Overland Conveyor E-stop oull cords wired through PLCs
Overland Conveyor E-stop oull cords wired through PLCs
(OP)
We have a 3km overland conveyor project that requires emergency pull-cord stops. The customer wants to know which safety switches is pulled via a PLC/HMI.
Anyone have experience with this type of application?
Thanks
Anyone have experience with this type of application?
Thanks





RE: Overland Conveyor E-stop oull cords wired through PLCs
RE: Overland Conveyor E-stop oull cords wired through PLCs
RE: Overland Conveyor E-stop oull cords wired through PLCs
But as far as a safety plc that is driven by different industries maybe that is a requirement in the robot or auto industry.
As a general rule its always better to be too safe than not safe enough. Also, if your in a court room, did you do your due dilegence in following regs that applied?
ht
this refers to access not if up in air by itself.
To reduce the severity of an injury, an emergency button or pull cord designed to stop the conveyor must be installed at the employee's work station. Continuously accessible conveyor belts should have an emergency stop cable that extends the entire length of the conveyor belt so that the cable can be accessed from any location along the belt. The emergency stop switch must be designed to be reset before the conveyor can be restarted. Before restarting a conveyor that has stopped due to an overload, appropriate personnel must inspect the conveyor and clear the stoppage before restarting.
Osha
see below if access by personnel
29 CFR 1910.212(a)(1), copy enclosed, requires that on any machine, nip points and hazards, such as the rollers and the edge of the moving conveyor, must be guarded. Since the moving belt must be guarded, a standard railing or some sort of an effective barrier guard must be provided on the inside of the platform between the employee and the belt edge. In any event, an emergency stop pull cord along the length of the conveyor is also required.
RE: Overland Conveyor E-stop oull cords wired through PLCs
I'm sorry, I'm in learning mode.
The way I believe these units work is that PULL CORD will have two contactors. One contact will be hard wired, so to stop the conveyor. The other (contactor 2) serves as the I/O for the PLC.
1) If the 2nd contactor serves the I/O of the PLC only for signaling location purposes, why does it have to be a Safety PLC?
2) For the hardwire system, how to deal with voltage drop of a 3km hardwire signal?
Thanks.
RE: Overland Conveyor E-stop oull cords wired through PLCs
If it is feasible you could run a network (ethernet, devicenet, controlnet, profibus, or whatever) and have distributed input blocks of io near each estop on the machine and have the network xmit the signals back.
RE: Overland Conveyor E-stop oull cords wired through PLCs
You would bring back a separate pair of wires from each switch to the PLC in order to pinpoint which switch was pulled, unless you got very creative and maybe measured the resistance in the monitoring circuit, using the aux contacts to shunt out the rest of the loop. This might require adding some additional resistors at the switches. This should be a dc control circuit, btw.
RE: Overland Conveyor E-stop oull cords wired through PLCs
Some e-stops have a lamp built in.
RE: Overland Conveyor E-stop oull cords wired through PLCs
RE: Overland Conveyor E-stop oull cords wired through PLCs
2nd round question is what if the conventional hardwired method is used. Not PLC, but strictly wire the pull switch contacts in series, yet how to account for a 3km Vdrop?
RE: Overland Conveyor E-stop oull cords wired through PLCs
A dc interposing relay (fail safe) should not draw too much current - you just need to get the coil data and check the voltage drop. You may need to increase the wire size beyond what you would normally use, but I think it is possible using dc relay coil. AC will be a problem.
RE: Overland Conveyor E-stop oull cords wired through PLCs
Check this recent thread:
thread240-208641: Voltage drop
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Overland Conveyor E-stop oull cords wired through PLCs
Why would it be necessary to interlock the panels as your suggesting? If one control panel stops on estop would not the other just stop on regular control? Is it necessary to interlock the estop zones between panels?
If this is a long belt it might be better to ramp down the belt then pull estop on the power on the motor. Are you sure your not going to damage the belt on estop?
RE: Overland Conveyor E-stop oull cords wired through PLCs
http://www.aeec.com/Conveyor/Pull_Cord_Switches/
Something like these will be located all along the length of the conveyor. When you get your arm stuck in the belt sometimes it's a long reach to the control panel.
RE: Overland Conveyor E-stop oull cords wired through PLCs
Exactly what I was looking for. Interesting info, and simple solution really. Thanks for teaching it to me.
Through the other thread I was recommended to read
"Distant Control of AC Relays, Contactors, and Starters" from square D. I found the article here:
h
Cheers,
Maj :)
RE: Overland Conveyor E-stop oull cords wired through PLCs
Roy
RE: Overland Conveyor E-stop oull cords wired through PLCs
http://www.aeec.com/Conveyor/Pull_Cord_Switches/
I've use them twice recently. To get tech support from the manufacturer is really hard (they are in south africa), I strongly recommend to take a look at http://www.ringway.com.au/
and their Ring Line product. I have a few other long overland conveyor projects and I'm thinking to use this for the emergency stop system.
Another advantage using these systems is that you offload the voltage drop calculations and concerns to the system supplier.
RE: Overland Conveyor E-stop oull cords wired through PLCs
Omron, Pilz, Allen-Bradley have some good safety relay products which give you Cat-3 safety in conjunction with a regular PLC.
RE: Overland Conveyor E-stop oull cords wired through PLCs
I have attached a sketch showing switch indication circuit. I used 100 Ohm resistors as this minimized the effect of wire resistance or dirty contact.
The Ohmeter had the 2 least significant digits blanked out so it read in units of 100 Ohms.
It wasn't perfect, occasionaly you would get a switch half pulled.
Most important with pull cords to have them quite loose otherwise cold weather can be a problem.
Roy
RE: Overland Conveyor E-stop oull cords wired through PLCs
I don't recommend trying to roll your own system such as has been suggested in previous posts. After more than 25 years in the mining industry around the world, the personal liability in doing such a thing just isn't worth it.
RE: Overland Conveyor E-stop oull cords wired through PLCs
No-one is going to be working on the conveyor with just the pullcord pulled. It must be locked out!
The problem with long conveyors is finding the switch that has beem pulled. I don't think running each switch back to a common point is an option. My suggestion uses 1 4c cable to pick up all the switches in series.
Roy
RE: Overland Conveyor E-stop oull cords wired through PLCs
One switch was wired in series along the conveyor using a DC source then hard wired directly to the conveyor's power source using an interposing relay.
The second switch were grouped per 200ft, and then wired into a remote I/O port, they were then radio back to the main PLC for "pulled switch" detection.
Maj
RE: Overland Conveyor E-stop oull cords wired through PLCs
Keith Cress
kcress - http://www.flaminsystems.com
RE: Overland Conveyor E-stop oull cords wired through PLCs
Thanks for the feedback
Roy
RE: Overland Conveyor E-stop oull cords wired through PLCs
Love it. :)
RE: Overland Conveyor E-stop oull cords wired through PLCs
regards.
CE