AME Unit 9 Q13

A strain gauge is a transducer that converts mechanical strain into an electrical signal. It’s widely used in various applications to measure force, pressure, weight, and acceleration.  

1. Transducer-specific strain gauges | Tokyo Measuring Instruments Laboratory Co., Ltd.

2. Strain Gauge Applications | Dewesoft

Principle

The fundamental principle of a strain gauge is based on the change in electrical resistance of a conductor due to mechanical strain. When a conductor is stretched or compressed, its dimensions change, affecting its resistance. A strain gauge is designed to exploit this phenomenon.  

1. Strain Gauge – Principle, Applications, Types [GATE Notes] – BYJU’S

2. [Updated] Strain Gauge: Principle, Types, Features and Applications – Encardio Rite

Construction

A typical strain gauge consists of a thin metallic foil pattern bonded to a flexible backing. The foil is arranged in a zigzag pattern to maximize the change in resistance for a given strain.  

1. Strain Gauges, How does it work? – Omega Engineering

2. [Updated] Strain Gauge: Principle, Types, Features and Applications – Encardio Rite

Operation

1. Bonding: The strain gauge is bonded to the object under observation using a suitable adhesive.   1. Strain Gage Bonding Procedure – Learn/Examine – Kyowa Electronic Instruments product.kyowa-ei.com
2. Strain Application: When the object is subjected to a force, it deforms, causing the strain gauge to stretch or compress.   1. [Updated] Strain Gauge: Principle, Types, Features and Applications – Encardio Rite www.encardio.com
3. Resistance Change: As the strain gauge deforms, its resistance changes proportionally to the applied strain.   1. Measuring Strain with Strain Gages – NI – National Instruments www.ni.com
4. Signal Conditioning: The change in resistance is typically very small, so it’s often measured using a Wheatstone bridge circuit to amplify the signal.   1. Measuring Strain with Strain Gages – NI – National Instruments www.ni.com
5. Output: The amplified signal can then be converted into a digital format for display or further processing.

Key Points:

• Sensitivity: The gauge factor is a measure of the strain gauge’s sensitivity, representing the change in resistance per unit strain.   1. Strain Measurement Glossary – HBK www.hbkworld.com
• Temperature Effects: Temperature can affect the resistance of the strain gauge, so temperature compensation is often necessary for accurate measurements.   1. Strain Gauges: How to Prevent Unwanted Temperature Effects on Your Measurement Result www.hbkworld.com
• Strain Range: Strain gauges have a limited operating range, beyond which their performance may be compromised.

By carefully selecting and applying strain gauges, it’s possible to accurately measure various physical quantities with high precision.

Opens in a new windowwww.michsci.com

strain gauge

Strain gauges are invaluable tools for monitoring the structural integrity and performance of a superyacht. Here are some common applications:

Structural Monitoring:

• Hull and superstructure: Measuring stress and strain on critical components to assess structural integrity and detect potential issues.
• Mast and rigging: Monitoring load distribution and fatigue on these vital elements for sailing yachts.
• Propeller shafts: Measuring torque and vibration to assess engine performance and propeller efficiency.

Equipment Monitoring:

• Hydraulic systems: Measuring pressure and load on pumps, valves, and cylinders.
• Generators: Monitoring engine vibration and load to assess performance and identify potential problems.
• Stabilizer systems: Measuring forces and loads on the stabilizers to optimize performance and detect anomalies.

Performance Monitoring:

• Sailing yachts: Measuring loads on sails, rigging, and hull to optimize performance and identify areas for improvement.
• Power yachts: Monitoring engine loads and propeller thrust to optimize fuel efficiency and performance.

By strategically placing strain gauges throughout a superyacht, engineers and technicians can gather crucial data to ensure the vessel’s safety, performance, and longevity.

The fundamental formula for a strain gauge relates the change in resistance to the applied strain:

Gauge Factor (GF) formula:

• GF = (ΔR/R) / ε   1. Introduction to Strain Gauges – Siemens Communities community.sw.siemens.com

Where:

• GF: Gauge factor (unitless)   1. Gauge factor – Wikipedia en.wikipedia.org
• ΔR: Change in resistance (Ω)   1. Introduction to Strain Gauges – Siemens Communities community.sw.siemens.com
• R: Original resistance (Ω)
• ε: Strain (unitless)

Strain Calculation:

• ε = (ΔR / R) / GF

This formula allows you to calculate the strain experienced by the material based on the measured change in resistance and the known gauge factor of the strain gauge.

Additional Considerations:

• Wheatstone Bridge: Strain gauges are often used in a Wheatstone bridge configuration to amplify the small resistance changes and improve accuracy.   1. How Is Temperature Affecting Your Strain Measurement Accuracy? – NI www.ni.com
• Temperature Compensation: Temperature can affect the resistance of the strain gauge, so temperature compensation techniques might be necessary.   1. Strain Gauges: How to Prevent Unwanted Temperature Effects on Your Measurement Result www.hbkworld.com
• Strain Gauge Rosette: For complex strain analysis, multiple strain gauges can be used in a rosette configuration to measure strain in different directions.   1. Strain Gauge Fundamentals – HBM www.hbm.com

By understanding these formulas and considering the factors mentioned above, you can accurately determine the strain experienced by a material using strain gauges.

To accurately measure pressure using a strain gauge, it’s typically integrated into a pressure transducer, and the resulting strain is converted into an electrical signal using a Wheatstone bridge circuit.  

