Unity Pro Totalizer Under Calculating


Thread Starter


We just finished a PLC upgrade from 984 processors to Quantum Unity processors. We did a conversion, not a re-write, so 90+% of the logic is still in 984LL.

What it appears is the following:

1. The 984LL conversion is overwhelming the Unity Pro and we are getting slow scan times, over 90ms.

2. The slow scan times are causing the totalizers to be far off. Initially we were using .6s clocking and they were way off, then moved to 6s and they are 4+% off.

3. We have tried both the IEC totalizers built into Unity and we tried our own custom built totalizers with better success, but still not accurate.

4. When we called Schneider, they said if this was really a problem, their phones would be ringing off the hook about it, so it must not be a problem. I really have an issue with that stance.

5. How do we know what it should be? We basically are also recording through SCADA and using those values and an average to verify the daily total. We would prefer to use the PLC for totalizing, but we will use the SCADA system if there is not alternative.


1. Has anyone noticed this issue of Schneider IEC totalizing being incorrect?

2. Has anyone had speed problems with Unity conversions that contain a large percentage of 984LL?

3. Are there any other thoughts?

I am involved with a Modsoft 987LL program conversion to Unity Pro XL V11. The completed project has nine (9) remote drops and approximately 700 984LL networks plus a fair amount of IEC FBD programming. It also communicates with three other PLCs (2 Schneider Momentum and 1 AB PLC) plus multiple HMIs.

The conversion went very well, all 984LL continued to function in Unity as it had in Modsoft. Not a lot of "math" but extensive decisions and table manipulations.

The scan time is less than 30 mSec. So you either have a very large project or you have done something unique.

I am doing extensive online programming and continual "builds" without impact on scan time.

I have used the totalizer that Schneider provides in their Flow Library and found it to be 100% accurate. In my geographical area, there are multiple application in oil and gas and if there were totalizer issues then I would have expected a "fix" from Schneider.

Schneider support has always provided me with competent and full resolution of issues that I have reported to them. Sometimes the results are not what I would like but at least I know what I can or cannot do for a particular application.