GE Fanuc PSU Loading Proficy indication

What does the Cimplicity software assume, when it calculates the PSU loading?, and how accurate is it if says a PSU is over-loaded to say 112%?, and at what point should I get concerned?

Background: I have got a customer, who has three hydro-electric turbines in Scotland, that each have been controlled by their own Alspa PLC, programmed using P8 software (GE Fanuc - rebadged - Series 90/30, & logic master respectively), and which have been running with no problems for the last 15 years or so.

However, due concern that that CPU being used is technically obsolete (CPU311), and the site programming laptop (with DOS O/S) is getting towards the end of its life.

He is looking to update, so as to be able to continue site running.

We are looking to use a CPU350 (to match other existing CPUs onsite), and will have to replace the CPU PSUs with IC693PWR331, as Alspa renumbered their PSUs (from PWR322 to PWR325), and the Proficy software which is to replace the P8 (logic-master) software, doesn't recognise it.

However, when I import the old PLC program into the Proficy; the Proficy says that the CPUs are overloaded: (2 are at 105%, and one is at 112%), despite the fact they have been running without any problems for several years.

Is there a problem or not?

The software's power usage calculations are based on worst-case assumptions. That doesn't mean you should ignore them. When the load exceeds the power supply capacity, the backplane voltage will drop below a threshold level and the PLC will shut down. Asking for advice on how much you can exceed the published ratings is a bit like asking how much faster you can drive over the speed limit without getting a ticket. You'll know when you've gone too far and Murphy's Law says that the day it happens will the worst possible time.

A CPU350 will consume significantly more power than the CPU311. If you're already borderline with a CPU311, you will be in worse shape with a CPU350. Also, as the power supply ages, its capacity declines. Don't forget that the power supply also provides power for the RS485/RS232 converter that you will be using to program the PLC. I once connected my laptop to a PLC and had it crash because the added load of the converter tipped it over the limit.

Since you're moving from a non-expandable CPU311 to a CPU350, take advantage of the fact that you can add an additional rack to the new system.

BTW, what modules do you have in a five-slot CPU311 system that add up to 112 percent of power supply capacity?

Correction: The current CPU is CPU331, not a CPU311. (my mistake)
The modules in the 10-slot rack are:
- IC693CMM311
- IC693MDL655
- IC693MDL655
- IC693MDL655
- IC693MDL753
- IC693MDL753
- IC693ALG442
- IC693ALG221

Result: 5v @ 76.63%, & 24v Isol @ 108.2% = Result Total Power @ 110.45%

N.B. Additional Rack are not an option, insufficent space in enclosure.

The 24 VDC Isolated is the DC terminals on the power supply for your use. If you are not using it, you're well within the rating. If you are using it, consider installing a separate 24 VDC powerr supply to relieve the burden on the PLC's supply. Personally, I don't like using the PLC's power supply for field devices. If one of the field devices shorts out and drags down the power supply voltage, I don't want the PLC to shut down.

Thanks, that accounts for why it is working, despite the what Proficy is saying. It is assuming that it is powering the Field Wiring, when in reality these are alresdy have their own 24v supply.

The only thing that is powered off the 24v isolated is the HMI, and it wouldn't be too hard to change that over to the panel supply.

This one less item to worry about. Thanks

Marc,

I simulated your setup in my PME. I would go to the 331 hi cap power supply for this setup, the requirements dropped to less than 50%. That will bring the system well within the capabilities of the power suppy. The smaller one would likely work, but it sounds like you have a history of reliability with this system that I'm sure you want to continue.

You will like the 350 (and above) processors much better than the 331 I think. Fanuc worked in some of the 9070 features into these CPUs.