The calculation results show "NaN"，pls help me

[auto_man]

I have a project used PCS7V8.2 & IL & 315-2DP,
and I create a FB like "Lag" in APL.
The SCL program is shown as follows：

Code: Select all

OUT := SEL(G:=LAG_T<=0.0,IN0:=IN + (sr_lv_out-IN)*(EXP(-Sample_T/LAG_T)),IN1:=IN);
sr_lv_out := OUT;

If the input ("IN") is fixed in a negative number always , and a few hours later,the output("OUT") shows “NaN”.
Why?
Is floating-point calculation overflow ？

[qqwww]

Show whole FB (with interface)

[Enrico999]

"NaN" means "Not a Number".

To find the error we need to see the whole block !

[AlekMalek]

Check your formula. It seems that the output of your function divides on 0 or the output is infinit or out of range of your variable.