Advantages and disadvantages of moving iron instruments. Mcq on measuring instruments 1 how engineering works. Movingiron instruments physics homework help, physics. 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. Moving iron instruments principle, operation and type. Difference between moving coil measuring instrument and. Moving coil instrument working principle your electrical. In addition to above instruments, we have wattmeters, power factor meters, frequency meters etc. When you go for viva or interview most often question on electrical measurements is what is the difference between mi and mc type 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. Basic electrical engineering pdf notes bee pdf notes. Still mi instruments are cheap as compared to any other type of a. The main sources of errors in moving coil instruments. An ammeter is always connected in series with a circuit branch and measures the current flowing in it.
It works on the principle that the iron place near the magnet attracts towards it. Which of the following instrument is free from hysterisis and eddy current error. Power proportional to 3 phase power if the load is balanced. General theory permanent magnet moving coil pmmc instruments 57. 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. Moving iron instrument this instrument is one of the most primitive forms of measuring and relay instrument. 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. The deflection of a moving iron meter is proportional to the square of the current.
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. Ammeter working principle and types of ammeter electrical4u. 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. A pointer attached to the moving coil deflects up scale as the moving coil rotates. Pmmc instruments, moving iron of ammeters and voltmeters elementary treatment only unit 8. Moving iron type instruments are of mainly two types. Nevertheless, by making the fixed iron curved and tapering as shown in fig. Moving iron instruments indicate the rms value of any ac waveform applied. Moving iron measuring instruments for alternating voltage with inbuilt measuring point selector switch pdf product description pdf operating manual. 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. Multiple choice questions and answers on measurement and instrumentation. The pointer of a moving coil instrument gives full scale deflection of 20ma. 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.
Moving iron instruments moving iron instruments are the most common instruments used for measurements of electrical quantities. Broadly, the analog instruments and for that matter digital instruments may be classified according to the quantity they measure. Basic principle operation of moving iron instruments 61. Click here to download the pdf of this topic moving iron instruments. I instrument the most common ammeter and voltmeter for laboratory or switch board use at power frequency are the moving iron instruments. The current coil of a wattmeter is connected to the ct of rphase. A hollow circular coil is used and one of the iron pieces is attached inside the hollow coil. Moving iron instrument multiple choice questions and answers. Voltmeter selector switch pdf product description pdf betriebsanleitung. In case of aminstruments with doubled overload range the overload range corresponds to approximately 20 % of the full scale length. Home advantages and disadvantages of moving iron instruments. Both moving coil and moving iron instruments are used measure the voltage and current of circuits.
Construction and working of repulsion type moving iron construction and working of repulsion type moving iron. Permanent magnet moving coil or pmmc instrument definition. Measurement and instruments objective questions and answers pdf free download. Advantages and disadvantages of movingiron instruments. The instrument to be used is 200a for full scale deflection. 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. 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. Working principle of moving iron instruments electrical.
Moving iron instruments measuring instrument electromagnetic. What is the difference between movingiron and movingcoil. Some errors are also caused due to the ageing of control springs and the permanent magnets. 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. This wire is wound on a very light metal frame and mounted in such a setting so that it can rotate freely. Moving iron instruments attraction type study buddy.
Analog instruments classification of analog instruments. The potential coil is connected across y and b phases. Voltage measuring ranges are 100150250 400500600 v. Moving iron instruments principle, operation and type, theory of. These instruments can measure current and voltage to a great accuracy. When the instrument is connected in the circuit, the operating current flows through the coil. When the frequency of the incoming alternator is same as that of the bus bars. One iron vane is held fixed to the coil frame and other is free to rotate, carrying with it. 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. 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. What is permanent magnet moving coil or pmmc instrument. Whenever a piece of iron is placed nearer to a magnet it would be attracted by the magnet.
Moving iron measuring mechanisms are also used in ratio meters. When a 100 v moving iron voltmeter is of accuracy class 1 0 is used in a circuit. The movement of the pointer is equal to the phase difference between the two voltages. Pdf classification of moving iron instruments atul. In moving iron instruments, a plate or van of soft iron or of high permeability steel forms the moving element of the system. In this article all major differences between moving iron and moving coil instruments are discussed. An instrument may be defined as a machine or system which is. This instrument is one of the most primitive forms of measuring and relay instrument. The general theory of movingcoil instruments may be dealt with considering a rectangular coil of turns, free to rotate about a vertical axis.
The deflection of needle of moving iron instrument is given in terms of rms value of voltage or current. Attraction type moving iron instruments these instruments use soft iron which is a ferromagnetic material. Moving iron instruments free download as powerpoint presentation. A moving iron measuring instrument has a magnet attached to the indicator, surrounded by a coil. Friction and temperature might introduce some errors. Let us have a comparison between two major type of electrical measuring instruments they are moving coil mc and moving iron mi instruments. 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. The potential difference across the meter when carrying 20ma is 400mv.
It operates on the principle that the torque is exerted on the moving coil placed in the field of the permanent magnet. This construction can be arranged to give a longer and more uniform scale than is possible with the rods shown in fig. Moving iron instruments principle and operation repulsion type. The repulsion type instrument is a nonpolarized instrument, i. Ammeters, voltmeters are some of the examples of mi instruments. Moving iron movement with springtype oilfilled bearing, nonflammable. In repulsion type moving iron instrument consists of two cylindrical soft iron vanes mounted within a fixed currentcarrying coil.
Moving coil instruments electrical technology duration. Differences between moving coil mc and moving iron mi. In other words, the coil behaves like a magnet and, therefore, it attracts the soft iron piece towards it. As the angular deflection of moving iron instrument is proportional to square of operating current, therefore the instrument has basically square law response. The current to be measured is passed through the coil, coil produced the magnetic field. The most widely used moving iron instruments are switchboard instruments of classes 1. These are costlier in comparison of moving iron instruments. 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. If there is no phase difference between the two voltages. 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. The instrument in which the moving iron is used for measuring the flow of current or voltage is known as the moving iron instrument.
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