Industrial Safety Systems With Redundant Communications Networks
•White Paper: Industrial Safety Systems With Redundant Communications Networks
Introduction
Dramatic shifts in electronics technology over the past five years have affected the design of industrial safety systems for oil/gas applications, as well as applications in other process industries. Multi-drop serial communications networks are slowly replacing the long standard 4-20mA current loop for measuring process variables.
Two purposes are served by this change: it provides more information about the process to the process control computer, and it significantly reduces installation-wiring costs. Instead of each instrument being wired directly to the control room in a plant, a multi-drop network is implemented using one network cable. While such networks may be based on different protocols and hardware specifications, they all provide the same benefits: reduced costs and better control of plant operations.
Employing serial communications for safety instruments has been slower to find acceptance. Safety instruments are installed for the protection of personnel and property, usually under state or federal regulations. It has been difficult to convince plant safety engineers to give up their hard-wired solution for so-called "unreliable" communications networks.
To allay these concerns, one method developed is to provide a dual-redundant serial communications network. A separate communications card in the DCS system is connected to each network. Another alternative is separate distributed control systems (DCS's), one connected to each network that results in complete system redundancy.
There are a number of inherent advantages to designing a dual-redundant serial communications network for industrial safety instruments. This type of network results in the ability to communicate on either communication channel separately, or with both channels simultaneously. Such versatility provides the ability to work with many different plant control system configurations.
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