TR4 Direct safety sensors for high-integrity series connection

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TR4 Direct safety sensors for high-integrity series connectionWith its new TR4 Direct safety sensors for machine guarding doors and gates, Sick believes it 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.

Seb Strutt, a Safety Specialist with Sick (UK), says that for the first time, the company's TR4 Direct non-contact sensors overcome the limitations on series connection imposed by the BS EN 13849-1 and ISO/DIS 14119: "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 electromechanical switches are connected in series and are not individually monitored.

"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 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, thereby saving time and money. The use of 24V DC dual-channel outputs ensures the sensors are compatible with many widely used safety relays and PLCs.

A large sensing range of 25mm overcomes door alignment and vibration problems that may affect the performance of other devices, and IP69K environmental protection enables TR4 Direct switches to be used in hygienic and other high-humidity applications.

Sick's TR4 Direct comes in a number of variants, either multicode or in a unique code format in which each sensor is paired with an actuator that is 'taught-in' during commissioning.

For more information on the TR4 Direct safety sensors or any of Sick safety products, please email or visit the website at

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