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A light curtain is tied into a PLC input only. Who can tell me that Will this meet safety codes?
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James Ingraham
No, it does not.
In order to meet safety codes, the light curtain must remove motive power from everything it is protecting through hardware. Further still, you can't just use any old relay; you must use a safety-rated relay.
-James Ingraham
Sage Automation, Inc.
In order to meet safety codes, the light curtain must remove motive power from everything it is protecting through hardware. Further still, you can't just use any old relay; you must use a safety-rated relay.
-James Ingraham
Sage Automation, Inc.
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mike
I see you are applying to a job at JMP engineering since you are asking all the interview questions. Way to fool them!!!
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Anonymous
No it doesn't, see the above reply.
If you want to have the benefits of a PLC and even of a Fieldbus you can use ASI - Safety at Work. It's expensive - but great. It depents on how much safe devices you need, to consider using this new technology.
It'a approved in Europe and USA.
Unfortunately i've never used it, but seen some demos and played a little with these devices.
If you want to have the benefits of a PLC and even of a Fieldbus you can use ASI - Safety at Work. It's expensive - but great. It depents on how much safe devices you need, to consider using this new technology.
It'a approved in Europe and USA.
Unfortunately i've never used it, but seen some demos and played a little with these devices.
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Ricardo Godoy
You also have to make a analysis of the risk. There are risks that asks for redundancy and other safety issues. Thy to contact Rockwell or Pilz corporation to help you to find the right safety equipment. Think that you can go to jail if something wrong happens in a bad safety configuration.
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Bob Peterson
Depends entirely on what it is being used for.
Bob Peterson
Bob Peterson
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Jiri Baum
No.
It'd have to be a special PLC with a verified, locked-down program.
Jiri
--
Jiri Baum <[email protected]> http://www.csse.monash.edu.au/~jirib
MAT LinuxPLC project --- http://mat.sf.net --- Machine Automation Tools
It'd have to be a special PLC with a verified, locked-down program.
Jiri
--
Jiri Baum <[email protected]> http://www.csse.monash.edu.au/~jirib
MAT LinuxPLC project --- http://mat.sf.net --- Machine Automation Tools
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Joe Jansen/ENGR/HQ/KEMET/US
No.
If you need a safety circuit, hire someone to implement one. Seriously, this is a huge area for liability. You don't want something like that coming out during a lawsuit.
--Joe Jansen
If you need a safety circuit, hire someone to implement one. Seriously, this is a huge area for liability. You don't want something like that coming out during a lawsuit.
--Joe Jansen
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Dale Witman
Raymond,
This is definitely not safe! Light curtains or any safety devices need to remove power from any safety related devices directly. The output needs to be wired as per the local or country regulations it is located. Regulations vary, but
the common thing is directly removing the power or energy sources that can cause motion or place a person in harms way. Most light curtain manufacturers have excellent information in regards to this. Contact them and reference the local regulations.
Dale
This is definitely not safe! Light curtains or any safety devices need to remove power from any safety related devices directly. The output needs to be wired as per the local or country regulations it is located. Regulations vary, but
the common thing is directly removing the power or energy sources that can cause motion or place a person in harms way. Most light curtain manufacturers have excellent information in regards to this. Contact them and reference the local regulations.
Dale
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robert trask
> A light curtain is tied into a PLC input only. Who can tell me that Will this meet safety codes?<
Absolutely NOT! Well not in any country that has an OSHA or equivalent.
You need to do a lot of research in 'control reliability'.
Robert Trask, PE
MindSpan eSciences
Wilmington, NC
mindspan@ ec.rr.com
Absolutely NOT! Well not in any country that has an OSHA or equivalent.
You need to do a lot of research in 'control reliability'.
Robert Trask, PE
MindSpan eSciences
Wilmington, NC
mindspan@ ec.rr.com
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Dobrowolski, Jacek
Hi,
Sometimes it will. Depending on national safety codes for that kind of machinery and safety-rating of a PLC (There're safety-rated PLCs out there - check PILZ for instance). If your PLC isn't safety rated - definitely no.
Regards,
Jacek Dobrowolski, M. Sc. E. Eng.
