Hello,

I am trying to generate energy values from power values that I am working with. I am getting amp readings from around 130 Mudbus current sensors. I am getting the Line and Phase voltage from another Modbus diver. From this and the different machines power factor, I am generating about 100 one-phase and 30 three-phase Power values. I downloaded an integration block from her: 

https://support.industry.siemens.com/cs/ke/en/view/42469594

to be able to sum up the Power to get the Energy. 

I take the Power and divide it by 3600 and store it in a Real tag. Then I integrate that Tag. The problem is that after exactly one hour then I am not getting an exact result out. I put a constant 60 in which is 0,0166666 after dividing it into seconds. After exactly an hour the I get out about 53,6 which sould be 60 again.

I figured it might by that it is losing sum data from the missing decimal point so I tried:

1> to integrating 60 without dividing it and then divide the result afterwards, but that gave me the same result.

2> to store the division in an Lreal and alter the integration block so it works on Lreal instead of Real. That did not do a lot, the result became around 53,8.

Does anyone know a better and more accurate way to do this?

P.S. I am only using simulation as is. Could that somehow be less accurate then if I would do it on the PCU?

Integrating with floating point values is a definite known problem!  

Check out Kahn Summation

The sudo code given at the begin of the article can be translated for use in a PLC.  Just let me know if you need help with that part.

That is a rather large error which may not be due to rounding or truncated digits.  Although your algorithm looks correct, I would suspect that there is a problem in the implementation, possibly in the integration. 

Could you post the code?

After I removed unrelated stuff from my code then the result from the Integration-block changed. I tried the code from online and it to behaves weirdly. First time I ran the code then the outcome changed very slowly and after a while, it stopped. Can anyone tell my why this is behaving in this way?

In this link ( http://we.tl/194lGETRJ3 ) is the original integration-code and my code. (Basically the same).

Jeff Casagrande

...

Could you post the code?

 Hi Jeff.

Did you see my code? Do you think you see what could be wrong?