PowerFailureUnsensitive
- Thread starter juan
- Start date
rdrast
Lifetime Supporting Member
I've used UPS's in the past. They work fine, but need to be checked regularly. If your CPU is 24VDC, diode isolated sealed batteries on a float charger might be a better alternative.
I don't power up the I/O with the standby supply, and usually have a relay on the main that will drop out, driving an input to the PLC so it can shut down outputs and such in an orderly fashion; independent even of an ESTOP type input.
Frankly, I'm not terribly fond of using a UPS because of the cost and maintanence aspect.
I don't power up the I/O with the standby supply, and usually have a relay on the main that will drop out, driving an input to the PLC so it can shut down outputs and such in an orderly fashion; independent even of an ESTOP type input.
Frankly, I'm not terribly fond of using a UPS because of the cost and maintanence aspect.
rdrast
Lifetime Supporting Member
I've used UPS's in the past. They work fine, but need to be checked regularly. If your CPU is 24VDC, diode isolated sealed batteries on a float charger might be a better alternative.
I don't power up the I/O with the standby supply, and usually have a relay on the main that will drop out, driving an input to the PLC so it can shut down outputs and such in an orderly fashion; independent even of an ESTOP type input.
Frankly, I'm not terribly fond of using a UPS because of the cost and maintanence aspect.
I don't power up the I/O with the standby supply, and usually have a relay on the main that will drop out, driving an input to the PLC so it can shut down outputs and such in an orderly fashion; independent even of an ESTOP type input.
Frankly, I'm not terribly fond of using a UPS because of the cost and maintanence aspect.
Tom Jenkins
Lifetime Supporting Member
I don't like UPS systems on PLCs, with one exception.
In general, if the power is out, there is nothing the PLC can do anyway, unless the entire machine is on the UPS! If you have a UPS you need to include a power loss contact and interlock it with the logic to prevent nuiscance alarms, prevent trying to start equipment that won't have power, etc.
The one exception is remote PLCs on a telemetry system, where teh UPS is required so the master station knows the remote location is without power, and corrective action can be taken.
Most PLCs have battery back-up to retain tuning as well as logic during power failure. It is uncommon to loose data during a power loss. What type of system was this?
In general, if the power is out, there is nothing the PLC can do anyway, unless the entire machine is on the UPS! If you have a UPS you need to include a power loss contact and interlock it with the logic to prevent nuiscance alarms, prevent trying to start equipment that won't have power, etc.
The one exception is remote PLCs on a telemetry system, where teh UPS is required so the master station knows the remote location is without power, and corrective action can be taken.
Most PLCs have battery back-up to retain tuning as well as logic during power failure. It is uncommon to loose data during a power loss. What type of system was this?
seppoalanen
Member
Tom Jenkins said:
And some cases for PLC/Computer-communitions if needed.
Good Computer program can understand that message is interrupted and PLC is not present. It can continue correctly when communication works again. Bad Computer programs can not do it.
jdbrandt
Lifetime Supporting Member
don't scrimp...use an ONLINE ups
I was at a manufacturing site (cement) where all PLC processors
were UPS protected.
The UPS selected by the end user was an off-line UPS, meaning
that its output switches to the load very quickly when a line
disturbance is sensed.
The problem was, at this site, the power quality was such that
the UPS was always finding some sort of disturbance or the other,
and, as a result, would sit there and switch on and off, all day.
It did not affect the PLC, but was a distraction.
They do make online UPS's that present a cleaned up version of
the incoming line, at all times, without switching.
I was at a manufacturing site (cement) where all PLC processors
were UPS protected.
The UPS selected by the end user was an off-line UPS, meaning
that its output switches to the load very quickly when a line
disturbance is sensed.
The problem was, at this site, the power quality was such that
the UPS was always finding some sort of disturbance or the other,
and, as a result, would sit there and switch on and off, all day.
It did not affect the PLC, but was a distraction.
They do make online UPS's that present a cleaned up version of
the incoming line, at all times, without switching.
rogerhollingsworth
Member
UPS
In my last project, installing A-B PLCs in substations and PanelViews in a control center, the substation PLCs, Fiber Optic Ethernet hubs, and PanelViews were required to be on UPS systems.
Each substation and the control center had a bank of batteries that supplied 125vdc for control and operating voltage for the high voltage breakers and switchgear. Breakers could be operated and their status could be monitored during a catastrophic power failure. I never experienced any UPS problems with this system it worked as designed. (PanelViews were on SPC brand UPS.)
Roger
In my last project, installing A-B PLCs in substations and PanelViews in a control center, the substation PLCs, Fiber Optic Ethernet hubs, and PanelViews were required to be on UPS systems.
Each substation and the control center had a bank of batteries that supplied 125vdc for control and operating voltage for the high voltage breakers and switchgear. Breakers could be operated and their status could be monitored during a catastrophic power failure. I never experienced any UPS problems with this system it worked as designed. (PanelViews were on SPC brand UPS.)
Roger