I work at Cape Canaveral in Florida on America's Space Program where we process satellites for launch in a facility that was built in the early 1980’s. 4 Demag cranes are in use in the facility and they have Allen Bradley SLC-150 PLCs. We maintain these cranes monthly and they have worked fine for years, no problems. They are in cleanroom environment, about 75 +/-3 degrees F 35 to 50% RH.
Recently we went to use one of the cranes and it would not respond to commands from the pendant. The troubleshooting tracked the problem to the SLC-150, which had a "PLC Fault" code. We swapped it with the PLC from another crane in the next bay over and were back in business.
We were aware of the 2002 announcement that the SLC-150 was obsolete so we had a spare one ready for just such a situation, but had to program it before we replaced it into the crane we took the other one from.
The electrical engineer that was assigned to determine the root cause of the failure theorized that the failure may have been due to leaky electrolytic capacitors. He stated that these capacitors are only reliable for 15 years or so and the current PLCs are unreliable. Mind you he did not find a “smoking gun”. He is proposing that we must upgrade to a more current PLC.
I'm all for modernization, but the cost for all 4 cranes is estimated at about $272,000! That's like 4 people's jobs out the door. We only have missions for this building four or so more years.
I feel like these PLCs were working fine up until now and we should stick with our plan to keep a programmed spare on the shelf and swap them out if another failure should occur. Now if frequent failures start occurring I'd say we need to upgrade. But this was only a 1 time occurrence, and the true root cause has not been determined.
The engineer insists the risk of failure is too high due to capacitor age and we should spend the $272,000 (jobs like that can double in costs when all is said and done). As you know all government contracts are looking to cut their budgets, not spend. I've seen capacitors that were 50 years old, I'm not convinced of the imminent failure.
The crane is fail safe; if you don't send a command the brake does not release. However, the load can be a multi-million or billion dollar satellite. Also, our company loses award fee if we miss a milestone.
The Allen Bradley web site says they don't support the SLC-150s anymore but that some parts may still be available. This seems to imply they are still viable, there is nothing that says the capacitors are doomed and failure is imminent.
Does anyone here have experience with these PLCs failing due to capacitor age? How hard would it be to change out all the capacitors in one SLC-150 to return its reliability?
What tests could be done to determine the health of the PLCs? Does anyone provide root cause failure analysis on these PLCs?
Recently we went to use one of the cranes and it would not respond to commands from the pendant. The troubleshooting tracked the problem to the SLC-150, which had a "PLC Fault" code. We swapped it with the PLC from another crane in the next bay over and were back in business.
We were aware of the 2002 announcement that the SLC-150 was obsolete so we had a spare one ready for just such a situation, but had to program it before we replaced it into the crane we took the other one from.
The electrical engineer that was assigned to determine the root cause of the failure theorized that the failure may have been due to leaky electrolytic capacitors. He stated that these capacitors are only reliable for 15 years or so and the current PLCs are unreliable. Mind you he did not find a “smoking gun”. He is proposing that we must upgrade to a more current PLC.
I'm all for modernization, but the cost for all 4 cranes is estimated at about $272,000! That's like 4 people's jobs out the door. We only have missions for this building four or so more years.
I feel like these PLCs were working fine up until now and we should stick with our plan to keep a programmed spare on the shelf and swap them out if another failure should occur. Now if frequent failures start occurring I'd say we need to upgrade. But this was only a 1 time occurrence, and the true root cause has not been determined.
The engineer insists the risk of failure is too high due to capacitor age and we should spend the $272,000 (jobs like that can double in costs when all is said and done). As you know all government contracts are looking to cut their budgets, not spend. I've seen capacitors that were 50 years old, I'm not convinced of the imminent failure.
The crane is fail safe; if you don't send a command the brake does not release. However, the load can be a multi-million or billion dollar satellite. Also, our company loses award fee if we miss a milestone.
The Allen Bradley web site says they don't support the SLC-150s anymore but that some parts may still be available. This seems to imply they are still viable, there is nothing that says the capacitors are doomed and failure is imminent.
Does anyone here have experience with these PLCs failing due to capacitor age? How hard would it be to change out all the capacitors in one SLC-150 to return its reliability?
What tests could be done to determine the health of the PLCs? Does anyone provide root cause failure analysis on these PLCs?
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