Relay logic help needed!

RayK

Member
RayK
Join Date
May 2004
Location
Geraldton West Australia
Posts
90
Have a situation in an old pane which is controlling about 20items Conveyors elevators etc, where if the e-stop is pushed everything stops, OK up to this point BUUUT because they are all switched with toggle switches instead of PBs as in modern boards, when the e-stop is rengaged everything starts up instantly! not a good thing, Sparky has suggested I install a small PLC to control a reset which will not allow startup if any of the toggles are still on, but I dont see why a couple of relays will be a better option, I have tried the logic but for the life of me cannot figure it out! Help. I sure there must be a simple way to do this and no replacing the toggles with PBs is not an option. attached is one attempt that does'nt work!
 
One simple solution, will be to add a timer and a buzzer. After the e-stop is rengaged, the buzzer will go on for a few seconds and after that time, the buzzer will stop and the system will start.
 
Use the toggle switches in the on position to drive a relay that interrupts the reset button (Or use aux contacts on the toggles if you can). That way if any of the toggle switches are on, the reset is not issued. The downside is that you have to go and turn all the toggle switches off and then go reset it.... And anyone who doesn't know this SOP will end up calling you when "It won't reset".
 
I hate to put the cat amongst the pigeons

If you are rewiring this control system under AS1404

You can not use this wiring as an Emergency stop system

You need to do a risk assessment on your machine

This may be a Cat.2 of if you are lucky a Cat.1.
Your current wiring has been voided in the AS update in 1999

Sorry mate
 
The diagram you present shows a reset button "bypassing" the estop. Ouch! In other words holding the reset button defeats the estop.

Separate out your MCR circuit and make sure that the reset button only bridges across the normally open contact of the MCR. Then tap off the high side of the MCR coil logic to supply everything else.
 
DamianInRochester said:
The diagram you present shows a reset button "bypassing" the estop. Ouch! In other words holding the reset button defeats the estop.

Separate out your MCR circuit and make sure that the reset button only bridges across the normally open contact of the MCR. Then tap off the high side of the MCR coil logic to supply everything else.
Click to expand...

Agree totally.

Beyond that I would replace existing toggles with momentary position toggles, and create latching circuits for each toggle. Then nwhen you drop power they return to an off state and cannot energize until the momentary is toggled again.
 
Of course you are correct with the wiring diagram.
But
Regardless of how the MCR is wired now.
In Australia. A change to the control circuit safety system must meet the regulations
This means -the machine needs a risk analysis.

Your suggested modifications may not be legal

This sucker needs safety relay and contractors to be fitted.
Pneumatic and Hydraulic control safety also needs to be considered.
 
You will have to use a better estop circuit as to meet regulations anyway.
however a simple solution could be to have a plc contact in the line from each toggle switch. when the PLC is energized (as it runs after the estop.) from all toggle switches a line to an input of PLC, if any of them is high do not start else outputs are started in a sequence (depending on the factory ) to prevent high currents.
this way you can use old boards, only some extra wires are needed to the PLC. one from the toggle switch and one back to the rest.
 
Safety!

Thanks for the replies guys, and yes you are right Ian doe's at this point need a safety analysis done to comply with Aussie regs, I am not a sparky but was asked to see if there was a simple solution to prevent mass startups, so I will have a word with our sparky to see what we need to bring the board up to spec. Thanks
 
RayK said:
Thanks for the replies guys, and yes you are right Ian doe's at this point need a safety analysis done to comply with Aussie regs, I am not a sparky but was asked to see if there was a simple solution to prevent mass startups, so I will have a word with our sparky to see what we need to bring the board up to spec. Thanks
Click to expand...

With respect Ray
Most country sparkles don't have a clue about this type of interfacing

An earlier post pointed out some basic wiring errors in the original design.
Most Electricians see this type of electrical drawing for about 3 months of their apprenticeship. Then usually not again.

Some of us have been in the control systems of the industry for 38 years. Myself included. Repco then Toyota now self employed. 🍺
 
Thanks Ian: I know what you mean about country sparkys! enclosed is an example of his work, great guy good sparky but limited knowledge of process control electrics and PLCs, frustrating at times!, attached is a pic of some PLC wiring, also as an exercise only!! is a possible solution to the problem.

P1020367.JPG
 

Attachments

  • Orange No2.pdf
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(have to use a better estop circuit as to meet regulations anyway.)
Sorry shooter. But this comment is definitely correct. The plc can not normally be used for safety.
 
there are a few details missing on these drawings.
the actual safety relay

if there are any pneumatics/hydraulics they are not catered for.
with the 3 phase interface.
this is almost a CAT.4 system - mechanical guarding and guard switches are not included
 

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