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Questions and Answers
What is the primary application of piezoresistive strain gauges?
What is the primary application of piezoresistive strain gauges?
Which type of strain gauge is most susceptible to electromagnetic interference?
Which type of strain gauge is most susceptible to electromagnetic interference?
What is the primary advantage of optical fiber strain gauges?
What is the primary advantage of optical fiber strain gauges?
What is the purpose of temperature compensation in strain measurement?
What is the purpose of temperature compensation in strain measurement?
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What type of strain gauge circuit is commonly used in experimental stress analysis?
What type of strain gauge circuit is commonly used in experimental stress analysis?
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What is the primary advantage of bonded strain gauges?
What is the primary advantage of bonded strain gauges?
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What type of material is commonly used in metallic foil strain gauges?
What type of material is commonly used in metallic foil strain gauges?
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What is the primary application of strain gauges in mechanical engineering?
What is the primary application of strain gauges in mechanical engineering?
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What is the primary advantage of semiconductor strain gauges?
What is the primary advantage of semiconductor strain gauges?
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What is the purpose of calibration in strain measurement?
What is the purpose of calibration in strain measurement?
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What is the primary advantage of a Full-Bridge Circuit over a Half-Bridge Circuit?
What is the primary advantage of a Full-Bridge Circuit over a Half-Bridge Circuit?
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What is the purpose of generating a calibration curve in strain gauge calibration?
What is the purpose of generating a calibration curve in strain gauge calibration?
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Which of the following is a method for temperature compensation in strain gauge measurements?
Which of the following is a method for temperature compensation in strain gauge measurements?
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What is the key consideration when using strain gauges to measure torque and stress on rotating shafts?
What is the key consideration when using strain gauges to measure torque and stress on rotating shafts?
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What is the primary criterion for selecting a strain gauge for a particular application?
What is the primary criterion for selecting a strain gauge for a particular application?
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What is the purpose of surface preparation in the installation of strain gauges?
What is the purpose of surface preparation in the installation of strain gauges?
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What type of pressure measurement is typically used for fluid dynamics applications?
What type of pressure measurement is typically used for fluid dynamics applications?
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What is the principle of operation of a strain gauge pressure cell?
What is the principle of operation of a strain gauge pressure cell?
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Which of the following is NOT a consideration for selecting a strain gauge?
Which of the following is NOT a consideration for selecting a strain gauge?
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What is the purpose of applying protective coatings or coverings to strain gauges?
What is the purpose of applying protective coatings or coverings to strain gauges?
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Which of the following is a common application of strain gauges?
Which of the following is a common application of strain gauges?
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What is the principle of operation of a Wheatstone bridge circuit?
What is the principle of operation of a Wheatstone bridge circuit?
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What is the primary component of a Bridgeman gauge?
What is the primary component of a Bridgeman gauge?
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Which of the following is NOT a type of thermal conductivity gauge?
Which of the following is NOT a type of thermal conductivity gauge?
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What is the principle of operation of a McLeod gauge?
What is the principle of operation of a McLeod gauge?
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Which of the following gauges is suitable for measuring extremely high pressures in scientific research?
Which of the following gauges is suitable for measuring extremely high pressures in scientific research?
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What is the principle of operation of an Ionization gauge?
What is the principle of operation of an Ionization gauge?
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Which of the following gauges is used in vacuum systems and laboratories for very low pressure measurements?
Which of the following gauges is used in vacuum systems and laboratories for very low pressure measurements?
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What is the principle of operation of a Knudsen gauge?
What is the principle of operation of a Knudsen gauge?
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Which of the following is a factor to consider when selecting a pressure measurement method?
Which of the following is a factor to consider when selecting a pressure measurement method?
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What is the primary limitation of using semiconductor strain gauges in mechanical engineering applications?
What is the primary limitation of using semiconductor strain gauges in mechanical engineering applications?
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Which of the following is a key consideration when using strain gauges on rotating shafts?
Which of the following is a key consideration when using strain gauges on rotating shafts?
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What is the primary advantage of using a Quarter-Bridge Circuit in strain measurement?
What is the primary advantage of using a Quarter-Bridge Circuit in strain measurement?
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Which of the following pressure measurement methods is typically used for measuring extremely low pressures?
Which of the following pressure measurement methods is typically used for measuring extremely low pressures?
