06 Strain Gages Problem Set
STRAIN GAGES | PRACTICE PROBLEMS
Complete the following to reinforce your understanding of the concept covered in this module.
PROBLEM 1: A metallic strain gage is fastened to a steel beam in a power plant. During operation of the plant, the strain gage is subjected to a strain of 1 × 10%& . If the nominal resistance value of the strain gage is 130 Ω, what is the change in resistance closest too: A. 0.0026 B. 0.026 C. 0.26 D. 2.6
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SOLUTION 1:
As we are given the strain, initial resistance, and type of strain gage, we can simply plug these into the formula for gage factor, and solve for the change in resistance.
The formula for the GAGE FACTOR can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 125 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing.
A GAGE FACTOR (GF) is the ratio of fractional change in electrical resistance to the fractional change in length (strain). The gage factor represents the ratio of the change in gage resistance to the change in length or strain of the gage.
GF =
ΔR/R ΔR/R = ΔL/L ε
Where: • R is the nominal resistance of the strain gage at nominal length L • ΔR is the change in resistance due to the change in length ΔL • ε is the normal strain sensed by the gage The value for the GAGE FACTOR OF METALLIC STRAIN GAGES can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 125 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing.
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As we are told the strain gage is metallic, we know that the gage factor a metallic strain gage is typically around 2. Plugging in the given values into the formula for strain gage, we can re-write formula as: GF = 2=
ΔR/R ε
ΔR/(130 Ω) 1 × 10%&
We can now solve for the change in resistance: ΔR = 0.0026
Therefore, the correct answer choice is A. 𝟎. 𝟎𝟎𝟐𝟔
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PROBLEM 2: A resistance Wheatstone bridge circuit made up of four resistors each 120 Ω has an excitation voltage of 5 V. The output voltage change when one resistor’s value changes by 1.2 Ω is closest too: A. 8.7 B. 9.3 C. 12.5 D. 14.7
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SOLUTION 2:
The formula for an ¼ QUARTER WHEATSTONE BRIDGE can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A ¼ quarter arm Wheatstone bridge circuit is used for individual strain gages where the resistance 𝑅@ is the strain gage and the other three resistances are precision resistors equal to the nominal resistance of equivalent resistance. If the strain gage experiences a strain, the strain gage resistance changes, causing the bridge to become unbalanced. The resulting output voltage is given by: 𝑉B ≈
𝛥𝑅 ∙𝑉 4𝑅 FG
As we are given the strain, initial resistance, and type of strain gage, we can simply plug in the given values to calculate the output voltage as:
VB =
(1.2 Ω) ∙ 5 V = 12.5 mV 4(120 Ω)
Therefore, the correct answer choice is C. 𝟏𝟐. 𝟓
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PROBLEM 3: A strain gage is measured to determine the gage factor. A strain gage with an initial resistance of 200.00 Ω and final resistance of 199.79 Ω when subjected to a strain that causes the gage to compress to 0.9994 cm. The initial length of the gage was 1.0000 cm. What is the gage factor? A. 1.75 B. 2.00 C. 2.25 D. 2.50
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SOLUTION 3:
As we are given the strain, initial resistance, and type of strain gage, we can simply plug these into the formula for gage factor, and solve for the change in resistance.
The formula for the GAGE FACTOR can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 125 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A GAGE FACTOR (GF) is the ratio of fractional change in electrical resistance to the fractional change in length (strain). The gage factor represents the ratio of the change in gage resistance to the change in length or strain of the gage.
