Q1: Floating control action

ANS:A - moves the final control element at constant speed in either direction in response to an error signal.

The statement "moves the final control element at constant speed in either direction in response to an error signal" describes a specific type of control action known as proportional control. Explanation:

1. Proportional Control: In proportional control, the final control element (such as a valve, damper, or motor) responds to the error signal generated by comparing the desired setpoint with the actual process variable. The error signal represents the deviation between the setpoint and the actual value of the process variable.
2. Constant Speed: In proportional control, the final control element is adjusted or moved at a constant speed proportional to the magnitude of the error signal. The larger the error signal, the faster the control element moves. This ensures that the control action is proportional to the deviation from the setpoint.
3. Bidirectional Movement: Proportional control allows the final control element to move in either direction based on the sign of the error signal. If the process variable is below the setpoint, the control element moves in one direction to increase the process variable. Conversely, if the process variable is above the setpoint, the control element moves in the opposite direction to decrease the process variable.
4. Response to Error Signal: The movement of the final control element is directly proportional to the magnitude of the error signal. This means that as the error signal decreases (indicating that the process variable is approaching the setpoint), the speed of movement of the control element decreases as well, eventually coming to a stop when the error signal reaches zero and the process variable matches the setpoint.
5. Proportional Band: The proportionality of the control action is determined by the proportional band, which is a range of error values within which the control action is proportional to the error signal. Outside this range, other control actions such as integral or derivative control may be applied to improve control performance.