In my current project, I am looking to implement a safety function using a safety relay in conjunction with a flame detector as the sensing element. The flame detector features relay contact outputs which I plan to utilize alongside a safety relay to establish the necessary safety measures. This setup is intended to serve as the primary safety function within the system, with the goal of avoiding the use of a safety PLC due to cost and complexity concerns, particularly regarding lifecycle management. While adhering to IEC 61511 standards internally, it's important to note that this application falls between the realms of machine safety and process safety, rather than a Safety Instrumented System (SIS). Despite most safety relays being primarily designed for machine safety applications such as E-Stops and guard doors, I am faced with the challenge of adapting them for a SIL2-rated application. Most safety relays are capable of achieving SIL3 or SIL2 ratings, but the single-channel relay outputs on the sensor I am considering limit its efficiency to SIL1 in typical application scenarios. However, given the abundance of DC on the sensor, I believe it is feasible to meet the required safety level. The key now lies in documenting and substantiating the capability of the safety function to achieve the desired target level within this unique setup. Attached is an image from a Phoenix Contact 2963763 relay datasheet illustrating my approach to this safety function for flame detection, utilizing safety relays instead of a safety PLC. My objective is to confirm that this alternative method is indeed appropriate for the task at hand.
Is the flame detector capable of providing an analog output (4-20MA) that meets SIL2 requirements? If it does, you could potentially connect the 4-20MA output to a SIL2 capable limit controller equipped with 2 complementary relay contacts linking to the safety relay.
Inquiring about the flame detector's analog output (4-20mA) SIL2 compatibility, g.mccormick questioned the possibility of connecting the output to a SIL2 capable limit controller with dual relay contacts for safety relay integration. The flame detector indeed has a 4-20mA signal for non-safety feedback at the PLC. However, searching for a suitable limit value switch like the MACX MCR-SL-UI-REL proved to only convert the signal to a contact output, lacking the necessary de-energization and reset monitoring functions. The objective was to find a simple solution without the need for programming software to comply with IEC 61511 requirements for safety applications. Any recommendations for a limit controller that fits these criteria? Thank you.
Can a second flame detector be utilized to provide dual channels for a safety relay?
tarik1978 inquired about the possibility of using a second flame detector to create 2 channels for a safety relay. It is feasible, but there are two options to consider: wiring the sensors in series through a single channel or wiring them as single channel inputs through a relay that requires 2 enabling inputs. Parallel wiring of two separate sensors as a dual channel device is not recommended unless they are integrated into the same device, like a dual channel E-Stop. This is because variations in the timing of the contacts' rising and falling edges can trigger the safety relay.
When it comes to flame detection safety circuits, it is essential to comply with specific requirements and undergo scrutiny from various departments such as safety, maintenance, and plant engineering. Approval from both state authorities and insurance companies is also necessary. This was the process we followed when upgrading our system in 2005. Although not directly involved in the project, my supervisor outlined the steps that needed to be taken. - James
Looking at your setup, it's clear that you've thought this through pretty well. It's rather uncommon to use safety relays in lieu of a safety PLC, but cost considerations can often force such implementations. In terms of achieving the required SIL level, you may want to consider using a sensor with dual-channel relay outputs instead. This could potentially increase your system's efficiency to SIL2, making it more robust and cost-effective in the long run. Nevertheless, your approach is feasible as long as you carefully document its performance and rigorously test it under variable conditions before implementation. Remember the safety relay will need to go through a functional safety assessment as per IEC 61508 and IEC 61511 standards to ensure all is well. Good luck and keep us posted on your progress.
Your approach for implementing safety function by pairing a safety relay with a flame detector seems quite innovative and cost-effective. Considering the constraints of your project, avoiding a safety PLC for reasons of expense and complexity management appears to be a practical consideration. However, moving forward with this setup, you might face some decision-making related to balancing cost savings against potential risks. The issue of achieving a SIL2 rating with your sensor offering only SIL1 efficiency in usual application is indeed a challenging one, but that doesn't mean it's impossible—your idea to leverage the sensor's DC abundance makes sense. Try to carefully document your methodology and gather substantial proof to support your claim. Be sure to perform rigorous reliability and field testing to ensure that your setup can indeed deliver the promised safety level. Lastly, it's always good to seek a second opinion. Engaging a systems safety engineer or an industry consultant to review your safety function could provide useful insights and inputs that you may have overlooked. Good luck with your project!
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Answer: - Yes, safety relays can be a cost-effective alternative to safety PLCs for flame detection applications. By utilizing relay contact outputs from flame detectors alongside safety relays, one can establish the necessary safety measures within the system.
Answer: - It is important to adhere to relevant safety standards such as IEC 61511 when implementing safety functions using safety relays and flame detectors. Additionally, considering the application falls between machine safety and process safety realms rather than a Safety Instrumented System (SIS) is crucial.
Answer: - While most safety relays can achieve SIL3 or SIL2 ratings, limitations in relay outputs may restrict efficiency to SIL1 in typical scenarios. However, by assessing the abundance of DC on the sensor and documenting the capability of the safety function, it may be feasible to meet the required safety level for SIL2 applications.
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