AME 9 End of Unit

Correct Answer:

C. Ceramic materials and metal oxides.

Explanation:

• C. Correct: Thermistors are commonly constructed from ceramic materials and metal oxides. These materials have properties that change significantly with temperature, allowing thermistors to accurately measure temperature variations.
• A. Incorrect: Silicon and gallium arsenide are used in semiconductor devices, not typically in thermistors.
• B. Incorrect: Iron and cobalt are not standard materials for thermistor construction; they are more commonly used in magnetic and structural applications.
• D. Incorrect: Aluminum and copper are metals used in various electrical applications but are not typical materials for thermistor construction.

Correct Answer:

A. A Bourdon tube can be used to measure the temperature of the engine room exhaust gases, typically located near the exhaust manifold.

Explanation:

• A. Correct: Although Bourdon tubes are primarily used for pressure measurement, in some specific applications, they might be used in conjunction with other systems to measure temperature, such as monitoring exhaust gases where accurate pressure and temperature data are crucial.
• B. Incorrect: The measurement of fuel oil temperature would typically be done with a thermometer designed for liquids, not a Bourdon tube.
• C. Incorrect: Temperature measurements of seawater intake are generally performed with temperature sensors or probes designed for such conditions, not with a Bourdon tube.
• D. Incorrect: Measuring the temperature of boiler water typically requires temperature sensors designed for high-temperature environments, rather than a Bourdon tube.

Correct Answer:

B. The impeller rotation generates pulses, which are counted electronically and converted to an analogue voltage proportional to flow rate.

Explanation:

• A. Incorrect: The mechanical movement of an impeller does not directly translate to an analogue dial reading without electronic processing.
• B. Correct: In an impeller-type flowmeter, the rotation of the impeller generates electrical pulses. These pulses are counted over time, and the count is proportional to the flow rate. This count is then electronically processed and converted to an analogue voltage that corresponds to the flow rate in litres per minute.
• C. Incorrect: An impeller-type flowmeter does not work by creating a pressure differential; instead, it relies on the rotational speed of the impeller.
• D. Incorrect: The impeller does not produce significant heat due to friction, and heat is not used as a means of measuring flow rate in this type of flowmeter.

Correct Answer:

C. By detecting changes in the capacitance between the probe and the tank wall as the liquid level rises or falls, which is then converted into an electrical signal.

Explanation:

• A. Incorrect: Capacitance probes do not generate or use magnetic fields to measure liquid levels.
• B. Incorrect: Capacitance probes measure changes in capacitance, not resistance, to determine liquid levels.
• C. Correct: A capacitance probe works by detecting changes in the capacitance between the probe and the tank wall. As the liquid level changes, the dielectric constant between the probe and the wall changes, altering the capacitance. This change is then converted into an electrical signal that can be used to measure the liquid level.
• D. Incorrect: This describes the operation of an ultrasonic level sensor, not a capacitance probe.

Correct Answers:

A. Monitoring the strain on the ship’s hull to detect structural weaknesses.

C. Monitoring the load on a ship's cargo crane to prevent overloading.

Explanation:

• A. Correct: Strain gauges are used to monitor the strain on a ship's hull, which can help in detecting structural weaknesses or potential failures.
• B. Incorrect: Strain gauges are not used for measuring temperature; thermocouples or resistance temperature detectors (RTDs) would be used for that purpose.
• C. Correct: Strain gauges are commonly used to monitor the load on cargo cranes to ensure that they are not overloaded, which is crucial for safety.
• D. Incorrect: Strain gauges do not measure speed; devices like tachometers are used for this.
• E. Incorrect: Strain gauges do not measure pH levels; specialized sensors are required for pH measurement.

Correct Answer:

A. Pressure transducer

Explanation:

• A. Correct: A pressure transducer is designed to measure pressure, making it suitable for monitoring lubricating oil pressure remotely.
• B. Incorrect: A thermocouple measures temperature, not pressure.
• C. Incorrect: A flowmeter measures the flow rate of fluids, not pressure.
• D. Incorrect: A strain gauge measures strain, not pressure.
• E. Incorrect: A tachometer measures rotational speed, not pressure.

