How do you design and tune a cascade control system?

Cascade design requirements: secondary loop must be faster than primary (typically 3-5 times faster), secondary measurement must indicate disturbances affecting the primary, and secondary variable should respond to the primary manipulation. Tuning procedure: first tune secondary loop with primary in manual (fast, tight tuning), then tune primary loop with secondary in cascade (slower, conservative tuning). Secondary should reject disturbances before affecting primary. External reset from primary to secondary prevents windup during mode changes.