Seeking idea on long E-Stop Chain

harryting

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We have a very long conveyor that has multiple Emergency Stops along its route. Over the years, additional equipments were added along the conveyor's route adding more E-stop to the conveyor.

The problem is, whenever someone pushed in a E-stop, we had to search all along the route to find out which E-stop was pushed. This can be resolved by adding one additional pair of input wiring to the PLC and along with a HMI of some sort to indicate the location and status of each E-stop. The HMI would be easy but I hate the idea of running so many pairs of wires for such long distances.

Is there some technical solution out there?
 
Is the entire string daisy-chained together or does each pull cord run separately back into a control panel? How is the string powered? If they run back individually to a control panel (not using a safety relay) you could tap off of each break into an input. If you are using a safety relay then I don't think this will work as you won't have enough voltage to source the inputs.
 
LJBMatt said:
If they run back individually to a control panel (not using a safety relay) you could tap off of each break into an input.
I would not advise this. By doing so you severly risk the integrety of the E-stop circuit.

Steve
 
Ooops, forgot to add that it's wired as a long chain into a relay right now.

I'm sitting here thinking, it would be nice if the E-stop accept a old fashioned NC contact PLUS a networked type input (ie. devicenet, ASI-bus) for indication input to the PLC. Does such thing exist?
 
How about replacing it with a safety cable. You don't say how long but two safety switches and a couple of tensioners can go a long way
 
I'm actually in the middle of doing something similiar. We've put an addition onto the building, and we must tie in our existing chemical feed system into the new building. We have remote boxes all around the plant which can call for chemical. The e-stops are all daisy-chained to a master estop relay, we then us a second contact off of each estop switch as a signal to the plc, constantly looking at the switches status. In the event of an e-stop, our master relay drops out killing all output power and signals the e-stop alarm. The system looks at the status of each estop switch. If the master relay has dropped out, and it finds that the status of an e-stop has changed, I know where it came from.
 
Last edited:
If you are using a PLC that supports Device Net very well, for example Omron or AB, both of these companies have safety Device Net available.
 
Thanks for suggestion so far.

-Lighted switch might help but not much, we simply got too many button, flashing lights, etc..

-too long for a roped system. More than a football field long and the line loops around too much.

I don't think the code here allow AS-I Safety yet. However, AS-I used as the indication would be great. I will contact a few vendors to see if such product is available (ie. AS-I ESTOP with a regular NC contact).

Thanks all.
 
On most systems I built with a lot of control consoles that included e-stops, I had a remote I/O drop either inside the console or nearby that all the pushbutton I/O went to.

The E-stop pushbuttons were pull-to-reset or twist-to-reset types with one Normally Closed contact that was in the series E-Stop circuit and one Normally Open contact that used separate control power to provide an input along with the other control panel pushbuttons. When an e-stop was pushed, the safety relay back at the main panel cut power to the appropriate parts of the system and the input merely indicated where the pushed button was.

Virtually all pushbuttons allow you to add contact blocks to them. Your expense will be to run wire to the nearest spare input module for the control system.

Are your E-Stop stations standalone boxes with only an e-stop, or is there some other I/O nearby ?
 
We used safety cables to help reduce the number of pushbuttons and increaase the actual safety of the machinery. There was always at least one pushbutton and two safety cables per motor. Sometimes there were many more for the longer conveyors.

We used big red rotating beacons mounted above the machinery to make the location of the offending switch easy to spot from anywhere along the line. Due to the expense of the beacons, we used only one per area, so it might be lit by one of up to four switches in close proximity to the lamp. Usually there was one PB and two cable swtiches per beacon, so it was easy to follow the flashing light, and check the nearby switches.

Our conveyors were mostly overhead and the E-Stop pushbuttons up there on the catwalk were not easily visible from the floor. Otherwise, we would have just used red mushroom head maintained pushbuttons with integrated indicator lamps instead of the expensinve rotating red beacons.

We used separate contact blocks to power the lamps to ensure isolation from the e-stop string.
 

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