To tune a cascade control-system the following procedure is suggested ?
1.Place both controllers in manual.
2.Adjust proportional and integral settings to conservative values (wide proportional band and long integral time) on the secondary controller
3.Place secondary controller in automatic and tune
4.Adjust the proportional integral and derivative settings on the primary controller to conservative starting values.
5.Place the primary controller in automatic and then tune.
Always tune the secondary controller first(with the primary controller in manual) and then the primary controller.