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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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Description :

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

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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 :

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

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Answer :

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

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

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

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

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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 :

A neodymium magnet is a permanent magnet made from an alloy of _________ A) Neodymium and iron B) Neodymium, iron and iodine C) Neodymium and boron D) Neodymium, iron and boron

Answer :

A neodymium magnet is a permanent magnet made from an alloy of Neodymium, iron and boron

Description :

Compare variable reluctance and permanent magnet motors.

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Variable reluctance Motor  Permanent magnet motors   The rotor is not magnetised The rotor is magnetised  High torque to inertia ratio  Low torque to inertia ratio  ... rotor has salient pole construction The rotor has mostly smooth cylindrical type of construction. 

Description :

What is permanent magnet and electromagnet?

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Permanent magnet: A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. As the name suggests, a permanent magnet is 'permanent'. ... an electric current passes through the coil. If the current is interrupted, the magnetism is lost.

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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

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 :

Answer :

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

Description :

A permanent magnet moving coil instrument gives full scale deflection of 25mA when a voltage of 75mV is applied across it. Calculate: (i) Resistance of shunt required for full scale deflection of 150 A. (ii) Series resistance for full scale deflection of 500 V.

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Description :

Permanent Magnet Moving Coil (PMMC) Instrument

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Permanent Magnet Moving Coil (PMMC) Instrument

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The multiplier and the meter coil in a voltmeter are in series.

Description :

The self inductance of a coil can be measured using (A) Wien’s Bridge (B) Schering Bridge (C) Anderson’s Bridge (D) Wheatstone Bridge

Answer :

The self inductance of a coil can be measured using Anderson’s Bridge

Description :

A permanent magnet moving coil ammeter has a coil resistance of 99 ohm and Full Scale Deflection (FSD) current of 0.1mA. Shunt resistance is 1 ohm. Current through the meter at 0.5 F.S.D is:

Answer :

A permanent magnet moving coil ammeter has a coil resistance of 99 ohm and Full Scale Deflection (FSD) current of 0.1mA. Shunt resistance is 1 ohm. Current through the meter at 0.5 F.S.D is: 0.05mA

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

Answer :

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

Description :

Two voltmeters of same range, one moving iron type and other permanent magnet moving coil type, are connected in parallel for measuring a.c. supply voltage. If the reading of MI type is 300V, the reading of PMMC type will be (a) zero (b) higher-than M.I. type (c) lower than M.I. type (d) same

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

Description :

Answer :

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

Description :

Answer :

In a dynamo-meter type of moving coil instrument a swamping resistance is provided inorder to: Provide equal time constant for moving coil and fixed coil, when used for ac measurement

Description :

The inductance of a coil can be increased by?

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The inductance of a coil can be increased by choosing core material having high relative permeability.

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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.

Description :

 The main sources of Errors in Permanent Magnet moving Coil (PMMC) are due to : - a) weaking of the permanent magnet due to aging at temperature effects b) weaking of spring due to aging and temperature effects c) change of resistance of the moving coil with temperature d) all the above

Answer :

 The main sources of Errors in Permanent Magnet moving Coil (PMMC) are due to : - a) weaking of the permanent magnet due to aging at temperature effects b) weaking of spring due to aging and temperature effects c) change of resistance of the moving coil with temperature d) all the above

Description :

Answer :

In a low power factor wattmeter the compensating coil is connected in series with pressure coil.

Description :

Answer :

In a low power factor wattmeter the pressure coil is connected to the load side of the current coil.

Description :

Why energy meter is integrating type measuring instrument?

Answer :

Energy Meter is Integrating Type Measuring Instrument: Energy meter is used for measurement of energy, which is obtained by integration (summation) of power supplied over the particular time duration, hence it the integrating type measuring instrument. 

Description :

differences between temporary and permanent magnets

Description :

Hard steel is suitable for making permanent magnets because?

Answer :

Hard steel is suitable for making permanent magnets because it has good residual magnetism.

Description :

Those materials are well suited for making permanent magnets which have _____ retentivity and _______ coercivity.

Answer :

Those materials are well suited for making permanent magnets which have high retentivity and high coercivity.

Description :

Permanent magnets are normally made of?

Answer :

Permanent magnets are normally made of alnico alloys.

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 :

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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Answer :

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

Description :

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

Answer :

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 :

Peterson coil is used for :  (A) shunt compensation of lines (B) grounding of system neutral (B) reduce fault currents (D) connecting interconnected systems

Answer :

Peterson coil is used for : grounding of system neutral

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 :

An instrument which detects electric current is known as?

Answer :

An instrument which detects electric current is known as galvanometer.

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