Two-Wire Routing for Backup De-Energization of Safety Field Devices

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Solution Overview

Problem

In fully digital safety instrumented systems and distributed control systems, there is a lack of a secondary or backup technique for placing field devices in a safe state, as analog communication links are no longer present, leading to potential unsafe operation when digital communication fails.

Innovation Solution

A two-wire routing device with an upstream communication interface, a two-wire communication and power interface, and a router electronic controller that receives a safe state command, transmits it to a field device as a digital signal, and executes a secondary de-energization scheme by cutting power over the two-wire link to ensure the field device enters a safe state.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If digital communication protocols are used for field devices, then communication efficiency and system modernization are improved, but the ability to de-energize field devices for safety purposes is lost

Engineering Contradiction:

Improvecommunication efficiencyVSAvoidsafety de-energization capability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent combines digital communication functionality with power control functionality into a single two-wire interface. The routing device receives digital safe state commands through the two-wire link and automatically executes power de-energization when safety conditions require it, merging communication and power control functions that were previously separate in analog systems.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The routing device acts as an intermediary between the digital control system and the field device. It receives digital safe state commands, processes them, and executes the appropriate power de-energization action, serving as a mediator that translates digital communication into physical power control to ensure safety.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If analog communication links are replaced with digital protocols, then system modernization and communication capabilities are improved, but backup de-energization techniques are eliminated

Engineering Contradiction:

Improvecommunication capabilitiesVSAvoidbackup de-energization technique

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The routing device is pre-configured with the capability to execute power de-energization actions. When a safe state command is received through the digital two-wire interface, the device has already established the power control pathway and can immediately execute de-energization without requiring separate analog communication infrastructure, thus preparing the system in advance for safety actions.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The two-wire interface serves multiple functions: it provides digital communication for normal operation and simultaneously serves as a control pathway for safe state commands and power de-energization. This multi-functional approach replaces the need for separate analog communication links while maintaining safety capabilities.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Speed

If power is continuously supplied to field devices, then device availability and response time are improved, but safety risks increase when communication fails

Engineering Contradiction:

Improveresponse timeVSAvoidsafety risk from communication failure

Core Design Contradiction:

SpeedVSObject-affected harmful factors

Solution Approach 1:

The routing device monitors the status of field devices through digital communication on the two-wire link. When a safe state command is received or communication failure is detected, the device provides feedback control by automatically executing power de-energization to transition the field device to a safe state, thus closing the safety control loop.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system establishes a pre-programmed response to communication failures or safe state commands. When such conditions occur, the routing device automatically executes power de-energization as a preliminary safety action, preventing potentially harmful continued operation of field devices before any unsafe conditions can manifest.

Inventive Principle:

Principle #9Preliminary anti-action

Data Source

PatentUS12316469B2Secondary control for de-energizing safety field devices with digital protocols

Publication Date: 2025.05.27 FISHER ROSEMOUNT SYST INC

AI summary

A two-wire routing device includes an upstream communication interface for communication with a controller, a two-wire communication and power interface configured to convey communication and power to a field device over a two-wire link, and a router electronic controller. The router electronic controller is coupled to the upstream communication interface and the two-wire communication and power interface. The router electronic controller receives, via the upstream communication interface, a safe state command from the controller, and transmits, via the two-wire communication and power interface, the safe state command to a field device over the two-wire link. The router electronic controller further executes a secondary de-energization scheme for the field device to control a power switch to cut power over the two-wire link to the field device.