The moving system of the instrument is attached to the soft iron piece and the operating current is passed through a coil placed near it. Movingiron instruments are generally used to measure alternating voltages. Working principle and construction of pmmc polytechnic hub. Pdf classification of moving iron instruments atul. Feb 01, 2017 moving iron type instruments are of mainly two types slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Apr 20, 2018 in moving iron instruments, a van of soft iron forms the moving element of the system.
Moving iron instruments principle and operation repulsion type. Working principle of moving iron instruments electrical. Thus, repulsion type moving iron instrument can be used on dc as well as on ac systems. When the current to be measured is passed through the coil, then coil produces a magnetic field and attracts the ovalshaped disc, hence disc will swing into the coil.
In both the attraction and repulsion type moving iron instruments it is found that for a given position of the moving system, the value of the deflecting torque is proportional to the square of the current, so long as the iron is working below saturation. For low voltage range the power consumption is higher. A hollow circular coil is used and one of the iron pieces is attached inside the hollow coil. Since the stationary parts and the moving parts of the instrument are simple so they are cheapest. To understand the basic construction of a permanent magnet moving coil. There are two general types of moving iron instruments namely. The deflection of moving iron instruments is independent of direction of current, because the needle of the moving iron instrumen. In this page you can learn various important moving iron instrument multiple choice questions answers,mcq on moving iron instrument with answers,mcq on moving iron instrument,sloved moving iron instrument objective questions answers etc. Inside the coil, there are two soft iron pieces rods or vanes placed parallel to each other and along the axis, of the coil. The instrument in which the moving iron is used for measuring the flow of current.
It consists of a fixed cylindrical hollow coil which carries the operating current. Construction of attraction type moving iron instruments. Dynamometer type wattmeter working your electrical guide. H mi instruments may be seriously affected by waveform both on account of the change in the form of flux waveform and in case of voltmeter, the effect of harmonic upon the inductance.
Moving iron instrument type iqe type iqe 72 iqe 96 front flange mm 72 x 72 96 x 96 housing mm 66 x 66 89 x 89 class 1. Thus it is possible to design an instrument having a scale which is very nearly uniform over a. Hi friends, in this article, i am discussing the dynamometer type wattmeter working principle and related information, if you are interested in it then you at the right place. In attraction type moving iron instruments, an ovalshaped disc made up of soft iron is pivoted on the spindle near the coil. Capable of giving an accuracy within limits of both precision and industrial grades. The action of these instruments is based on the motoring principle. Thus moving iron instruments are unpolarised instruments i.
Classification of moving iron instruments a media to get. The instrument can be constructed to measure current and voltage to an accuracy needed in most engineering works and still be cheaper as compared any other type of a. Creeping in energy metre implies a slow rotation of rotor with only voltage coil excited. It works on the principle that the force acting on the coil places between the magnetic field of the. Advantages and disadvantages of movingiron instruments. This instrument is one of the most primitive forms of measuring and relay instrument. The pmmc stands for permanent magnet moving coil and it is also called as darsonval instruments. Oct 14, 2017 moving iron instruments attraction type and repulsion type complete concept duration. These instruments are based on the principle that when an unmagnetised soft iron piece is placed in the magnetic field of a coil, then the piece is attracted towards the coil. Whenever a piece of iron is placed nearer to a magnet it would be attracted by the magnet. Dec 25, 2014 construction of attraction type moving iron instruments points. When a current carrying coil is placed in the magnetic field produced by permanent magnet, the coil experiences a force and moves. Attraction type the instrument in which the iron plate attracts from the weaker field towards the stronger field such type of instrument is known as the attraction type. Attraction type moving iron instruments these instruments use soft iron which is a ferromagnetic material.
This method cannot be used in instruments where the introduction of a permanent magnet required for producing eddy currents will distort the existing magnetic field as in moving iron or dynamometer type of instruments. Nov 02, 2017 moving iron instruments repulsion type study buddy. The basic principle of a repulsion type moving iron instruments is that the repulsive forces will act when two similarly magnetized iron pieces, are placed near each other construction. A permanent magnet is used to produce magnetic flux and a coil that carries the current to be measured moves in this field. Construction and working of repulsion type moving iron construction and working of repulsion type moving iron. Deflection torque is proportional to the square of the current. Oct 21, 2016 before answering your question let me explain the working principle of both moving coil and moving iron instruments that will give you a basic idea. The necessity for the ac calibration of moving iron instruments as well as another type of instruments which cannot be correctly calibrated requires the use of a transfer type of instrument. Which of the following meter is an integrating type instrument.