GF =
ΔR/R ΔR/R = ΔL/L ε
Where: • R is the nominal resistance of the strain gage at nominal length L • ΔR is the change in resistance due to the change in length ΔL • ε is the normal strain sensed by the gage Plugging in the given values into the formula for strain gage, we can re-write formula as: 199.79 Ω − 200 Ω ΔR/R 200 Ω GF = = = 1.75 0.9994 cm − 1 cm ε 1 cm
Therefore, the correct answer choice is A. 𝟏. 𝟕𝟓
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PROBLEM 4: There are three high-precision resistors known to be 10 kΩ in a quarter bridge circuit. R@ is a sensor with a small resistance difference from 10 kΩ. What is the change in resistance closest too if VOP = 5 V and VB = 0.03 V: A. 0.12 B. 0.24 C. 0.36 D. 0.48
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SOLUTION 4:
The formula for an ¼ QUARTER WHEATSTONE BRIDGE can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A ¼ quarter arm Wheatstone bridge circuit is used for individual strain gages where the resistance 𝑅@ is the strain gage and the other three resistances are precision resistors equal to the nominal resistance of equivalent resistance. If the strain gage experiences a strain, the strain gage resistance changes, causing the bridge to become unbalanced. The resulting output voltage is given by: 𝑉B ≈
𝛥𝑅 ∙𝑉 4𝑅 FG
As we are given the strain, initial resistance, and type of strain gage, we can simply plug in the given values:
(0.03 V) =
ΔR ∙ 5 V 4(10 kΩ)
Solving for the change in resistance: ΔR = 0.24 kΩ
Therefore, the correct answer choice is B. 𝟎. 𝟐𝟒
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PROBLEM 5: A strain gage is placed on a steel beam for a length of 10 cm, and is noted to have a resistance of 23 𝛺. If the beam is stretched to a distance of 12 cm, the resistance increases proportionally to 28 𝛺. What is the gage factor of the strain gage closest too: A. 1.10 B. 1.20 C. 2.25 D. 2.50
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SOLUTION 5:
As we are given the change in length and change in resistance, we can simply plug these into the formula for gage factor, and solve for the value of the gage factor.
The formula for the GAGE FACTOR can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 125 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A GAGE FACTOR (GF) is the ratio of fractional change in electrical resistance to the fractional change in length (strain). The gage factor represents the ratio of the change in gage resistance to the change in length or strain of the gage.
GF =
ΔR/R ΔR/R = ΔL/L ε
Where: • R is the nominal resistance of the strain gage at nominal length L • ΔR is the change in resistance due to the change in length ΔL • ε is the normal strain sensed by the gage Plugging in the given values into the formula for strain gage, we can re-write formula as:
GF =
ΔR/R ε
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Solving for the gage factor, we find: 28 Ω − 23 Ω 23 Ω GF = = 1.08 12 cm − 10 cm 10 cm
Therefore, the correct answer choice is A. 𝟏. 𝟏𝟎
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PROBLEM 6: In order to maximize the voltage output for the Wheatstone bridge shown below, which resistor(s) should be tensed in addition to resistor 4, 𝑅S ?
A. 𝑅@ B. 𝑅T C. 𝑅U D. 𝐴𝑙𝑙 𝑜𝑓 𝑡ℎ𝑒 𝑎𝑏𝑜𝑣𝑒
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SOLUTION 6: The formula for a BALANCED WHEATSTONE BRIDGE can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. In the case that the resistance in each resistor is not identical, the equivalent resistance on the left leg and right leg is equivalent, the bridge is said to still be balanced. This is due to the current division being equally divided for each leg as shown by the formula:
𝐼𝑓
𝑅@ 𝑅U = 𝑡ℎ𝑒𝑛 𝑉B = 0 𝑉 𝑅T 𝑅S
As we are told that resistor 4, 𝑅S is tensed, the resistor equal and opposite to it in the diamond configuration should be tensed as well to maximize the voltage output.
Therefore, the correct answer choice is A. 𝐑 𝟏
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PROBLEM 7: Looking at the Wheatstone bridge configuration below, what value of 𝑅T will balance the Wheatstone bridge so the voltage output is 𝑉B = 0. Assume the resistance values are the following: 𝑅@ = 1400 𝛺, 𝑅U = 21 𝛺, 𝑎𝑛𝑑 𝑅S = 638 𝛺.
