Relay Circuit Self-Test via Parallel Contact Pairs
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Solution Overview
Problem
Safety relays with forcibly guided contacts in industrial processes face reliability concerns due to potential failures that go undetected until energization, leading to uncertainty and the need for periodic shutdowns for verification, resulting in downtime.
Innovation Solution
A relay circuit with four relays arranged in pairs, using microcontroller-operated forcibly guided contacts to test and verify the functionality of each relay without interrupting the process, allowing for self-testing and monitoring as an automated process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If periodic verifications are performed to check relay operation and reliability, then reliability is improved, but system downtime increases
Solution Approach 1:
The patent applies preliminary action by performing self-tests on relay contacts during normal operation before failures occur. The test circuitry proactively checks contact resistance and integrity while the relay is still functioning, allowing detection of degradation trends and potential failures before they affect safety-critical operations, thus avoiding unplanned downtime and maintenance shutdowns.
2Reliability
If relays are energized only in case of safety issues, then safety function is improved, but detection capability worsens
Solution Approach 1:
The system performs preliminary self-tests on relay contacts during normal operation before actual safety-critical events occur. By proactively measuring contact resistance and integrity while the relay is still energized and functioning, the system detects potential failures early, allowing maintenance to be scheduled during non-critical periods rather than waiting for failures during safety events.
Solution Approach 2:
The relay circuit performs self-testing through integrated test circuitry that automatically measures contact resistance and integrity without external intervention. The system monitors its own health status continuously, generating diagnostic information about contact condition, which enables predictive maintenance and reduces the need for manual testing and system shutdowns.
Data Source
AI summary
A relay circuit and a method for performing a self-test. The relay circuit has four relays, each relay having a first forcibly guided contact and a second forcibly guided contact. The four relays are arranged in a first and a second pair of two in series connected first forcibly guided contacts. The first and second relay pair are arranged in parallel between a power supply connection and a load connection for switching a power supply to a load through the first forcibly guided contacts. Such a relay circuit enables supplying power via one of the relay pairs, while cutting power via the other relay pair, which facilitates testing of the relay pair which has cut power without interrupting the process supervised by the Safety Instrumented System which the relay circuit forms part of.