Professional Marine Training
A high-detail TST infographic for MCA oral preparation covering closed-loop control, P/PI/PID action, tuning, marine control signals, thermocouples and PT100 temperature measurement.
Sections
10
Focus
Orals
Signals
4-20mA
Sensors
TC/PT100
This page supports MCA oral preparation by turning control theory into spoken engineering answers. It links the quiz and flashcards into one structured revision sheet.
A closed-loop controller measures the process variable, compares it with the set point, calculates error and adjusts the final control element to reduce that error.
Module 29
Instrumentation senses, displays and transmits process conditions. Control systems compare operator demand with the measured condition and alter the process through a final control element.
Define the process, state the set point, read the measured value, calculate error, correct through a final element and use feedback to self-correct.
Module 29
A closed loop contains set point, process variable, comparator, controller, final control element, process and feedback. The comparator creates error; the controller acts to reduce it.
Use this as the generic oral explanation route: set point → controller → final element → process → sensor/transmitter → feedback.
Exam example showing a practical marine loop with transmitter, controller, I/P converter, control valve, heat exchanger and disturbance input.
Draw the loop and explain it clockwise. Do not just name the equipment.
Module 29
Two-step control has on/off output and a dead band. Continuous control gives modulating output and holds the process closer to set point.
Use thermostat and jacket-water temperature control examples.
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Proportional responds to present error. Integral removes steady offset by accumulating error. Derivative responds to rate of change and improves damping when the signal is clean.
Output changes in proportion to error. Too much gain can hunt; too little is sluggish.
Removes offset by accumulating error. Too much can create wind-up and slow oscillation.
Rate action improves damping but is sensitive to noisy feedback signals.
P = present error, I = accumulated error, D = rate of change.
Module 29
Safe tuning starts by verifying the loop and final element, using manual mode, proving direction, applying P-only tuning, then adding I gradually and D only if needed.
Never tune live critical plant aggressively. Use small changes, stable conditions, trends and records.
Module 29
Common signals include 4-20 mA current loops and 0.2-1 bar pneumatic signals. Both are live-zero ranges. Pneumatic actuators convert air pressure into valve stem motion.
Current loop; less affected by voltage drop; 4 mA live zero helps fault finding.
Pneumatic live-zero signal; simple and safe but needs clean dry air.
Valve, actuator, damper, VFD or fuel rack physically changes process energy or mass flow.
Explain why current signals reduce voltage-drop error and why live zero helps fault detection.
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A thermocouple uses two dissimilar metals. Temperature difference between hot and reference junctions creates an EMF by the Seebeck effect. Cold junction compensation is required.
Shows the hot junction, reference junction / cold-junction compensation, signal conditioning and the measurement path into the control or monitoring system.
Mention material pairs, high-temperature use, low signal level, signal conditioning and noise/wiring faults.
Module 29
A PT100 is a platinum RTD with 100 ohms at 0 C. Resistance changes predictably with temperature and is measured using bridge/transmitter circuits with lead compensation.
Platinum RTD, 100 ohms at 0 C.
Rt = R0(1 + alpha t) for basic oral explanation.
3-wire cancels lead resistance; 4-wire is used for longer/high-accuracy runs.
Useful for oral questions on RTD input, transmitter scaling, lead compensation and the 4–20 mA output to PLC / DCS / indicator systems.
Detailed sheet showing PT100 construction, 2-wire / 3-wire / 4-wire arrangements, transmitter path and a practical jacket-water control loop.
Use Rt = R0(1 + alpha t), then explain 3-wire and 4-wire compensation.
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Thermocouples are rugged, low cost, fast and high-temperature capable but less accurate. PT100s are accurate and stable but cost more and can be slower or vibration sensitive.
Select thermocouple for high-temperature rugged service; PT100 where accuracy and stability matter.
Module 29
For any question, define the term, place it in the loop, give the marine example, explain the failure/risk and state the safe practical action.
Use maker procedures, SMS, trend records and do not invent exact tuning constants.