication protocol. It has an Ethernet network and a Modbus interface. The two open data communication channels make the NETWORK6000 decentralized control a completely open control system.
Two T103 controller's Moudbus communication protocol NETWOK distributed control system T103 controller serial Modbus communication protocol has been solidified in T103, is part of the T103 controller software, can be easily and flexibly configured; because Modbus is an open asynchronous Serial communication protocol, so its communication protocol is completely transparent to the user, so the user's main task is to understand and determine the Modbus protocol information format and its related to the user's connection between NETWORK6000 and external real-time monitoring equipment. parameter.
The Modbus protocol is a serial communication protocol that includes master-slave reply and broadcast. It was first developed by the GOULD company in the US and applied to its PhC product. Because the communication protocol has a perfect command set and a clear and concise organization concept. At present, it has become a typical serial communication protocol and has been widely used. Due to the low speed of asynchronous serial communication, Modbm generally uses master-slave communication in the application. A master station and multiple slave stations are connected to the Modbus network. The master station is responsible for the management of the entire Modbus network. In order to actively transmit data online. A plurality of slave stations distinguished from each other by the slave station number cannot actively perform any action on the network. The slave station sends data to the network only when it receives a data request command from the master station.
The Modbus interface of the T103 controller uses Modicon Modbus RTU. The Modbus RTU protocol command words include the start bit, slave number, function code, data group, and CRC checksum of the command. The master system selects the slave device to be communicated with by the slave station number in the command, and uses the function code and data group to submit the data request to the slave device. After the slave device receives the request data command from the master system, it performs the corresponding action according to the function code requirements. The command word format returned by it also contains the start bit, slave device number, function code, data group, and CRC checksum. . The on-line equipment generates a CRC code according to the received command word and compares it with the CRC check code carried by the command word. If the two CRC codes are equal, the communication is deemed to be successful, otherwise the communication failure is marked.
The following uses the 03 function code as an example to illustrate the general rules of data transmission on the Modbus network in the master-slave communication mode. Using the 03 function code to read data from the slave station is a common method. The original PLC concept is ReadHoldingRegisters. The actual online data is shown in Table 1. First, the master station sends a data request to the slave station to make the command word. The slave station number in the example is 11 and the meaning of the data group is the starting address and data amount of the requested data. Such a command is sent to the No. 11 slave device on the Internet, requesting 3 data from 006B.
When the slave station No. 11 receives such a command word, it will return the command word as shown in Table 2. The function code requested by the master station is returned as it is, indicating that the slave station has correctly received the master station request command. The data group contains the data group length and each data required by the master station. In this example, slave number 1l returns 6 bytes of data, which are 022B, 0001, and 0002, respectively. When the Lord. After receiving this command word, the station marks the completion of this communication.
The Modbus configuration in the T103 controller is based on the concept of objects based on Modubs data tables. The T103 controller can be used as a master station or a slave station on the Modubs network. As a slave station, this station has a slave station number, in which the data composition is represented by a data table. In this table, the connection of the address and data of the data on the Mot,bus network to the T103 controller database is defined. As a master station, the data consists of a maximum of 16 data tables. For each data table, there is a station number to indicate which data from this data table will be transmitted with the corresponding data in the slave station.
The T103 controller can manage up to 16 slaves. There are two methods of communication management: By default, 16 tables are scanned in a cyclical manner in sequence; data transmission can also be controlled for any table, and the control conditions are configured using T103 control data. Therefore, the Modbus configuration in T103 provides us with great convenience and can be used to complete some of the more complex online behavior.
From the above discussion, it can be known that the role of the master station is critical on the Modbus. The working state is normal or not, and it is related to whether the entire Modbus work is normal. The T103 controller is the main station in the design. This is mainly based on the high reliability of the T103. Of course, considering the flow of data, the T103 controller is used as a slave. If it is not working properly, the data transmission in the design cannot be completed. Therefore, it is defined that the T103 controller is the master station, and the device to be communicated with is defined as the design of the slave station should be a more reasonable configuration.
