Open and Closed-Loop Feedback Systems:
Using a Gain-Only Controller

Since the gain-only controller can't get the PV to reach the SP, some adjustments must be made to use it successfully. One way to use a gain-only controller is to have a system that's repetitive. E.g., if the technician started the process furnace every day and the SP was only bumped once each day, a gain and setpoint could be determined that would bring the furnace up to a steady-state temperature of 100°F. Since the steady-state temperature will be below the SP, the trick would be to choose the SP high enough above 100°F so that the steady-state temperature would settle out at 100°F. Since the system is always started from 75°F (room temperature), and the steady-state temperature is always 100°F, the SP might be 110°F so that the temperature would always line out at 100°F. Since the system is so consistent, the setpoint and gain could be adjusted slightly to ensure that the steady-state temperature of 100°F could be reached. When gain is changed, the rate of change for the output signal would also be changed, which would make the furnace gain temperature faster if it's increased, and slower if it's decreased.

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