Software Eng.
Sometimes it will. Depending on national safety codes for that kind of machinery and safety-rating of a PLC (There're safety-rated PLCs out there - check PILZ for instance). If your PLC isn't safety rated - definitely no.
Regards,
Jacek Dobrowolski, M. Sc. E. Eng.
Software Eng.
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Paul T
Dale is right on... but a big point here is to make sure you know what safety code you had to (or want to) satisfy. Before you can really answer
the question, find out what standard the machine or plant or contract is being held accountable to.
In Europe, CE is pretty encompassing and almost completely ensures good practice in design and construction. If the machine is CE marked, then the light curtain almost certainly has to be part of a guarding system and safety circuit that removes power, etc.
In the US, that "remove power" requirement is per NFPA 79. You may find that your "Federal, state and local codes..." (to pseudo-quote some common
spec or RFQ language) don't mention NFPA 79 at all... and hence it will not legally apply. Nor does OSHA 29CFR mention it (at least I didn't find it in a couple of hours on-line searching). I just finished an E-stop go-round similar to this and we found that the legal requirements were not what we thought. The solution was to add NFPA 79 to our list of required specs that
vendors must comply with... but to get back to the original point to this e-mail, before you get wrapped around too many axels look at the contract
documents and determine what is/was required. You may still want changes to your machine, but it will save a lot of time if you determine what the
contract requirements were first.
Paul T
the question, find out what standard the machine or plant or contract is being held accountable to.
In Europe, CE is pretty encompassing and almost completely ensures good practice in design and construction. If the machine is CE marked, then the light curtain almost certainly has to be part of a guarding system and safety circuit that removes power, etc.
In the US, that "remove power" requirement is per NFPA 79. You may find that your "Federal, state and local codes..." (to pseudo-quote some common
spec or RFQ language) don't mention NFPA 79 at all... and hence it will not legally apply. Nor does OSHA 29CFR mention it (at least I didn't find it in a couple of hours on-line searching). I just finished an E-stop go-round similar to this and we found that the legal requirements were not what we thought. The solution was to add NFPA 79 to our list of required specs that
vendors must comply with... but to get back to the original point to this e-mail, before you get wrapped around too many axels look at the contract
documents and determine what is/was required. You may still want changes to your machine, but it will save a lot of time if you determine what the
contract requirements were first.
Paul T
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Bob Peterson
Everyone has made a leap that the light curtain is being used for safety purposes. I have seen them used for control purposes as well. In that case there is no safety issue.
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Anthony Kerstens
Raymond,
I'm curious if you happen to be applying to JMP for a job. Your question is word-for-word the same as a question on a JMP internet job posting.
I'm concerned that since you could not answer the question yourself that you would find yourself over your head in that job.
Anthony Kerstens P.Eng.
I'm curious if you happen to be applying to JMP for a job. Your question is word-for-word the same as a question on a JMP internet job posting.
I'm concerned that since you could not answer the question yourself that you would find yourself over your head in that job.
Anthony Kerstens P.Eng.
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tecnog
I once ran into the following safety issue:
a sort of machine performs a sequence of operations, then has to stop to a standby position awaiting for some manual operations to be performed by the operator (the operator has to cross the light curtain and enter within the
motion range of the machine). As soon as the operator terminates the manual operations, the machine resumes its working sequence. During the machine motion, the operator is protected by a light curtain, but it isn't possible to switch off the power when the machine is awaiting for manual operations being completed (loss of position and other issues).
The machine manufacturer placed a series of limit switches (mechanical contacts, not inductive or other non-contact detectors) which detect the
exact machine standby position. Once the machine is in standby position, the light curtain is bypassed and safety is then ensured by the limit
switches (three of them, one for each axis): should the machine move while the operator is working within the bypassed light curtain, the limit switches will cut the power.
My questions:
1. Was this solution safety compliant?
2. Were there other solutions?
3. If such a machine is not safe, is a programmer liable for any damage or injury?
Thanks in advance
Luca Gallina
a sort of machine performs a sequence of operations, then has to stop to a standby position awaiting for some manual operations to be performed by the operator (the operator has to cross the light curtain and enter within the
motion range of the machine). As soon as the operator terminates the manual operations, the machine resumes its working sequence. During the machine motion, the operator is protected by a light curtain, but it isn't possible to switch off the power when the machine is awaiting for manual operations being completed (loss of position and other issues).
