Experimental Physics and
Industrial Control System

Ben Franksen via Tech-talk <tech-talk at aps.anl.gov> · Sat, 13 Feb 2021 10:53:53 +0100

Oops, sorry for the botched subject.

Am 13.02.21 um 10:50 schrieb Ben Franksen via Tech-talk:
> I have a question regarding the epid record type, which is part of
> https://github.com/epics-modules/std.
> 
> According to the docs, the formula to calculate the output is
> 
>   OVAL = P + I + D
>   P = KP * E(n)
>   I = KP * KI * SUMi ( E(i) * dT(n) )
>   D = KP * KD * ( (E(n) - (E(n-1) ) / dT(n) )
> 
> I checked that the code (in the soft device support) really does that. I
> am ignoring the extra functionality that limits the output to be between
> DRVL and DRVH as this is irrelevant here.
> 
> Suppose we have been at the target position for some time, i.e.
> VAL=OVAL, so that E(n)=0 for all n. Then all terms become 0 and the
> output is OVAL=0 as well. But shouldn't it be OVAL=VAL instead?
> 
> Either I am mising something here or this is a bug and line 171 of
> stdApp/src/devEpidSoft.c should not be
> 
>             oval = p + i + d;
> 
> but rather
> 
>             oval += p + i + d;
> 
> and the formula above start with
> 
>   OVAL += P + I + D
> 
> Cheers
> Ben
> 

-- 
I would rather have questions that cannot be answered, than answers that
cannot be questioned.  -- Richard Feynman

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System