Three communication capabilities If an analog measurement point is calculated by three floating-point numbers, plus the start bit, the device slave station number, function code, data group, CRC checksum, etc., there are an average of about 54 bits, such as Modbus. Select 19200bit/s for the communication rate, and 40% for the communication load, and then transmit 142 analog measurement points per second. If the external device to be communicated is a temperature monitoring instrument, and the scanning speed of the general temperature monitoring instrument is 1 second in two seconds and the scanning period of a 60-point temperature measuring instrument is 2 minutes, theoretically a T103 has The communication capability of up to 280 60-point temperature testers, and it will not affect the speed of data response due to the Modbus communication capabilities.
Implementation of four application programs Two 125MW units at Nanjing Shimonoseki Power Plant use the NEqWORK6(X)0 decentralized control system to achieve unit data acquisition and closed-loop control functions. In order to save investment, the project implementation program successfully completed communication between six temperature monitoring instruments (about 360 temperature parameters) and one SOE meter (parameter switch parameters) through the Modbus interface of the T103 controller and DCS. The sharing of test data. Because the data transmission of the patrol meter is relatively simple, for each patrol meter, we have designed and configured a data table in the T103 controller. The T103 controller periodically sends data request commands to the patrol meter to complete the patrol. The instrument data is refreshed in the DCS; for the SOE instrument, it only needs to transmit the accident data sheet to the T103 controller in the event of a unit accident. So how can the T103 know that an SOE meter has an accident before sending a data request command to it? The plan is to design two data tables for SOE meters, one for the accident data sheet and the other for the accident status tag table. Under normal circumstances, the T103 controller periodically sends the request for the accident flag to the SOE. Once the accident flag is found, it is considered that an accident has occurred. Then the T103 controller sends a data request command to the SOE. In this Modbus network configuration design, only the T103 controller can actively send data. In this way, for the data communication capability and the very strong serial communication method, it can greatly reduce the load of online communication, and it is very significant to use the Modbus network resources rationally.
In the actual implementation of the program, the relevant parameters of Modbus are unified as follows:
Communication Protocol: ModbusRTU
Serial port type: RS~422
Baud rate: 9600BPS
Odd/even parity: No data bits: 8 bytes Stop bits: 1 bit No hardware handshaking 5 Conclusion The Modbus function of the T103 controller discussed here is similar to the fieldbus. Therefore, in addition to the equipment discussed in this case, the power plant has The control system of the M0dbus interface (such as the program control system) can also communicate data with the NETWORK6000 distributed control system in such a communication interface form to achieve data sharing. This has certain practical significance for improving the degree of integration of the process system and reducing the control system cost.
NETWORK6000 distributed control system with Modbus as an effective standard serial communication interface,
Makes the entire system's network more open. Due to the versatility of Modbus, the T103 can be interconnected with various devices running the Modbus protocol. At the same time, due to the openness and simplicity of the Modubs protocol, it is convenient for manufacturers to develop devices that support Modbus. Moreover, because the NETWORK6000 system Modbus configuration tool is convenient and flexible, more engineering designers have provided a stronger means of serial communication.
Looking at the development process of the decentralized control system and looking forward to its development trend, we believe that in terms of the openness of the system network, it is not appropriate to stay in the serial communication mode; at the same time, the DCS remote I installed in the field The development of /0 also requires the introduction of a high-performance fieldbus. If a general-purpose, standard, open fieldbus network can emerge, then this will be what we would like to see. It will be to include the NETWORK 6000 manufacturing. A new issue raised by DCS vendors including vendors.
One of the most important ideas for the design of decentralized control systems is centralized information and decentralized control. From its birth, development, and to the present, data networks are an important part of it. It is the "centralization" and "decentralization" of DCS. This kind of thinking is one of the key components.In the early stages of its development, major DCS manufacturers have developed high-performance network products for their own DCS, but with the further increase in the integration of industrial process control system requirements for network products It is no longer just the performance of reliable and excellent data transmission capabilities, the network's open performance has increasingly become an important indicator of the quality of its control system.
