Intelligent safety door monitoring Safe series connection of several safety door switches
Safety equipment is always required in machines if the hazards cannot be reduced to an acceptable level by design measures. In cases where it is necessary to intervene in the production process, movable guards such as safety doors, panels, or flaps are attached. When employees open the safety door to perform operation or service, the moving, potentially hazardous functions must be switched off. An interlock unit consisting of secure switches and monitoring components is used to monitor the position of the safety door.
Monitoring guards
A common practice when setting up safety-related systems is the logical series connection of several safety door switches, with a single safety relay or a safety PLC taking over the safety evaluation. When dealing with a logical series connection of interlocking devices with redundant mechanical contacts, a single error may go undetected. It is therefore likely that multiple safety doors are opened simultaneously or in a specific order as a part of the troubleshooting process. If this is the case, the single error of a switch contact will remain undetected, which could in turn lead to a chain reaction of multiple failures and a dangerous event. For a series connection, the maximum diagnostic coverage DC in accordance with DIN EN ISO 13849-1 must therefore be observed.
Logical series connection while maintaining safety
The PSRswitch is an electronic, RFID-coded, non-contact safety switch with a compact design. Thanks to a combination of integrated intelligence and a compatible evaluating device, it offers users the highest level of tamper protection and safety, even for series connections. The logical series connection with a constant level safety is implemented by two safe inputs and outputs. The outputs can be linked directly to the inputs of the next switch in the chain. Any faults in the switch or in the wiring (stuck-at faults) are detected immediately and displayed to the users for rapid localization and correction. In response to increasing cost pressure in field wiring, an 8-pos. M12 connection directly on the device enables a consistent SAC wiring concept from the sensor, through distributors, up to the safe I/O modules. To simplify wiring, a start circuit (reset button) can be implemented directly on the switch, eliminating the need for long wiring runs to the control cabinet.
High tamper resistance
RFID transponder technology has long since become a part of safe sensor technology, where it enables the coded exchange of signals between the sensor and actuator. Therefore, the PSRswitches satisfy two encoding levels of DIN EN ISO 14119 by applying three different sensors and a universal actuator. Unicode and Fixcode sensors, which feature a high encoding level, differ in that once the first actuator has been taught in, no other actuators can be taught into the Fixcode sensor. Multicode sensors have a lower encoding level and accept all actuators. Switches of this type need to be selected and installed so that they cannot be bypassed in any foreseeable manner. This can be achieved by installing them out of reach of the operator or in a hidden location, for example.
Smart diagnostics via IO-Link
Diagnosing the switching state of the sensor technology on the doors is helpful in ensuring a high degree of availability during ongoing operation. In the case of conventional wiring, this approach can often be implemented only with a great deal of effort, or not at all. The information is often limited to simple operating states, such as “door open” and “door closed”. In this context, the PSRswitch provides a complete diagnostic approach that is transmitted from the compatible safety relay to the controller via an integrated IO-Link gateway function. Each sensor continuously monitors the operating states and the secure inputs and outputs. If a door is opened or a wiring fault is detected, the safety outputs are immediately switched off and the diagnostic data is transmitted to the safety relay via a parallel wire. The safety relay, which is also configured as an IO-Link device, forwards the process data for the display to an IO-Link master or in the form of a warning message to the machine display.
