SIL3 SAFESERIES safety relays from Weidmüller

Part of range, the new SCS 24V DC SIL3 safety relay is designed to guarantee emergency shutdown of systems and system components operating in the process industry.

Safety shutdown is critical in the process industry because it serves functional safety, for instance in backup systems with high DC voltages. EN 61508 specifies that all devices used in safety circuits must fulfil particularly strict conditions. Safety Integrity Level makes it possible to classify corresponding devices according to the reliability of their safety function and the safety oriented design principles that must be maintained in order to minimise the risk of malfunctions.

The standard EN/IEC 61508 states that functional safety is given when safety systems and organisational measures minimise risk to an acceptable level. In this case, SIL3 relays can be deployed to ensure emergency shutdown. As a rule, operation in low demand mode is sufficient as emergency events are not usually seen as regular occurrences. However, in some industries, the high demand operating mode can also play a central role in creating functional safety. For instance, overfill protection solutions in tank systems need to ensure control on a permanent basis.

Whatever the requirements, the new Weidmüller safety relay is more than able to handle the conditions encountered and satisfies the highest demands with proven technology and sophisticated features.

One such example is the status indicators to indicate that the relay is operating flawlessly: two yellow LEDs, one 'Relay Output' (safety circuit) and one 'Monitor' (monitoring circuit) simplify error analysis considerably.

Three relays are connected in series in the output of the safety circuit (SIL circuit). This circuit arrangement guarantees reliable isolation in the safety circuit. One of the challenges when deploying safety relays in process engineering and control systems is to accommodate different supply voltages - for example, backup systems are operated with very high DC voltages. It is for this reason that Weidmüller has added a monitoring circuit to its safety relay which is equipped with a wide voltage input, and is a highly adept method to meet this requirement.

These design features, which are all contained in a single device, therefore provide safety-oriented shutdown functionality (SIL3), as well as electrically isolated 24-230 V AC/DC field signals to the higher-level controls.

A special circuit arrangement makes the input circuit immune to test pulses, which are usually used in distributed control systems to monitor the status of signal circuits. The maximum permissible switching voltage is 250 VAC/30 VDC and the maximum permissible switching current is limited to 5A. A standard internal fuse provides short-circuit protection. The typical break time is about 14ms and the make time 7ms. The input of the safety circuit of the SCS 24V DC SIL3 safety relay has a rated control voltage of 24 VDC (+/- 20%) and 35mA current consumption. To ensure rapid onsite replacement, the fuse is easily accessible.

The design of the monitoring circuit is compelling and has a wide voltage input from 24 V AC/DC to 230 V AC/DC which forms the basis for individual application solutions.

The safety relay is designed for use in a wide range of temperatures from -25°C to +50 °C without restrictions. Thanks to its compact dimensions of just 113.6 mm x 22.5 mm x 117.2 mm (l/w/h) the SAFESERIES safety relay requires just a small amount of space on DIN TS 35 mounting rails in electrical cabinets (IP20).