The Feedback Control Loop & Damping

A jacket-water control loop must maintain temperature at 90°C. The sensor reads 85°C after a disturbance. Which controller action best reduces the error while avoiding excessive overshoot in the shortest settling time?

• Aggressive gain with underdamped response and quick oscillations

• Critically damped tuning balancing speed and stability

• Highly overdamped tuning with very slow correction

• Integral-only action with prolonged windup effects

You are diagnosing a control loop where the PV oscillates around the SP with repeated overshoot after a step change. Valve wear is increasing. What tuning change should you recommend first?

• Increase damping to move toward critically damped behavior

• Decrease damping to reduce sluggishness and increase speed

• Remove proportional action and rely on integral only

• Raise the set point to reduce the controller error

A process loop uses a controller to compare PV and SP, compute error e(t)=SP−PV, and drive the final control element. A sudden disturbance D reduces PV. Which sequence best describes how the loop restores PV?

• Sensor lowers SP, controller reduces OP, process raises PV

• Controller detects error, increases OP, FCE manipulates process

• Process increases PV, controller sets SP, sensor closes loop

• FCE senses PV, controller changes SP, process changes OP

You must choose between two tunings for a fuel viscosity loop. Option A reaches SP quickly but oscillates with 10% overshoot. Option B reaches SP slowly with no overshoot and long settling. Which selection minimizes mechanical stress while keeping response practical for operations?

• Option A because faster rise time outweighs oscillation impacts

• Option B because overdamped response prevents wear entirely

• A compromise near critical damping balancing rise and overshoot

• Neither option; disable feedback and switch to manual mode

You are tuning a tank level controller. The valve saturates fully open for several minutes while inflow is restricted upstream. When supply returns, the level surges and overshoots badly. What mechanism most plausibly caused this behavior, and what mitigation is most defensible?

• Integral windup; implement output clamping and integrator back-calculation

• Derivative kick; increase derivative filter time constant substantially

• High proportional gain; halve Kp and leave other terms unchanged

• Deadband nonlinearity; tighten valve resolution and increase hysteresis

During commissioning, a flow loop exhibits jittery valve motion when derivative action is enabled. The sensor has significant high-frequency noise. Which reasoning leads to the most appropriate controller adjustment?

• Disable or heavily filter derivative because D amplifies noise

• Increase integral time because I averages noise over time

• Increase proportional gain because P rejects measurement noise

• Add feedforward because derivative cannot respond to noise

After a setpoint step, the proportional-only response shows a steady output below setpoint for a constant disturbance. Which explanation aligns with proportional control behavior and informs next steps?

• P needs nonzero error to create output, leaving offset

• P inherently integrates past error, eliminating offset

• P predicts future error using rate, removing offset

• P cancels disturbances by adding derivative kick automatically

You inherit a PID loop with severe overshoot and long settling time after actuator saturation events. As a systematic plan, which two-step sequence is most justified to restore robust behavior?

• Add anti-windup first, then retune Kp, Ti, and Td

• Increase derivative gain first, then disable integral term

• Reduce proportional gain first, then remove D action

• Disable P temporarily, then rely solely on integral action

In a thermal system showing overshoot after adding integral action during trial-and-error tuning, which adjustment best justifies a faster response without increasing oscillations?

• Add a small derivative term to damp overshoot

• Decrease Kp to eliminate steady-state error

• Increase integral time to amplify overshoot

• Remove P action and rely on I only

A loop tuned by Ziegler–Nichols exhibits marginal stability during Ku determination. Which action best preserves the method’s intent while ensuring safety and valid measurements?

• Approach Ku gradually with small Kp increments

• Jump Kp quickly to force large oscillations

• Enable integral action to stabilize during test

• Add derivative action to hold constant amplitude