Drives and Controls Magazine

Safety modules give you what you need

01 February, 2003

Safety modules give you what you need

Schmersal has developed a family of multi-function safety relay modules that allow machine builders and plant engineers to specify the ideal relay for an application without having to pay for unnecessary functions. The basic model of the Protect SRB family is said to satisfy 80% of all applications. Others deal with more demanding duties.

The modules, which comply with Category 4 of EN954-1, are designed for use with equipment such as safety switches, light grids, laser scanners, and emergency pushbuttons.

They incorporate "hybrid" fuses which can be restored following a short-circuit without having to access the hardware. However, unlike standard electronic fuses, the resetting is not automatic and only happens if the supply voltage is interrupted and switched on again. This avoids the danger of unexpected restarts following the rectification of a short circuit.

The relay modules have plug-in terminals, allowing pre-assembled cable harnesses to be used. Knife contacts loop the power supply through adjacent modules without extra wiring.

The seven-model range includes modules for: two-handed controls; time delays; normally open and normally closed two-channel inputs; and a version with delay enabling contacts for Category 1 stop applications. There is also a multi-output model that can be connected to a PLC with a programmable truth table to determine the status of the safety control system. More models are planned.