Open Loop Tuning using Ziegler Nichols

[bigbang]

I'm trying to tune a difficult temperature loop with a long response time (around 30 minutes) and thought I'd go back to proven methods rather than using the "suck it and see" approach.

Only problem is I'm confusing myself trying to determine the process gain which equals the %Change in Process Value/% Change in Manipulated Value.

How do you determine the % Change in Process Value. What is the change a percentage of?

For example if the temperature changes from 95Deg C to 105 Deg C with an output change of 35 to 42 % what is the process gain.

 

[JLSeagull]

Consider posting your question in Control Systems under the Industry forums.

 

[bigbang]

Thanks I'll do that