With its open and simple specifications, the Modbus protocol is widely used to control device communications in industrial applications. As indicated in the following table, Modbus modes and functions differ depending on cable type.
Yokogawa Engineering Asia Pte. Ltd. was engaged in an upstream supervisory control and data acquisition (SCADA) system project where there was a requirement for Modbus systems that could operate simultaneously as master and slave nodes. As STARDOM field control node (FCN) autonomous controllers allow both Modbus master and slave functions to run simultaneously, they were selected for this project.
While functioning as a Modbus master mode in this application, the FCN polls the fire and gas system (FGS) to obtain data. As a Modbus slave node, it then transmits FGS data to the Yokogawa FAST/TOOLS SCADA system via a Modbus gateway and a WAN. This gateway converts the Modbus RTU protocol to Modbus TCP protocol for communication over the WAN. The serial modules are duplexed for network redundancy.
Figure: System Configuration
Figure: Port name definition in Resource Configurator
The NFLR121 FCN serial communications module has two ports for either RS-422 or RS-485 communications, and each can be configured as slave or master. By installing two of these modules, the second module is made to be a backup.
With STARDOM, the following benefits are expected:
- Reduced installation costs
- Simplified system configuration
- Increased system reliability
|Figure: Setting of virtual name for port in POU|
STARDOM supports the IEC61131-3 programming language. The following two engineering tools are available:
- Resource Configurator: for hardware settings
- Logic Designer: for application logic
By keeping the application logic separate from the physical addresses, engineers can write programs for specific applications without having to consider the hardware configuration. This allows programs to be reused and improves engineering efficiency. The following screenshot from the Resource Configurator tool shows how the virtual name for a physical port is defined. In this case, SERIAL 1 is set for port1 and SERIAL 2 is set for port2 of the NFLR121 module.
By setting a virtual name for the program organization unit (POU) parameter, it is possible to link the physical hardware and the application logic. In the following figure, SERIAL 1 is set for SD_CMDBSM_BM_OPEN, which executes a Modbus master task. This specifies that port1 on an NFLR121 module is used as the communications port.
The NFLR121 FCN serial communications module has two ports for either RS-422 or RS-485 communications that support communication speeds between 300 bps and 115.2 kbps. In this project, one port was set as a Modbus master and the other as a Modbus slave. For redundancy purposes, two modules are installed in the following side-by-side configuration:
|PSU Power Supply Unit||PSU Power Supply Unit||CPU||CPU||Spare||AI||DI||DO||COM||COM|
Figure: Unit Configuration
For this application, the following tasks were carried out in the sequence shown:
- Port configuration
- Modbus RTU master and slave programming for the same module
- Redundant Modbus RTU slave programming
|Figure: Setting of wiring method for port 2 on NFLR121|
With the Resource Configurator, the following communication settings were made for each port:
- Port name
- Wiring method (2 wire/ 4 wire connection)
- Half duplex / full duplex
- Baud rate
- Data bits
- Parity setting
Programming the Same Module as Modbus RTU Master and Slave
|Figure: Port name definition with Resource Configurator|
For this application, port name SERIAL 1 was set to port 1 and port name SERIAL 2 was set to port 2 for the NFLR121 module in slot 9.
As shown below, two POUs were used in this application: SD_CMDBSM_BM_OPEN POU for the Modbus RTU master node and SD_CMDBSM_BS_OPEN POU for the slave node. Port 1 on the NFLR121 module was used for communication as a Modbus RTU master node and port 2 was used as a slave node.
Redundant Modbus RTU Slave Programming
|Figure: Port name definition with Resource Configurator|
NFLR121 modules were installed in slots 9 and 10. In this application, port name SERIAL 3 was set to port 1 and SERIAL 4 was set to port 2 for the redundant NFLR121 module in slot 10.
The two SD_CMDBSM_BS_OPEN POUs shown below were used in this application. Port 2 of the NFLR121 module in slot 9 and port 2 of the NFLR121 module in slot 10 were used for communication as a Modbus RTU slave node. In the event of a failure of port 2 on the NFLR121 module in slot 9, communication would not be disrupted.
Each of the communications modules on a STARDOM FCN autonomous controller can simultaneously function as Modbus master and slave nodes without affecting the other settings in the customer site. The use of two modules makes communications fully redundant.
In this application, the FCN Modbus master node simultaneously polls data from the FGS while the Modbus slave node transmits the FGS data to FAST/TOOLS. This keeps installation costs to a minimum. Furthermore, the use of the redundant module configuration ensures that there will be no interruption in the communications between FAST/TOOLS and the FCN autonomous controller.
Apă & Ape Uzate
Yokogawa has been providing control solutions for sustainable water production by developing more energy-efficient technology, helping to reduce the carbon footprint of operations, and building rock-solid products that protect the environment from contaminants. With our leading-edge technology and extensive application know-how, we work with you to provide sustainable water solutions that boost your business and add high value throughout the plant lifecycle. Our technology and products improve the performance of plants and ensure that they can operate competitively in today's water markets, and also reduce their running costs. Yokogawa supports a wide range of water control applications in both the municipal and industrial water markets.
In the mid 1970s, Yokogawa entered the power business with the release of the EBS Electric Control System. Since then, Yokogawa has steadfastly continued with the development of our technologies and capabilities for providing the best services and solutions to our customers worldwide.
Yokogawa has operated the global power solutions network to play a more active role in the dynamic global power market. This has allowed closer teamwork within Yokogawa, bringing together our global resources and industry know-how. Yokogawa's power industry experts work together to bring each customer the solution that best suits their sophisticated requirements.
Epurarea Apelor Uzate
Wastewater treatment plants use many motors, pumps, blowers, etc., and so it is important to reduce their electricity consumption in order to reduce running costs. Yokogawa provides optimum control solutions to improve energy efficiency.
Offshore (FPSO FLNG & FSRU)
Offshore exploration and production requires maximum uptime under harsh conditions. Manned and unmanned facilities need reliable integrated control and safety systems (ICSS) with advanced remote monitoring capabilities. Yokogawa has state-of-the-art technology and extensive experience in executing offshore projects of all sizes and automation levels of complexity.
Petrol & Gaze
Yokogawa has a wealth of experience in every part of the oil and gas business, from offshore and onshore facilities to pipelines, terminals, and deepwater operations. We provide solutions that enhance safety, ensure accurate and reliable operation, and increase plant efficiency.
Yokogawa provides optimum solutions to improve the reliable operation of water treatment plants. These solutions include sophisticated technologies, unsurpassed product quality, and extensive application know-how throughout the lifecycle.
The upstream industry includes offshore and onshore activities including wellhead automation, fractionation, completion, and separation to recover and prepare underground or underwater crude oil and natural gas.
As petroleum is brought to the surface, it must be separated prior to transport. Primary and secondary separation stages commonly distribute gas flow, water flow, and oil flow in three phase separation. Gas movement requires pipeline and can include a fractionation process in the upstream stage prior to movement. Liquids can be placed into a tanks or pipelines and sent for processing, requiring accurate level measurements.
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