push button contact

[webfst]

Dear all,

I have been working as an instrument engineer in Refinery and chemical factory.
As you might know, we use push button switch to stop machine or process.
We use NC because safety. However sometimes machine or process would be stop by push button contact failure.
So, we would like to improve push button reliability using voting contacts or push button.

If you know standard or code where i refer to apply, please rely my thread..
And I would like to discuss about how to solve this matter.


thank you for reading...


Young from Korea

 

[Besoeker]

Dear all,

I have been working as an instrument engineer in Refinery and chemical factory.
As you might know, we use push button switch to stop machine or process.
We use NC because safety. However sometimes machine or process would be stop by push button contact failure.
So, we would like to improve push button reliability using voting contacts or push button.

If you know standard or code where i refer to apply, please rely my thread..
And I would like to discuss about how to solve this matter.


thank you for reading...


Young from Korea

Try a Pilz relay.

 

[kwired]

Dear all,

I have been working as an instrument engineer in Refinery and chemical factory.
As you might know, we use push button switch to stop machine or process.
We use NC because safety. However sometimes machine or process would be stop by push button contact failure.
So, we would like to improve push button reliability using voting contacts or push button.

If you know standard or code where i refer to apply, please rely my thread..
And I would like to discuss about how to solve this matter.


thank you for reading...


Young from Korea

What is reason for contact failure? Make sure they are being used within their ratings. If they are really inexpensive devices, upgrade to better quality devices. If mounted on the machine, vibration maybe contributing to deterioration, but again maybe better quality device will last longer.

 

[petersonra]

How often does this happen?

It could be that you are using poor quality contact pushbuttons. If so, changing to a better quality of pushbutton may solve your problem.

Maybe there is some environmental factor that is causing the failure. Could be corrosive fumes, even vibration. Maybe sealed contact blocks would help with corrosion. Vibration is a little tougher but you might be able to find mounting locations that are less susceptible to vibration.

It could also be that you are using them outside of their ratings, although that seems unlikely.

Without more information it is hard to give you any good advice.

I don't know how going to some kind of voting scheme is going to solve the failures. Better to fix the problem than to mask it.

 

[Besoeker]

I don't know how going to some kind of voting scheme is going to solve the failures. Better to fix the problem than to mask it.

Voting scheme?

 

[GoldDigger]

Voting scheme?

One switch with three contacts or three switches ganged together with one contact each.
Switches feed into logic that determines the state of the switch by either all three or any two out of three being in a particular state.
Majority rules.

 

[Besoeker]

One switch with three contacts or three switches ganged together with one contact each.
Switches feed into logic that determines the state of the switch by either all three or any two out of three being in a particular state.
Majority rules.

Thanks for that. New one on me.
Proves that I'm not a specialist who knows absolutely everything about absolutely nothing.................

 

[kwired]

One switch with three contacts or three switches ganged together with one contact each.
Switches feed into logic that determines the state of the switch by either all three or any two out of three being in a particular state.
Majority rules.

Does the logic warn you if one of the contacts isn't working so you can repair it before too many of them cause a total failure?

Never heard of that scheme myself, but can see it used on something very critical in nature.

 

[Lectricbota]

Thanks for that. New one on me.
Proves that I'm not a specialist who knows absolutely everything about absolutely nothing.................

Nice play on words.

 

[GoldDigger]

An Engineer starts out knowing a lot about a few things and as time goes on knows more and more about less and less until he knows everything about nothing.
A Salesman starts out knowing a little about lots of things and as time goes on he knows less and less about more and more until he ends up knowing nothing about everything.
A Purchasing Agent starts out knowing a lot about a lot of things, but through continuing interaction with engineers and salesmen ends up not knowing anything about anything.
(Sign over Purchasing Agent's desk)

Sent from my XT1585 using Tapatalk

 

[webfst]

Tank for reply

Tank for reply

How often does this happen?

It could be that you are using poor quality contact pushbuttons. If so, changing to a better quality of pushbutton may solve your problem.

Maybe there is some environmental factor that is causing the failure. Could be corrosive fumes, even vibration. Maybe sealed contact blocks would help with corrosion. Vibration is a little tougher but you might be able to find mounting locations that are less susceptible to vibration.

It could also be that you are using them outside of their ratings, although that seems unlikely.

Without more information it is hard to give you any good advice.

I don't know how going to some kind of voting scheme is going to solve the failures. Better to fix the problem than to mask it.

I dont think it happen much, maybe once a 5 years even though we have huge amount of push button swich in our site.
I know voting scheme is not a best solution and cannot apply all of push button considering efficiency but it can be reduce failure rate.
As you mention above, we are trying to mitigate environment factor to push button, for example, exmergency stop switch is hard to do maintenace during normal operation.
More, if it' faiure could happen, we are going to lose alot of money on refinery plant characteristic.
If you have any experience with that kind of matter, I would love to share the best practice or let us know if you know where I can refe to code/standard.
I think if we apply voting scheme for pushbutton, we must set criteria up considering engineering effiency.


Please let us discuss and I want to be always with you as engineer.

from Korea

 

[kwired]

I dont think it happen much, maybe once a 5 years even though we have huge amount of push button swich in our site.
I know voting scheme is not a best solution and cannot apply all of push button considering efficiency but it can be reduce failure rate.
As you mention above, we are trying to mitigate environment factor to push button, for example, exmergency stop switch is hard to do maintenace during normal operation.
More, if it' faiure could happen, we are going to lose alot of money on refinery plant characteristic.
If you have any experience with that kind of matter, I would love to share the best practice or let us know if you know where I can refe to code/standard.
I think if we apply voting scheme for pushbutton, we must set criteria up considering engineering effiency.


Please let us discuss and I want to be always with you as engineer.

from Korea

Switch built to higher specifications sounds like a start, presuming you aren't already using what you have beyond it's design specifications. Most of the 30 mm switch designs seem to take more abuse then 22 mm switch designs when it comes to general purpose pushbuttons and their associated contact blocks.

 

[Jraef]

One switch with three contacts or three switches ganged together with one contact each.
Switches feed into logic that determines the state of the switch by either all three or any two out of three being in a particular state.
Majority rules.

Most safety relays (ala "Pilz" mentioned above) use a dual contact channel, not 3, but yes they "vote" in that both sets must agree.


It should be noted however, a Safety Relay monitoring system will not PREVENT a shutdown if an E-Stop contact fails, it will prevent OPERATION if one of the contacts fails to CLOSE. The problem being described here is almost exactly the OPPOSITE of what a Safety Relay is intended for, in that you are undoubtedly getting nuisance Emergency Stops. That to my mind would preclude the use of a "voting" system because for EMERGENCY stop you do NOT want to interfere with initiating the command by having something 'decide" whether or not the circuit should be open.

The suggestion that you use better quality contact blocks is probably your better option here. There are a few mfrs out there who's contact blocks are prone to open on high vibration; ABB is notorious for that. I'm not sure of what's readily available in Korea, but if you are using ABB, that's something I would suggest changing out.