Moving iron instruments having scales that are nonlinear and somewhat crowded in the lower range of calibration. Classification of moving iron instruments a media to. This distortion in moving iron instrument scale can be controlled by suitable design i. I instrument the most common ammeter and voltmeter for laboratory or switch board use at power frequency are the moving iron instruments. Both moving coil and moving iron instruments are used measure the voltage and current of circuits.
Click here to download the pdf of this topic moving iron instruments. Electrodynamometer type instruments construction and operation. Ferromagnetic materials magnetize in the direction of a magnetic field, therefore, if they are brought near one end of a current carrying coil, poles of opposite polarity are induced in them. Essentials of indicating instruments moving coil, moving. But in these instruments, the operating field is produced by the fixed coil instead of a permanent magnet. Moving iron instruments are generally used to measure alternating voltages and currents. Jan 15, 2019 a permanent magnet moving coil pmmc meter also known as a darsonval meter or galvanometer is an instrument that allows you to measure the current through a coil by observing the coils angular deflection in a uniform magnetic field.
Apr 20, 2018 due to this, moving iron instrument scale gets distorted from the square law response. The force of this attraction depends upon the strength said magnetic. In repulsion type, a fixed vane or rod is also used and magnetized with the same polarity. Moving iron instruments principle, operation and type, theory of. Moving coil instruments there are two types of moving coil instruments namely, permanent magnet moving coil type which can only be used for direct current, voltage measurements and the dynamometer type which can be used on either direct or alternating current, voltage measurements. Moving iron instruments principle, operation and type, theory. Classification, absolute and secondary instruments, indicating instruments, control, balancing and damping, constructional details, characteristics, errors in measurement, ammeters, voltmeters. It is clear that whatever may be the direction of the current in the coil of the instrument, the iron vanes are so magnetized that there is always a force of attraction in the attraction type and repulsion in the repulsion type of instruments. The iron van is so situated that it can move in the magnetic field produced by a stationary coil.
Moving iron instruments repulsion type study buddy. The attraction and the repulsion are the types of the moving iron instruments. A small piece of soft iron in the form of a vane or rod. Permanent magnet moving coil mechanism pmmc mathematical. Another type of instrument that is usually classed with the attractive types of instrument is shown in fig. If you continue browsing the site, you agree to the use of cookies on this website. The writer, also known variously as the pen motor, galvanometer or recorder, is an electromagnetic system of moving coil or moving iron type. Repulsion or double iron type figure 1 attraction or single iron type figure 2 the brief description of different components of a moving iron instrument is given below. Type of instrument moving iron for current and voltage moving coil for current and voltage moving coil with rectifiers for current and voltage moving coil with builtin transducer for frequency measurement maximum demand indicators combined md with moving iron movement format 48 x 48 mm 72 x 72 mm 96 x 96 mm 144 x 144 mm 48 x 48 mm 72 x 72 mm.
In moving iron instruments the movable system consists of one or more pieces of speciallyshaped soft iron, which are so pivoted as to be acted upon by the magnetic field produced by the current in coil. Permanent magnet moving coil instruments pmmc the permanent magnet moving coil instruments are most accurate type for direct current measurements. Construction of attraction type moving iron instruments the simplest form of attraction type moving iron instrument uses a solenoid and a moving oval shaped soft iron pivoted eccentrically. The instrument in which the coil rotates between the magnetic field of the permanent magnet for measuring the dc such type of instrument is known as the moving coil instrument.
Moving iron type instruments are of mainly two types. Moving iron instrument multiple choice questions and answers. What is the difference between movingiron and movingcoil. Classification of moving iron instruments moving iron instruments are of two types i attraction type. Mcq on measuring instruments 1 how engineering works. Jul 25, 2018 this instrument is one of the most primitive forms of measuring and relay instrument. Whereas in moving coil instrument the conductor coil is used for dc measurement. Rotation is opposed by a hairspring that produces the restoring torque.
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