UPS Power Supply....."Online" or "Offline"?

NetNathan

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......Though this might be an interesting question....

In my existing standard control system....

I am currently using a 2KVA APC Surta UPS (120VAC output):
1. To supply clean power to PC, Instrumentation, PLC...etc.
2. Ability to save data during power fluctuations, or power failure for as long as UPS battery lasts

On UPS power during runtime and power failure:

HMI/Scada System:
17" panel monitor
Dell XE2 PC

Instruments:
Temperature Controller
Temperature High Limit
Vacuum Controller

Panel Devices:
Power to PLC PS
Power to PLC Digital Inputs (only when on UPS). (Digital Outputs are not under UPS power)
2.5 Amp / 24 VDC PS (for PLC back plane, Analog I/O and Ethernet Switch)



NOW the question...

Would you, or do you, use an "Online" or the more common "Offline" type UPS?

I have been using "Online" under idea of the better prevention of any noise or power dip during an "Offline" UPS switching over to battery power.
But.... An Online UPS is over double the price than a standard "Offline" ups.
 
Last edited:
However online can break too, so i would go for offline for display and not needed stuff like controllers (because when power is down the controller can not do anything.
maybe only critical equipment like the PLC itself (for timing and safety reasons on an online unit.
 
I have used both. For critical applications, online is the choice.

I guess that begs the question... how critical is your application? You have excluded the DO points from UPS power, so my first take is that this is not necessarily a failsafe operation. We have some of those, and for that we have big banks of batteries to give our online UPS extended runtime, and we power everything with it.
 
Last edited:
shooter said:
However online can break too, so i would go for offline for display and not needed stuff like controllers (because when power is down the controller can not do anything.
maybe only critical equipment like the PLC itself (for timing and safety reasons on an online unit.
Click to expand...

I am still powering controllers.....so PLC gets analog in from them and I can continue to monitor/record temperature and pressure data.
 
NetNathan said:
......Though this might be an interesting question....

In my existing standard control system....

I am currently using a 2KVA APC Surta UPS (120VAC output):
1. To supply clean power to PC, Instrumentation, PLC...etc.
2. Ability to save data during power fluctuations, or power failure for as long as UPS battery lasts

On UPS power during runtime and power failure:

HMI/Scada System:
17" panel monitor
Dell XE2 PC

Instruments:
Temperature Controller
Temperature High Limit
Vacuum Controller

Panel Devices:
Power to PLC PS
Power to PLC Digital Inputs (only when on UPS). (Digital Outputs are not under UPS power)
2.5 Amp / 24 VDC PS (for PLC back plane, Analog I/O and Ethernet Switch)



NOW the question...

Would you, or do you, use an "Online" or the more common "Offline" type UPS?

I have been using "Online" under idea of the better prevention of any noise or power dip during an "Offline" UPS switching over to battery power.
But.... An Online UPS is over double the price than a standard "Offline" ups.
Click to expand...

+1 for online. I had a harrowing experience in a cement plant with an offline type UPS - it simply could not switch fast enough to prevent the PLC's power supply (in this example, a GE 90-70) from detecting the glitch, and forcing the PLC to re-initialize. Replaced the offline with an online, and the problem went away.
 
jdbrandt said:
+1 for online. I had a harrowing experience in a cement plant with an offline type UPS - it simply could not switch fast enough to prevent the PLC's power supply (in this example, a GE 90-70) from detecting the glitch, and forcing the PLC to re-initialize. Replaced the offline with an online, and the problem went away.
Click to expand...


1+ This.
 
That's good Nathan Online is the way to go, I had to prove to my upper Management also in the past to buy Online UPS's. It's strange how they think an Online UPS only costs about 700 dollars and anyone of the Module in your PLC cost more than that.
 

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