JNTU
JNTU B.Tech IV MEASURING INSTRUMENTS Previous Question Paper (September - 2022 - R18)
Answer any five questions
All questions carry equal marks
Main
Explain about sources of errors different types of errors and precautions to minimize them.
Answer
Errors in measurements arise from various sources and are generally classified into three categories:
- Gross Errors: Primarily caused by human mistakes in reading, recording, or misusing instruments. These can be minimized by taking multiple readings, using two or more observers, and maintaining careful records.
- Systematic Errors: These are consistent, repeatable errors categorized into instrumental errors (due to inherent design or wear), environmental errors (due to temperature, pressure, or magnetic fields), and observational errors (parallax). These are minimized by proper calibration, environmental control, and using instruments with high precision.
- Random Errors: These are unpredictable variations caused by unknown small fluctuations in the system. They are minimized by taking a large number of readings and applying statistical analysis, such as calculating the arithmetic mean.
The accuracy of five digital voltmeters are checked by using each of them to Measure a standard 1.0000V from a calibration instrument. The voltmeter readings are as follows: V1=1.001V, V2=1.002V, V3=0.999V, V4=0.998V and V5=1.0000V. Calculate the average measured voltage and the average deviation.
Answer
Given readings: V1=1.001V, V2=1.002V, V3=0.999V, V4=0.998V, V5=1.000V.
The average measured voltage (Vavg) is calculated as:
The deviations (d) from the average are:
- d1 = |1.001 - 1.000| = 0.001
- d2 = |1.002 - 1.000| = 0.002
- d3 = |0.999 - 1.000| = 0.001
- d4 = |0.998 - 1.000| = 0.002
- d5 = |1.000 - 1.000| = 0.000
The average deviation (Davg) is:
Explain the difference between basic standards and secondary standards.
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Calculate the maximum percentage error in the sum and difference of two voltage measurements when V1 = 100V ± 1% and V2 = 80V ± 5%.
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Derive gauge factor due to change in dimensions of a strain gauge element when it is subjected to tensile force.
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Calculate the gauge factor S if a 1.5 mm diameter conductor that is 24 mm long Changes length by 1 mm and diameter by 0.02 mm under a compression force.
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Explain how LVDT is used to measure linear displacement.
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Show that a parallel plate capacitor serves as the most suitable transducer for measurement of linear and angular displacements.
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Discuss how length is measured using optical method.
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Explain how roughness is measured accurately.
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Explain the velocity measurement method and discuss about the possible errors in measurement.
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Using multiplexing, explain multi-channel data acquisition system.
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Illustrate the principle of force summing devices with an example.
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What are the main differences in measuring low pressure and high pressure?
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Show that a parallel plate capacitor serves as the most suitable transducer for measurement of linear and angular displacements.
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A transducer that measures force has nominal resting resistance of 300 Ω and is excited by 7.5V. When a 980 dyne force is applied, all four equal resistance bridge elements change resistance by 5.2 Ω. Find the output voltage E0.
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