In a moving iron ammeter, the field coil is connected in series to the circuit containing the current to be measured. I instrument the most common ammeter and voltmeter for laboratory or switch board use at power frequency are the moving iron instruments. According to the fundamental law of electromagnetic force, the coil will rotate in the magnetic field when it. Moving iron instrument working operation electrical edition. Moving iron type instruments are of mainly two types.
Due to square low response, the scale of the moving iron instrument is nonuniform. Let us have a comparison between two major type of electrical measuring instruments they are moving coil mc and moving iron mi instruments. The two irons lie in the magnetic field due to a solenoidcoil c. When the frequencies match, the moving vanes will rotate to a position corresponding to the phase difference between the two sources. The following are severe errors in this type of wattmeter. The incoming machine can then be adjusted in speed so that the two systems are in phase agreement. The deflecting torque in any movingiron instrument is due to forces on a small piece of magnetically soft iron that is magnetized by a coil carrying the operating current. Mar 11, 2018 the angular deflection of needle of moving iron instruments is related to the current flowing through the field coil. Why do moving iron instruments measure both ac and dc. The writer, also known variously as the pen motor, galvanometer or recorder, is an electromagnetic system of moving coil or moving iron type. A sectional view of the attraction type moving iron instrument is shown. 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.
Attraction type moving iron instruments,moving iron instruments. Every electrical engineer or technician, at work, requires measuring instruments to measure such electrical quantities as current, voltage and resistance. Difference between moving coil measuring instrument and. And also, in the case of moving iron voltmeters, for the ranges up to 0 750 v, multipliers are used and for the ranges higher than that, pts are used. Range extension of ammeters voltmeters your electrical. In the moving iron instrument, an iron vane is mounted on a shaft along with the pointer. Differences between moving coil mc and moving iron mi. Multiple choice questions and answers on measurement and instrumentation. Capable of giving an accuracy within limits of both precision and industrial grades. Moving iron instrument multiple choice questions mcq and. For low voltage range the power consumption is higher. 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.
The moving iron meter was invented by austrian engineer friedrich drexler in 1884. Pdf classification of moving iron instruments atul. The angular deflection of needle of moving iron instruments is related to the current flowing through the field coil. This principle is utilized in the moving iron repulsion type instrument.
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. 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. Movingiron instrument a measuring instrument whose operation is based on the interaction between a magnetic field that is proportional to the quantity to be measured and a core made of a ferromagnetic material. Jul 25, 2018 this instrument is one of the most primitive forms of measuring and relay instrument. Attraction type, repulsion type moving iron ammeter pdf.
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. Considering the energy relations when there is a small increment in current supplied to the instrument may derive an expression for the torque moving iron instrument. Attraction or singleiron type figure 2 the brief description of different components of a movingiron instrument is given below. Electrical technology playlist pl5fcg6tovhr493p0pd6m1uyh4yfbjozgj unit 1 millmans theorem. Learn what moving iron instruments are, a working animation, how they are constructed, and the attraction type moving iron instruments. Figure 2 attraction moving iron instrument measurement of electric voltage and current. When this happens there will be a small deflection. The controlling torque is provided by two phosphor bronze hair springs. Moving iron instruments attraction type study buddy. A feature of the moving element is that it is fitted with synthetic sapphire jewels.
Repulsiontype moving iron instrument is shown in fig. This type of meter responds to both direct and alternating currents as opposed to the moving coil ammeter, which works on direct current only. Here there are two irons, one fixed a and the other mounted on a short arm fixed b to the instrument spindle. Mcq on measuring instruments 4 how engineering works. Since the stationary parts and the moving parts of the instrument are simple so they are cheapest. Operating principles of moving iron instruments ammeters and. Classification of moving iron instruments a media to.
A moving iron measuring instrument has a magnet attached to the indicator, surrounded by a coil. It is a horseshoe shaped permanent magnet with soft iron. After reading this article you will learn about the electrical test equipment used in mines. 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. Measurements and instrumentation questions and answers pdf 26. Range extension of ammeter by shunt shunts are used for the range extension of ammeters. The instrument can be constructed to measure current and voltage to an accuracy needed in most engineering works and still be ch.
All structured data from the file and property namespaces is available under the creative commons cc0 license. Moving coil instrument or generally referred as the darsonval meter or a permanent magnet moving coil pmmc meter is mostly used in direct current measurement. A hollow circular coil is used and one of the iron pieces is attached inside the hollow 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. Suitable for low frequency and high power circuits.
Construction and working of moving iron instruments. Electrical technology playlist unit 1 millmans theorem. These instruments can withstand overloads momentarily. As the angular deflection of moving iron instrument is proportional to square of operating current, therefore the instrument has basically square law response.
The iron element consists of a moving vane attached to a pointer, and a fixed vane, surrounded by a coil. There are two general types of movingiron instruments namely. Nov 09, 2017 the deflection of needle of moving iron instrument is given in terms of rms value of voltage or current. Learn what moving iron instruments are, a working animation, how they are constructed, and the. The pmmc stands for permanent magnet moving coil and it is also called as darsonval instruments. Moving iron construction and working of repulsion type moving iron. A permanent magnet is used to produce magnetic flux and a coil that carries the current. Working principle and construction of pmmc polytechnic hub. Moving iron instruments are used as voltmeter and ammeter only. In attraction type moving iron instruments, an ovalshaped disc made up of soft iron is pivoted on the spindle near the coil. In a low power factor wattmeter the pressure coil is connected a to the supply side of the current coil. Pdf classification of moving iron instruments atul patel.
