wiigelec
Member
- Location
- Red Desert
What are your thoughts / opinions on running the Hand/Stop inputs through the PLC versus hardwired to the contactor / VFD?
Thanks
Thanks
What are your thoughts / opinions on running the Hand/Stop inputs through the PLC versus hardwired to the contactor / VFD?
Thanks
It's something we commonly do except for emergency stop circuits - it's usually a requirement here (UK) to have these hard wired.What are your thoughts / opinions on running the Hand/Stop inputs through the PLC versus hardwired to the contactor / VFD?
Thanks
THE STOP BUTTON SHOULD BE A NORMALLY CLOSED DEVICE with the logic using a normally open function ...Where this is an issue for me is when the IO is distributed. Communication from IO card to the CPU is made via comm link, generally fiber. If comm link fails IO has no access to logic and pressing stop button will potentially do nothing...
Plc processors can lock up also. So even if the stop button is wired NC, the motor could stay on (if the plc does not have a watch dog circuit).
Most panels have a hard wired e-stop button close to the (I/o wired)start/stop for safety. Its also wise to have a hard wired contact on the same stop button that will drop out the contactor even if the input or PLC screw up.[/QUOTE
I belive the E-stop are all suppose to be Hard wired. At are Facility we have a double contact on our E-stops one to drop out a realy that kills all the contactors and another one back to PLC for diagonstic/ added logic to drop out contactors.
The fact that it is a stop button is what bothers me, when I push the stop button the motor should stop, with reasonable reliability. Run indication is not as important.Is it the fact that it is a stop button that bothers you? If it was a box on a panelview display that lit up when the motor was running and darkened when it stopped, would that make any difference?