Tag Archives: Safety

Why Use Safety Relays?

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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:

  1. Power loss diagnostics to field devices such as the Beacons, Solenoid Valves and Fire Sounders.
  2. Field devices disconnection diagnostics.
  3. Alerts when Field Devices short circuit.
  4. Welded relay contacts diagnostics.
  5. Able to Proof Test relay points without the use of external power.
  6. 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.
  7. Option for redundant connection to the relay coil.
Safety Relay Connections

Safety Relay Connections

 

PSR-PC50 Series SIL Coupling Relay

PSR-PC50 Series SIL Coupling Relay

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.

 

If you have any questions or want to know more about this product, please feel free to send me an enquiry via the form below and a product representation can be arranged to discuss in more detail.

 

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Safety is by Choice, Not by Chance.

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Phoenix Contact's Safety RelaysAre you selecting a safety relay just to meet the SIL3 requirements?

Who will be responsible for conducting the Proof Test to ensure it is still safety relays are still safe to use?

Which is critical? Safety relays without diagnostics or the Safety relays with diagnostics?

Safety is a Choice, Not by Chance

The graphics below explains the functional principle of the force guided /positive driven contacts in the event of a welded contacts and that’s where the normally closed contacts come into action to provide feedback to inform the system of the failure in relay contacts.

In this case when the relay is de-energized, the normally closed contact cannot close properly having a gap of 0.5mm.

Animation of how Force-guided relays work

Click the image to see the animation of how Force-guided relays work

Safety relays for ESD-Emergency Shut-Down Systems should have:

1) Force guided relay enables a feedback path just in case of welded contacts eliminate the need for and simplifies Proof Testing. (ESD-Emergency Shut Down and F&G-Fire & Gas systems)

Emergency Shut Down System Circuit

Emergency Shut Down System Circuit

Safety relays for F&G-Fire & Gas Systems should have:

The diagram below shows connection details for a safety relay used by Fire & Gas Systems. The Fire & Gas System is always on standby mode and it becomes more important to have multiple diagnostics to make sure the Fire and Gas System Safety Relay is still functional and all wirings are connected.

Fire & Gas System

Fire & Gas System

  1. Diagnostics for lost power input to field devices: Beacons, Solenoid Valves, Fire Alarm Bell.
  2. Field devices disconnection diagnostics.
  3. Short circuit field device diagnostics.
  4. Diagnostics for any welded contacts.
  5. Proof Test points (TP1, TP2, TP3) without the use of external power.
  6. All diagnostics via the same cable (A1,A2) by the use of test pulse filtering.
  7. Option for redundant connection (A1’, A2’).

If you have sales enquires to know more about this product, please feel free to send me an enquiry and a sales visit can be arranged to discuss in more detail.

What product(s) would you like more information on? (required)