Weidmuller SIL 3 Safety Relay
04 November 2009
Weidmüller has launched the “WRS 24Vdc SIL 3” safety relay for emergency shutdown of process industry plants and plant components.
The Technical Inspection Agency TÜV NORD has certified the safety relay according to EN 61508 to safety requirement level SIL 3. The “SIL circuit” has a redundant connection of three series relays, this type of connection guarantees reliable isolation within the output circuit. There is also a yellow LED on the front panel to indicate that the relay is functioning. An internal 5 A fuse protects the “SIL circuit” against short-circuit.As an extra feature the “WRS 24V DC SIL3” safety relay has an additional monitoring circuit, this is designed to allow connection of the field power to the monitoring relay and the output can be used by the control system to confirm that the field device has been switched. There is also a separate yellow LED on the front panel to indicate that the monitoring relay is functioning. With dimensions of 92.4 mm x 22.5 mm x 112.4 mm (length, width, height) the safety relay has a compact design and thus requires little space in the control cabinet when mounted on DIN rail TS35 and with a wide temperature range of -25°C up to +50°C, the safety relay is suitable for international use. Reliable and vibration-proof connection of conductors ranging from 0.5 mm² up to 2.5 mm² is possible thanks to Weidmuller’s trusted screw clamp connection.
About 20 % of the signals in process and energy technology are processed in safety-related applications, e.g. emergency shutdown systems. Their task is clearly defined: Immediate and automatic initiation of corrective measures - up to the shutdown of plants and plant components - in case of danger. Safety relays are particularly suitable for these tasks and applications. They guarantee safe electrical isolation of the “safety PLC” to the field and initiate protective measures in safety sections or immediately cut the energy supply.
Possible applications are to be found in emergency shutdown systems, emergency discharges or emergency control systems for valves and gates, including the indication of an emergency case. Process industry plants have to be built and operated in compliance with the EN 61508 standard for functional safety, including general guidelines for revention and control concerning the malfunction of electric, electronic or programmable electronic devices. There are four security levels for both, plants and risk minimising measures – ranging from SIL 1 for low risk up to SIL 4 for very high risk. The higher the risk level, the more reliable the risk minimising measures have to be; this is even valid for the operation of single devices.
The new “WRS 24V DC SIL 3” offered by Weidmüller is a safety relay for the emergency shutdown of plants and plant components in the process industry. The relay considerably increases plant availability and safety. It fulfils the requirements of safety level SIL 3 (Safety Integrity Level) and has been certified by the Technical Inspection Agency TÜV NORD according to EN 61508. The safety relay convinces with its strong overall concept. Yellow LEDs, marked “RELAY OUTPUT” (safety circuit) and “MONITOR” (monitoring circuit), indicate faultless operation of the relay. In the output of the safety circuit – “SIL circuit”” – three relays are conected in parallel, with their makers connected in series.
Due to its redundant layout, the relay qualifies for safety level SIL 3 and guarantees a permanent and reliable isolation – even in case of fused contacts. 240 V AC is the maximum admissible switching voltage and 5 A the maximum admissible switching current with an internal 5 A standard fuse for short-circuit protection. Switch-on delay is 5.1 ms and switch-off delay 6.8 ms. The input of the “WRS 24V DC SIL 3” safety circuit shows the following values: Rated operational voltage of 24 V DC and 30 mA current draw. And there are further convincing technical data and constructional details for the monitoring circuit: The time span between “Relay ON” and “Response” only comes up to 4.5 ms (230 V AC), respectively 5.7 ms (120 V AC). 240 V AC is the maximum switching voltage at the output of the safety circuit, offering a widespread rated operational voltage of 120 / 230 V AC at the input of the monitoring circuit.
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