CCST Instrumentation & Process Control 4

Question 1

Which PID tuning method involves cycling the process at the ultimate gain to determine ultimate period and then applying tuning formulas?

Accepted Answer

Ziegler-Nichols closed-loop (ultimate cycling) method

Answer

The Ziegler-Nichols closed-loop method increases controller gain until sustained oscillation occurs, then uses the ultimate gain and ultimate period to calculate PID settings.

Question 2

A thermowell is installed around a temperature sensor in a process pipe. What is the primary function of the thermowell?

Accepted Answer

To protect the sensor from process pressure, corrosion, and flow erosion while allowing removal without process shutdown

Answer

A thermowell mechanically isolates the sensor from the process fluid, protecting it from pressure and corrosion, and allowing in-service removal without process interruption.

Question 3

What is 'integral windup' in a PID controller, and when does it typically occur?

Accepted Answer

Accumulation of integral action during periods when the output is saturated, causing overshoot when the constraint is removed

Answer

Integral windup occurs when the controller output saturates (e.g., valve fully open/closed) while the integral term keeps accumulating error, resulting in large overshoot when the process variable returns to range.

Question 4

For a vortex flowmeter to operate correctly, which condition is most important regarding the process fluid?

Accepted Answer

The Reynolds number must be sufficiently high (turbulent flow)

Answer

Vortex meters require a minimum Reynolds number (typically >10,000–20,000) to ensure the Kármán vortex street is well-established and measurable.

Question 5

A 4-wire RTD is preferred over a 2-wire RTD in precision temperature measurement because:

Accepted Answer

It eliminates lead wire resistance error from the measurement

Answer

A 4-wire RTD uses two wires to supply excitation current and two separate wires to sense voltage, so lead resistance does not contribute to the measured value.

(CCST) Certified Control Systems Technician Practice Test

(CCST) Certified Control Systems Technician Practice Test

CCST Instrumentation & Process Control 4