A. 12,380 B. 21,480 C. 42,533 D. 𝑁𝑜𝑛𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑎𝑏𝑜𝑣𝑒
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SOLUTION 7: The formula for a BALANCED WHEATSTONE BRIDGE can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. In the case that the resistance in each resistor is not identical, the equivalent resistance on the left leg and right leg is equivalent, the bridge is said to still be balanced. This is due to the current division being equally divided for each leg as shown by the formula:
𝐼𝑓
𝑅@ 𝑅U = 𝑡ℎ𝑒𝑛 𝑉B = 0 𝑉 𝑅T 𝑅S
As we are given three of the four resistance values, we can simply use the ratio of resistors for a balanced bridge, and solve for the missing resistance value. Plugging in the given resistance values, we find: 1400 21 = R T 638 Solving for the resistance in resistor 2, we find the value needed to get an output voltage of zero is:
R T = 42,533.33 𝛺
Therefore, the correct answer choice is C. 42,533
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PROBLEM 8: What can be used to construct a quarter-bridge measurement circuit? A. 𝑂𝑛𝑒 𝑠𝑡𝑟𝑎𝑖𝑛 𝑔𝑎𝑔𝑒, 𝑜𝑛𝑒 𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟, 𝑎𝑛𝑑 𝑡𝑤𝑜 𝑓𝑖𝑥𝑒𝑑 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟𝑠 B. 𝑂𝑛𝑒 𝑠𝑡𝑟𝑎𝑖𝑛 𝑔𝑎𝑔𝑒, 𝑜𝑛𝑒 𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟, 𝑎𝑛𝑑 𝑜𝑛𝑒 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟 C. 𝑇𝑤𝑜 𝑠𝑡𝑟𝑎𝑖𝑛 𝑔𝑎𝑔𝑒𝑠 𝑎𝑛𝑑 𝑜𝑛𝑒 𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟 D. 𝑇𝑤𝑜 𝑠𝑡𝑟𝑎𝑖𝑛 𝑔𝑎𝑔𝑒𝑠, 𝑜𝑛𝑒 𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟, 𝑎𝑛𝑑 𝑜𝑛𝑒 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟
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SOLUTION 8:
The formula for an ¼ QUARTER WHEATSTONE BRIDGE can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A Wheatstone bridge measurement has a total of four resistive elements. In a fullbridge arrangement, all four elements are strain gages. In a half-bridge arrangement, only two strain gages are used. A fixed (reference) resistor and an adjustment (variable) resistor constitute the rest of the bridge. In a quarter bridge arrangement, only one strain gage is used. Two fixed resistors and an adjustment resistor constitute the rest of the bridge.
Therefore, the correct answer choice is A. 𝑶𝒏𝒆 𝒔𝒕𝒓𝒂𝒊𝒏 𝒈𝒂𝒈𝒆, one variable
resistor, and two fixed resistors
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Complete the following to reinforce your understanding of the concept covered in this module.
PROBLEM 1: A metallic strain gage is fastened to a steel beam in a power plant. During operation of the plant, the strain gage is subjected to a strain of 1 × 10%& . If the nominal resistance value of the strain gage is 130 Ω, what is the change in resistance closest too: A. 0.0026 B. 0.026 C. 0.26 D. 2.6
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SOLUTION 1:
As we are given the strain, initial resistance, and type of strain gage, we can simply plug these into the formula for gage factor, and solve for the change in resistance.
The formula for the GAGE FACTOR can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 125 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing.
A GAGE FACTOR (GF) is the ratio of fractional change in electrical resistance to the fractional change in length (strain). The gage factor represents the ratio of the change in gage resistance to the change in length or strain of the gage.
GF =
ΔR/R ΔR/R = ΔL/L ε
Where: • R is the nominal resistance of the strain gage at nominal length L • ΔR is the change in resistance due to the change in length ΔL • ε is the normal strain sensed by the gage The value for the GAGE FACTOR OF METALLIC STRAIN GAGES can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 125 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing.
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As we are told the strain gage is metallic, we know that the gage factor a metallic strain gage is typically around 2. Plugging in the given values into the formula for strain gage, we can re-write formula as: GF = 2=
ΔR/R ε
ΔR/(130 Ω) 1 × 10%&
We can now solve for the change in resistance: ΔR = 0.0026
Therefore, the correct answer choice is A. 𝟎. 𝟎𝟎𝟐𝟔
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PROBLEM 2: A resistance Wheatstone bridge circuit made up of four resistors each 120 Ω has an excitation voltage of 5 V. The output voltage change when one resistor’s value changes by 1.2 Ω is closest too: A. 8.7 B. 9.3 C. 12.5 D. 14.7
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SOLUTION 2:
The formula for an ¼ QUARTER WHEATSTONE BRIDGE can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A ¼ quarter arm Wheatstone bridge circuit is used for individual strain gages where the resistance 𝑅@ is the strain gage and the other three resistances are precision resistors equal to the nominal resistance of equivalent resistance. If the strain gage experiences a strain, the strain gage resistance changes, causing the bridge to become unbalanced. The resulting output voltage is given by: 𝑉B ≈
𝛥𝑅 ∙𝑉 4𝑅 FG
As we are given the strain, initial resistance, and type of strain gage, we can simply plug in the given values to calculate the output voltage as:
VB =
(1.2 Ω) ∙ 5 V = 12.5 mV 4(120 Ω)
Therefore, the correct answer choice is C. 𝟏𝟐. 𝟓
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PROBLEM 3: A strain gage is measured to determine the gage factor. A strain gage with an initial resistance of 200.00 Ω and final resistance of 199.79 Ω when subjected to a strain that causes the gage to compress to 0.9994 cm. The initial length of the gage was 1.0000 cm. What is the gage factor? A. 1.75 B. 2.00 C. 2.25 D. 2.50
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SOLUTION 3:
As we are given the strain, initial resistance, and type of strain gage, we can simply plug these into the formula for gage factor, and solve for the change in resistance.
