Issue
What is the behavior of Sigma controllers using global communications when the network fails?
Product Line
Satchwell BAS & SigmaEnvironment
Satchwell Sigma
Cause
A site is preparing for a planned network shutdown or has experienced an unexpected network failure. Understanding how Sigma controllers respond is critical for maintaining operational continuity, especially for systems controlling critical plant equipment.
Resolution
When the network fails:
- Sigma controllers continue to operate using the last known value of the global variable.
- No updates or changes to global values will be received or processed during the outage.
- Controllers will not respond to changes in global variables until communication is restored.
Best Practice Recommendations
- Design with resilience in mind: If a controller manages critical systems, ensure fallback logic or local overrides are programmed.
- Document expected behavior during outages for operational teams.
- Test failover scenarios to validate controller responses and ensure safety.