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What is the primary purpose of surface preparation in the installation of strain gauges?
What is the primary purpose of surface preparation in the installation of strain gauges?
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Which of the following is a common application of strain gauges in mechanical engineering?
Which of the following is a common application of strain gauges in mechanical engineering?
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What is the primary advantage of using optical fiber strain gauges in harsh environments?
What is the primary advantage of using optical fiber strain gauges in harsh environments?
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Which of the following is a key consideration when selecting a strain gauge for a particular application?
Which of the following is a key consideration when selecting a strain gauge for a particular application?
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What is the primary purpose of calibration in strain measurement?
What is the primary purpose of calibration in strain measurement?
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Which of the following is a limitation of using bonded strain gauges in mechanical engineering applications?
Which of the following is a limitation of using bonded strain gauges in mechanical engineering applications?
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What occurs when pressure is applied to a diaphragm with bonded strain gauges?
What occurs when pressure is applied to a diaphragm with bonded strain gauges?
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In a Bridgeman gauge, what is the purpose of the pressure vessel?
In a Bridgeman gauge, what is the purpose of the pressure vessel?
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What is the principle of operation of a McLeod gauge?
What is the principle of operation of a McLeod gauge?
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What is the purpose of a thermocouple in a Knudsen gauge?
What is the purpose of a thermocouple in a Knudsen gauge?
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What is the principle of operation of a Pirani gauge?
What is the principle of operation of a Pirani gauge?
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What is the primary advantage of using a Wheatstone bridge circuit in strain gauge measurements?
What is the primary advantage of using a Wheatstone bridge circuit in strain gauge measurements?
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What is the principle of operation of an Ionization gauge?
What is the principle of operation of an Ionization gauge?
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What is the purpose of a manometer in a McLeod gauge?
What is the purpose of a manometer in a McLeod gauge?
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What is the principle of operation of a Bridgeman gauge?
What is the principle of operation of a Bridgeman gauge?
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What is the primary application of Thermal Conductivity Gauges?
What is the primary application of Thermal Conductivity Gauges?
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What is the primary advantage of using a Half-Bridge Circuit over a Quarter-Bridge Circuit?
What is the primary advantage of using a Half-Bridge Circuit over a Quarter-Bridge Circuit?
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What is the purpose of using a dummy gauge in the Dummy Gauge Method?
What is the purpose of using a dummy gauge in the Dummy Gauge Method?
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What is the primary consideration when selecting a strain gauge for measuring torque and stress on rotating shafts?
What is the primary consideration when selecting a strain gauge for measuring torque and stress on rotating shafts?
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What is the primary advantage of using a strain gauge pressure cell over a Bridgeman gauge?
What is the primary advantage of using a strain gauge pressure cell over a Bridgeman gauge?
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What is the primary purpose of bonding a strain gauge to a test specimen?
What is the primary purpose of bonding a strain gauge to a test specimen?
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What is the primary advantage of using a Full-Bridge Circuit over a Half-Bridge Circuit?
What is the primary advantage of using a Full-Bridge Circuit over a Half-Bridge Circuit?
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What is the primary purpose of generating a calibration curve in strain gauge calibration?
What is the primary purpose of generating a calibration curve in strain gauge calibration?
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What is the primary consideration when selecting a strain gauge for a particular application?
What is the primary consideration when selecting a strain gauge for a particular application?
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What is the primary purpose of applying known loads to a test specimen in strain gauge calibration?
What is the primary purpose of applying known loads to a test specimen in strain gauge calibration?
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What is the primary advantage of using a strain gauge over a Bridgeman gauge in pressure measurement?
What is the primary advantage of using a strain gauge over a Bridgeman gauge in pressure measurement?
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Study Notes
Strain Measurement
- Strain gauges are essential tools in mechanical engineering for measuring strain on various structures.
- Types of strain gauges:
- Metallic Foil Strain Gauges: consist of a grid of thin metallic foil bonded to an insulating backing material.
- Semiconductor Strain Gauges: made from silicon or germanium, with higher sensitivity but more temperature-sensitive.
- Bonded and Unbonded Strain Gauges: bonded gauges are fixed to the surface of the test specimen, while unbonded gauges are mounted on a frame.
- Optical Fiber Strain Gauges: use changes in light transmission to measure strain, immune to electromagnetic interference.