The formula for the GAGE FACTOR can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 125 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A GAGE FACTOR (GF) is the ratio of fractional change in electrical resistance to the fractional change in length (strain). The gage factor represents the ratio of the change in gage resistance to the change in length or strain of the gage.
GF =
ΔR/R ΔR/R = ΔL/L ε
Where: • R is the nominal resistance of the strain gage at nominal length L • ΔR is the change in resistance due to the change in length ΔL • ε is the normal strain sensed by the gage Plugging in the given values into the formula for strain gage, we can re-write formula as: 199.79 Ω − 200 Ω ΔR/R 200 Ω GF = = = 1.75 0.9994 cm − 1 cm ε 1 cm
Therefore, the correct answer choice is A. 𝟏. 𝟕𝟓
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PROBLEM 4: There are three high-precision resistors known to be 10 kΩ in a quarter bridge circuit. R@ is a sensor with a small resistance difference from 10 kΩ. What is the change in resistance closest too if VOP = 5 V and VB = 0.03 V: A. 0.12 B. 0.24 C. 0.36 D. 0.48
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SOLUTION 4:
The formula for an ¼ QUARTER WHEATSTONE BRIDGE can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A ¼ quarter arm Wheatstone bridge circuit is used for individual strain gages where the resistance 𝑅@ is the strain gage and the other three resistances are precision resistors equal to the nominal resistance of equivalent resistance. If the strain gage experiences a strain, the strain gage resistance changes, causing the bridge to become unbalanced. The resulting output voltage is given by: 𝑉B ≈
𝛥𝑅 ∙𝑉 4𝑅 FG
As we are given the strain, initial resistance, and type of strain gage, we can simply plug in the given values:
(0.03 V) =
ΔR ∙ 5 V 4(10 kΩ)
Solving for the change in resistance: ΔR = 0.24 kΩ
Therefore, the correct answer choice is B. 𝟎. 𝟐𝟒
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PROBLEM 5: A strain gage is placed on a steel beam for a length of 10 cm, and is noted to have a resistance of 23 𝛺. If the beam is stretched to a distance of 12 cm, the resistance increases proportionally to 28 𝛺. What is the gage factor of the strain gage closest too: A. 1.10 B. 1.20 C. 2.25 D. 2.50
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SOLUTION 5:
As we are given the change in length and change in resistance, we can simply plug these into the formula for gage factor, and solve for the value of the gage factor.
The formula for the GAGE FACTOR can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 125 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A GAGE FACTOR (GF) is the ratio of fractional change in electrical resistance to the fractional change in length (strain). The gage factor represents the ratio of the change in gage resistance to the change in length or strain of the gage.
GF =
ΔR/R ΔR/R = ΔL/L ε
Where: • R is the nominal resistance of the strain gage at nominal length L • ΔR is the change in resistance due to the change in length ΔL • ε is the normal strain sensed by the gage Plugging in the given values into the formula for strain gage, we can re-write formula as:
GF =
ΔR/R ε
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Solving for the gage factor, we find: 28 Ω − 23 Ω 23 Ω GF = = 1.08 12 cm − 10 cm 10 cm
Therefore, the correct answer choice is A. 𝟏. 𝟏𝟎
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PROBLEM 6: In order to maximize the voltage output for the Wheatstone bridge shown below, which resistor(s) should be tensed in addition to resistor 4, 𝑅S ?
