IGC’s operations area personnel are experiencing problems with a particular feedback control loop on an interstage cooler. Appelpolscher has asked you to assess the situation and report back what remedies, if any, are available. The control loop is exhibiting an undesirable sustained oscillation that the operations people are sure is caused by the feedback loop itself (e.g., poor controller tuning). They want assistance in retuning the loop. Appelpolscher thinks that the oscillations are caused by external disturbances (e.g., cyclic disturbances such as cycling of the cooling water temperature); be wants the operations people to deal with the problem themselves. Suggest a simple procedure that will allow you to determine quickly what is causing the oscillations. How will you explain your logic to Appelpolscher?