PLC closed outputs and power loss

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
I have a control panel using an Eaton ELC controller for operation and for alarm outputs. The outputs OPEN on a fault. Recently, there have been some power issues at this location, and we've gotten multiple alarms. I'm thinking the power outage (before a generator kicks in) is opening these outputs, but that seems like a stupid design. Is this at all common?
The Eaton manual says the controller will continue operating with a power loss of 5-10ms, but that's obviously way to quick for a utility-out, generator start, transfer situation. I've added a delay between the output going to alarm and when somebody gets notified, but the whole opening on fault seems crazy except for very certain situations.
 
I know a UPS is a solution. I was more curious as to how common it is to wire/program alarm outputs in a way that they would trigger on power loss. It seems like a questionable design to me.
Thanks
 
I know a UPS is a solution. I was more curious as to how common it is to wire/program alarm outputs in a way that they would trigger on power loss. It seems like a questionable design to me.
Thanks
I think you need to talk to the programmer. They are the ones to correct an issue with logic, if there is one. We, or at least I, have no idea what the goal is. All of the small projects I did had an operator in attendance and power loss was very apparent.
 
Sounds like it may be intended as a "fail safe" design... as in, if a wire break, fuse pop, loose wire, or unintended wire lift situation occurs, you get the alarms. That means someone has to get up and out of the control room and go look or the operators know to get a tech involved ASAP.

For the power loss thing, UPS is the way to go like previously stated.
 
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This is at a sewage lift station. It should be set up to operate unattended almost all the time. If there is a fault, an auto-dialer starts calling the pump crew members. This is a brand new system (not necessarily new design) from Smith & Loveless. I would think they'd know better than to program it this way. The other day, the guys got called for failures on both pumps and high-water and low-water at the same time!
I've simply set the delay on the auto-dialer to be a bit longer than it takes the station to transfer to generator power.
 
This is at a sewage lift station. It should be set up to operate unattended almost all the time. If there is a fault, an auto-dialer starts calling the pump crew members. This is a brand new system (not necessarily new design) from Smith & Loveless. I would think they'd know better than to program it this way. The other day, the guys got called for failures on both pumps and high-water and low-water at the same time!
I've simply set the delay on the auto-dialer to be a bit longer than it takes the station to transfer to generator power.
I gotcha now. Sounds like some field testing should have been done before this system was originally turned over and that would have saved some heartache. Hopefully the delay works, sounds like it might be a good simple solution.
 
I know a UPS is a solution. I was more curious as to how common it is to wire/program alarm outputs in a way that they would trigger on power loss. It seems like a questionable design to me.
Thanks
Some places you might not want motors automatically restarting when the power comes back on for safety reasons.
Thus, in a way having the outputs open is a safety feature.
 
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