Process Control Basics interview questions

1. A.Laplace-domain ratio of output to input deviation variables for a linear system with zero initial conditions
2. B.raise proportional gain until sustained oscillation, then set PID constants from the ultimate gain and ultimate period
3. C.controller acts on the error between set point and measured variable only after a disturbance has already moved the output
4. D.choice of air-to-open or air-to-close so the valve moves to the safe position (fuel valve shuts, cooling valve opens) on loss of instrument air

Answer + AI explanation with Pro

1. A.Fail-safe valve action
2. B.Feedback control
3. C.Ziegler-Nichols closed-loop tuning
4. D.Bode stability criterion

Answer + AI explanation with Pro

1. A.Feedback control — span of measurement over which controller output moves from 0 to 100%, equal to 100 divided by the proportional gain
2. B.Feedback control — closed loop is unstable when the open-loop amplitude ratio exceeds 1 at the frequency where phase lag reaches 180 degrees
3. C.Feedback control — integral term keeps accumulating while the valve is saturated, causing large overshoot when control is regained; cured by anti-reset-windup logic
4. D.Feedback control — controller acts on the error between set point and measured variable only after a disturbance has already moved the output

Answer + AI explanation with Pro

1. A.steady-state error left by a proportional-only controller after a load change, removed by adding integral action
2. B.first-order-plus-dead-time approximation using gain, time constant and delay, fitted from a step test and used for Cohen-Coon or open-loop tuning
3. C.integral term keeps accumulating while the valve is saturated, causing large overshoot when control is regained; cured by anti-reset-windup logic
4. D.span of measurement over which controller output moves from 0 to 100%, equal to 100 divided by the proportional gain

Answer + AI explanation with Pro

1. A.Fail-safe valve action
2. B.Bode stability criterion
3. C.Proportional band
4. D.FOPDT model

Answer + AI explanation with Pro

1. A.Proportional band — controller acts on the error between set point and measured variable only after a disturbance has already moved the output
2. B.Proportional band — span of measurement over which controller output moves from 0 to 100%, equal to 100 divided by the proportional gain
3. C.Proportional band — raise proportional gain until sustained oscillation, then set PID constants from the ultimate gain and ultimate period
4. D.Proportional band — Laplace-domain ratio of output to input deviation variables for a linear system with zero initial conditions

Answer + AI explanation with Pro

1. A.integral term keeps accumulating while the valve is saturated, causing large overshoot when control is regained; cured by anti-reset-windup logic
2. B.raise proportional gain until sustained oscillation, then set PID constants from the ultimate gain and ultimate period
3. C.steady-state error left by a proportional-only controller after a load change, removed by adding integral action
4. D.first-order-plus-dead-time approximation using gain, time constant and delay, fitted from a step test and used for Cohen-Coon or open-loop tuning

Answer + AI explanation with Pro

1. A.FOPDT model
2. B.Fail-safe valve action
3. C.Integral windup
4. D.Offset

Answer + AI explanation with Pro

1. A.Offset — span of measurement over which controller output moves from 0 to 100%, equal to 100 divided by the proportional gain
2. B.Offset — steady-state error left by a proportional-only controller after a load change, removed by adding integral action
3. C.Offset — closed loop is unstable when the open-loop amplitude ratio exceeds 1 at the frequency where phase lag reaches 180 degrees
4. D.Offset — first-order-plus-dead-time approximation using gain, time constant and delay, fitted from a step test and used for Cohen-Coon or open-loop tuning

Answer + AI explanation with Pro

1. A.span of measurement over which controller output moves from 0 to 100%, equal to 100 divided by the proportional gain
2. B.integral term keeps accumulating while the valve is saturated, causing large overshoot when control is regained; cured by anti-reset-windup logic
3. C.Laplace-domain ratio of output to input deviation variables for a linear system with zero initial conditions
4. D.raise proportional gain until sustained oscillation, then set PID constants from the ultimate gain and ultimate period

Answer + AI explanation with Pro

1. A.Bode stability criterion
2. B.Proportional band
3. C.Transfer function
4. D.Offset

Answer + AI explanation with Pro

1. A.Transfer function — closed loop is unstable when the open-loop amplitude ratio exceeds 1 at the frequency where phase lag reaches 180 degrees
2. B.Transfer function — raise proportional gain until sustained oscillation, then set PID constants from the ultimate gain and ultimate period
3. C.Transfer function — Laplace-domain ratio of output to input deviation variables for a linear system with zero initial conditions
4. D.Transfer function — integral term keeps accumulating while the valve is saturated, causing large overshoot when control is regained; cured by anti-reset-windup logic

Answer + AI explanation with Pro

1. A.span of measurement over which controller output moves from 0 to 100%, equal to 100 divided by the proportional gain
2. B.integral term keeps accumulating while the valve is saturated, causing large overshoot when control is regained; cured by anti-reset-windup logic
3. C.first-order-plus-dead-time approximation using gain, time constant and delay, fitted from a step test and used for Cohen-Coon or open-loop tuning
4. D.raise proportional gain until sustained oscillation, then set PID constants from the ultimate gain and ultimate period

Answer + AI explanation with Pro

1. A.Offset
2. B.Proportional band
3. C.FOPDT model
4. D.Bode stability criterion

Answer + AI explanation with Pro

1. A.FOPDT model — integral term keeps accumulating while the valve is saturated, causing large overshoot when control is regained; cured by anti-reset-windup logic
2. B.FOPDT model — choice of air-to-open or air-to-close so the valve moves to the safe position (fuel valve shuts, cooling valve opens) on loss of instrument air
3. C.FOPDT model — span of measurement over which controller output moves from 0 to 100%, equal to 100 divided by the proportional gain
4. D.FOPDT model — first-order-plus-dead-time approximation using gain, time constant and delay, fitted from a step test and used for Cohen-Coon or open-loop tuning

