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A moving iron instrument can be used for both D.C. and A.C.

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Description :

Eddy current damping cannot be used for moving iron instrument because

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Eddy current damping cannot be used for moving iron instrument because the presence of a permanent magnet required for such purpose would affect the deflection and hence the reading of the instrument

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A moving-coil permanent-magnet instrument can be used as flux-meter by eliminating the control springs.

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A moving-coil permanent-magnet instrument can be used as ammeter by using a low resistance shunt.

Description :

An unshielded moving iron voltmeter is used to measure the voltage in an AC circuit. The stray DC magnetic field having a component along the axis will be  (1) unaffected (2) decreased (3) increased (4) either decreased or increased depending on the direction of the DC field

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An unshielded moving iron voltmeter is used to measure the voltage in an AC circuit. The stray DC magnetic field having a component along the axis will be either decreased or increased depending on the direction of the DC field

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Name the material used for :- (i) Moving coil (ii) Permanent magnet in PMMC instrument.

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(i) Material used for Moving coil: Copper, Aluminum( some times)  (ii) Permanent magnets are made of special alloys such as :  Aluminum-Nickel-Cobalt (Alnicos)  Strontium-Iron  Neodymium-Iron-Boron  Samarium-Cobalt.

Description :

Permanent magnet moving coil instruments are used for

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PMME are mostly used for measuring voltage and current.

Description :

A moving coil of meter has 100 turns, and a length and depth of 10mm and 20mm respectively. It is positioned in a uniform radial flux density of 200 mT. The coil carrier current capacity is 50 mA. The torque on the coil is

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A moving coil of meter has 100 turns, and a length and depth of 10mm and 20mm respectively. It is positioned in a uniform radial flux density of 200 mT. The coil carrier current capacity is 50 mA. The torque on the coil is 200µNm

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A damping device prevents the oscillation of the moving system and enables the latter to reach its final position quickly.

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State the material used for moving coil and former for PMMC instruments. 

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Material Used for Moving Coil and Former for PMMC Instruments:  Material used for moving coil: Copper  Material used for Former: Aluminium

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Iron loss of a transformer can be measured by low power factor wattmeter.

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Select insulating materials for following parts : (i) Insulation between heating element and base plate of electric iron. (ii) Insulation used over copper or aluminium conductor used for making coils. (iii) Transformer bushings. (iv) Insulation between transmission line and pole.

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Parts Insulating Materials  Insulation between heating element and base plate of electric iron. Mica Insulation used over copper or aluminium conductor used for making coils.  ... Transformer bushings Porcelain  Insulation between transmission line and pole. Porcelain

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The disc of an instrument using eddy current damping should be of conducting and non-magnetic material.

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The pointer of an indicating instrument should be very light.

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If an instrument has cramped scale for larger values, then it follows logarithmic law.

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The iron alloy, ALNICO is mainly used to make ________ A) Temporary magnets B) Permanent magnets C) Transmission lines D) None of these

Answer :

The iron alloy, ALNICO is mainly used to make Permanent magnets

Description :

In AC. circuits, laminated iron is invariably used in order to?

Answer :

In AC. circuits, laminated iron is invariably used in order to reduce eddy current loss.

Description :

When secondary of a current transformer is open-circuited its iron core will be?

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When secondary of a current transformer is open-circuited its iron core will be hot because of heavy iron losses taking place in it due to high flux density.

Description :

A Pyrheliometer is an instrument to measure :  (A) temperature of solar photovoltaic cell  (B) intensity of direct solar radiation at normal incidence  (C) intensity of indirect solar radiation  (D) efficiency of a solar photovoltaic cell

Answer :

A Pyrheliometer is an instrument to measure : intensity of direct solar radiation at normal incidence 

Description :

In a PMMC instrument, the damping provided is :  (A) air damping (C) eddy current damping (B) fluid damping (D) magnetic damping using a magnet

Answer :

In a PMMC instrument, the damping provided is : eddy current damping 

Description :

A PMMC instrument has FSD of 100 μA and a coil resistance of 1 kΩ. To convert the instrument into an ammeter with full scale deflection of 100 mA, the required shunt resistance is (A) 1 Ω (B) 1.001 Ω (C) 0.5 Ω (D) 10 Ω

Answer :

A PMMC instrument has FSD of 100 μA and a coil resistance of 1 kΩ. To convert the instrument into an ammeter with full scale deflection of 100 mA, the required shunt resistance is 1.001 Ω

Description :

Identify the instrument that does not exist (A) Dynamo-meter type ammeter (B) Dynamo-meter type wattmeter (C) Moving-iron voltmeter (D) Moving-iron wattmeter

Answer :

Identify the instrument that does not exist (A) Dynamo-meter type ammeter (B) Dynamo-meter type wattmeter (C) Moving-iron voltmeter (D) Moving-iron wattmeter

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Answer :

A multirange instrument has multiple shunt or series resistances inside the meter.

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Answer :

The scale of a rectifier instrument is linear.

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In a portable instrument, the controlling torque is provided by spring.

Description :

What is the definition of a primary instrument?