The machine manufacturer placed a series of limit switches (mechanical contacts, not inductive or other non-contact detectors) which detect the
exact machine standby position. Once the machine is in standby position, the light curtain is bypassed and safety is then ensured by the limit
switches (three of them, one for each axis): should the machine move while the operator is working within the bypassed light curtain, the limit switches will cut the power.
My questions:
1. Was this solution safety compliant?
2. Were there other solutions?
3. If such a machine is not safe, is a programmer liable for any damage or injury?
Thanks in advance
Luca Gallina
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Michael Griffin
I wouldn't want to express any opinion about it being safety compliant without knowing more about the machine (probably more than you could describe in an e-mail).
However, to address your situation, the primary means of protecting the operator seems to be the light curtain. Muting (disabling) the light curtain appears to be an accepted practice in the literature I have read, although I have never actually seen this done. A few questions might clarify the situation for you.
a) Is the light curtain capable of protecting the operator (will it reliably stop it in time) when the machine is active (cycling)? If the answer to this question is "no", then any other considerations are irrelevent.
b) When the machine is in the "load" position (inactive), is the hazard within the operator's zone of reach? A possible problem with limit switches (even positive break redundant ones) can be that the machine may be capable of limited motion before the switches open and the machine stops. Does this present a hazard? More to the point, are you sure it doesn't present a
hazard?
c) Since the operator exposure is every cycle, I assume the application requires the highest level of safety system design. Is the muting system (switches, safety relays, etc.) designed to this level? The type and number of switches used may be a problem. I imagine you would need two safety rated switches for each axis, and to monitor each one independently (that is, do not connect them in series). I can elaborate on this point later if that would be of assistance.
I can imagine circumtstances under which a system of this type might be acceptable or not acceptable. However you can see why I would be reluctant to say whether it is marginally OK, or definitely not OK.
As for alternate means, I have heard of using lock pins to block a machine while the operator is in the range of motion. Since the exposure to the hazard is frequent (each cycle), the system which detects the lock pins are in place has to be designed to the highest safety levels. The lock pins must be in place before the operator is allowed to enter the machine. Obviously this doesn't work with a light curtain.
Another possibility is to use brakes (if this is compatable with the machine). The brakes must have switches which are monitored by the safety circuit. The brakes cannot be energised (unlocked) when the light curtain is not ready (broken or faulted).
As to the legal question, I am not familiar with Italian law. However, I would point out that you have not said anything about the software being intended as part of the means of protecting the operator. However leaving the
legal question aside, the person in question may have a moral obligation to express to the equipment owner any reservations he may have reasonable grounds for.
I cannot of course offer any valid advice on your situation, but perhaps the above will give you a few things to think about. In the province of Ontario, Canada (where I live), these sorts of questions would be dealt with by a
qualified P Eng. working for a safety consultancy who would be hired to provide an engineering report on whether the machine met the applicable
standards (most of which by the way, originate in Europe). We would not be allowed under the law to operate the machine without such a report.
I don't know how these things are handled where you are, but there may be some form of documentation or report covering the safety systems of the machine you are referring to.
As an aside, even if the safety system meets all requirements, I can imagine some practical problems with the system as described. If the operator breaks the light curtain prematurely, the machine element is de-energised. You have said that this is a problem for the machine. It is quite common for operators to break a light curtain at the wrong time (particularly with their elbows if they have to turn) or to reach into the machine before the cycle has completely finished. If the machine or process cannot tolerate this, then a light curtain may not be the right protective measure for the job.