A. 𝑅@ B. 𝑅T C. 𝑅U D. 𝐴𝑙𝑙 𝑜𝑓 𝑡ℎ𝑒 𝑎𝑏𝑜𝑣𝑒
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SOLUTION 6: The formula for a BALANCED WHEATSTONE BRIDGE can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. In the case that the resistance in each resistor is not identical, the equivalent resistance on the left leg and right leg is equivalent, the bridge is said to still be balanced. This is due to the current division being equally divided for each leg as shown by the formula:
𝐼𝑓
𝑅@ 𝑅U = 𝑡ℎ𝑒𝑛 𝑉B = 0 𝑉 𝑅T 𝑅S
As we are told that resistor 4, 𝑅S is tensed, the resistor equal and opposite to it in the diamond configuration should be tensed as well to maximize the voltage output.
Therefore, the correct answer choice is A. 𝐑 𝟏
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PROBLEM 7: Looking at the Wheatstone bridge configuration below, what value of 𝑅T will balance the Wheatstone bridge so the voltage output is 𝑉B = 0. Assume the resistance values are the following: 𝑅@ = 1400 𝛺, 𝑅U = 21 𝛺, 𝑎𝑛𝑑 𝑅S = 638 𝛺.
A. 12,380 B. 21,480 C. 42,533 D. 𝑁𝑜𝑛𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑎𝑏𝑜𝑣𝑒
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SOLUTION 7: The formula for a BALANCED WHEATSTONE BRIDGE can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. In the case that the resistance in each resistor is not identical, the equivalent resistance on the left leg and right leg is equivalent, the bridge is said to still be balanced. This is due to the current division being equally divided for each leg as shown by the formula:
𝐼𝑓
𝑅@ 𝑅U = 𝑡ℎ𝑒𝑛 𝑉B = 0 𝑉 𝑅T 𝑅S
As we are given three of the four resistance values, we can simply use the ratio of resistors for a balanced bridge, and solve for the missing resistance value. Plugging in the given resistance values, we find: 1400 21 = R T 638 Solving for the resistance in resistor 2, we find the value needed to get an output voltage of zero is:
R T = 42,533.33 𝛺
Therefore, the correct answer choice is C. 42,533
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PROBLEM 8: What can be used to construct a quarter-bridge measurement circuit? A. 𝑂𝑛𝑒 𝑠𝑡𝑟𝑎𝑖𝑛 𝑔𝑎𝑔𝑒, 𝑜𝑛𝑒 𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟, 𝑎𝑛𝑑 𝑡𝑤𝑜 𝑓𝑖𝑥𝑒𝑑 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟𝑠 B. 𝑂𝑛𝑒 𝑠𝑡𝑟𝑎𝑖𝑛 𝑔𝑎𝑔𝑒, 𝑜𝑛𝑒 𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟, 𝑎𝑛𝑑 𝑜𝑛𝑒 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟 C. 𝑇𝑤𝑜 𝑠𝑡𝑟𝑎𝑖𝑛 𝑔𝑎𝑔𝑒𝑠 𝑎𝑛𝑑 𝑜𝑛𝑒 𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟 D. 𝑇𝑤𝑜 𝑠𝑡𝑟𝑎𝑖𝑛 𝑔𝑎𝑔𝑒𝑠, 𝑜𝑛𝑒 𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟, 𝑎𝑛𝑑 𝑜𝑛𝑒 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟
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SOLUTION 8:
The formula for an ¼ QUARTER WHEATSTONE BRIDGE can be referenced under the topic of INSTRUMENTATION, MEASUREMENT, AND CONTROLS on page 126 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. A Wheatstone bridge measurement has a total of four resistive elements. In a fullbridge arrangement, all four elements are strain gages. In a half-bridge arrangement, only two strain gages are used. A fixed (reference) resistor and an adjustment (variable) resistor constitute the rest of the bridge. In a quarter bridge arrangement, only one strain gage is used. Two fixed resistors and an adjustment resistor constitute the rest of the bridge.
Therefore, the correct answer choice is A. 𝑶𝒏𝒆 𝒔𝒕𝒓𝒂𝒊𝒏 𝒈𝒂𝒈𝒆, one variable
resistor, and two fixed resistors
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