Thanks Justin. I will try to implement. I think is the problem is the # of
bit I have to use a floting point rutine. BTW, in the formula I dont know
what means "Time since error ocurred", maybe Is a fool question but I am
trying to understand anything before implement the code.

Mark Lezama.

Justin Grimm escribis:

> Funny you should ask, Im working on the same project at the moment.
> The only problem Im having is the maths routines, they seem to be getting
> up to
> 64 bit.
> The actual calculation is-
> dMV=G[dE + E*T1*I + D* (dE/T2)]
> where-
> dMV  = change in Manipulated Variable
> G      = Gain (100/Proportional Band)
> E      = Error (SetPoint - ProcessVariable) for reverse action,
>            Error (ProcessVariable - Setpoint) for direct action
> dE    = ErrorThisScan - ErrorLastScan
> T2     = Time between scans (in minutes)
> T1     = Time since error occured (in minutes)
> I       = Integral time (R/M)
> D     = Derivative time (minutes)
>
> There are other things to consider as well, integral windup, bumpless
> transfer
> from manual to auto, etc
>
> Anyone knowing any alterations to this equation or anything else
> that might make writing this code easier are most welcome to reply
>
> Justin Grimm    reaper@southwest.com.au
>
> ----------
> > From: Mark Lezama <mfidel@TELCEL.NET.VE>
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: PID question.
> > Date: Friday, 6 March 1998 21:09
> >
> > I have working with RTU designe base in PIC16c74. I have to control a
> > valve with a 4-20 ma signal, but I want to implement a digital PID
> > controller, anyone here have a PID code or can explain me how I have to
> > implement.
> >
> > Thanks in advance!
> >
> > Mark Lezama