The NETWORK6000 decentralized control system (UK EUROTHERM products) complies with this trend, from the highest to the lowest Ethemet network, LIN network, and ALIN network. The Ethernet network can be connected to external devices that conform to the Ethernet communication protocol. Communication; LIN network connects the operator station of the decentralized control system with the T103 controller; the ALIN network completes the communication between the T103 controller and the process I/O modules. On the T103 controller, there is an RS/485 serial communication port (the Modicon Modbus protocol is fixed on the T103 controller). It is easy to communicate with an external real-time control device that supports the Modbus communication protocol. It has an Ethernet network and a Modbus interface. The two open data communication channels make the NETWORK6000 decentralized control a completely open control system.
The Modbus protocol is a serial communication protocol that includes master-slave reply and broadcast. It was first developed by the GOULD company in the US and applied to its PhC product. Because the communication protocol has a perfect command set and a clear and concise organization concept. At present, it has become a typical serial communication protocol and has been widely used. Due to the low speed of asynchronous serial communication, Modbm generally uses master-slave communication in the application. A master station and multiple slave stations are connected to the Modbus network. The master station is responsible for the management of the entire Modbus network. In order to actively transmit data online. A plurality of slave stations distinguished from each other by the slave station number cannot actively perform any action on the network. The slave station sends data to the network only when it receives a data request command from the master station.
The Modbus interface of the T103 controller uses Modicon Modbus RTU. The Modbus RTU protocol command words include the start bit, slave number, function code, data group, and CRC checksum of the command. The master system selects the slave device to be communicated with by the slave station number in the command, and uses the function code and data group to submit the data request to the slave device. After the slave device receives the request data command from the master system, it performs the corresponding action according to the function code requirements. The command word format returned by it also contains the start bit, slave device number, function code, data group, and CRC checksum. . The on-line equipment generates a CRC code according to the received command word and compares it with the CRC check code carried by the command word. If the two CRC codes are equal, the communication is deemed to be successful, otherwise the communication failure is marked.
The following uses the 03 function code as an example to illustrate the general rules of data transmission on the Modbus network in the master-slave communication mode. Using the 03 function code to read data from the slave station is a common method. The original PLC concept is ReadHoldingRegisters. The actual online data is shown in Table 1. First, the master station sends a data request to the slave station to make the command word. The slave station number in the example is 11 and the meaning of the data group is the starting address and data amount of the requested data. Such a command is sent to the No. 11 slave device on the Internet, requesting 3 data from 006B.
When the slave station No. 11 receives such a command word, it will return the command word as shown in Table 2. The function code requested by the master station is returned as it is, indicating that the slave station has correctly received the master station request command. The data group contains the data group length and each data required by the master station. In this example, slave number 1l returns 6 bytes of data, which are 022B, 0001, and 0002, respectively. When the Lord. After receiving this command word, the station marks the completion of this communication.
The Modbus configuration in the T103 controller is based on the concept of objects based on Modubs data tables. The T103 controller can be used as a master station or a slave station on the Modubs network. As a slave station, this station has a slave station number, in which the data composition is represented by a data table. In this table, the connection of the address and data of the data on the Mot,bus network to the T103 controller database is defined. As a master station, the data consists of a maximum of 16 data tables. For each data table, there is a station number to indicate which data from this data table will be transmitted with the corresponding data in the slave station.
The T103 controller can manage up to 16 slaves. There are two methods of communication management: By default, 16 tables are scanned in a cyclical manner in sequence; data transmission can also be controlled for any table, and the control conditions are configured using T103 control data. Therefore, the Modbus configuration in T103 provides us with great convenience and can be used to complete some of the more complex online behavior.
