# What is PMMC?

What is PMMC in measurement subject of 3rd semester electrical engineering.

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Definition: The instruments which use the permanent magnet for creating the stationary magnetic field between which the coil moves is known as the permanent magnet moving coil or PMMC instrument. It operates on the principle that the torque is exerted on the moving coil placed in the field of the permanent magnet. The PMMC instrument gives the accurate result for DC measurement.

Construction of PMMC Instrument

The moving coil and permanent magnet are the main part of the PMMC instrument. The parts of the PMMC instruments are explained below in details. ## Related Questions

List two advantages of PMMC instrument.
Last Answer : 1. It has uniform scale. 2. Power consumption is low 3. It can be obtained in wide ranges. 4. High sensitivity & accuracy 5. It is unaffected by external magnetic field. 6. Additional damping device not required. 7. Hysteresis problem is not there. role of the series resistance connected in PMMC movement.
Last Answer : A PMMC Instrument can be used as voltmeter by just connecting a series resistance with the moving coil. This series resistance is called Voltmeter Multiplier. This combination of moving coil and ... current whose voltage is to be measured. Ideally the resistance of voltmeter should be infinite feature of PMMC instrument.
Last Answer : Consumes less power Great accuracy. High torque to weight ratio What modifications are necessary if ac is applied to a PMMC instrument?  State the function of former and control spring in PMMC instrument.
Last Answer : Function of Former: To support the coil and provide eddy current damping.  Function of Control Spring: To provide control torque or force and in some instruments springs can be used as current leads. ‘PMMC instrument is not suitable to measure AC quantity’. State the reason.
Last Answer : The direction of force exerted on moving coil depends on the direction of current flowing through moving coil. If the direction of magnetic field is kept constant, it produces unidirectional torque if the current is ... on the coil in one cycle to zero. Hence the meter cannot read A.C. quantities. Name the material used for :- (i) Moving coil (ii) Permanent magnet in PMMC instrument.
Last Answer : (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. State the material used for moving coil and former for PMMC instruments.
Last Answer : Material Used for Moving Coil and Former for PMMC Instruments:  Material used for moving coil: Copper  Material used for Former: Aluminium State working principle of PMMC instrument.
Last Answer : Working Principle of PMMC Instrument: When current carrying conductor is placed in a constant magnetic field, it experiences a force proportional to the current and produces proportional deflection torque. Compare PMMC & MI instrument.
Last Answer : MI Instrument  PMMC Instrument  It works on the principles of magnetism.  It works on the principle of DC motor Deflection torque is proportional to square of current  Deflection ... , Voltmeter and Watt meter  Can be used as voltmeter, Ammeter, Galvanometer, ohmmeter In a PMMC instrument, the damping provided is :  (A) air damping (C) eddy current damping (B) fluid damping (D) magnetic damping using a magnet
Last Answer : In a PMMC instrument, the damping provided is : eddy current damping 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
Last 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 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 ... resistance of the battery, in Ohm , is (A) 150 (B) 100 (C) 50 (D) 200
Last 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 Which of the following instruments have least torque/weight ratio: a) Dynamometer type b) PMMC c) Attraction type moving iron d) Repulsion type moving iron A 0-10 mA PMMC ammeter reads 5mA in a circuit; its bottom control spring snaps out suddenly the meter will now read. a) 5mA b) 10mA c) 2.5mA d) 0 Controlling torque in PMMC Basically, a PMMC instrument can be used only in Another name for PMMC instrument Derive the relation for deflection torque in PMMC instrument.
Last Answer : Ans: The length of coil be l meter and width of coil be d meter. Assume I is the current flowing in the ciol having N turns. Assume B as the flux density in the air gap then F=BIL ... a direct indication of the current in the coil. The pointer deflection can therefore be used to measure current. Draw the construction and explain working principle of PMMC instruments
Last Answer : Working: When current passes through the coil a deflecting torque is produced. This deflecting torque is produced due to interaction between magnetic field produced by permanent magnet ... equilibrium; this is possible only when the controlling torque becomes equal to the deflecting torque Draw the diagram of PMMC instrument and state the deflection torque equation
Last Answer : Equation Ʈ= B*A*I*N Where r= torque Newton. Meter B = flux density in the air gap. Wb/m2 A = effective coil area (m) N= number of turns of wire of the coil Draw PMMC meter movement and describe it.
Last Answer : Working principle of PMMC: 1. The working principle of PMMC is based on basic meter movement known as D'Arsonval principle stated as when current passes through the coil ... controlling torque becomes equal to deflecting torque then pointer attached with scale become stable at equilibrium. Explain D’Arsonal PMMC movement in detail.
Last Answer : OR Working: When current passes through the coil a deflecting torque is produced. This deflecting torque is produced due to interaction between magnetic field produced by permanent ... equilibrium; this is possible only when the controlling torque becomes equal to the deflecting torque. Permanent Magnet Moving Coil (PMMC) Instrument
Last Answer : Permanent Magnet Moving Coil (PMMC) Instrument Last Answer : Working Principal of PMMC Analog Instrument: When current carrying conductor is placed in a magnetic field, it experiences mechanical force. In PMMC instrument, when current flows through a coil ... coil rotates and pointer attached to the coil shows deflection proportional to the current magnitude.  The full scale range of PMMC voltmeter is 100 V and its sensitivity is 1000 Ω/V. If the meter reads 50 V, the current through the voltmeter is (A) 0.05 mA (B) 0.5 mA (C) 5 mA (D) 50 mA Which of the following factors limit the deflection of the pointer of a PMMC instrument of about 90o?  1. Its damping mechanism  2. Linearity of magnetic field in which the coil moves  3. Control spring arrangement  4. ... Only 1 and 3 (b) Only 2 and 4 (c) Only 2 and 3 (d) Only 1 and 4
Last Answer : Which of the following factors limit the deflection of the pointer of a PMMC instrument of about 90o?  1. Its damping mechanism  2. Linearity of magnetic field in which the coil moves  3. Control spring arrangement  4. ... Only 1 and 3 (b) Only 2 and 4 (c) Only 2 and 3 (d) Only 1 and 4 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
Last 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 If one of the control springs of PMMC ammeter is broken when it is connected in a circuit, the meter will read  A) Half the correct value of current B) Twice the correct value of current C) An indefinite figure D) Zero Last Answer : PMMC type instruments normally use Eddy current damping. Last Answer : In the case of PMMC rectifier type instruments, the deflecting torque is proportional to Average value of AC current. PMMC instrument gives uniform scale because:
Last Answer : PMMC instrument gives uniform scale because: It uses spring control and The deflection torque is proportional to the instrument current. Last Answer : Moving iron and PMMC instruments can be distinguished from each other by looking at: Scale  