Intrinsically safe relay??

Adam303

Lifetime Supporting Member
Adam303
Join Date
Aug 2009
Location
Chicago
Posts
587
Dear friends,
I need some help on detecting a belt raise fault. The piece of equipment is a spiral tunnel with a stainless steel belt. In the event that the belt would raise itself up from the track I want to stop the belt. I do have in my possession old print from this tunnel but it just has a neutral wire from a 24 dc – going straight to the rods and in the event the belt is raised it grounds the neutral therefore closing the relay. I’m not so sure this is safe and I’m looking for something to replace this with. I’m thinking a Intrinsically safe relay. Does anyone have any information on anything like this. Cost is obviously an issue here as this is coming out of my pocket. I also heard somethig of a switching repeater but I’m not sure what it does.
Thanks
 
How safe does it have to be? Is it just for machine protection? Belt moving + lifted belt = broken belt?

It sounds like you could just add a normally closed limit switch that is opened when the belt lifts up. Opening the limit switch would drop out the belt command.
 
That's correct Tharon. Pardon that I didn't specify but this spiral tunnel is for deep frezzing useing nitogen. Class I Div 1
 
Last edited:
Photo beam

I would ask is it possible to shoot a light beam down either side of the conveyor? Similar to a light curtain.
 
Adam303 said:
That's correct Tharon. Pardon that I didn't specify but this spiral tunnel is for deep frezzing useing nitogen. Class I Div 1
Click to expand...

What else is in there besides nitrogen? Nitrogen is an inert gas and not flammable. So that makes me wonder why Class I Div 1 which if I recall correct is for flammable gases (or liquids with high vapor pressure)

Dan Bentler
 
Yeah, if it's just a nitrogen environment, it is not Cl 1.

Class 1 = Combustible vapors (Nitrogen is not combustible...)
Class 2 = Combustible dusts
Class 3 = Combustible fibers/filings (I think...)

Div 1 = where combustible material is normally present in a quantity to be combustible/explosive during normal operating conditions.
Div 2 = where combustible material is not normally present in combustible/explosive quantities during normal operation, but may be during an upset condition.
 
Setting the area classification aside. For Intrisically safe you need what is known as a barrier. These come in all kinds of shapes and sizes. The brand I use is Pepperl +Fuchs. Check out there web page and you can get alot of info on the product line and all the finer details for using them.

http://www.pepperl-fuchs.us/cps/rde/xchg/usa/hs.xsl/21.htm

As far as what you are doing you could take your current setup and attach it directly to a barrier and this would make it Intrsically Safe. Just remeber what an IS Barrier does. It limits power. If your current circuit requires more than 2.88 watts of power it will not change states. Limit Switchs and the such generally do not require that much power so I would bet you setup would work with an IS Barrier.
 
I thought intrinsically safe was a classification of electrical equipment (flashlights meters etc) for use in potentially combustible atmospheres. They are supposed to not have enough energy to create an arc which may have enough energy to meet or exceed activation energy of combustible material to result in fire / explosion.

So for his application where it is nitrogen saturated and with no combustible or flammable materials / products he would not need intrinsically safe rated or Cl 1 Div 1 components.

Personell protection is another issue with an oxygen deficient atmosphere. Main trick here is to keep people out so you do not have to remove dead bodies.

Dan Bentler
 
leitmotif said:
I thought intrinsically safe was a classification of electrical equipment (flashlights meters etc) for use in potentially combustible atmospheres. They are supposed to not have enough energy to create an arc which may have enough energy to meet or exceed activation energy of combustible material to result in fire / explosion.

So for his application where it is nitrogen saturated and with no combustible or flammable materials / products he would not need intrinsically safe rated or Cl 1 Div 1 components.

Personell protection is another issue with an oxygen deficient atmosphere. Main trick here is to keep people out so you do not have to remove dead bodies.

Dan Bentler
Click to expand...

Yes having to remove dead bodies does raise a few eyebrows. So does blowing the place up.

I hope this guy responds back I am curious what they are doing that is hazardous and deep freezing. I know nitrogen is used as a blanketing gas in lots of hazardous processes but I have never heard of a deep freezing one.


It sounds like this is a flash freezer and the trip system is for frost build up jamming the links in the conveyor.
 
More information

More information is required about the environment, and the intended purpose of the installation.

Also, depending on the device used, to attach a sensory device to a barrier, one must do the entity parameter calculations to ensure that the circuit cannot build up enough stored energy to provide an ignition source. One cannot just select a barrier, hook up a device, and consider the circuit Intrinsically Safe. Also, correct wiring separation is required and the conduiting in and out of the area will still require seal offs, light blue wiring, and a host of other special wiring methods.
 
Gentlemen. As you stated before nitrogen is a non combustible gas, I was wondering this myself as I got the project scope on this week. The freezer tunnel is used for deep freezing of poultry in a food processing plant. I think the plant engineer or whoever wrote this may be confusing the safety issue here with confined space? Anyway pardon the miscommunication. What he wants to implement on this project is a probe on every lever of the spiral tunnel, once the belt would raise it would touch the probe and stop the motor. The reason he doesn’t want to use any type of limit switches or beam lights, mechanics is because of the low temperature in the tunnel. I think it runs below -100 ferinheight This is why he was asking about intrinsically safe relay, not that the tunnel is a hazardous place but that he could use the ground rods. I have never deal with intrinsically safe circuits but here is what I have so far, attached is a pdf of the electrical schematic and hopefully this will work fine as I haven’t tested this at all. Thanks to all of you for a great input on this. The part number of the galvanic isolator(isn’t this a fancy word for a diode) Ab 897H-G231 but is made by STAHL using two resistors in theory this should work fine.
 
The problem with Galvanic isolators is grounding is critical.

Never thought of using an IS barrier in this method but I see where your going here. Your looking at the IS Barrier as a current limiting device not for it's hazardous loction uses. One thing you may consider is using a safety relay. Similar current limiting abilities and not as sensitive to grounding issues.

Your right a mechinal limit switches, they are usless at this tempature.
 
What is your safety concern? Is it that the detection method is not solid enough to detect a fault? Or is it that the detection method itself poses a possible electrical safety issue?

Keith
 

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