The moving element is the flat disc of the iron core. If the file has been modified from its original state, some details such as the timestamp may not fully reflect those of the original file. Moving iron instrument this instrument is one of the most primitive forms of measuring and relay instrument. Moving ironelectrodynamo meter and induction typeextension of range. The following types of instruments are used for dual purpose. In pmmc meter or darsonval meter or galvanometer all are the same. Moving coil instruments permanent magnet moving coil mechanism. 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. 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. The action of these instruments is based on the motoring principle. Hence moving iron instruments can be used for both a. The moving iron is a flat disc or a sector eccentrically mounted. Range extension of ammeters voltmeters your electrical.
Explanation of errors in dynamometer type instrument. Operating principles of moving iron instruments ammeters and voltmeters moving iron instruments are generally used to measure alternating voltages and currents. Attraction or singleiron type figure 2 the brief description of different components of a movingiron instrument is given below. Moving iron instruments principle, operation and type. Repulsion type moving iron instrument is shown in fig. In the repulsion type, there are two vanes inside the coil. 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. Home advantages and disadvantages of movingiron instruments. Working principle of moving iron instruments electrical. Permanent magnet moving coil or pmmc instruments are the most accurate type for the measurement of dc current or voltage. Moving iron instruments are generally used for measuring ac voltage and currents. 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.
Construction of attraction type instrument the stationary coil of the attraction type instrument is flat and has a narrow opening. 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 instrument. 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. The iron van is so situated that it can move in the magnetic field produced by a stationary coil. The instrument which uses the soft iron piece as a moving element such type of instrument is known as the mi instrument. Front flange mm 72 x 72 96 x 96 housing mm 66 x 66 89 x 89 class 1. Attraction type moving iron instruments these instruments use soft iron which is a ferromagnetic material. In case of attraction type moving iron instruments, a thin iron disc is placed in front of the coil in which a pointer is mounted which moves in the dial see the pic. In other words, the coil behaves like a magnet and, therefore, it attracts the soft iron piece towards it. Moving iron instruments attraction and repulsion type. Basic effects of electromechanical instrumentsammeter and voltmetermoving coil. There are two general types of moving iron instruments namely. The permanent magnet moving coil instruments are most accurate type for direct current measurements. Moving iron instruments are of two types i attraction type.
The instrument in which the moving iron is used for measuring the flow of current or voltage is known as the moving iron instrument. Which of the following meter is an integrating type instrument. Operating principles of moving iron instruments ammeters. These are similarly magnetized when the current flows through the coil and there is a force of repulsion between the two vanes resulting in the movement of the moving vane. I instrument the most common ammeter and voltmeter for laboratory or switch board use at power frequency are the moving iron instruments. Here there are two irons, one fixed a and the other mounted on a short arm fixed b to the instrument spindle. Moving iron instruments having scales that are nonlinear and somewhat crowded in the lower range of calibration. The moving iron and polarizedvane instruments put less burden on the system and can operate for a longer time without overheating. The force of this attraction depends upon the strength said magnetic field. Attraction type, repulsion type moving iron ammeter pdf. Movingiron instruments are generally used to measure alternating voltages. There are two general types of movingiron instruments namely.
The movement is light, quick acting, but extremely robust. 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. Creeping in energy metre implies a slow rotation of rotor with only voltage coil excited. Whereas the moving coil instrument is used as a voltmeter, ammeter, galvanometer and ammeter. Permanent magnet moving coil instruments pmmc the permanent magnet moving coil instruments are most accurate type for direct current measurements. There are two types of moving coil instruments namely, permanent magnet moving coil. Explanation of extending the range of ammeters and. 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. When the current flows through the coil, a magnetic field is produced and the moving. The working principle of pmmc instruments are same as that of darsonaval type of galvanometer, difference being that a direct reading instrument is provided with pointer and scale. The moving iron instrument can be used as an ammeter, voltmeter and wattmeter. Electronic digital systems can measure and display the phase angle difference directly.
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 and voltage measurements and the dynamometer type which can be used on either direct or alternating current and voltage measurements. Pmmc instruments construction and working principle. To understand the basic construction of a permanent magnet moving coil. Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. When a current carrying coil is placed in the magnetic field produced by permanent magnet, the coil experiences a force and moves. The coil is flat and has a narrow slot like opening.
This instrument is one of the most primitive forms of measuring and relay instrument. Construction and working of repulsion type moving iron construction and working of repulsion type moving iron. This file contains additional information such as exif metadata which may have been added by the digital camera, scanner, or software program used to create or digitize it. Moving iron instruments repulsion type study buddy. Advantages, disadvantages, errors in moving iron instrument. It is a permanent magnet moving coil instrument plus a rectifier is also suitable for acdc measurements.
Measurement and instruments objective questions and answers pdf free download. Crosscoil type instruments draw a relatively large amount of power from the systems and are intended for only brief operation. Repulsion or double iron type figure 1 attraction or singleiron type figure 2 the brief description of different components of a movingiron instrument is given below. Classification of moving iron instruments, construction of moving iron instruments, torque equation of moving iron instruments, errors of moving iron instruments, advantages of moving iron instruments, and disadvantages of moving iron instruments.
Classification of moving iron instruments moving iron instruments are of two types i attraction type. Measurement of ac currents and ac voltages, adjusted for frequency range 1665hz. Another type of instrument that is usually classed with the attractive types of instrument is shown in fig. A hollow circular coil is used and one of the iron pieces is attached inside the hollow coil. It is a horseshoe shaped permanent magnet with soft iron pole pieces attached to it.
In moving iron instruments, a van of soft iron forms the moving element of the system. The two irons lie in the magnetic field due to a solenoidcoil c. 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. 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. Click here to download the pdf of this topic moving iron instruments. There are two types of errors which occur in moving iron instruments. Types of ammeters, voltmeters electrical instruments. Due to square low response, the scale of the moving iron instrument is nonuniform. Derive the torque equation of a moving iron instrument. What is the difference between movingiron and movingcoil. Why is dynamometer type instrument chiefly used as a wattmeter. Whenever a piece of iron is placed nearer to a magnet it would be attracted by the magnet. When the instrument is connected in the circuit, the operating current flows through the coil.
It is a moving iron instrument which operates on the principle of variation of impedance i. This instrument can be used for the measurement of voltage, current and power. 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. Range extension of ammeter by shunt shunts are used for the range extension of ammeters. The following are the main errors in moving moving iron instruments, when these are used either on dc or ac. Moving iron instruments are generally used to measure alternating voltages and currents.
Moving iron type instruments are of mainly two types this instrument is one of the most primitive forms of measuring and relay instrument. Basics of measuring instruments and types moving coil instruments electrical technology. When a capacitor was connected to the terminal of ohmmeter, the pointer indicated a low resistance initially and then slowly came to infinity position. 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 type instruments are of mainly two types. When current flows through the coil iron disc moves from lesser magnetic field to higher magnetic field which in turns the pointer in the dial. The difference between the pmmc and dynamometer type instrument is that the. Thus whatever may be the direction of the current in the coil, the deflection in the moving iron instruments is in the same direction. The basic construction of this instrument is shown in figure 2. Moving iron instruments principle, operation and type, theory of. Advantages and disadvantages of movingiron instruments. The current to be measured is passed through the coil, coil produced the magnetic field. Mcq on measuring instruments 1 how engineering works.
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