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These 10 free C-271 questions are organized by exam domain, so you can see how each part of the Process Control Systems 2 - Temperature blueprint is tested. Reveal the answer and explanation under each question.
A heated circulation vessel is approaching its high-temperature limit. The controller demands 0% heat and the solid-state relay has no input drive, yet the heater ammeter still shows full load current. The heater emergency-stop opens a separate supply contactor and leaves the circulation pump running. What is the immediate operating response?
Correct answer: D - Operate the heater emergency-stop to open the supply contactor.
The approved loop sheet for TT-204 specifies a linear 4-20 mA signal for −40 to 160°C. The transmitter is correctly configured and has passed its calibration checks. During commissioning, its output measures 12.0 mA. The receiving indicator is configured for 0-200°C and displays 100°C. Which temperature and corrective action belong in the commissioning record?
Correct answer: C - 60°C; correct the receiving indicator range to −40 to 160°C.
An I/P converter serving a three-way temperature-control valve is specified for 4-20 mA input, 3-15 psig output, and a 20 psig air supply. At a verified 20.0 mA input, its output reaches only 10.5 psig. A calibrated gauge at the converter supply port reads 11 psig under the same conditions. Before changing calibration adjustments, the technician should:
Correct answer: C - Restore the specified air supply at the converter, then retest.
A three-way water-mixing valve is at half stroke. Measured inlet flows are 2.0 kg/s at 80°C through port A and 1.0 kg/s at 20°C through port B; both streams leave through AB. Assume steady flow, equal specific heat, and negligible heat loss. The required outlet temperature is 50°C. What outlet temperature should be expected, and in which direction should the hot-water fraction be adjusted?
Correct answer: D - 60°C; decrease the hot-water fraction.
A bench transmitter is configured for Type K with internal cold-junction compensation and no offset. Its input terminals are bridged with a copper jumper at a uniform 28°C; the stabilized indication is 28°C. How should this particular check be judged?
Correct answer: D - The reading is correct: a shorted, compensated input indicates terminal temperature.
An isolated three-wire Pt100 probe has leads marked P, Q, and R. Stable resistance measurements are P-Q = 110.7 Ω, P-R = 1.0 Ω, and Q-R = 110.7 Ω. The transmitter diagram requires terminals 1 and 2 to connect separately to the same end of the element, with terminal 3 at the opposite end. Which wiring preserves three-wire lead-resistance compensation?
Correct answer: B - P to terminal 1, R to terminal 2, and Q to terminal 3.
A four-wire Pt100 and an independent reference are held in a stable, well-stirred bath. Increasing RTD excitation makes the Pt100 indication settle at a higher temperature, while the reference remains unchanged. Reducing excitation reverses the shift. A precision resistor substituted for the probe reads correctly at both excitation settings. These findings point to:
Correct answer: A - Self-heating of the RTD element.
After an NTC thermistor is replaced, an indicator agrees with a reference at 25°C but develops a substantial error at 75°C. Both the old and new parts are rated 10 kΩ at 25°C, but their specified resistance-temperature curves differ. The replacement measures correctly against its own datasheet at both test temperatures. The indicator supports both curves but still uses the old selection. Which correction addresses the cause?
Correct answer: B - Configure the input for the resistance-temperature curve of the installed NTC.
A three-way mixing valve regulates hot water entering a jacket. Increasing the controller current increases I/P output pressure; increasing that pressure closes the hot-water port and opens the cooler return-water port. The measured jacket temperature is rising above a fixed setpoint. To provide negative feedback, how must the controller change its output?
Correct answer: A - Increase output current to raise actuator pressure and close the hot-water port.
Maintenance is called because a tank heater remains ON at 61°C, above the displayed 60°C setpoint. Its approved on/off settings turn heat ON at or below 58°C, turn it OFF at or above 62°C, and retain the previous state between those thresholds. The temperature has risen steadily from 57°C to 61°C without reaching 62°C; the approved operating band is 56-64°C. The service call should be resolved by:
Correct answer: A - Leaving the settings unchanged; the OFF threshold has not been reached.
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