Safety switch uses radio frequency ID technology

Paul Boughton

The T 4000 multi electronic safety interlock system from Sick offers users a host of features that make it suitable for a wide range of sensing applications. With its EN 954-1 Category 4 certification, it is particularly suitable for high-hazard environments.

Features offered by the T 4000 include a long switching distances (15mm maximum), up to four RFID (radio frequency identification) sensors can be connected to a single evaluation unit, and high immunity to impacts and vibrations.

Applications include the protection of access doors to robot cells, or for protective barriers alongside production and assembly lines - such as in the automotive industry. Movable covers on machines, such as protective hoods, can also be monitored to prevent unsafe access.

One customer request that is now available from the T 4000 multi is separate door signalling outputs so that each connected sensor can be individually assigned to a particular door and evaluated on this basis.

The reading head of the T 4000 multi is mounted to the fixed part of a guard assembly and connected to the evaluation unit by a cable that is available in two versions for the simultaneous connection of two or four sensors. The reading head uses induction to generate the energy required for the transmission of the transponder code.

The actuator (transponder) is mounted on the moveable part of the assembly, such as an access door, so that it is located a safe switching distance from the reading head during machine operation.

While the machine is operating – with the safety device closed – the bit pattern of the code is continuously compared with the stored code. If the codes match, the safe relay outputs and the separate semiconductor outputs for each door are released and the machinery can start. If the safety device is opened, this is detected by the interruption of the data communication, and machine operation is immediately halted.