Soft iron core provides formation of uniform magnetic field. Dynamometer type wattmeter working your electrical guide. In moving iron instruments, a plate or van of soft iron or of high permeability steel forms the moving element of the system. Moving iron instruments are generally used for measuring ac voltage and currents. The reading of the instrument may be affected by stray fields acting on the moving coil. There are two general types of moving iron instruments namely. 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. The instrument in which the moving iron is used for measuring the flow of current or voltage is known as the moving iron instrument. Moving iron llc was created to have a place for ag equipment remarketing and used equipment managers to find and share ideas. Whereas in moving coil instrument the conductor coil is used for dc measurement.
A moving coil instrument consists basically of a permanent magnet to provide a magnetic field and a small lightweight coil is wound on a rectangular soft iron core. A measuring instrument in which current or voltage is determined by the couple on a small coil pivoted between the poles of a magnet with curved poles, giving a radial magnetic field. It is a horseshoe shaped permanent magnet with soft iron pole pieces attached to it. 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. Oct 14, 2017 moving iron instruments attraction type study buddy. Moving iron instruments principle, operation and type. Jan 15, 2019 what is a permanent magnet moving coil pmmc. Moving iron instruments are generally used to measure alternating voltages and currents. Which of the following meter is an integrating type instrument. In movingiron instruments the movable system consists of one or more pieces of speciallyshaped soft iron, which are so pivoted as to be acted upon by. Click here to download the pdf of this topic moving iron instruments.
When a current flows through the coil it turns against a return spring. The deflecting torque in any moving iron instrument is due to forces on a small piece of magnetically soft iron that is magnetized by a coil carrying the operating current. At one end of the coil, a ovalshaped soft iron disc is pivoted eccentrically so that it can be attracted into the coil and the pointer attacted to the disc can show reading. Mcq on measuring instruments 1 how engineering works. Nov 09, 2017 working principle of moving iron 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 current in coil. Classification of moving iron instruments a media to get. The current to be measured is passed through the coil, coil produced the magnetic field. Ban, where b is the magnetic flux density, a is the area of the. 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. The iron van is so situated that it can move in the magnetic field produced by a stationary coil. It works on the principle that the iron place near the magnet attracts towards it.
Advantages and disadvantages of movingiron instruments. Always connected in series with the circuit and carries the current to be measured. This light rectangular coil carries the current to be measured. Figure below shows a simple moving iron instrument. Moving iron ammeters and voltmeters are manufactured, mainly for measurements in 50hertz ac circuits. Moving iron instruments principle, operation and type, theory of. The deflection of moving iron instruments is independent of direction of current, because the needle of the moving iron instrumen. Whenever a piece of iron is placed nearer to a magnet it would be attracted by the magnet. Movingiron instrument article about movingiron instrument. Advantages, disadvantages, errors in moving iron instrument. The movingiron meter was invented by austrian engineer friedrich drexler in 1884. The moving coil type has the pen attached to a coil carrying current and so behaves like a magnet whose strength is proportional to the current. The basic construction of this instrument is shown in figure 2. The main elements of a movingiron instrument are a measuring circuit that converts the quantity to be measured into a dc or ac current and a.
Learn what moving iron instruments are, a working animation, how they are constructed, and. Instruments capable of making these measurements accurately must be of good design and of extremely high quality, accuracy and. Electrical test equipment used in mines with diagram. Hence moving iron instruments can be used for both a. The deflection of needle of moving iron instrument is given in terms of rms value of voltage or current. In both cases, the indicator is driven by magnetic torque caused by current flow in the coil. The damping torque is provided by eddy current damping. The basic construction of pmmc is shown in above fig. The movement is light, quick acting, but extremely robust. It is obtained by movement of aluminum former, moving in the magnetic field of the permanent magnet. Classification of moving iron instrument moving iron instrument are of two types attraction type repulsion type 4. Moving iron instruments voltmeter and ammeter analog ammeter and voltmeter designed to measure a. When you go for viva or interview most often question on electrical measurements is what is the difference between mi and mc type instruments.
A moving iron ammeter may be compensated for frequency errors by a. In this article all major differences between moving iron and moving coil instruments are discussed. This page was last edited on 30 november 2017, at 05. Moving iron instruments principle, operation and type, theory. Moving coil meter an overview sciencedirect topics. This type of meter responds to both direct and alternating currents as opposed to the movingcoil ammeter, which works on direct current only. On this site you will find moving iron podcast, a podcast dedicated to ag equipment dealer issues and trends moving iron blog covers topics outlining processes important to the remarketing of used equipment. The moving iron instruments use the stationary coil of copper or aluminium wire which acts as an electromagnet when an electric current passes through it. This instrument is one of the most primitive forms of measuring and relay instrument.
Files are available under licenses specified on their description page. The permanent magnet moving coil instruments are most accurate type for direct current measurements. Creeping in energy metre implies a slow rotation of rotor with only voltage coil excited. Whereas in moving coil instrument the conductor coil. Let the axis of the iron disc, when instrument is not in use i. Permanent magnet moving coil mechanism pmmc in pmmc meter or darsonval meter or galvanometer all are the same instrument, a coil of fine wire is suspended in a magnetic field produced by permanent magnet. Multiple choice questions and answers on measurement and. The force of attraction depends on the strength of the magnet field.
In movingiron 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. When this happens there will be a small deflection d. Working principle of moving iron instruments electrical. Deflection torque is proportional to the square of the current. To prevent it, magnetic shielding is provided by enclosing the instrument in an iron case.
696 1482 1147 1093 1088 840 1056 987 594 291 1140 430 284 913 808 141 372 1442 1024 1241 1110 1215 626 597 342 1484 11 361 1120 1092 313 1394 340 363 304 582 183 915 1282 750