************************
Michael Griffin
London, Ont. Canada
************************
However, to address your situation, the primary means of protecting the operator seems to be the light curtain. Muting (disabling) the light curtain appears to be an accepted practice in the literature I have read, although I have never actually seen this done. A few questions might clarify the situation for you.
a) Is the light curtain capable of protecting the operator (will it reliably stop it in time) when the machine is active (cycling)? If the answer to this question is "no", then any other considerations are irrelevent.
b) When the machine is in the "load" position (inactive), is the hazard within the operator's zone of reach? A possible problem with limit switches (even positive break redundant ones) can be that the machine may be capable of limited motion before the switches open and the machine stops. Does this present a hazard? More to the point, are you sure it doesn't present a
hazard?
c) Since the operator exposure is every cycle, I assume the application requires the highest level of safety system design. Is the muting system (switches, safety relays, etc.) designed to this level? The type and number of switches used may be a problem. I imagine you would need two safety rated switches for each axis, and to monitor each one independently (that is, do not connect them in series). I can elaborate on this point later if that would be of assistance.
I can imagine circumtstances under which a system of this type might be acceptable or not acceptable. However you can see why I would be reluctant to say whether it is marginally OK, or definitely not OK.
As for alternate means, I have heard of using lock pins to block a machine while the operator is in the range of motion. Since the exposure to the hazard is frequent (each cycle), the system which detects the lock pins are in place has to be designed to the highest safety levels. The lock pins must be in place before the operator is allowed to enter the machine. Obviously this doesn't work with a light curtain.
Another possibility is to use brakes (if this is compatable with the machine). The brakes must have switches which are monitored by the safety circuit. The brakes cannot be energised (unlocked) when the light curtain is not ready (broken or faulted).
As to the legal question, I am not familiar with Italian law. However, I would point out that you have not said anything about the software being intended as part of the means of protecting the operator. However leaving the
legal question aside, the person in question may have a moral obligation to express to the equipment owner any reservations he may have reasonable grounds for.
I cannot of course offer any valid advice on your situation, but perhaps the above will give you a few things to think about. In the province of Ontario, Canada (where I live), these sorts of questions would be dealt with by a
qualified P Eng. working for a safety consultancy who would be hired to provide an engineering report on whether the machine met the applicable
standards (most of which by the way, originate in Europe). We would not be allowed under the law to operate the machine without such a report.
I don't know how these things are handled where you are, but there may be some form of documentation or report covering the safety systems of the machine you are referring to.
As an aside, even if the safety system meets all requirements, I can imagine some practical problems with the system as described. If the operator breaks the light curtain prematurely, the machine element is de-energised. You have said that this is a problem for the machine. It is quite common for operators to break a light curtain at the wrong time (particularly with their elbows if they have to turn) or to reach into the machine before the cycle has completely finished. If the machine or process cannot tolerate this, then a light curtain may not be the right protective measure for the job.
************************
Michael Griffin
London, Ont. Canada
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Jiri Baum
Paul Tolsma:
> In the US, that "remove power" requirement is per NFPA 79.
... [which your contract may not specify] ...
> before you get wrapped around too many axels look at the contract
> documents and determine what is/was required.
There is such a thing as professional ethics that may require one to follow good safety practices even where no actual legal requirement exists.
Jiri
--
Jiri Baum <[email protected]> http://www.csse.monash.edu.au/~jirib
MAT LinuxPLC project --- http://mat.sf.net --- Machine Automation Tools
> In the US, that "remove power" requirement is per NFPA 79.
... [which your contract may not specify] ...
> before you get wrapped around too many axels look at the contract
> documents and determine what is/was required.
There is such a thing as professional ethics that may require one to follow good safety practices even where no actual legal requirement exists.
Jiri
--
Jiri Baum <[email protected]> http://www.csse.monash.edu.au/~jirib
MAT LinuxPLC project --- http://mat.sf.net --- Machine Automation Tools
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Paul T
Absolutely. It turns out, tho, that unless your ethics match your vendor's up front... it will cost you money to align them after the system is
delivered. That's why engineers have to write specs and contracts for systems...
Paul T
Jiri Baum wrote:
>There is such a thing as professional ethics that may require one to follow good safety practices even where no actual legal requirement
exists.<
delivered. That's why engineers have to write specs and contracts for systems...
Paul T
Jiri Baum wrote:
>There is such a thing as professional ethics that may require one to follow good safety practices even where no actual legal requirement
exists.<
