CONTROLLER FUNCTIONS -The controller is the decision-maker in the control loop. -You are the controller when a manual hand valve requires adjustment. INPUT SIGNALS -The input signals are information telling the controller the existing conditions relating to the desired result. -The controller may receive one input signal, two or more in determining the appropriate corrective action. -The controller may sense the existing conditions directly with its own sensing element or receive information signals from transmitters. -When you are manually adjusting a valve, you must obtain information allowing decision to be made regarding the desired position of the valve. OUTPUT SIGNAL -The output signal is the action taken by the controller after the controller compares the desired result (set point) to the actual condition of the controlled environment. The difference is the error from set point or sometimes called droop. -Output signals can be either two position or proportional. Two position will have the controlled device (valve, damper, etc.) either fully open or fully closed. Proportional will gradually modulate the controlled device ranging from fully open to fully closed. -Some controllers can be set up for several specific steps from fully open to fully closed. -When you are required to manually adjust a valve, you must be able to physically change the degree of opening of the valve. PROPORTIONAL BAND, SENSITIVITY, GAIN -These terms relate to the same function, which is the amount of output signal change relating to a specific amount of input change on the controller. -The more insensitive a controller, the more error from set point occurs at load extremes. This error from set point is called droop or offset. -If a controller is hunting or sometimes called cycling, the controller is over-shooting and the sensitivity has to be lessened to settle the system. -When you are manually operating a valve you must gradually open the valve to the proper position or the system will over-shoot. INTEGRAL RESET -Reset is a controller function that corrects the error from set point or droop. Not all controllers have this function. -When manually operating a hand valve on steam you would position the valve more open in cold weather than in warm weather to attain the same degree of heat in the air or water. This is similar to integral reset in controllers. AUTHORITY, RESET -This function allows the set point to vary based on another variable. An example is outdoor/indoor reset on heating hot water. As the outside air becomes colder, the set point for the heating hot water becomes hotter. When manually operating a water temperature for heating, you would likely target a hotter water temperature in cold weather than in warm weather conditions. This is similar to the authority function in controllers. 4.34
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