Yoshio Yoshida1 Masayuki Fukasawa1 Naoyuki Fujimoto1 Masahito Endo1 Rongcai Hu2 Hao Li2
Yokogawa has developed a large-scale, highly reliable, next-generation, plant-wide field wireless system that conforms to the ISA100.11a wireless communication standard for industrial automation. By separating the access point function from the system manager and gateway functions, this system has achieved a more flexible system configuration. It can manage up to 500 field wireless devices and achieves the world's first full system- wide redundancy as well as high reliability. This paper introduces the products and their technologies.
The introduction of wireless technologies into plants is anticipated as one of the measures for implementing field digital solutions not only to reduce cable wiring costs but also to improve plant wide safety/stable operations, operating efficiency, and so on.
To respond to such expectations, Yokogawa has released the world's first field wireless devices that conform to the ISA100.11a standard1 and has accumulated business results by supplying these devices to a wide range of fields everywhere around the world. Through these results and experiences, Yokogawa has understood that, rather than installing field wireless devices separately on a case-by- case basis, large scale plant wide field wireless systems are preferable in order to improve plant production efficiency .
To satisfy this requirement, Yokogawa has developed new products for field wireless systems based on the following three concepts:
This paper outlines a new field wireless system configuration proposed by Yokogawa, the new products composing it, and their technical features.
Figure 1 Example of field wireless system configuration
Figure 1 shows an example of a large scale field wireless system configuration with full redundancy covering from a host system to its field wireless network.
A set of two YFGW410 field wireless management stations connected to each other via a synchronization cable provides redundant wireless network management and gateway functions for the host system and the YFGW510 field wireless access points. In each wireless subnet, the installation of multiple YFGW510s achieves the redundant field wireless network for field wireless devices. A pair of YFGW410s can handle up to 20 subnets and up to 500 field wireless devices. In an environment where the YFGW410 is already operating, the additional connection of the YFGW510 to the field wireless backbone network makes it possible to add a wireless subnet without suspending the field wireless system. This allows for the sequential expansion of the system responding to changes in the site being monitored or controlled.
|Figure 2 Newly developed field wireless system devices|
Figure 2 shows the external views of the new field wireless system devices developed as components of a field wireless system.
The YFGW410 Field Wireless Management Station
The YFGW410, which incorporates the ISA100.11a- compliant wireless network management functions (i.e., system manager and security manager functions) and gateway function, has the following features:
The YFGW510 Field Wireless Access Point
The YFGW510 has the backbone router function conforming to the ISA100.11a. In a large field wireless system, the YFGW510 must cover as many field wireless devices as possible. In addition, multiple YFGW510s are required to be installed at various locations in plants, including hazardous areas, and to communicate with the backbone network through various backbone communication interfaces. To satisfy these requirements, the YFGW510 has the following features:
The YFGW610 Field Wireless Media Converter
The YFGW610 converts the connection interface of the backbone communication between the YFGW410 and YFGW510. The YFGW610, a four port media converter, is installed between the YFGW410 and the YFGW510, and converts the lower level metal network interface connection (for 100BASE-TX) of the YFGW410 to the optical network interface connection (for 100BASE-FX) to connect with the remote YFGW510. This features a low latency of 50 m s enabling high precision time synchronization as well as a wide temperature operating range from - 40°C to 65°C.
Figure 3 shows the redundant system configuration and operation of the YFGW410.
Figure 3 Redundant system configuration of the YFGW410
The YFGW410 employs a stand-by redundant system, whereby if the in-service YFGW410 fails, the stand-by YFGW410 takes over and continues the ongoing process. In the redundant operation, two YFGW410s operate virtually as a single YFGW410. The host system communicates with both by using a single virtual IP address assigned to them. Therefore, even if a switchover occurs, the host system can continue the process regardless of which hardware is in-service. Likewise, accepting requests through the single virtual IP address, the in-service YFGW410s perform such processes as connecting field wireless devices and downloading their settings. When parameters kept in the in-service YFGW410 are changed, they are instantly copied to the stand-by YFGW410 via the synchronization cable. Thus the switchover completes within one second after failure detection, even in a large system.
The faulty YFGW410 can be replaced with a new one without any special settings to it while keeping the system running. The new YFGW410 automatically obtains the configuration information from the in-service one upon the startup, and starts the stand-by operation.
The following describes the improvements in the redundancy for wireless routes comparing conventional field wireless systems:
Figure 4 Advantage of Duocast
If the communication between the primary YFGW510 and field wireless devices fails, the YFGW410 transmits the sensor data received via the secondary YFGW510 to the host system. Because Duocast provides redundant communication paths without any data retransmissions, sensor data is not lost and communication latency does not increase even if the communication through one route fails. Compared with Unicast, which deals with a communication failure by retransmissions, Duocast achieves the same reliability with one half of the communication time.
For data transmitted to field wireless devices such as output values and control parameters, the redundant communication routes are established by consecutive and alternate transmission using Unicast from the primary and secondary YFGW510s to field wireless devices.
The field wireless backbone network, which connects the YFGW410 and the YFGW510, has the following features to achieve a highly reliable, large scale, distributed field wireless system which conforms to the ISA100.11a standard.
Precision Time Synchronization
In the field wireless network based on the ISA100.11a standard, the time division multiplexed communication is performed, where all of the connected devices synchronously communicate within a precision of one msec. This allows stable communication with no data loss caused by wireless signal collision and no latency increased by retransmission even if many field wireless devices are located within a radio wave propagation distance from each other.
When implementing a larger scale field wireless network based on the ISA100.11a, to avoid radio wave interference among distributed subnets and establish the redundant wireless routes using multiple YFGW510s, the following time synchronization technology is introduced:
Other Features of Field Wireless Backbone Communication
The communication between field wireless devices and the YFGW410 via the backbone network is protected by the robust transport layer security encryption based on ISA100.11a. This ensures end to end communication security regardless of the type of communication for the backbone network. Furthermore, the ISA100.11a backbone communication for the next-generation plant wide field wireless system has the following features:
The new field wireless system configured using the YFGW 410/510/610 as main components enables the field wireless to shift from one for simple monitoring applications to one for control applications.
Yokogawa will make it easier to configure the backbone network using existing instrumentation cables, and also will make efforts for achieving the fusion of wireless technologies combining wireless LAN applications and field digital solutions integrating wired and wireless technologies.