JNTU
JNTU B.Tech II ELECTRONIC MEASUREMENTS Previous Question Paper (September - 2021 - R18)
Answer any five questions. All questions carry equal marks.
Main
A multimeter having a sensitivity of 2000Ω/V is used to measure the voltage across a circuit having an output resistance of 10kΩ. The open circuit voltage of the circuit is 6V. Find the reading of the multimeter when it is set to its 10V scale. Find the percentage error.
Answer
First, calculate the internal resistance of the multimeter (Rm) on the 10V scale: Rm = Sensitivity × Range = 2000 Ω/V × 10 V = 20,000 Ω (or 20 kΩ). The circuit can be modeled as a 6V source in series with a 10 kΩ output resistance (Rs). When the multimeter is connected, it forms a voltage divider with the output resistance. The voltage measured (Vm) is:
The percentage error is calculated by comparing the measured value to the true open-circuit voltage:
What are the three types of constructions have been used for capacitance primary standards?
Answer
Capacitance primary standards are designed to provide highly stable and calculable values. The three main types of constructions used are:
- Cross-Capacitors (Thompson-Lampard Capacitors): These are based on the Thompson-Lampard theorem, where the capacitance is determined by the length of a cylindrical electrode. They are the most accurate primary standards, as the capacitance value depends only on the length of the electrode and the speed of light.
- Parallel-Plate Capacitors: These consist of two parallel conducting plates separated by a precise dielectric gap. They are used for lower-frequency measurements where the geometry can be precisely measured and controlled to minimize edge effects.
- Cylindrical (Coaxial) Capacitors: These utilize a coaxial geometry where the capacitance is defined by the radii of the inner and outer conductors and the length of the overlap. These are often used as reference standards due to their mechanical stability and ability to be shielded effectively against external electromagnetic interference.
What are the considerations should be taken into account while designing and constructing Inductance standards?
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The resistance of a circuit is found by measuring current flowing and the power fed into the circuit. Find the limiting error in the measurement of resistance when the limiting errors in the measurement of power and current are respectively ±1.5% and ±1.0%?
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The dead zone in a certain pyrometer is 0.125 percent of span. The calibration is 400°C to 1000°C. What temperature change might occur before it is detected?
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Prove that if any two units are available as samples of calibration, the instruments which measure the third unit may also be calibrated.
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How to calibrate the Voltmeter and what are the advantages if the voltmeter is calibrated?
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How errors are reduced in measurements if the calibration against standards are applied?
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Draw the circuit diagram of rectifier voltmeter using bridge full wave rectifier and explain the working of it.
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What are the advantages of digital voltmeter?
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Draw the simple circuit of wave analyzer and explain its working and How to overcome limitations of it?
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How to measure the power in circuits? Explain the basic principle of such a meter?
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What are the different factors that has to be consider while measuring resistance with Wheatstone bridge?
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The four arms of a Hay’s alternating current bridge are arranged as follows: AB is a coil of unknown impedance; BC is a non-reactive resistor of 1000Ω; CD is a non-reactive resistor of 833Ω in series with a standard capacitor of 0.38μF; DA is non-reactive resistor of 1680Ω. If the supply frequency is 50Hz determine the inductance and the resistance at the balanced condition.
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Draw the simplified block diagram of CRO and explain the function of each block.
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Explain the principle of sampling oscilloscope with basic diagrams.
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