1. Strain Gauges, How does it work? – Omega Engineering

The Process:

1. Pressure Transducer: A pressure transducer is a device that converts pressure into a measurable physical quantity. In this case, we’re interested in converting pressure into strain. A common design involves a diaphragm that flexes under pressure.   1. How Does A Pressure Transducers Work? – Omega Engineering www.omega.com2. Pressure Transducers and Transmitters – OMEGA Engineering Australia au.omega.com
2. Strain Gauge Placement: Strain gauges are bonded to the diaphragm in a configuration that maximizes the resistance change due to pressure-induced strain. This can be a single, half, or full bridge configuration.
3. Wheatstone Bridge Circuit: The strain gauges are connected to a Wheatstone bridge circuit. This circuit consists of four resistors arranged in a diamond shape. One or more of these resistors are the strain gauges.   1. Measuring Strain with Strain Gages – NI – National Instruments www.ni.com2. Wheatstone bridge – Wikipedia en.wikipedia.org3. Strain Gauges, How does it work? – Omega Engineering www.omega.com
4. Excitation Voltage: A stable voltage is applied across the bridge.   1. Measuring Strain with Strain Gages – NI – National Instruments www.ni.com
5. Output Voltage: When pressure is applied to the transducer, the strain gauges’ resistance changes, causing an imbalance in the bridge. This imbalance results in a small output voltage proportional to the applied pressure.   1. Measuring Strain with Strain Gages – NI – National Instruments www.ni.com
6. Amplification and Conditioning: The output voltage is often very small, so it requires amplification and conditioning before it can be used for measurement or control purposes.   1. 8 Tips to Consider When Buying a Strain Gage Amplifier – Gantner Instruments www.gantner-instruments.com
7. Analog-to-Digital Conversion (ADC): For digital systems, the amplified voltage is converted into a digital signal for processing and display.

Considerations:

• Calibration: The pressure transducer and the Wheatstone bridge circuit need to be calibrated to accurately relate the output voltage to the applied pressure.
• Temperature Compensation: Temperature can affect the resistance of the strain gauges, so temperature compensation techniques might be necessary to ensure accurate measurements.   1. Temperature Compensation of Strain Gauges – HBM www.hbm.com
• Strain Gauge Placement: The optimal placement of strain gauges on the diaphragm depends on the desired sensitivity and accuracy.
• Bridge Configuration: The choice of a single, half, or full bridge configuration depends on the required sensitivity and the available space on the transducer.

By carefully designing and calibrating the pressure transducer and its associated electronics, it’s possible to achieve high accuracy and precision in pressure measurements using strain gauges.

Opens in a new windowwww.researchgate.net

pressure transducer with strain gauge and Wheatstone bridge

Strain gauges, when integrated into pressure transducers, find numerous applications on sea-bearing vessels for monitoring various parameters and ensuring optimal performance and safety.

Propulsion and Machinery

• Engine monitoring: Measuring cylinder pressures, bearing loads, and crankshaft stresses.
• Propeller shaft monitoring: Measuring torque, vibration, and shaft alignment.
• Pump and compressor monitoring: Assessing performance and detecting anomalies.

Hull and Structure

• Hull stress monitoring: Measuring stresses on the hull under various loading conditions (waves, cargo, etc.).
• Structural integrity: Monitoring critical components like bulkheads, frames, and decks for potential fatigue or damage.
• Seawater system monitoring: Measuring pressures in piping systems and pumps.

Cargo Handling

• Cargo weight distribution: Measuring loads on cargo hold structures and hatch covers.
• Crane and winch monitoring: Assessing load capacities and preventing overload.

Other Applications

• Hydraulic system monitoring: Measuring pressures and loads in hydraulic systems.
• Ballast system monitoring: Monitoring tank pressures and levels.
• Environmental monitoring: Measuring wave heights and pressures for research purposes.

By utilizing strain gauge-based pressure transducers in these areas, ship operators can enhance safety, optimize performance, and extend the lifespan of the vessel.

The marine environment presents unique challenges for strain gauge applications due to its harsh conditions:

Environmental Factors:

• Corrosion: Saltwater exposure can rapidly corrode strain gauges and their connections, affecting accuracy and reliability.
• Humidity: High humidity can lead to electrical resistance changes and sensor instability.
• Temperature fluctuations: Extreme temperature variations between air and water can impact strain gauge performance.
• Pressure: Deepwater applications require strain gauges capable of withstanding high hydrostatic pressure.

Installation and Maintenance:

• Accessibility: Installing and maintaining strain gauges in marine structures can be difficult and costly due to the challenging environment.
• Vibration: The marine environment is characterized by constant vibration, which can affect strain gauge readings and accelerate component wear.
• Biofouling: Marine organisms can attach to and damage strain gauge installations, requiring regular cleaning and maintenance.

Signal Conditioning and Data Acquisition:

• Noise: Electrical noise from the marine environment can interfere with strain gauge signals, requiring careful signal conditioning.
• Data transmission: Reliable data transmission from underwater or remote locations can be challenging.

Overcoming Challenges:

To address these challenges, engineers often employ the following strategies:

• Material selection: Using corrosion-resistant materials for strain gauges and enclosures.
• Encapsulation: Protecting strain gauges with epoxy or other protective coatings.
• Hermetic sealing: Ensuring complete isolation of the strain gauge from the marine environment.
• Compensation techniques: Implementing temperature and pressure compensation measures.
• Robust signal conditioning: Employing advanced signal conditioning techniques to reduce noise and interference.
• Regular inspection and maintenance: Implementing a rigorous inspection and maintenance program.

By carefully considering these factors and implementing appropriate measures, strain gauges can be successfully used in marine applications to provide valuable data for structural monitoring, equipment performance evaluation, and safety.