Chapter 8 · MCQ Read Mode

Instrumentation and Process control

The primary objective of a process control system is

A control problem in which the set point is held constant and the controller must counteract disturbances is called

The proportional band of a controller is related to its gain by

A purely proportional controller always leaves a steady-state offset because

Increasing the gain of a proportional controller will

Integral action in a controller is used principally to

Reset windup in a PI controller occurs when

Derivative action cannot be used alone as a control mode because

Derivative action is generally avoided on flow control loops because

An air-to-open control valve will, on failure of the instrument air supply,

For cooling water supplied to an exothermic reactor, the control valve should be selected as

An equal percentage valve characteristic means that

Cavitation in a control valve occurs when the pressure at the vena contracta falls below the liquid's vapour pressure and

The principal advantage of feedforward control over feedback control is that it

The most serious limitation of pure feedforward control is that

In a cascade control system, the output of the master controller serves as

For cascade control to be effective, the inner (slave) loop must be

In a cascade control system, integral action is normally required in

In ratio control, the stream that is measured but not manipulated is called the

The preferred implementation of ratio control multiplies the measured wild flow by the desired ratio rather than dividing two measurements because

Split-range control refers to an arrangement in which

Tray temperature is commonly used to control composition in a distillation column because

Pressure control is established first on a distillation column because

In the relative gain array, a relative gain of exactly 1.0 for a particular pairing indicates that

A pairing with a negative relative gain should

Cascade control of reactor temperature onto jacket temperature is used because

A first-order system subjected to a step input reaches what percentage of its final value in one time constant?

A first-order system responding to a step change

A liquid level tank whose outflow is maintained by a constant-displacement pump behaves as

A second-order system with a damping coefficient of 0.5 will

The fastest response of a second-order system that exhibits no overshoot at all occurs when the system is

The decay ratio of an underdamped second-order response is related to the overshoot by

Two non-interacting first-order systems in series will produce a response that is

A U-tube manometer is a classic example of a second-order system because it possesses

Compared with the corresponding non-interacting system, two interacting tanks in series give a response that is

The transfer function representing a dead time of θ is

Dead time is particularly troublesome in a feedback control loop because it

A process with a large ratio of dead time to time constant is best handled by

Inverse response, in which the output initially moves in the direction opposite to its eventual change, is caused by

For a simple feedback loop, the closed-loop transfer function for a set point change is

When a first-order process is placed under proportional control, the closed-loop time constant is

For a first-order process under proportional control with loop gain product KcKp, the offset following a unit step change in set point is

Adding integral action to a proportional controller on a first-order process

The characteristic equation of a feedback control system is

A feedback control system is stable if and only if

If one coefficient of the characteristic polynomial is negative while the others are positive, the system is

In the Routh array, the number of roots lying in the right half of the complex plane equals

The ultimate gain of a control loop is the proportional gain at which

Which of the following changes tends to make a control loop less stable?

A first-order process controlled by a purely proportional controller is

The standard electronic instrument signal range is

Persistent cycling of an otherwise well-tuned control loop is most commonly caused by

When a stable linear system is subjected to a sustained sinusoidal input, the output is

For a first-order lag at the corner frequency, the amplitude ratio and phase angle are

The high-frequency asymptote of the Bode amplitude plot for a first-order lag has a slope of

The amplitude ratio of a pure dead time element is

According to the Bode stability criterion, a closed-loop system is stable if the open-loop amplitude ratio is

The phase angle contributed by a pure integrating element is

The gain margin of a control loop is defined as

A recommended design value for the phase margin of a control loop is

In the Ziegler-Nichols continuous cycling method, the controller gain for a PI controller is set at

The principal practical objection to the Ziegler-Nichols continuous cycling tuning method is that

The process reaction curve method of tuning requires

Among the integral error criteria, the one that gives the least oscillatory controller settings is

A control loop that cycles slowly and continuously, and whose behaviour does not improve at any controller setting, most probably suffers from

The accuracy of an instrument refers to

A thermocouple generates an EMF as a result of

Compared with a thermocouple, a platinum resistance thermometer offers

A piezoelectric pressure transducer is unsuitable for measuring

An electromagnetic flowmeter can be used only when the fluid

The instrument that measures true mass flow rate directly, rather than inferring it from volumetric flow, is the

Differential pressure measurement of liquid level requires that

The Karl Fischer titration is used specifically for the determination of

At 25 °C, the theoretical response of a glass pH electrode is approximately

The glass membrane of a pH electrode must never be allowed to dry out because

pH control is regarded as one of the most difficult control problems because

In reversed phase HPLC, the stationary phase is non-polar and the mobile phase polar, so

HPLC is preferred to gas chromatography for the analysis of