The problem is that I cannot align the machine because there’s a message on the control panel’s screen saying “Close operator door” even with the door closed. My first guess was that the safety interlock switch might be damaged so I’ve opened it and checked the 4 NC contacts and they are ok. I also checked that the 4 wires from the door contacts (2 from coil and 2 from key) enter the SIGUARD safety relay (3TK2825-2BB40) and the distributed I/O Siemens SIGUARD module (PM-D-F2), and I didn’t find any problem.
When I switched ON the main power switch, the safety relay on the door lock’s coil contacts had the Channel 1 / Channel 2 LEDs lit at startup and not lit when the message I mentioned was displayed on the panel. If, when the message was displayed and both LEDs not lit, I was manually forcing the coil to lock the door – though the coil had 24Vcc on command terminals, it was triggered and was unlocking the door – both LEDs on the channels input in the safety relay SIGUARD were lit. In this case the machine was starting.
The machine was not starting because, as far as I could tell, the coil needed to lose the 24Vcc command so the door would have been locked and the NC contacts closed, in this way the safety relay receiving both channels on positive pulse. In this case the machine would start (I’ve described above the situation when we forced the coil to lock the door and close the NC contacts).
The coil’s command signal’s drop to zero is from my point of view conditioned by one or more signals received by the PLC/Control computer from the machine – sensors, proximity switches, etc. Another possibility is that the module of the distributed I/Os of the machine which has as inputs the two contacts coming from the door’s key (the PM-D-F2 SIGUARD 3RK1903-1BB00) may be damaged. Since I do not have the logical diagrams or logical conditions of some machine commands such as locking/unlocking the door I cannot tell why the door’s coil doesn’t lock the door though the doors are closed.
Please give me a feedback.