One iron vane is held fixed to the coil frame and other is free to rotate, carrying with it the pointer shaft. Moving iron measuring mechanisms are also used in ratio meters. In case of aminstruments with doubled overload range the overload range corresponds to approximately 20 % of the full scale length. Both moving coil and moving iron instruments are used measure the voltage and current of circuits.
Deflection torque is proportional to the square of the current. When the frequency of the incoming alternator is same as that of the bus bars. Consequently, such meters would normally have a non linear scale, but the iron parts are usually modified in shape to make the scale fairly linear over most of its range. Friction and temperature might introduce some errors. Some errors are also caused due to the ageing of control springs and the permanent magnets. It operates on the principle that the torque is exerted on the moving coil placed in the field of the permanent magnet. In both cases, the indicator is driven by magnetic torque caused by current flow in the coil. In addition to above instruments, we have wattmeters, power factor meters, frequency meters etc. General theory permanent magnet moving coil pmmc instruments 57. The potential difference across the meter when carrying 20ma is 400mv. What is the difference between movingiron and movingcoil.
Whenever a piece of iron is placed nearer to a magnet it would be attracted by the magnet. Analog instruments classification of analog instruments. 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. In moving iron instruments, a plate or van of soft iron or of high permeability steel forms the moving element of the system. Measurement and instruments objective questions and answers pdf free download. An instrument may be defined as a machine or system which is. In commercial instruments, it is usual for the moving iron b to be in the form of a thin curved plate and for the fixed iron a to be a tapered curved sheet. Due to this square law response, the moving iron instrument scale is nonuniform. Click here to download the pdf of this topic moving iron instruments. Moving iron instruments construction and working principle in hindi duration. Broadly, the analog instruments and for that matter digital instruments may be classified according to the quantity they measure. Still mi instruments are cheap as compared to any other type of a. Moving iron instrument multiple choice questions and answers.
Ammeters, voltmeters are some of the examples of mi instruments. An ammeter is always connected in series with a circuit branch and measures the current flowing in it. Therefore, these are widely used in laboratories and on switching panels. Pmmc instruments, moving iron of ammeters and voltmeters elementary treatment only unit 8.
The pointer of a moving coil instrument gives full scale deflection of 20ma. 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. 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. Moving iron instruments principle, operation and type. Basic principle operation of moving iron instruments 61. Moving iron instruments can be used a to measure dc currents only b to measure ac currents only c to measure a. Classification of moving iron instruments moving iron instruments are of two types i attraction type. Multiple choice questions and answers on measurement and instrumentation.
These instruments can measure current and voltage to a great accuracy. Construction and working of repulsion type moving iron construction and working of repulsion type moving iron. If there is no phase difference between the two voltages. The most widely used moving iron instruments are switchboard instruments of classes 1. Moving iron instruments free download as powerpoint presentation. In repulsion type moving iron instrument consists of two cylindrical soft iron vanes mounted within a fixed currentcarrying coil. This instrument is one of the most primitive forms of measuring and relay instrument. Basic electrical engineering pdf notes bee pdf notes. 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. Movingiron instruments physics homework help, physics. Mcq on measuring instruments 1 how engineering works.
The instrument to be used is 200a for full scale deflection. Moving iron instruments moving iron instruments are the most common instruments used for measurements of electrical quantities. Two irons lie in the magnetic field produced by the coil that consists of only few turns if the instrument is an ammeter or of many turns if the instrument is a voltmeter. When the instrument is connected in the circuit, the operating current flows through the coil. Moving iron instruments principle and operation repulsion type. The deflection of needle of moving iron instrument is given in terms of rms value of voltage or current. One iron vane is held fixed to the coil frame and other is free to rotate, carrying with it. Home advantages and disadvantages of moving iron instruments. A pointer attached to the moving coil deflects up scale as the moving coil rotates.
