Control.com - Nerds in Control

We are using DCS for process control. We have given floating UPS power supply to DCS & Computer systems used as HMI. Our computer systems are failing very frequently. Is this due to floating UPS power supply given to them?

Which type of power supply is normally recommended for Computer Systems and control systems?

Normally DCS system are grounded as per suppliers recommendation. Normally we have a set of earthing conductors, separate from electrical ground, connected to DCS systems. Any wrong doing with grounding can disturb plant control but NOT COMPUTERS. Now without trying to investigate give normal plant power to computers instead of UPS. You can also put in a dedicated UPS for computer only. This will definitely resolve problem.

It's possible that the sine wave generated by the UPS has harmonics that are harmful to the PC power supplies. Is your UPS one that is always on or does it just pick up the load on power failure? As Topak says, perhaps you should have one or two separate UPS systems, that way you could use systems specifically designed for computers.

Do you need to have the UPS floating?

Regards,
Roy

Thanks for your reply. Actually our plant UPS is always ONLINE and it output is floating 110 VAC, i.e. we get 65 VAC between phase & neutral & 55 VAC between neutral & ground. Is this floating power supply suitable for computer systems!! Please reply.

Most Computer Manufacturers specify less than 3 VDC between neutral and ground. The first things to get damaged in this scenario is devices connected through serial and parallel port to the PC. Gradually other devices will fail.

If no other source of power is available, then an isolation transformer with neutral grounded can be used.

Regards,
Tomy Zacharia