- Piezoresistive Strain Gauges: primarily used in pressure sensors, utilizing the change in electrical resistance with applied strain.
Strain Gauge Circuits
- Quarter-Bridge Circuit: uses a single active strain gauge and three fixed resistors in a Wheatstone bridge configuration, simplest and least expensive.
- Half-Bridge Circuit: uses two strain gauges in the Wheatstone bridge, can measure bending strains and temperature compensation to some extent.
- Full-Bridge Circuit: uses four strain gauges in the Wheatstone bridge, provides maximum sensitivity and temperature compensation, can measure axial and bending strains accurately.
Calibration
- Calibration is essential to ensure accurate strain measurements.
- Process involves applying known loads, generating a calibration curve, and deriving a calibration factor.
Temperature Compensation
- Temperature changes can affect strain gauge readings due to thermal expansion of the specimen and the gauge itself.
- Methods for temperature compensation include:
- Using temperature-compensated strain gauges.
- Dummy gauge method.
- Quarter-Bridge temperature compensation.
Use of Strain Gauges on Rotating Shafts
- Strain gauges can be used to measure torque and stress on rotating shafts.
- Key considerations include:
- Wireless data transmission.
- Slip rings.
- Careful installation.
Selection and Installation of Strain Gauges
- Selection criteria:
- Strain range.
- Gauge factor.
- Environmental conditions.
- Material compatibility.
- Installation process:
- Surface preparation.
- Bonding.
- Wiring.
- Protection.
Pressure Measurements
- Basic methods of pressure measurement:
- Strain gauge pressure cells.
- High pressure measurement using the Bridgeman type gauge.
- Low-pressure measurement techniques:
- McLeod gauge.
- Knudsen gauge.
- Ionization gauge.
- Thermal conductivity gauges.
Strain Gauge Pressure Cell
- Principle: measures pressure using the deformation of a diaphragm or other elastic element under pressure.
- Components:
- Diaphragm.
- Strain gauges.
- Wheatstone bridge circuit.
- Operation:
- Diaphragm deforms under pressure, causing strain in the strain gauges.
- Resistance change in the strain gauges is measured using a Wheatstone bridge circuit.
High Pressure Measurement - Bridgeman Type Gauge
- Principle: measures high pressures by using the change in electrical resistance of a wire or material under pressure.
- Components:
- Pressure vessel.
- Electrical circuit.
- Operation:
- Material's electrical resistance changes under pressure.
- Resistance change is measured and correlated with the pressure.
Low Pressure Measurement
-
McLeod Gauge:
- Principle: measures low pressures by compressing a known volume of gas and measuring the resulting increase in pressure.
- Components:
- Bulb and capillary tube.
- Manometer.
-
Operation:
- Gas is trapped in a bulb and compressed into a capillary tube.
- Increase in pressure is measured with a manometer.
-
Knudsen Gauge:
- Principle: measures pressure based on the thermal transpiration effect.
- Components:
- Porous plug.
- Thermocouples.
-
Operation:
- Gas flows through the porous plug from the hot side to the cold side.
- Pressure difference created by this flow is measured and related to the absolute pressure.
-
Ionization Gauge:
- Principle: measures very low pressures by ionizing the gas and measuring the resulting ion current.
- Components:
- Ionization chamber.
- Electron source.
- Collector electrode.
-
Operation:
- Electrons from a hot filament or cold cathode ionize the gas molecules.
- Ions are collected, and the ion current is measured.
-
Thermal Conductivity Gauges:
- Principle: measures pressure based on the thermal conductivity of the gas, which varies with pressure.
- Types:
- Pirani gauge.
- Thermocouple gauge.
-
Operation:
- Pirani gauge: heat loss from a heated wire to the gas depends on the gas pressure.
- Thermocouple gauge: heat loss from a heated element to the gas depends on the gas pressure.
Summary
- The selection of a pressure measurement method depends on the range and accuracy required, the environment, and the specific application.
Strain Measurement
- Strain gauges are essential tools in mechanical engineering for measuring strain on various structures.
- Types of strain gauges:
- Metallic Foil Strain Gauges: consist of a grid of thin metallic foil bonded to an insulating backing material.
- Semiconductor Strain Gauges: made from silicon or germanium, with higher sensitivity but more temperature-sensitive.