From the above discussion, it can be known that the role of the master station is critical on the Modbus. The working state is normal or not, and it is related to whether the entire Modbus work is normal. The T103 controller is the main station in the design. This is mainly based on the high reliability of the T103. Of course, considering the flow of data, the T103 controller is used as a slave. If it is not working properly, the data transmission in the design cannot be completed. Therefore, it is defined that the T103 controller is the master station, and the device to be communicated with is defined as the design of the slave station should be a more reasonable configuration.
Three communication capabilities If an analog measurement point is calculated by three floating-point numbers, plus the start bit, the device slave station number, function code, data group, CRC checksum, etc., there are an average of about 54 bits, such as Modbus. Select 19200bit/s for the communication rate, and 40% for the communication load, and then transmit 142 analog measurement points per second. If the external device to be communicated is a temperature monitoring instrument, and the scanning speed of the general temperature monitoring instrument is 1 second in two seconds and the scanning period of a 60-point temperature measuring instrument is 2 minutes, theoretically a T103 has The communication capability of up to 280 60-point temperature testers, and it will not affect the speed of data response due to the Modbus communication capabilities.
Implementation of four application programs Two 125MW units at Nanjing Shimonoseki Power Plant use the NEqWORK6(X)0 decentralized control system to achieve unit data acquisition and closed-loop control functions. In order to save investment, the project implementation program successfully completed communication between six temperature monitoring instruments (about 360 temperature parameters) and one SOE meter (parameter switch parameters) through the Modbus interface of the T103 controller and DCS. The sharing of test data. Because the data transmission of the patrol meter is relatively simple, for each patrol meter, we have designed and configured a data table in the T103 controller. The T103 controller periodically sends data request commands to the patrol meter to complete the patrol. The instrument data is refreshed in the DCS; for the SOE instrument, it only needs to transmit the accident data sheet to the T103 controller in the event of a unit accident. So how can the T103 know that an SOE meter has an accident before sending a data request command to it? The plan is to design two data tables for SOE meters, one for the accident data sheet and the other for the accident status tag table. Under normal circumstances, the T103 controller periodically sends the request for the accident flag to the SOE. Once the accident flag is found, it is considered that an accident has occurred. Then the T103 controller sends a data request command to the SOE. In this Modbus network configuration design, only the T103 controller can actively send data. In this way, for the data communication capability and the very strong serial communication method, it can greatly reduce the load of online communication, and it is very significant to use the Modbus network resources rationally.
In the actual implementation of the program, the relevant parameters of Modbus are unified as follows:
Communication Protocol: ModbusRTU
Serial port type: RS~422
Baud rate: 9600BPS
Odd/even parity: No data bits: 8 bytes Stop bits: 1 bit No hardware handshaking 5 Conclusion The Modbus function of the T103 controller discussed here is similar to the fieldbus. Therefore, in addition to the equipment discussed in this case, the power plant has The control system of the M0dbus interface (such as the program control system) can also communicate data with the NETWORK6000 distributed control system in such a communication interface form to achieve data sharing. This has certain practical significance for improving the degree of integration of the process system and reducing the control system cost.
NETWORK6000 distributed control system with Modbus as an effective standard serial communication interface,
Makes the entire system's network more open. Due to the versatility of Modbus, the T103 can be interconnected with various devices running the Modbus protocol. At the same time, due to the openness and simplicity of the Modubs protocol, it is convenient for manufacturers to develop devices that support Modbus. Moreover, because the NETWORK6000 system Modbus configuration tool is convenient and flexible, more engineering designers have provided a stronger means of serial communication.
Looking at the development process of the decentralized control system and looking forward to its development trend, we believe that in terms of the openness of the system network, it is not appropriate to stay in the serial communication mode; at the same time, the DCS remote I installed in the field The development of /0 also requires the introduction of a high-performance fieldbus. If a general-purpose, standard, open fieldbus network can emerge, then this will be what we would like to see. It will be to include the NETWORK 6000 manufacturing. A new issue raised by DCS vendors including vendors.
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