AME 9 End of Unit

Correct Answer:

A. Tachometer

Explanation:

• A. Correct: A tachometer is specifically designed to measure rotational speed, making it suitable for measuring the speed of a ship’s main propeller shaft in RPM.
• B. Incorrect: Pressure transducers measure pressure, not rotational speed.
• C. Incorrect: Strain gauges measure strain or deformation, not rotational speed.
• D. Incorrect: Temperature sensors measure temperature, not rotational speed.
• E. Incorrect: Flowmeters measure the flow rate of fluids, not rotational speed.

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.

Correct Answer:

A. Flowmeter

Explanation:

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

Correct Answer:

A. To Compensate for Lead Wire Resistance: The additional wires are used to compensate for the resistance of the lead wires, ensuring accurate temperature measurements by measuring only the resistance of the sensing element itself.

Explanation:

• A. Correct: PT100 probes use three or four wires to separate the current-carrying wires from the measurement wires. This configuration eliminates errors caused by the resistance of the lead wires, ensuring that the temperature measurement reflects only the resistance of the sensing element.
• B. Incorrect: The extra wires do not enable measurement across multiple temperature ranges. The primary function is to compensate for lead wire resistance.
• C. Incorrect: The additional wires are not for improving mechanical strength but for ensuring measurement accuracy by accounting for lead wire resistance.
• D. Incorrect: The extra wires do not enable connecting multiple probes; they are used for accurate measurement of a single probe by compensating for lead wire resistance.

Correct Answer:

B. A floating buoy that rises and falls with the liquid level, activating a switch to send an electrical signal to a control system.

Explanation:

• A. Incorrect: A weighted ball typically does not produce an electrical or digital output signal; it usually provides a direct mechanical action.
• B. Correct: A floating buoy or float switch moves with the liquid level and triggers an electrical switch when it reaches a certain point. This switch sends a signal to a remote control system, which can then adjust the liquid level by controlling pumps or valves.
• C. Incorrect: A submerged probe might measure pressure changes, but it is not a flotation device and does not directly control the liquid level through flotation.
• D. Incorrect: A rotating vane typically measures flow rate rather than liquid level and does not operate based on flotation principles.

Correct Answer:

A. Two Dissimilar Metals Produce a Voltage: A thermocouple operates by generating a voltage when two dissimilar metals are joined together and exposed to different temperatures, with the voltage being proportional to the temperature difference.

Explanation:

• A. Correct: A thermocouple consists of two different metals joined at one end. When this junction is exposed to different temperatures, it produces a voltage that can be measured. The voltage generated is directly related to the temperature difference between the junctions, allowing for temperature measurement.
• B. Incorrect: A thermocouple does not operate based on the expansion of a single metal but on the voltage produced by the junction of two dissimilar metals.
• C. Incorrect: Changes in electrical resistance are not the basis of thermocouple operation; that principle is more relevant to resistance temperature detectors (RTDs).
• D. Incorrect: Thermocouples do not operate based on magnetic fields; they generate voltage from the temperature difference at the junction of two dissimilar metals.

Correct Answer:

A. A Bourdon tube cannot be used to measure temperature as it is specifically designed for pressure measurement.

Explanation:

• A. Correct: A Bourdon tube is specifically designed for measuring pressure. It operates by detecting changes in pressure that cause mechanical movement of the tube, which is not suitable for measuring temperature.
• B. Incorrect: Filling a Bourdon tube with a temperature-sensitive liquid is not a standard method for measuring temperature. This approach does not apply to the operation of a Bourdon tube.
• C. Incorrect: A Bourdon tube does not connect to a temperature sensor for measuring temperature. It is designed for pressure measurement and does not integrate with temperature sensors in this way.
• D. Incorrect: A Bourdon tube operates based on pressure changes, not temperature. It does not convert temperature changes into mechanical movement directly.

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:

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 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.

Explanation:

• A. Correct: This is the correct formula. The strain ($\epsilon$) is calculated by the change in resistance ($\Delta R$) divided by the original resistance ($R$), multiplied by the gauge factor (GF).
• B. Incorrect: This formula is for calculating percentage elongation or strain in terms of length change, not specifically related to strain gauges.
• C. Incorrect: This formula is for calculating stress ($\sigma$), not strain.
• D. Incorrect: This is the formula for calculating the equivalent resistance of two resistors in parallel, not related to strain gauges.

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.