PID controller

Nabil · Post by **Nabil** » Thu Aug 05, 2010 4:34 pm

Hi
Is it possible to build a PID controller with vensim, that is how to differentiate and integrate the the difference terms?
Regards

Nabil

bob@vensim.com · Post by **bob@vensim.com** » Fri Aug 06, 2010 9:45 am

Differentiation is always a sampling process, especially in real implementations. Generally the most sensible way to do differentiation in a Vensim model is to use

time derivative = (variable of interest - delayed variable of interest) / sampling interval
delayed variable of interest = INTEG((variable of interest - delayed variable of interest)/sampling interval,variable of interest)

Where sampling interval is bigger than TIME STEP (usually > 2*TIME STEP if it is not simply TIME STEP).

Nabil · Post by **Nabil** » Fri Aug 06, 2010 11:40 am

Thank you
Nabil