Loop check-list

Thorough loop checking is a complex task that confirms overall system integrity. It can be divided into five phases, performed in the order listed below. 

In the case where the final element is not tested, Operations performs a functional check of that loops final trip element during the next routine startup or shutdown of the process unit. Operations then takes test credit for the final element prooftest, which is listed separately as their responsibility on the Prooftest Program. 

Observe that the number 2 recurs, establishing that there is a recycle and that it includes operations 2 and 3. These operations are combined into one unit, label it 10. All operations within a loop must be solved together (usually by iteration). While following the streams, if an output stream is followed that is not a feed to another operation, e.g., S08 from operation 5, check for another output from that operation (there is one—509) and follow it. Continue listing the operations encountered ... 

The control computer/DCS system consists of controllers, A/D and D/A converters, and the signal conditioifing hardware and software, i.e., filtering and validation. Each of these components requires separate evaluation. Table 15.5 lists possible problems with the controller/DCS system. One way to initially check controller tuning is to place the control loop in manual (open the control loop) and observe whether the controlled variable lines out to a steady-state or near steady-state value. Comparing the open-loop and closed-loop performance indicates whether the controller is upsetting the process. If not, disturbances to the control loop in question are the primary source of the upsets. 

In Check it 2.3.12 a homonuclear COSY magnitude calculation spectrum [2.34] is converted into its various phase sensitive analogues. Fig. 2.8 shows the phase incrementation and loop commands necessary for this conversion. Table 3.5 in chapter 3 lists the recommended processing parameters to use for the different types of experiment. The gradient based Echo/Antiecho COSY experiment is discussed further in section... 

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