Correct Answer:

A. They have limited accuracy and resolution compared to electronic temperature sensors.

Explanation:

• A. Correct: Bi-metallic strips generally have lower accuracy and resolution compared to electronic sensors like thermocouples or RTDs. They are better suited for applications where high precision is not critical.
• B. Incorrect: Bi-metallic strips are sensitive to temperature changes, but they can have a slower response time compared to some electronic sensors. The issue is more about accuracy rather than sensitivity or response time.
• C. Incorrect: Bi-metallic strips are not typically affected by electromagnetic interference, as they operate on mechanical bending rather than electronic signals.
• D. Incorrect: Bi-metallic strips generally do not require frequent calibration. They are mechanical devices that maintain their calibration unless physically damaged or altered.

Correct Answer:

A. Linear variable differential transformer (LVDT)

Explanation:

• A. Correct: An LVDT is commonly used for precise and remote position measurement, making it suitable for measuring the position of a diesel engine governor or fuel rack.
• B. Incorrect: Pressure transducers measure pressure, not position.
• C. Incorrect: Thermocouples measure temperature, not position.
• D. Incorrect: Ultrasonic flowmeters measure flow rate, not position.
• E. Incorrect: Proximity sensors detect the presence or absence of an object but are not typically used for precise position measurements.

Correct Answers:

A. Monitoring fuel tank levels.
C. Detecting the presence of water in the bilge.

Explanation:

• A. Correct: Capacitance probes are commonly used to monitor liquid levels, such as in fuel tanks.
• B. Incorrect: Flow rate measurement typically involves devices like impeller flowmeters or ultrasonic flow sensors, not capacitance probes.
• C. Correct: Capacitance probes can detect the presence of liquids, making them suitable for bilge water detection.
• D. Incorrect: Temperature measurement is typically done using thermocouples or resistance thermometers, not capacitance probes.
• E. Incorrect: Pressure measurement is typically performed with pressure sensors like Bourdon tubes, not capacitance probes.

Correct Answer:

A. Pressure gauge

Explanation:

• A. Correct: A pressure gauge is designed to measure local pressure readings, making it suitable for measuring the pressure in a ship’s fire-main.
• B. Incorrect: A flowmeter measures flow rate, not pressure.
• C. Incorrect: A thermocouple measures temperature, not pressure.
• D. Incorrect: A strain gauge measures strain, not pressure.
• E. Incorrect: A tachometer measures rotational speed, not pressure.

Correct Answer:

B. By converting rotational movement into a variable resistance through a rotating wiper that contacts a resistive element, which then provides a corresponding voltage output.

Explanation:

• B. Correct: A potentiometer measures rotary movement by having a rotating wiper (contact) that moves along a circular resistive track. As the wiper rotates, it changes the resistance in the circuit. The corresponding voltage output from the potentiometer varies with the angle of rotation, allowing measurement of rotary movement.
• A. Incorrect: A linear resistive track is used for linear movement measurements, not rotary. Potentiometers for rotary movement have a circular resistive track.
• C. Incorrect: This describes a capacitive position sensor, not a potentiometer. A potentiometer does not measure rotary movement by changes in capacitance.
• D. Incorrect: This describes a type of rotary position sensor or analog meter, not a potentiometer. Potentiometers do not use magnetic fields for measuring rotary movement.

Correct Answer:

A. Temperature gauges and thermostats

Explanation:

• A. Correct: Bi-metallic strips are commonly used in temperature gauges and thermostats. They are designed to bend with temperature changes, making them suitable for mechanical temperature measurement and control.
• B. Incorrect: Bi-metallic strips are not typically used in pressure sensors. Pressure sensors generally use different technologies like strain gauges or piezoelectric materials.
• C. Incorrect: Bi-metallic strips are not used in flow meters. Flow meters typically use methods such as electromagnetic, ultrasonic, or turbine principles.
• D. Incorrect: Bi-metallic strips are not used as vibration dampers. Vibration damping is usually handled by materials or devices specifically designed for that purpose, such as rubber mounts or damping pads.