04/25/2005 • Machine safety, industrial safety • Sensor Technology

The T 4000 multi RFID safety system: transponder technology that copes with tolerances and impacts

Longer switching distances of up to 15 mm, up to four RFID sensors connectable to a single evaluation unit, and high immunity to impacts and vibrations are the most important advantages of the T 4000 multi electronic safety interlock. Its uses include the protection of access doors to robot cells or in protective barriers along production and assembly lines, for example in the automotive industry. Often requested and now achieved in the T 4000 multi: separate door signalling outputs with which each connected sensor can be individually assigned to the particular door and evaluated.

With its EN 954-1 Category 4 certification, the T 4000 multi system is approved, and particularly suitable, for extremely hazardous machines.

Non-contact monitoring, highly tamperproof

The reading head of the T 4000 multi is mounted on the fixed part of a guard (e.g. the actual robot cell) and connected to the evaluation unit by a cable, available in two versions for the simultaneous connection of two or four sensors. The actuator – a transponder – is mounted on the access door in such a way that it is located at a safe switching distance of 15 mm from the reading head during machine operation. The energy required for transmission of the transponder code is transferred from the reading head to the actuator by induction.

The entire monitoring process takes place without contact via radio frequency identification (RFID). While the machine is operating, i.e. the protective door is 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 semi-conductor outputs for each door are released and the robot can start. Opening of the protective equipment is detected by interruption of the data communication, and the hazardous movement of the machine is immediately stopped. The same occurs if the power supply of the T 4000 is interrupted or if the actuator is damaged. In such cases there is no need to replace the entire system (as is necessary for mechanical interlocks), but only the actuator, because the evaluation device can learn any number of codes. As only the last code that was learned is valid, and multiple teach-in of the same actuator to the same evaluation device is impossible, the system is highly tamperproof.

Versatile in use

The sensor's large response range offsets tolerances between the door and the protective barrier, reliably preventing false alarms. The lock's immunity to impacts and vibrations is particularly important when safeguarding elevators, palletisers and depalletisers, or machines for securing loads. Movable covers on machines, e.g. protective hoods, can also be monitored with the electronic safety system to prevent unauthorised reaching into a running machine. In plants for paper production and further processing, the switches are characterised by their robustness and their insensitivity to dirt and contamination.

The same applies for food processing plants, e.g. spice mills and cutting machines, that are not only highly contaminating during operation, but consequently also require regular intensive cleaning.
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