Seventh lecture moving coil instruments 8 b series ohmmeter. Attraction type moving iron instruments these instruments use soft iron which is a ferromagnetic material. Moving iron instruments there are of two types of moving iron instruments. Construction and working of repulsion type moving iron construction and working of repulsion type moving iron. Another type of instrument that is usually classed with the attractive types of instrument is shown in fig. Measurement and instruments objective questions and answers pdf free download. Working principle of moving iron instruments electrical. Measurements and instrumentation questions and answers pdf 26. The damping torque is provided by the movement of a thin vane v in a closed sectorshaped box b, or. Moving iron instruments, classification of moving iron. 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. 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. It works on the principle that the iron place near the magnet attracts towards it.
Both moving coil and moving iron instruments are used measure the voltage and current of circuits. The iron van is so situated that it can move in the magnetic field produced by a stationary coil. Movingiron instruments are generally used to measure alternating voltages and currents. 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. Mcq on measuring instruments 1 how engineering works. Moving iron instrument multiple choice questions and answers. 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. Differences between moving coil mc and moving iron mi. Learn what moving iron instruments are, a working animation, how they are constructed, and.
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. The action of these instruments is based on the motoring principle. Electrical technology playlist pl5fcg6tovhr493p0pd6m1uyh4yfbjozgj unit 1 millmans theorem. Hence moving iron instruments can be used for both a. Electrical test equipment used in mines with diagram. A permanent magnet is used to produce magnetic flux and a coil that carries the current to be measured moves in this field.
Moving iron type instruments are of mainly two types. Due to square low response, the scale of the moving iron instrument is nonuniform. Permanent magnet moving coil instruments pmmc the permanent magnet moving coil instruments are most accurate type for direct current measurements. The scale of series ohmmeter is nonlinear with zero at the right and infinity at extreme left. When a current carrying coil is placed in the magnetic field produced by permanent magnet, the coil experiences a force and moves. This instrument is one of the most primitive forms of measuring and relay instrument. A hollow circular coil is used and one of the iron pieces is attached inside the hollow coil. Capable of giving an accuracy within limits of both precision and industrial grades.
Moving iron instruments principle, operation and type, theory of. Moving iron instruments indicate the rms value of any ac waveform applied. 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. View and download powerpoint presentations on moving iron instruments ppt.
I instrument the most common ammeter and voltmeter for laboratory or switch board use at power frequency are the moving iron instruments. In moving iron instruments, a van of soft iron forms the moving element of the system. The pmmc stands for permanent magnet moving coil and it is also called as darsonval instruments. The work carried out by the department of measuring devices of the kiev polytechnical institute has shown that the frequency range of movingiron instruments can.
Since the stationary parts and the moving parts of the instrument are simple so they are cheapest. General options include red supplementary pointers, red indexes quadrant scales, red, green or blue lines, bands or segments, finely spaced divisions, multiscales, special scales and captions to customer requirements. Moving iron instrument working operation electrical edition. The necessity for the ac calibration of moving iron instruments as well as another type of instruments which cannot be correctly calibrated requires the use of a transfer type of instrument. 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. Electronic digital systems can measure and display the phase angle difference directly. Moving iron instruments principle, operation and type. Pdf classification of moving iron instruments atul. Moving iron instruments attraction and repulsion type. For low voltage range the power consumption is higher.
Inside this coil there are two pieces of soft iron, one piece the fixed iron remains stationary, while the other the moving iron is fitted to a spindle and can swing away from the fixed iron. It is because the division of current between the operating coil and the shunt varies with frequency since reactance of the coil depends upon frequency. The suspension system provides excellent reproducibility without friction, and good resistance to shock impact. Advantages and disadvantages of movingiron instruments. A cap shield mechanism serving to reduce external magnetic. The current to be measured is passed through the coil, coil produced the magnetic field. The magnetic field induces by the electromagnet whose strength depends.
On passing current through the coil produces magnetic field which attracts soft. The moving iron and polarizedvane instruments put less burden on the system and can operate for a longer time without overheating. This combination of moving coil and multiplier is connected across the point whose voltage is to be measured. Moving iron instruments are generally used to measure alternating voltages and currents. Shunts can not be used to extend the range of moving iron ac ammeters accurately. Moving iron instruments attraction type easiest explained. Working principle and construction of pmmc polytechnic hub.
It is a horseshoe shaped permanent magnet with soft iron pole pieces attached to it. The internal impedance are 30,000 ohms and 20,000 ohms. The control torque is provided by two hairsprings s1 and s2 in the same way as for a pmmc instrument, but in such instruments, springs are not used to carry any current gravity control can also be used for vertically mounted panel type mi meters. In a moving iron meter, the current to be measured flows through a flat coil as shown in fig. This construction can be arranged to give a longer and more uniform scale than is possible with the rods shown in fig. Models 20 and 2014 are moving iron type instruments using a tautband suspension system. 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. This series resistance is called voltmeter multiplier.
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. Electrical measurements and instrumentation questions. When you go for viva or interview most often question on electrical measurements is what is the difference between mi and mc type instruments. Moving iron instruments construction and working principle in hindi duration. Electrodynamometer type instruments construction and.
Then as seen from figure, the voltage drop across r is v. 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. 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. A transfer instrument is one that may be calibrated with a d. Rx is the unknown resistor to be measured, r2 is variable adjusted resistance so that the pointer read zero at short circuit test. Click here to download the pdf of this topic moving iron instruments. Multiple choice questions and answers on measurement and instrumentation. The instrument in which the moving iron is used for measuring the flow of current or voltage is known as the moving iron instrument.
What is the difference between movingiron and movingcoil. Moving iron instruments principle and operation repulsion type. The basic construction of this instrument is shown in figure 2. Let us have a comparison between two major type of electrical measuring instruments they are moving coil mc and moving iron mi instruments. A moving iron ammeter may be compensated for frequency errors by a. Suitable for low frequency and high power circuits. 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. Whenever a piece of iron is placed nearer to a magnet it would be attracted by the magnet. 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. 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.
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