Let’s say you are asked to be a Design Engineer for a day and are tasked to come up with a Process Control Safety System. What are the questions you should ask?
- What happens to the Safety Instrumented Systems (SIS) when the relay contact is welded?
- When did it happen?
- Where can you find this faulty relay?
- Why did this happen?
- Who will be responsible for monitoring this fault?
Safety Relays are devices that implement safety functions. In the event of a hazard, a safety relay must work to reduce risk to an acceptable level. The safety relay must initiate a safe and reliable response as well as monitor the integrity of its function.
The Process Automation Fire & Gas System is always on standby mode and it becomes more important to have multiple diagnostics to make sure the relays used in the Fire and Gas System Safety remain functional with all wiring connected.
7 Functions the ideal safety relay should have for Fire & Gas Systems:
- Power loss diagnostics to field devices such as the Beacons, Solenoid Valves and Fire Sounders.
- Field devices disconnection diagnostics.
- Alerts when Field Devices short circuit.
- Welded relay contacts diagnostics.
- Able to Proof Test relay points without the use of external power.
- Diagnostics via the same cable to the relay coil by the use of test pulse filtering. This also saves money as there is no need for additional DI cards and cables for monitoring function.
- Option for redundant connection to the relay coil.
The Phoenix Contact PSR-PC50 series SIL Coupling Relay has the 7 functions you are looking for and it can also be used for power adaptation and electrical isolation in Safe-State-ON applications up to SIL 3 according to IEC 61508 as well as IEC 61511.
This category 3 device is designed for installation in zone 2 potentially explosive areas. By filtering the controller test pulses, premature failure of the safety relays is prevented. The contact side is fully monitored for open circuits and short circuits as well as load and diagnostics supply voltage. If an error occurs, the internal device input impedance is affected. As such, the test pulses sent from the controller are disrupted and the error is reported to the corresponding digital output without additional wiring effort.
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