JNTU
JNTU B.Tech II ELECTRICAL AND ELECTRONIC MEASUREMENTS Previous Question Paper (March - 2021 - R16)
Answer any five questions. All questions carry equal marks.
Main
Discuss about various errors and their compensation in indicating instruments.
Answer
Errors in indicating instruments arise from internal design, external environmental conditions, and human factors. These are categorized as follows:
- Instrumental Errors: Caused by mechanical friction, incorrect spring tension, or aging of permanent magnets. These are compensated by precise manufacturing, using high-quality jewel bearings, and periodic recalibration.
- Environmental Errors: Result from temperature fluctuations, external magnetic fields, or humidity. Temperature errors are compensated by using swamping resistors (manganin) in series with the moving coil, which have a near-zero temperature coefficient. Magnetic shielding using soft iron cases protects against external fields.
- Observational Errors: Caused by parallax during reading. These are mitigated by using mirror scales and knife-edge pointers to ensure the observer's line of sight is perpendicular to the scale.
Explain with a neat sketch, the construction and operation of a moving iron instrument.
Answer
Moving iron instruments operate on the principle of electromagnetic attraction or repulsion. The construction consists of a stationary coil carrying the current to be measured and a light-weight soft iron vane attached to the spindle.
In the attraction type, a single soft iron vane is placed near the coil. When current flows, the coil becomes an electromagnet and attracts the iron vane into the coil, causing the spindle to rotate against the control spring. In the repulsion type, two iron vanes are placed inside the coil; one is fixed and the other is movable. When current flows, both vanes become magnetized with the same polarity, causing them to repel each other, which deflects the pointer.
The deflecting torque is proportional to the square of the current,
Derive the torque equation of a moving iron instrument and further comment up on the nature of scale.
Answer
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Explain the constructional details of PMMC instrument with neat sketch.
Answer
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Explain the operation of DC Crompton Potentiometer with a neat diagram.
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Describe with help of suitable diagrams how a AC potentiometer can be used for measurement unknown inductance and capacitance.
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Explain with the help of neat diagram the principle and working of co-ordinate type A.C potentiometer. Also discuss the problem in using A.C potentiometers.
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A simple slide wire is used for measurement of current in a circuit. The voltage drop across a standard resistor of 1.0 ohm is balanced at 75 cm. Find the magnitude of current if the standard cell emf of 1.45V is balanced at 50 cm.
Answer
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Explain different sources of errors in induction type energy meter and how these are compensated.
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With a neat diagram explain the working of moving iron type power factor meter.
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Explain with a neat diagram, the measurement of Inductance using Hay bridge and also derive the relation for inductance under balanced condition using a neat phasor diagram.
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With a neat sketch, explain the working Megger for measurement of resistance in very high values.
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Explain with a neat diagram of a Kelvin’s double bridge method for measurement of resistance and derive the necessary equation under balanced condition.
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The four arms of a bridge are as follows: AB=100Ω. The galvanometer has a resistance; DA=50Ω; CD=4Ω, BC=10Ω and is connected across BD. A source of 10V d.c. connected across arm AC. Find the current through the galvanometer. What should be the resistance in the arm DA for no current through the galvanometer?
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What is a transducer? How are they classified enumerate briefly.
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With a neat diagram explain the operation of LVDT.
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