Multiply the ultimate gain setting in the controller by 0.45. Multiply the ultimate period by 0.83. Multiply the ultimate gain setting in the controller by 0.67. Multiply the ultimate period by 0.50. Control loops likely to have significant noise are pressure and flow.
Information produced by the open-loop test is the loop deadtime and the loop time constant.
Following an open-loop test the recorded information should closely resemble the Open Loop Test Results diagram below. A side benefit to conducting and recording the open-loop test is the establishment of a loop signature for future reference in determining if the process has changed. For example, if the loop signature is for a temperature controller on a heat exchanger, a significant change in the loop signature could indicate the heat exchanger is losing efficiency. Controller scan times should be at least eight times faster than the loop time constant. Level, batch temperature, batch pressure, and pH tanks are examples of integrating processes.