intrinsically safe barrier safety rated

[JeffKiper]

OK I just got dropped in another somewhat odd job. I have to do have safety door switches E-stops in a classified area Class 1 DIV 1. The mechanics of installing them is not the issue my concern is the intrinsic barrier that I have found are not rated for safety devices. Anybody have a clue about this.

The last couple of jobs the customer has signed off on the barriers being non safety rated as-long as we did 4 wire 1 wire on an individual barrier. So we used 4 barriers per E-Stop and Gate Switch. I usually use 2 channel barriers but for these I only used 1 channel.



Any Ideas?

Thanks for your time

 

[leitmotif]

Jeff you need more complexity and challenge in your life.

Bit confused on terms
Intrinsic do you mean intrinsically safe - I recall vaguely these are at a voltage or was it watts that were so low they did not provide sufficint activation energy to a chemical reaction ie ignition.

Barrier - do you mean a light screen? Such as those used on presses etc?

Is this robot spray painting in a car plant? Now that has to be a can of worms.
Uhhh must you use electrical switches - could compressed air be used for sensing which then turns a switch on or off in non classified area?

Do people really have to go there? Is it possible to put this machine in a room and put safety controls on the access doors? Sets up for other issues ie people cheating the "counter" etc etc but worth asking the question.

Dan Bentler

 

[JeffKiper]

Dan what fun is doing the same job over and over?

Yes you are correct Intrinsically safe is the reduction in energy to below the point at which a spark can be produced.

A intrinsic barrier (commonly called Intrinsically safe barrier or galvanic isolation barrier) reduces the energy from the higher energy that could spark to the low level.

No this is distilled beverage, spirit, or liquor etc... I have done a few of these and like anything else it always grows and grows. We have people emptying aged spirits and then refilling the Barrels. Everyone of the Barrels are hand made so each one is different. I haven't figured out a way to automate some of this yet.

quick run down of the operation.
load the pallet, index to the drill station (if a new barrel drill the Bung hole), index to the bung pulling station, index to color check station, index to emptying station, index to filling station, eject. At every station except the drilling station someone touches each barrel. Labor intensive operation.

 

[leitmotif]

Hoo boy I think I can now say
1. For a while boredom will not be a problem for you.
2. I see no way to get rid of the people - too much variety in the drums.
3. complete automation is not an option.
4. In theory pneumatics or hydraulics would minimize the electrical but that is for motors etc. I do not think you can eliminate all electrical especially so in case of sensing - either position or weight or liquid level.

Dan Bentler

 

[JeffKiper]

The standard stuff like LED and PB are no problem. I just run them throughan intrinsically safe barrier and then to my PLC that is located out side of the classified are. The problem is when I get into the safety gates. On this system ther are 3 barrels wide on the pallet so the people have to walk out onto the conveyor. The conveyor drives are all on Safe-off. The safety gate is where I have a problem. I can't find an intrinsically safe barrier rated for safety devices.

Maybe I am over-thinking this but everything else we do in the electrical world has to say it is rated for x,y,&z if it doesn't say it is rated then it is not rated. The only think I seen that is OK is fiber optics I just don't have a good feeling about pulling a thin fiber cable out in a shop where 1/4" steel plate gets bent up like it is nothing.

 

[rpoet]

The only think I seen that is OK is fiber optics I just don't have a good feeling about pulling a thin fiber cable out in a shop where 1/4" steel plate gets bent up like it is nothing.

What about armoring the fiber - if you have a fiber optic-based solution - with something like Sch. 80 pipe? Installation would kind of suck, but would it be pretty tough. What about placing fiber in IMC conduit?



rpoet

 

[JeffKiper]

After I typed that I thought about all the other cable that is running up overhead so why not put the fiber in there as well?

 

[iant]

I have an Idea that the Pilz Multi might be ok as the EStops are not actually powered
It is late sunday night here, I am sure the other safety suppliers offer similar.
But I could well be wrong with my belief. Sorry in advance if I am,
I think they use a frequency rather than a voltage.

 

[danw]

This short thread on Control.com raises the same issue.
http://control.com/thread/1026172542#1026172610

 

[leitmotif]

After I typed that I thought about all the other cable that is running up overhead so why not put the fiber in there as well?

I am sure that these drums of booze are about 50 gallon and about 450 to 500 lbs and fully agree that in this operation the machinery can destroy 1/4 plate steel. No matter what electrical or other type control system you put in it is going to get mangled at some time or other.

Mangled electricl could result in either an open circuit or a short - in essance two "signals" to PLC. Broken fiber would result in only one signal ie a "dark" (very loose term) and thus only one possible outcome -- uuh would it not???. If a "dark" is the safest control signal and puts machinery is safest condition then that may be the way to go.

I think fibre in this application is worth a bit of study time.

Dan Bentler

 

[Kent Hostetler]

Is there anything requiring you to design the circuit as intrinsically safe? If you can't find a suitable barrier, why don't you just design the circuits using explosionproof methods instead?

 

[JeffKiper]

Is there anything requiring you to design the circuit as intrinsically safe? If you can't find a suitable barrier, why don't you just design the circuits using explosionproof methods instead?

The X P conduit is an option. I hate going thinking about going to a third world country and running conduit while I am there. I have Don a couple of light curtains that way and they where around $12k per set plus pipe work.

 

[kekrahulik]

I am so glad to finally be working in an area that has no Class 1 Div 1 issues - sorry to see that you're not - always a pain.

I like the fiber concept, but do your homework on it. I was looking into fiberoptic sensors a few weeks ago and recall a statement that the fibers were not acceptable for explosionproof areas bacause the fiber could be a pathway for vapors to follow (or something like that - didn't read it that closely at the time). As I think about it now, I'm guessing the particular fiber may have had a braided covering or something(because I would think normal fiber wouldn't be an issue), but just throwing the idea out to you.

 

[iant]

I have spoken to a collegue that does do IS wiring - he has said that there is a zoned area so anything in tht area needs to be IS of Flame/explosian proof.
Could you not use IS barriers by wiring them in Flame proof fittings.

It is funny that both the GAS and Petrol systems still use single contact E/stops in their control systems

 

[JeffKiper]

Update
AB does have an intrinsically safe barrier rated for use with safety devices.I don't have the part number handy. My Rep said he has hem in the safety catalog.