- Bonded and Unbonded Strain Gauges: bonded gauges are fixed to the surface of the test specimen, while unbonded gauges are mounted on a frame.
- Optical Fiber Strain Gauges: use changes in light transmission to measure strain, immune to electromagnetic interference.
- Piezoresistive Strain Gauges: primarily used in pressure sensors, utilizing the change in electrical resistance with applied strain.
Strain Gauge Circuits
- Quarter-Bridge Circuit: uses a single active strain gauge and three fixed resistors in a Wheatstone bridge configuration, simplest and least expensive.
- Half-Bridge Circuit: uses two strain gauges in the Wheatstone bridge, can measure bending strains and temperature compensation to some extent.
- Full-Bridge Circuit: uses four strain gauges in the Wheatstone bridge, provides maximum sensitivity and temperature compensation, can measure axial and bending strains accurately.
Calibration
- Calibration is essential to ensure accurate strain measurements.
- Process involves applying known loads, generating a calibration curve, and deriving a calibration factor.
Temperature Compensation
- Temperature changes can affect strain gauge readings due to thermal expansion of the specimen and the gauge itself.
- Methods for temperature compensation include:
- Using temperature-compensated strain gauges.
- Dummy gauge method.
- Quarter-Bridge temperature compensation.
Use of Strain Gauges on Rotating Shafts
- Strain gauges can be used to measure torque and stress on rotating shafts.
- Key considerations include:
- Wireless data transmission.
- Slip rings.
- Careful installation.
Selection and Installation of Strain Gauges
- Selection criteria:
- Strain range.
- Gauge factor.
- Environmental conditions.
- Material compatibility.
- Installation process:
- Surface preparation.
- Bonding.
- Wiring.
- Protection.
Pressure Measurements
- Basic methods of pressure measurement:
- Strain gauge pressure cells.
- High pressure measurement using the Bridgeman type gauge.
- Low-pressure measurement techniques:
- McLeod gauge.
- Knudsen gauge.
- Ionization gauge.
- Thermal conductivity gauges.
Strain Gauge Pressure Cell
- Principle: measures pressure using the deformation of a diaphragm or other elastic element under pressure.
- Components:
- Diaphragm.
- Strain gauges.
- Wheatstone bridge circuit.
- Operation:
- Diaphragm deforms under pressure, causing strain in the strain gauges.
- Resistance change in the strain gauges is measured using a Wheatstone bridge circuit.
High Pressure Measurement - Bridgeman Type Gauge
- Principle: measures high pressures by using the change in electrical resistance of a wire or material under pressure.
- Components:
- Pressure vessel.
- Electrical circuit.
- Operation:
- Material's electrical resistance changes under pressure.
- Resistance change is measured and correlated with the pressure.
Low Pressure Measurement
-
McLeod Gauge:
- Principle: measures low pressures by compressing a known volume of gas and measuring the resulting increase in pressure.
- Components:
- Bulb and capillary tube.
- Manometer.
-
Operation:
- Gas is trapped in a bulb and compressed into a capillary tube.
- Increase in pressure is measured with a manometer.
-
Knudsen Gauge:
- Principle: measures pressure based on the thermal transpiration effect.
- Components:
- Porous plug.
- Thermocouples.
-
Operation:
- Gas flows through the porous plug from the hot side to the cold side.
- Pressure difference created by this flow is measured and related to the absolute pressure.
-
Ionization Gauge:
- Principle: measures very low pressures by ionizing the gas and measuring the resulting ion current.
- Components:
- Ionization chamber.
- Electron source.
- Collector electrode.
-
Operation:
- Electrons from a hot filament or cold cathode ionize the gas molecules.
- Ions are collected, and the ion current is measured.
-
Thermal Conductivity Gauges:
- Principle: measures pressure based on the thermal conductivity of the gas, which varies with pressure.
- Types:
- Pirani gauge.
- Thermocouple gauge.
-
Operation:
- Pirani gauge: heat loss from a heated wire to the gas depends on the gas pressure.
- Thermocouple gauge: heat loss from a heated element to the gas depends on the gas pressure.
Summary
- The selection of a pressure measurement method depends on the range and accuracy required, the environment, and the specific application.
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Description
Learn about the different types of strain gauges used in mechanical engineering to measure strain on various structures. Understand the characteristics and applications of metallic foil, semiconductor, and bonded and unbonded strain gauges.
