TWO STEP CONTROLLER ACTION is the action of a controller whose output signal changes from one predetermined value to another when the deviation changes sign. This controller action is mainly on/off control, for example, a refrigeration unit controlling room temperature, when the temperature rises to a predetermined value the refrigerating compressor motor automatically starts, then when the temperature falls to a predetermined value the motor is stopped. PROPORTIONAL CONTROLLER ACTION is the basic action form of a continuous controller whose output signal is proportional to the deviation. In the case of a boiler water level control, if the water level in the boiler, due to increased steam demand, drops by 20 mm, then the automatic controller output to the feed water inlet valve may change from 0.6 to 0.7 bar. If the level drops by 40mm, then the automatic controller output would change from 0.6 to 0.8 bar. Offset or droop is an inherent characteristic of proportional controllers. When a load change occurs in a controlled system a proportional change occurs in the controller which results in an offset or steady state error to the desired value. INTEGRAL CONTROLLER ACTION is the action of a controller whose output signal changes at a rate which is proportional to the deviation. It is used in conjunction with proportional control in order to remove offset inherent in the proportional controller. DERIVATIVE CONTROLLER ACTION is the action of a controller whose output signal is proportional to the rate at which the deviation is changing. The principle object of derivative control is to give quicker response to system changes. Sophisticated controllers for rapid response, minimum offsets and reset action would be three term controllers i.e. proportional plus integral plus derivative. 1.TWO STEP CONTROLLER ACTION is mainly _____. A. proportional control B. integral control C. derivative control D. on-off control 2. The word "offset" most probably means _____. A. predetermined value B. measured value C. off-limit D. sustained deviation 3.Which kind of the following controllers is the most sophisticated controller? A. Proportional controller B. Integral controller C. Derivative controller D. PID controller 4.From the passage, we can learn that the simplest controller action is _____. A. TWO-STEP CONTROLLER action B. PROPORTIONAL CONTROLLER action C. INTEGRAL CONTROLLER action D. DERIVATIVE CONTROLLER action