PID Equations in PLCs


Thread Starter


Hello everyone, I am collecting PID equations implemented in various PLCs. Some of these can be found at: Can I ask you to (1) Double check these PID equations, and/or (2) Provide me with more PID equations implemented in other well-known PLCs or any industrial PID controllers? Your help will be very much appreciated. Danyang Liu Email: [email protected] WWW: Telephone: +1-780-424-5074
I'm not sure I understand your posting. Probably you would like us to visit the suggested site, and then come back with suggestions or things like that. Is it ? I will satisfy myself visiting the site. In the mean time accept this: Until recently, most DCS & PLC system if not all had insufficient I (integral) and nearly absent capability in Derivative. This has been mentioned for years in Chemeng. and reposted by Expertune. There are perfect or near perfect PID in other domains (not those crude ones "Industrial Systems"). I'm dropping dead at the moment: watching that Irish born Jim Corcoran. He is now a poet writing french so perfect, and on his own ! Nice derivative product too. By the way, I have my own derivative algorithm as well as Integral. They are private. It is so simple seen what are P, I, D and what to do to make then operate. These tools are private. I will only release them if an Enterprise would approach me, so that they will not miss the purpose. You know they would say "yes sir" (oui Monsieur) and do nothing the day after. And few years down the road, they would have "discovered something" Is it true ? isn't it indeed ? [email protected]


Nice information! But I need the equation for Foxboro I/A DCS too, someone can help me? Thanks.
Dear Jean, There are two points in my posting. Please read it again. It is true that most industrial PID controllers are actually PI controllers, especially in process industry. The reason: In a PID controller there are three parameters Kp, Ki, Kd to tune. But in a PI controller there are only two parameters Kp, Ki to tune. The former is much easier than the latter. A well-tuned PI controller performs better than a poorly tuned PID controller. However, usually a well tuned PID controller performs better than a well tuned PI controller. But how to tune a PID controller that has three tuning constants? My answer is to use BESTune( The PID equations I collected are all in continous-time form. Before implementing them in a digital computer, we have to discretize them. How? Very easy and simple. I will post the discretized PID equations some time later. Danyang Liu

Friedrich Haase

Moin Danyang Liu, moin all, >I am collecting PID equations implemented in various PLCs. PID algorithms not only differ by the equation they use. Consider to analyse the method for anti-integrator-wind-up and for the ringing problem. Just my 0.01 Euro. Regards Friedrich Haase