PaulKraemer
Member
- Join Date
- Jan 2005
- Posts
- 24
Hi,
I design control systems where I use 24 VDC I/O. I always try to make my E-Stop circuit hard-wired (not relying on logic inside the PLC to stop/remove power from the necessary components that have to be "taken out" by an E-Stop).
I have a hard-wired E-Stop circuit that includes all of my E-Stop "mushroom-head" pushbuttons in series with a momentary contact "E-Stop Reset" pushbutton. When none of the mushrooms are pushed in and the operator presses the "E-Stop Reset" pushbutton, this energizes my "Control Power" contactor. The "Control Power" contactor is latched on at this time (latching method is hard-wired as well). If one of the E-Stop mushrooms is then pushed in, the "Control Power" contactor is de-energized. Pulling out the E-Stop mushroom does not re-energize the "Control Power" contactor. The "Control Power" contactor is not re-energized until the operator presses the momentary "E-Stop Reset" pushbutton again.
In order to make sure an E-Stop "takes out" what I need it to, I feed my "+24 VDC" lead into one of the normally-open contacts of the "Control Power" contactor. Coming out of this contact, I have a wire I'll call "+24 VDC (E-Stopped)", which is only engergized when the "Control Power" contactor is energized.
I use this "+24 VDC (E-Stopped)" wire to power my discrete 24 VDC PLC outputs. This way, all of my PLC outputs will not be powered in the event of an E-Stop, even if the PLC was malfunctioning.
This works fine for me when I have everything in one panel. On larger machines, I have three control panels. My PLC / local I/O rack is in one panel, and I have remote I/O racks in the other two panels. My PLC communicates with these remote I/O racks over Ethernet/IP. Ideally, I would like my three panels to just be connected by an ethernet cable. However, I don't see how this is possible if still want my E-Stops to be hard-wired, and I need an E-Stop to "take out" my PLC outputs in my remote I/O racks,
Right now, I think that I will have to send my "+24 VDC (E-Stopped)" wire out to my remote I/O racks and use this wire to power my 24 VDC PLC outputs in the remote I/O racks, just like I do in my main panel (local rack).
I can do this, but I was just wondering if anyone else has any other suggestions that might be better. (I use Allen-Bradley ControlLogix PLC's for the most part, but I would be interested in hearing how any of you handle this sort of thing in other brands as well.)
Thanks in advance,
Paul
I design control systems where I use 24 VDC I/O. I always try to make my E-Stop circuit hard-wired (not relying on logic inside the PLC to stop/remove power from the necessary components that have to be "taken out" by an E-Stop).
I have a hard-wired E-Stop circuit that includes all of my E-Stop "mushroom-head" pushbuttons in series with a momentary contact "E-Stop Reset" pushbutton. When none of the mushrooms are pushed in and the operator presses the "E-Stop Reset" pushbutton, this energizes my "Control Power" contactor. The "Control Power" contactor is latched on at this time (latching method is hard-wired as well). If one of the E-Stop mushrooms is then pushed in, the "Control Power" contactor is de-energized. Pulling out the E-Stop mushroom does not re-energize the "Control Power" contactor. The "Control Power" contactor is not re-energized until the operator presses the momentary "E-Stop Reset" pushbutton again.
In order to make sure an E-Stop "takes out" what I need it to, I feed my "+24 VDC" lead into one of the normally-open contacts of the "Control Power" contactor. Coming out of this contact, I have a wire I'll call "+24 VDC (E-Stopped)", which is only engergized when the "Control Power" contactor is energized.
I use this "+24 VDC (E-Stopped)" wire to power my discrete 24 VDC PLC outputs. This way, all of my PLC outputs will not be powered in the event of an E-Stop, even if the PLC was malfunctioning.
This works fine for me when I have everything in one panel. On larger machines, I have three control panels. My PLC / local I/O rack is in one panel, and I have remote I/O racks in the other two panels. My PLC communicates with these remote I/O racks over Ethernet/IP. Ideally, I would like my three panels to just be connected by an ethernet cable. However, I don't see how this is possible if still want my E-Stops to be hard-wired, and I need an E-Stop to "take out" my PLC outputs in my remote I/O racks,
Right now, I think that I will have to send my "+24 VDC (E-Stopped)" wire out to my remote I/O racks and use this wire to power my 24 VDC PLC outputs in the remote I/O racks, just like I do in my main panel (local rack).
I can do this, but I was just wondering if anyone else has any other suggestions that might be better. (I use Allen-Bradley ControlLogix PLC's for the most part, but I would be interested in hearing how any of you handle this sort of thing in other brands as well.)
Thanks in advance,
Paul