Any instrument in which current is sent through one or more coils suspended or pivoted in a magnetic field, and the motion of the coils is used to measure. Nevertheless, by making the fixed iron curved and tapering as shown in fig. The general theory of movingcoil instruments may be dealt with considering a rectangular coil of turns, free to rotate about a vertical axis. Moving iron instruments attraction type study buddy. The movement of the pointer is equal to the phase difference between the two voltages. Moving coil instruments electrical technology duration. Working principle of moving iron instruments electrical. Differences between moving coil mc and moving iron mi. Advantages and disadvantages of movingiron instruments. Voltage measuring ranges are 100150250 400500600 v.
I instrument the most common ammeter and voltmeter for laboratory or switch board use at power frequency are the moving iron instruments. Moving iron mi instruments generally used to measure ac current or voltage but can measure dc current and voltage without any external circuit pointer is connected to specially designed soft iron that moves according to the intensity of magnetic field acting on it the magnetic field is produced by current carrying coil. Voltmeter selector switch pdf product description pdf betriebsanleitung. Moving iron instrument this instrument is one of the most primitive forms of measuring and relay instrument. 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. These are costlier in comparison of moving iron instruments. The instrument in which the moving iron is used for measuring the flow of current or voltage is known as the moving iron instrument. This construction can be arranged to give a longer and more uniform scale than is possible with the rods shown in fig. 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. In other words, the coil behaves like a magnet and, therefore, it attracts the soft iron piece towards it. Permanent magnet moving coil or pmmc instrument definition. Moving iron type instruments are of mainly two types. Moving iron instruments indicate the rms value of any ac waveform applied. What is permanent magnet moving coil or pmmc instrument.
Difference between moving coil measuring instrument and. Moving coil instrument working principle your electrical. Moving iron measuring instruments for alternating voltage with inbuilt measuring point selector switch pdf product description pdf operating manual. Moving iron instruments with four systems the instruments are suitable for simultaneous measurement of ac current and voltage in a 3phase system 2x current and 1xvoltage. The current to be measured is passed through the coil, coil produced the magnetic field.
The current coil of a wattmeter is connected to the ct of rphase. Moving iron instruments measuring instrument electromagnetic. In the attraction moving iron instrument a specially shaped piece of soft iron with a pointer attached is pivoted near to the open end of a. Let us have a comparison between two major type of electrical measuring instruments they are moving coil mc and moving iron mi instruments. For example, an instrument meant for measurement of current is classified as an ammeter while an instrument that measures voltage is classified as a voltmeter. 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.
In this article all major differences between moving iron and moving coil instruments are discussed. A hollow circular coil is used and one of the iron pieces is attached inside the hollow coil. When you go for viva or interview most often question on electrical measurements is what is the difference between mi and mc type instruments. The moving iron instruments or mi instruments are quite cheap in cost, simple in construction and very accurate at fixed power supply frequency. This wire is wound on a very light metal frame and mounted in such a setting so that it can rotate freely. The instrument in which the moving iron is used for measuring the flow of current. The deflection of a moving iron meter is proportional to the square of the current. The potential coil is connected across y and b phases. The repulsion type instrument is a nonpolarized instrument, i. 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. Ammeter working principle and types of ammeter electrical4u. Explanation of errors in moving iron instruments blogger. Attraction type moving iron instruments these instruments use soft iron which is a ferromagnetic material. Which of the following instrument is free from hysterisis and eddy current error.
Two irons lie in the magnetic field produced by the coil that. Advantages and disadvantages of moving iron instruments. The main sources of errors in moving coil instruments. A moving iron measuring instrument has a magnet attached to the indicator, surrounded by a coil. Moving iron movement with springtype oilfilled bearing, nonflammable. It works on the principle that the iron place near the magnet attracts towards it. When a 100 v moving iron voltmeter is of accuracy class 1 0 is used in a circuit. The iron van is so situated that it can move in the magnetic field produced by a stationary coil. Moving iron instruments principle, operation and type, theory of. As the angular deflection of moving iron instrument is proportional to square of operating current, therefore the instrument has basically square law response. Dc ammeter are mainly pmmc instruments, mi can measure both ac and dc currents, also electrodynamometer type thermal instrument can measure dc and ac, induction meters are not generally used for ammeter construction due to their higher cost, inaccuracy in measurement description of different types of ammeters pmmc ammeter.
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