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Answer :

Instrument transformers are potential transformers, current transformers.

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The rectifier instrument is not free from frequency error.

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Answer :

The gravity controlled instrument has crowded scale because current is proportional to sine of deflection angle.

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The ratio of maximum displacement deviation to full scale deviation of the instrument is called?

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The ratio of maximum displacement deviation to full scale deviation of the instrument is called linearity.

Description :

Answer :

Meggar is an instrument which measures the insulation resistance of an electric circuit relative to earth and one another.

Description :

Give the classification of the errors used in measuring instrument & state the reason for their occurrence.

Answer :

Types of errors in measuring instruments:  A) Gross error: These are due to mistakes on the part of person using the instrument.  B) Systematic Error:  i) Instrumental Error: These ... multiplying factor.  C) Random error: These persist even after gross and systematic errors are removed. 

Description :

A moving coil meter has a resistance of 3 Ω and gives full scale deflection with 30 mA. To measure voltage up to 300 V, the external resistance to be connected in series with the instrument is (A) 9997 Ω (B) 10000 Ω (C) 997 Ω (D) 10003 Ω

Answer :

A moving coil meter has a resistance of 3 Ω and gives full scale deflection with 30 mA. To measure voltage up to 300 V, the external resistance to be connected in series with the instrument is 9997 Ω

Description :

At full -load of a transformer, the iron loss and copper loss are 3000 W and 4000 W respectively. Then total loss at maximum efficiency is :  (A) 7000 W (B) 6000 W (C) 8000 W (D) 4000 W

Answer :

At full -load of a transformer, the iron loss and copper loss are 3000 W and 4000 W respectively. Then total loss at maximum efficiency is : 6000 W

Description :

A ferrite core has less eddy current loss than an iron core because?

Answer :

A ferrite core has less eddy current loss than an iron core because ferrites have high hysteresis.

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Answer :

Iron losses in a D.C. machine are independent of variations in load.

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Answer :

In a D.C. generator, the iron losses mainly take place in armature rotor.

Description :

Which is the best conductor: silver, carbon, or iron?

Answer :

Silver is the best conductor. Carbon is the semiconductor. Iron have less conductance as compared to silver.

Description :

In DC motor iron losses are occurred in?

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In DC motor iron losses are occurred in the armature.

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Answer :

In an actual transformer the iron loss remains practically constant from no load to full load because core flux remains practically constant.

Description :

Answer :

If the supply frequency to the transformer is increased, the iron loss will increase.

Description :

When the voltage across a battery is measured using a D.C potentiometer, the reading shows 1.08 V. But when the same voltage is measured using a Permanent Magnet Moving Coil (PMMC) voltmeter, the voltmeter reading shows 0.99 V. If the resistance of the voltmeter is 1100 Ohm , the internal resistance of the battery, in Ohm , is (A) 150 (B) 100 (C) 50 (D) 200

Answer :

When the voltage across a battery is measured using a D.C potentiometer, the reading shows 1.08 V. But when the same voltage is measured using a Permanent Magnet Moving Coil (PMMC) voltmeter, ... resistance of the voltmeter is 1100 Ohm , the internal resistance of the battery, in Ohm , is 100

Description :

Describe spring control method of producing controlling torque in measuring instrument. Write any two properties required for spring material.

Answer :

A)Spring control method: As shown in the figure, the inner ends of the both springs are attahced to the spindle, while outer end of upper spring is attached to the lever and outer ... of spring material: 1.Non Magnetic material 2.Low specific resistance 3.Low temperature coefficient of resistance

Description :

State the advantages of instrument transformer in using for extension of range of meters. 

Answer :

Advantages of instrument transformer: 1. Extension of instrument range is possible. 2. Isolation of instruments from high voltage side. 3. Power loss is less as compared to shunts and multipliers. 4 ... measurement. 5. It is economical method of range extension. 6. Increases in safety of operator.

Description :

The largest change of input quantity for which there is no output of instrument is called ______ A) Dead time B) Dead input C) Dead output D) Dead zone

Answer :

The largest change of input quantity for which there is no output of instrument is called Dead zone

Description :

Answer :

Moving iron and PMMC instruments can be distinguished from each other by looking at: Scale

Description :

Answer :

A moving coil instrument is used as an ohmmeter. The indicating scale of the meter will be Hyperbolic.

Description :

Moving iron instruments can be used for measuring (1) Direct currents and voltages (2) Radio frequency currents (3) A.C currents and voltages (4) Both (a) and (c)

Answer :

moving iron instruments areused to measure A.C curents &  voltages

Description :

What modifications are necessary if ac is applied to a PMMC instrument?

Description :

need of calibration and explain the procedure to calibrate the instrument.

Answer :

Need of calibration: Every measuring device degrades over time due to normal wear and tear. These changes can be caused by various reasons such as electric or mechanical shock or a hazardous manufacturing ... different magnitude are used to calculate the resistance based on ohm's law.

Description :

feature of PMMC instrument. 

Answer :

Consumes less power Great accuracy. High torque to weight ratio

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