Podcast
Questions and Answers
What is the gauge sensitivity or gauge factor commonly denoted as?
What is the gauge sensitivity or gauge factor commonly denoted as?
The formula for calculating the resistance of a wire includes the cross-sectional area and the resistivity.
The formula for calculating the resistance of a wire includes the cross-sectional area and the resistivity.
True
What does the symbol σ represent in the context of force measurements?
What does the symbol σ represent in the context of force measurements?
Stress
The _____ strain gauge has a higher gauge factor than its resistive counterpart.
The _____ strain gauge has a higher gauge factor than its resistive counterpart.
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Which material is most commonly used for wire-bonded strain gauges?
Which material is most commonly used for wire-bonded strain gauges?
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Match the following terms related to strain gauges:
Match the following terms related to strain gauges:
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A strain gauge can only measure strain in one direction.
A strain gauge can only measure strain in one direction.
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What relationship does the equation R(ε) = R0 (1 + g ε) describe?
What relationship does the equation R(ε) = R0 (1 + g ε) describe?
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What is the most common material used for strain gauges due to its properties and ease of production?
What is the most common material used for strain gauges due to its properties and ease of production?
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Strain gauges do not require temperature compensation.
Strain gauges do not require temperature compensation.
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What is the general behavior equation for a semiconductor strain gauge?
What is the general behavior equation for a semiconductor strain gauge?
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Strain gauges are subject to errors caused by ________ and the strain itself.
Strain gauges are subject to errors caused by ________ and the strain itself.
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Match the errors in strain gauges to their solutions:
Match the errors in strain gauges to their solutions:
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Which solution can help minimize errors caused by temperature in strain gauges?
Which solution can help minimize errors caused by temperature in strain gauges?
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What is the purpose of periodically re-calibrating strain gauges?
What is the purpose of periodically re-calibrating strain gauges?
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The gauge factor can be estimated by comparing the resistance of the sensor with and without ________.
The gauge factor can be estimated by comparing the resistance of the sensor with and without ________.
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The nominal resistance of the strain gauge at 20°C is 350 Ω.
The nominal resistance of the strain gauge at 20°C is 350 Ω.
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What is the maximum resistance expected for a maximum strain of 2%?
What is the maximum resistance expected for a maximum strain of 2%?
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The change in resistance due to a maximum strain of 2% is ______ Ω.
The change in resistance due to a maximum strain of 2% is ______ Ω.
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Match the following parameters with their respective values:
Match the following parameters with their respective values:
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What is the temperature range the sensor is exposed to?
What is the temperature range the sensor is exposed to?
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A temperature coefficient of resistance α = 0.00385 Ω°C means resistance increases with temperature.
A temperature coefficient of resistance α = 0.00385 Ω°C means resistance increases with temperature.
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Calculate the change in resistance due to a temperature change from 20°C to -50°C.
Calculate the change in resistance due to a temperature change from 20°C to -50°C.
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What does Vo represent in the given equation?
What does Vo represent in the given equation?
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The change in output voltage is zero if the resistance changes are equal for R1, R2, R3, and Rx.
The change in output voltage is zero if the resistance changes are equal for R1, R2, R3, and Rx.
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What happens to the output if a force is applied to the strain gauge S1?
What happens to the output if a force is applied to the strain gauge S1?
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The bridge sensitivity can be calculated by taking the first ______.
The bridge sensitivity can be calculated by taking the first ______.
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Match the variables with their corresponding definitions:
Match the variables with their corresponding definitions:
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What is the role of the resistor S3 in the experiment?
What is the role of the resistor S3 in the experiment?
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R2 and Rx are alleged to be different resistances in the system.
R2 and Rx are alleged to be different resistances in the system.
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What is the significance of having two identical resistors R2 and Rx?
What is the significance of having two identical resistors R2 and Rx?
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What happens to Vo when there is no change in resistance?
What happens to Vo when there is no change in resistance?
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The temperature coefficient of resistance for the strain gauge described is α = 0.00385 Ω◦ C.
The temperature coefficient of resistance for the strain gauge described is α = 0.00385 Ω◦ C.
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What is the gauge factor of the strain gauge in the example?
What is the gauge factor of the strain gauge in the example?
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The nominal resistance of the sensor at 20◦ C is ______.
The nominal resistance of the sensor at 20◦ C is ______.
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Which of the following resistances corresponds to a 2% strain condition?
Which of the following resistances corresponds to a 2% strain condition?
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Match the temperature conditions with their corresponding resistances at no strain:
Match the temperature conditions with their corresponding resistances at no strain:
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What is the maximum strain that the bridge circuit is designed to accommodate?
What is the maximum strain that the bridge circuit is designed to accommodate?
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The input voltage of the bridge circuit is set at ______.
The input voltage of the bridge circuit is set at ______.