Answer + AI explanation with Pro

1. A.steady-state error left by a proportional-only controller after a load change, removed by adding integral action
2. B.integral term keeps accumulating while the valve is saturated, causing large overshoot when control is regained; cured by anti-reset-windup logic
3. C.closed loop is unstable when the open-loop amplitude ratio exceeds 1 at the frequency where phase lag reaches 180 degrees
4. D.choice of air-to-open or air-to-close so the valve moves to the safe position (fuel valve shuts, cooling valve opens) on loss of instrument air

Answer + AI explanation with Pro

1. A.Fail-safe valve action
2. B.Integral windup
3. C.FOPDT model
4. D.Ziegler-Nichols closed-loop tuning

Answer + AI explanation with Pro

1. A.Integral windup — span of measurement over which controller output moves from 0 to 100%, equal to 100 divided by the proportional gain
2. B.Integral windup — Laplace-domain ratio of output to input deviation variables for a linear system with zero initial conditions
3. C.Integral windup — integral term keeps accumulating while the valve is saturated, causing large overshoot when control is regained; cured by anti-reset-windup logic
4. D.Integral windup — choice of air-to-open or air-to-close so the valve moves to the safe position (fuel valve shuts, cooling valve opens) on loss of instrument air

Answer + AI explanation with Pro

1. A.controller acts on the error between set point and measured variable only after a disturbance has already moved the output
2. B.span of measurement over which controller output moves from 0 to 100%, equal to 100 divided by the proportional gain
3. C.closed loop is unstable when the open-loop amplitude ratio exceeds 1 at the frequency where phase lag reaches 180 degrees
4. D.raise proportional gain until sustained oscillation, then set PID constants from the ultimate gain and ultimate period

Answer + AI explanation with Pro

1. A.Transfer function
2. B.Proportional band
3. C.Offset
4. D.Ziegler-Nichols closed-loop tuning

Answer + AI explanation with Pro

1. A.Ziegler-Nichols closed-loop tuning — choice of air-to-open or air-to-close so the valve moves to the safe position (fuel valve shuts, cooling valve opens) on loss of instrument air
2. B.Ziegler-Nichols closed-loop tuning — span of measurement over which controller output moves from 0 to 100%, equal to 100 divided by the proportional gain
3. C.Ziegler-Nichols closed-loop tuning — first-order-plus-dead-time approximation using gain, time constant and delay, fitted from a step test and used for Cohen-Coon or open-loop tuning
4. D.Ziegler-Nichols closed-loop tuning — raise proportional gain until sustained oscillation, then set PID constants from the ultimate gain and ultimate period

Answer + AI explanation with Pro

1. A.raise proportional gain until sustained oscillation, then set PID constants from the ultimate gain and ultimate period
2. B.integral term keeps accumulating while the valve is saturated, causing large overshoot when control is regained; cured by anti-reset-windup logic
3. C.closed loop is unstable when the open-loop amplitude ratio exceeds 1 at the frequency where phase lag reaches 180 degrees
4. D.controller acts on the error between set point and measured variable only after a disturbance has already moved the output

Answer + AI explanation with Pro

1. A.Proportional band
2. B.Transfer function
3. C.Fail-safe valve action
4. D.Bode stability criterion

Answer + AI explanation with Pro

1. A.Bode stability criterion — choice of air-to-open or air-to-close so the valve moves to the safe position (fuel valve shuts, cooling valve opens) on loss of instrument air
2. B.Bode stability criterion — steady-state error left by a proportional-only controller after a load change, removed by adding integral action
3. C.Bode stability criterion — first-order-plus-dead-time approximation using gain, time constant and delay, fitted from a step test and used for Cohen-Coon or open-loop tuning
4. D.Bode stability criterion — closed loop is unstable when the open-loop amplitude ratio exceeds 1 at the frequency where phase lag reaches 180 degrees

Answer + AI explanation with Pro

1. A.integral term keeps accumulating while the valve is saturated, causing large overshoot when control is regained; cured by anti-reset-windup logic
2. B.closed loop is unstable when the open-loop amplitude ratio exceeds 1 at the frequency where phase lag reaches 180 degrees
3. C.choice of air-to-open or air-to-close so the valve moves to the safe position (fuel valve shuts, cooling valve opens) on loss of instrument air
4. D.steady-state error left by a proportional-only controller after a load change, removed by adding integral action

Answer + AI explanation with Pro

1. A.Fail-safe valve action
2. B.Transfer function
3. C.Offset
4. D.Integral windup

Answer + AI explanation with Pro

1. A.Fail-safe valve action — first-order-plus-dead-time approximation using gain, time constant and delay, fitted from a step test and used for Cohen-Coon or open-loop tuning
2. B.Fail-safe valve action — controller acts on the error between set point and measured variable only after a disturbance has already moved the output
3. C.Fail-safe valve action — span of measurement over which controller output moves from 0 to 100%, equal to 100 divided by the proportional gain
4. D.Fail-safe valve action — choice of air-to-open or air-to-close so the valve moves to the safe position (fuel valve shuts, cooling valve opens) on loss of instrument air

Answer + AI explanation with Pro