System Optimization & Troubleshooting Flashcards

During system commissioning, a thermocouple reading shows a constant 25°C (room temperature) regardless of process temperature. What is the most likely cause?

Answer: Open thermocouple circuit (broken wire or failed junction)

An open thermocouple circuit causes the transmitter to default to the cold junction (ambient) temperature, resulting in a constant reading at room temperature.

What is 'split-range control' used for in process automation?

Answer: Driving two or more final control elements sequentially with a single controller output signal

Split-range control assigns different portions of the 0-100% controller output signal to different valves (e.g., 0-50% to cooling, 50-100% to heating) for wider rangeability.

A heat exchanger temperature control loop has been retuned multiple times but still shows poor performance. An energy balance reveals the steam supply pressure varies significantly. The best long-term solution is:

Answer: Install a cascade controller with steam pressure as the inner loop

Cascading steam pressure as the inner loop rejects pressure disturbances before they propagate to the temperature, giving the outer loop a more stable manipulated variable.

Which of the following best describes 'integral windup' and its typical remedy?

Answer: Accumulation of integral action when the output is saturated; remedy is to clamp or track the output

Integral windup occurs when the integrator keeps accumulating error while the output is already at its limit; anti-windup clamping or back-calculation stops the integrator at saturation.

A rotary control valve shows good linearity near mid-stroke but poor flow control near the closed position. Which trim characteristic would best correct this?

Answer: Equal-percentage trim

Equal-percentage trim provides higher resolution near the closed position by increasing flow more gradually, which improves controllability at low-flow conditions.

When troubleshooting a DCS network communications failure between a controller and remote I/O, which tool is most useful for diagnosing packet loss on an Ethernet-based fieldbus?

Answer: Network protocol analyzer (e.g., Wireshark)

A network protocol analyzer captures and decodes Ethernet frames, enabling visibility into packet retransmissions, errors, and timing issues causing communication failures.

In the context of ISA-106 (Procedural Automation), what is the key advantage of implementing automated startup procedures over manual operator procedures?

Answer: Reduces unit startup time and ensures consistent execution of each step

Procedural automation enforces a standardized, repeatable sequence every time, reducing both the time to achieve stable operation and the risk of human error during startups.