AME Unit 11 PID, Engine Governors, Control Terms
State the reasons for fitting a pneumatic process valve with a volume booster.
A) A volume booster is fitted to increase the flow rate of air to the actuator, enabling faster valve movement and reducing the time required to achieve the desired valve position.
How does hysteresis improve the performance of an On-Off control system?
B) It prevents rapid cycling by creating a dead zone between switching on and off.
What is the relationship between proportional band and gain in a control system?
B) Proportional band is inversely proportional to gain.
Explain integral action in control terms.
A) Integral action refers to the ability of a control system to eliminate steady-state error by continuously adjusting the control output based on the accumulated error over time.
Explain dead zone in control terms.
A) Dead zone refers to a range within which changes in input do not produce any change in the output of a control system. Reason: This correctly describes dead zone as a region where the system is unresponsive to inputs within that range.
In an On-Off control system, what happens when the controlled variable exceeds the set point?
B) The system switches off the output to bring the variable back to the set point.
Explain hysteresis in control terms.
A) Hysteresis is the phenomenon where the output of a control system depends on its past input, causing a lag or delay in response. Reason: This describes hysteresis correctly, where the system’s output is influenced by the history of inputs, leading to different responses for increasing versus decreasing inputs.
Explain the purpose of Derivative Action.
B) Derivative Action helps to anticipate future errors by reacting to the rate of change of the error, thereby improving the system’s stability and response time.
With reference to hydraulic governors fitted to alternators designed to run in parallel, explain why these governors have adjustable integral action.
B) To ensure that the governor can handle variations in load and maintain stable operation by adjusting the steady-state accuracy.
Describe the reasons for integrating the error signal and the effect it has on the governor fuel rack.
A) Integrating the error signal helps in eliminating steady-state error by providing continuous correction over time, leading to a gradual adjustment of the governor fuel rack to maintain the desired engine speed.
How can the gain of a control system be increased or decreased?
A) Increase the gain by reducing the proportional band; decrease the gain by increasing the proportional band.
State the reasons for fitting a pneumatic process valve with a feedback positioner.
A) A feedback positioner is fitted to monitor the valve position and provide real-time correction signals to ensure the valve remains at the desired position, improving accuracy and stability in the process control.
With reference to engine governors, explain speed droop.
A) Speed droop is the reduction in engine speed that occurs when the engine is subjected to an increase in load, relative to the no-load speed. Reason: Speed droop measures how much the engine speed decreases from its no-load speed when a load is applied.
With reference to engine governors, explain stability.
A) Stability refers to the governor's ability to maintain a constant engine speed without oscillations or fluctuations when subjected to varying loads. Reason: Stability in governors is about how consistently the engine speed is maintained despite changes in load or other disturbances.
What is a potential drawback of using an On-Off control system?
B) It is unable to achieve precise control, leading to oscillations around the set point.
Explain derivative action in control terms.
A) Derivative action involves adjusting the control output based on the rate of change of the error, aiming to predict future errors and reduce overshoot.
What is the primary characteristic of a Discontinuous (On-Off) control system?
B) The output is either fully on or fully off, with no intermediate states.
2. Which of the following is a typical application of an On-Off control system?
B) Temperature control in a household thermostat.
Explain the purpose of Integral Action.
B) Integral action integrates the error over time to eliminate steady-state error, ensuring that the system eventually reaches the setpoint.
With reference to hydraulic governors fitted to alternators designed to run in parallel, explain how two generators operating in parallel are able to achieve a stable load share with a 50/50 ratio.
C) By synchronizing the generators' speed and voltage settings, and using governors with equal proportional and integral action to balance the load distribution.
With reference to engine governors, explain sensitivity.
B) Sensitivity refers to the governor’s response to small changes in the fuel supply, affecting the engine speed control. Reason: A sensitive governor will react quickly to minor adjustments in fuel input, thereby maintaining precise engine speed control.
With reference to engine governors, explain hunting.
A) Hunting is the term used to describe a governor's inability to maintain a constant engine speed due to excessive fluctuation in engine speed around a set point. Reason: Hunting occurs when the governor repeatedly overshoots and undershoots the target speed, causing erratic engine performance.
What happens when the flow out is increased in a system where the water tank level is controlled by a float and lever proportional system?
B) The float drops, causing the control valve to close, reducing the inflow.
Explain proportional bandwidth in control terms.
C) Proportional bandwidth is the width of the proportional band within which the control action is active and varies linearly with the error.
Describe integral action in a control system.
B) Integral action increases the control output to eliminate steady-state error over time by integrating the error signal.
State with reasons, the type of actuator fitted to the process valves for a fuel supply system in which the valve must not move on loss of power to the control system.
A) Electric Actuator with Fail-Safe Mechanism: Reason: This actuator includes a fail-safe mechanism that ensures the valve remains in its last position or moves to a predetermined safe position if there is a loss of power.
Explain settling time in control terms.
B) Settling time is the time required for the system's output to remain within a specified range around the set point after a disturbance, and it measures the time until the output stops oscillating significantly. Reason: This correctly describes settling time as the time it takes for the output to stay within a certain percentage of the set point and cease significant oscillations.
Define the term Proportional Action.
A) Proportional action adjusts the control output based on the magnitude of the error, where the output is directly proportional to the difference between the setpoint and the actual value.
How is the level in a water tank controlled by a float and lever proportional system?
A) The float rises with the water level, causing the lever to close a valve, stopping the inflow of water when the desired level is reached.
Describe the effect of increasing the controller gain with respect to the steady-state tank level when the outflow is increased in a float and lever proportional system.
B) The steady-state tank level will oscillate more and be less stable.
Describe the effect of excessive Derivative Action.
B) Excessive Derivative Action can cause the system to become overly sensitive to noise, leading to oscillations and instability.
Explain repeatability in control terms.
A) Repeatability refers to the ability of a control system to return to the exact same output every time a specific input is applied, assuming no changes in system conditions. Reason: This accurately describes repeatability as the system's ability to consistently produce the same output for the same input under unchanged conditions.
With reference to engine governors, explain isochronous governing.
A) Isochronous governing ensures that the engine speed remains constant regardless of the load applied, maintaining the same speed even with varying demands. Reason: Isochronous governing is designed to keep the engine speed constant, independent of changes in load.
Describe using control block diagram terms how a governor maintains the speed of a diesel engine driving a generator.
B) The governor compares the actual engine speed to the desired speed setpoint and uses a proportional-integral-derivative (PID) control block to adjust the fuel input and maintain the engine speed.
State with reasons, the type of actuator fitted to the process valves for a lubrication oil cooling system in which the valve diverts the oil through a cooler.
B) Pneumatic Actuator: Reason: Pneumatic actuators provide reliable and fast operation and are well-suited for applications requiring frequent adjustments to the valve position, such as diverting oil flow through a cooler.
Describe a possible effect of excessive Integral Action.
B) Excessive Integral Action can cause the system to oscillate or exhibit sustained oscillations around the setpoint due to an overcompensation of errors.
Explain proportional bandwidth in control terms.
A) Proportional bandwidth refers to the range of input values over which the proportional control action is effective in adjusting the output of a system. Reason: This describes how the range within which proportional control can operate effectively is defined, focusing on the input values that impact the output.
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