Logix 5000 For Air/Fuel Curves

[Yoda_the_Teckie]

I am about to be upgrading several compressor engines to Logix 5000 and I am looking for the best, proven, ways to program in the various curves. I believe that this can best be accomplished using a lookup table function, but I have not personally done that before.

Any advice?

Thanks!

 

[drbitboy]

What is your desired accuracy?


If they are smooth, I would suggest a Chebyshev approach, converted to a polynomial.


What is the coding environment e.g. ST? Ladder?

 

[Yoda_the_Teckie]

The programming can be done in ladder or ST.

The accuracy of the curve needs to be pretty tight. We use the air/fuel curve to control ignition timing.

 

[drbitboy]

Does it look like the plot on page 18 here: https://www.osti.gov/servlets/purl/841083? Or the plot on page 10?




Maybe a better question is, what are you measuring, and what are you controlling?

 

[Phrog30]

Have you noticed the FGEN instruction? It's only in function block and ST, no ladder.

 

[drbitboy]

Have you noticed the FGEN instruction? It's only in function block and ST, no ladder.

Ooh, nice.

 

[Yoda_the_Teckie]

Does it look like the plot on page 18 here: https://www.osti.gov/servlets/purl/841083? Or the plot on page 10?




Maybe a better question is, what are you measuring, and what are you controlling?

It looks very much like that curve. And the formulas contained in that paper are exactly what i am looking for.

So, we are controlling engine ignition timing according to the air/fuel curve, exhaust manifold temp curves, etc. There are around 4 curves that are used. They work on a low signal select control scheme. So, basically I am looking for any way to program a curve into the PLC and have it produce an result that can be scaled and output.

 

[Yoda_the_Teckie]

Ooh, nice.

I have not looked at that yet. I will look at it as soon as I get the chance.

Thanks!