Sick TR4 safety sensors simplify high-integrity series connectionWith its new TR4 Direct safety sensors for doors and gates, Sick has solved the problem of cost-effective series connection of up to 30 switches, achieving PLe, Cat 4 integrity and full diagnostic coverage of an installation.
For the first time, Sick's TR4 Direct non-contact sensors overcome the limitations on series connection imposed by the BS EN13849-1 and ISO/DIS14119, explains Seb Strutt, Safety Specialist for SICK (UK). "The series connection of traditional mechanical and magnetic switches has been restricted by the requirements of existing and imminent safety standards because of the need to avoid undetected faults when electro-mechanical switches are connected in series and are not individually monitored," he says.
"In high risk applications where PLe or even PLd interlocking is required, fault exclusions are not advised in relation to mechanical actuators. Series connection of switches must consider the potential for faults to remain undetected and should reflect this fact in the declared diagnostic coverage of the functional safety system. These restrictions have led to considerable complexity and expense in providing effective safety integrity with many traditional sensor configurations.
"Sick's TR4 Direct safety sensors overcome the problem and enable simple and cost-effective series connection to continue. They ensure reliable monitoring of multiple access installations with full diagnostic coverage of individual faults."
With the new SICK TR4 Direct series, fault finding and trouble shooting is simplified. Each sensor in a chain can indicate a fault, open or closed status and the current sensing range of the device. Each sensor can also indicate the status of the preceding sensor in the chain which allows quicker identification of an open switch or fault in the system.
The TR4 Direct is easily installed for simple series connection using standard M12 connection cables and M12 T connectors, saving time and money. The use of 24v dc dual channel outputs ensures the sensors have compatibility with many widely-used safety relays and PLCs.
The large sensing range of 25mm overcomes door alignment and vibration problems which may affect other devices, and IP69K environmental protection allows use of the TR4 Direct in hygienic and other high-humidity applications.
The TR4 Direct comes in a number of variants, either multicode or in a unique code format where each sensor is paired with a unique actuator which is "taught-in" during commissioning.
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