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. 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. In moving iron instruments, a van of soft iron forms the moving element of the system. To understand the basic construction of a permanent magnet moving coil. One variation of moving iron instrument is repulsion type instrument.
Pdf classification of moving iron instruments atul. 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. This is achieved by utilizing the various effects of electric current or voltage. Basic principle operation of movingiron instruments 61. To this iron a pointer is attached so that it may deflect along with the moving iron over a graduated scale. The movingiron meter was invented by austrian engineer friedrich drexler in 1884. Nulltype and deflectiontype instruments deflection type. Due to square low response, the scale of the moving iron instrument is nonuniform. Classification, absolute and secondary instruments, indicating instruments, control, balancing and damping, constructional details, characteristics, errors in measurement, ammeters, voltmeters.
Moving iron instruments are generally used to measure alternating voltages and currents. Moving iron instruments are generally used for measuring ac voltage and currents. For these reasons this method is used in hot wire, moving coil and induction type instruments. Construction of attraction type moving iron instruments. Moving iron instruments principle and operation repulsion type. 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. Dc pmmc instruments, extension of range by shunts and multipliers. The most widely used movingiron instruments are switchboard instruments of classes 1. I instrument the most common ammeter and voltmeter for laboratory or switch board use at power frequency are the moving iron instruments.
Here we keep the shaft of the moving system along the axis of the coil. The instrument having its deflection depends upon average value is. Moving iron instruments attraction type and repulsion type complete concept duration. Attraction or single iron type figure 2 the brief description of different components of a moving iron instrument is given below. The iron van is so situated that it can move in the magnetic field produced by a stationary coil. Electrostatic voltmeters electrometer type and attracted disc type extension of range of e. Moving iron instruments principle, operation and type. Attraction type moving iron instruments are commonly used and therefore, we will focus on it. 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. When a current carrying coil is placed in the magnetic field produced by permanent magnet, the coil experiences a force and moves. Hence moving iron instruments can be used for both a. Broadly, the analog instruments and for that matter digital instruments may be classified according to the quantity they measure.
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 moving iron ammeter may be compensated for frequency errors by a. There are two general types of movingiron instruments namely. Permanent magnet moving coil instruments pmmc the permanent magnet moving coil instruments are most accurate type for direct current measurements. Download practical maritime ebooks with amazing bonuses. If there were no saturation, the change of inductance with the angle of deflection i. Coaxial vanes type in this type instrument the fixed and moving vanes are sections. Moving iron ammeters and voltmeters, dynamometer type watt meters, induction type energy meter. A permanent magnet is used to produce magnetic flux and a coil that carries the current to be measured moves in this field. Repulsion type moving iron instrument about circuit. Inside moving iron instruments repulsion type youtube. Moving iron instrument working operation electrical edition. Advantages and disadvantages of movingiron instruments.
The instrument in which the moving iron is used for measuring the flow of current or voltage is known as the moving iron instrument. The attraction and the repulsion are the types of the moving iron instruments. Moving iron instruments having scales that are nonlinear and somewhat crowded in the lower range of calibration. The difference between the pmmc and dynamometer type instrument is that the permanent magnet is replaced by an electromagnet. This type of meter responds to both direct and alternating currents as opposed to the movingcoil ammeter, which works on direct current only. Here are a few fantastic ebooks to get important maritime information in the next couple of minutes. Moving iron type instruments are of mainly two types. Both moving coil and moving iron instruments are used measure the voltage and current of circuits. The movement is light, quick acting, but extremely robust. Analog instruments classification of analog instruments. A feature of the moving element is that it is fitted with synthetic sapphire jewels. 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. Another type of instrument that is usually classed with the attractive types of instrument is shown in fig.
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. The action of these instruments is based on the motoring principle. 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. In repulsion type, a fixed vane or rod is also used and magnetized with the same polarity. Home advantages and disadvantages of movingiron instruments. Choosing a backup generator plus 3 legal house connection options transfer switch and more duration. Permanent magnet moving coil or pmmc instrument definition. Working principle of moving iron instruments electrical. Which of the following instruments can be used for full scale deflection of 300o. 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. Principle of generation thermal, hydel and nuclear. Moving iron instrument this instrument is one of the most primitive forms of measuring and relay instrument. Construction of repulsion type moving iron instrument.
Construction and working of repulsion type moving iron construction and working of repulsion type moving iron. A hollow circular coil is used and one of the iron pieces is attached inside the hollow coil. Construction of attraction type moving iron instruments points. But in actual instrument rate of change of inductance with angular deflection i. Click here to download the pdf of this topic moving iron instruments. The deflecting torque causes the moving system to move from its zero position. Rotation is opposed by a hairspring that produces the restoring torque.
Measuring instruments classification deflecting, control and damping torques ammeters and voltmeters pmmc, moving iron type instruments expression for the deflecting torque and control torque errors and compensations, extension of range using shunts and series resistance. What is the difference between movingiron and movingcoil. These instruments use soft iron which is a ferromagnetic material. Class 3 for bimetallic meter movements and class 1.
This method cannot be used in instruments where the introduction of a permanent magnet required for producing eddy currents will distort the existing magnetic field as in. Permanent magnet moving coil instrument pmmc working and. 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. What is permanent magnet moving coil or pmmc instrument. In both the attraction and repulsion type movingiron instruments it is found that for a given position of the moving system, the value of the deflecting torque is proportional to the square of the current, so long as the iron is working below saturation.
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. For such pure square response, moving iron instrument scale can easily be graduated uniformly. Moving iron instruments attraction and repulsion type. This instrument is one of the most primitive forms of measuring and relay instrument. Movingiron measuring mechanisms are also used in ratio meters. The damping torque is provided by the movement of a thin vane v in a closed sectorshaped box b, or. Construction of attraction type moving iron instruments the simplest form of attraction type moving iron instrument uses a solenoid and a moving oval shaped soft iron pivoted eccentrically. In repulsion type movingiron instrument consists of two cylindrical soft iron vanes mounted within a fixed currentcarrying coil.
The iron element consists of a moving vane attached to a pointer, and a fixed vane, surrounded by a coil. The pmmc stands for permanent magnet moving coil and it is also called as darsonval instruments. Moving coil instruments permanent magnet moving coil mechanism. The current to be measured is passed through the coil, coil produced the magnetic field. 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. We attach a soft iron bar or rod to the shaft so that it can move with the movement of the moving system. Measurements and instrumentation questions and answers pdf 26. Movingiron instruments are generally used to measure alternating pdf u3d vulnerability voltages and currents. Ferromagnetic materials magnetize in the direction of a magnetic field, therefore, if they are brought near one end of a current carrying coil. It operates on the principle that the torque is exerted on the moving coil placed in the field of the permanent magnet. In addition to above instruments, we have wattmeters, power factor meters, frequency meters etc. The force of this attraction depends upon the strength said magnetic. One important requirement in indicating instruments is the arrangement for producing operating or deflecting torque t d when the instrument is connected in the circuit to measure the given electrical quantity. 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.
28 7 1244 1421 1139 253 754 1523 308 571 341 143 1163 723 362 1064 1436 447 1095 824 146 1060 244 396 446 567 761 709 1469 1111 611 363 1188 752