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What is the value of R0 at 2% strain and T = 20°C?
What is the value of R0 at 2% strain and T = 20°C?
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At -50°C with no strain, the value of R0 is 350 Ω.
At -50°C with no strain, the value of R0 is 350 Ω.
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What is the formula for Vo in terms of Z1, Z2, Z3, and Z4?
What is the formula for Vo in terms of Z1, Z2, Z3, and Z4?
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The value of Vo at 2% strain and T = 20°C is ______.
The value of Vo at 2% strain and T = 20°C is ______.
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Which of the following values corresponds to R200 at 2% strain?
Which of the following values corresponds to R200 at 2% strain?
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Z2, Z3, and Z4 all have the same value of 350 Ω.
Z2, Z3, and Z4 all have the same value of 350 Ω.
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At 2% strain and T = -50°C, the value of R−50 is ______.
At 2% strain and T = -50°C, the value of R−50 is ______.
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Match the following resistance values with their respective strains:
Match the following resistance values with their respective strains:
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Study Notes
Course Information
- Course Title: Sensors, Measurements and Data Acquisition System
- Course Code: MSE 355
- Instructor: Dr. Mohamed Atef Ismail Kamel
- Program: Mechatronics Systems Engineering (MSE)
- University: MSA University
- Semester: Fall 2023
- Year Level: 3
Force, Tactile, and Pressure Sensors
-
Force Measurement Methods:
- Strain gauge
- Acceleration (F = ma)
- Spring displacement (F = kx)
- Pressure (F = PA)
- Piezoelectric transducer
-
Strain Gauges:
- Main tool for sensing force
- Strain is related to stress, force, torque, displacement, acceleration, and position
- Can measure temperature, level, and related quantities
- Resistance of a wire: R = (ρL)/A
- For small deformation: (ΔR/R) = gε
- g is the gauge sensitivity (gauge factor)
- Strain relationship to Resistance: R(ε) = Ro (1 + gε)
- Different types: Wire-bonded, Semiconductor
-
Wire-Bonded Strain Gauge
- Thin conducting material (Constantan) on an insulator (plastic/ceramic)
- Etched into a long, meandering wire
- Constantan (60% copper, 40% nickel) used for low temperature coefficient
- Multiple strain gauges used for multiple axis strain
- Standardized configurations for strain gauges
-
Semiconductor Strain Gauge
- Same operation principle as resistive gauges
- Higher gauge factor than metals
- Large change in conductivity due to strain compared to metals
- Sensitive to temperature variations (requires temp compensation)
- Silicon is common due to properties and ease of production
- Typical behavior: dR/R = g1ε + g2ε2 (nonlinear)
- Higher sensitivity is an advantage
-
Strain Gauges: Sources of Error
- Temperature changes (affect resistance: Ro (1 + α[T – To]))
- Solution: Use strain gauges with low temperature coefficients and use temp compensators
- Strain itself: Permanent gauge deformation over time
- Solution: Periodic re-calibration
- Temperature changes (affect resistance: Ro (1 + α[T – To]))
Example Calculations and Applications
- The Example section details calculations for resistance measurements under various conditions and strain levels, with provided materials data (conductivity and temp coefficients)
- Example calculations involve the given geometries and materials parameters
- These calculations and examples aim to illustrate calculating resistances for given scenarios, demonstrating sensor applications and error sources.
- Example calculation of gauge factor, showing the strain effect on resistance change and how to calculate the error.
- An example of how a bridge circuit is used to compensate for the temperature effect within the strain measurement
Tactile Sensors
- Low-force sensors
- Sense force presence with magnitude reaction
- Keypads, robotic arm grippers use tactile sensors
- Piezoelectric films; used for force distribution detection
- Examples: Conductive-foam (membrane keypads)
- Force sensitive resistive (FSR) tactile sensor (pressure-dependent material resistance)
Pressure Sensors
- Consists of two parts: pressure conversion and transduction
- Gauge pressure: Difference between measured pressure and ambient pressure
- Differential pressure: Difference between pressures at two locations
- Absolute pressure: Differential pressure referenced to zero
- Types include mechanical (Bourdon tube), bellows, and piezoelectric
Bourdon Tube
- Short bent tube, one end closed
- Pressurization causes tube straightening
- Proportional to pressure
- Position sensor or LVDT convert to electrical signal
Bellows
- Used to convert pressure into linear motion
- Expansion proportional to the pressure increase
- Detected by position sensors (like potentiometers)
Piezoelectric Pressure Sensor
- Uses piezoresistive property of silicon to measure pressure
- Advantage: no moving parts
Q&A and Discussion
- Open forum for questions
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Description
Test your knowledge on strain gauges and their properties. This quiz covers the fundamentals, including gauge sensitivity, materials, and formulae related to strain measurements. Understand the critical concepts that underpin the efficient use of strain gauges in various applications.
