Relay-feedback testing Sequential

The four composition control loops each have a 5 min deadtime. They were tuned using a sequential method. Because reboiler heat input affects aU of the controlled variables fairly quickly, the Xb(x/<2r loop was tuned first with the other three controllers on manual. Relay-feedback testing was used to find the ultimate gain and period. Tyreus-Luyben tuning rules were used. Next, since reflux affects all compositions, the Xixt)IR loop was tuned using the same procedure with the Xb(j) Q loop on automatic. Then the Xs(x> loop was tuned with the two loops on automatic. Finally, the ypio(x) loop was tuned with the other three loops on automatic. Table 12.2 gives controller tuning results for aU four loops. 

The two interacting temperature loops are tuned using conventional sequential tuning. The faster of the two loops (Stage 35-to-reboiler duty) is tuned first with the other loop on manual. Then the Stage 10-to-R/F loop is tuned with the first loop on automatic. Relay-feedback tests of this loop show the shark s tooth shape associated... 

Perform a sequential relay-feedback test to find the ultimate gain K and ultimate period (FJ. 

Once the controller structure is determined, sequential relay-feedback tests are performed to find the PI controller settings shown in Table 13.5. Similar to the settings for temperature control (Table 13.2), we have large reset times associated with the feed ratio and much smaller reset times for the heat input. Again, the control systems are designed in a systematic manner with minimal complexity in the design steps, identification, tuning, and controller types. 

Controller Timing. The composition controller and the temperature controller ate tuned by running relay-feedback tests and using Tyreus-Luyben tuning. Table 15.1 provides parameter values. The temperature controller was tuned first, with the composition controller on manual. Then the composition controller was tuned with the temperature stiU on automatic (sequential tuning). The level controllers are proportional only with gains of 2. 

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