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