According to the fundamental law of electromagnetic force, the coil will rotate in the magnetic field when it. F nbil where, where f force in newton, b flux density is tesla, i current is ampere, l length of conductor in meter, n number of turn in coil. The range of this instrument, when used as a dc voltmeter, can be increased by using a high resistance in series with it. Pmmc ammeter have uniform scale because of eddy current damping they are spring controlled their deflecting torque varies directly as current both spring controlled and having deflecting torque varies directly as current 2. The pmmc stands for permanent magnet moving coil and it is also called as darsonval instruments. Bi lab manual jawaharlal nehru engineering college. The action of the permanent magnet moving coil pmmc instrument is based on the motoring principle when a currentcarrying coil is placed in the magnetic field produced by the permanent magnet, the coil experiences a force and moves. A galvanometer is an electromechanical measuring instrument for electric current. The working principal of this instrument is same as that of the darsonval type of galvanometers,the difference being that a direct reading instrument is provide with a pointer and a scale. How can it be made to work as i a voltmeter to read 100 v on full scale ii an ammeter of 1 a, on full scale. There are some disadvantages of pmmc permanent magnet moving coil are given below. Pmmc instruments construction and working principle electrical. Application pmmc instruments can be used as dc ammeter.
The pmmc stands for permanent magnet moving coil and it is also called as d arsonval instruments. Permanent magnet moving coil is the basic measuring instrument which can be used for measuring current and voltages they can be converted into either voltmeter and ammeter 3. Advantages and disadvantages of pmmc permanent magnet moving. Q9 how the range of instrument can be extended in pmmc instruments. The basic principle of galvanometer is pmmc permanent magnetic moving coil.
Principle the pmmc type instrument works on magnetic principle. A moving coil galvanometer is an instrument used for detection and. Figure 1 shows the basic construction of a pmmc instrument. Sample ee8403 question bank measurements and instrumentation. This principle is used in moving iron attraction type instrument. Pmmc is the most accurate and useful for dc measurements. Pmmc instrument working principle permanent magnet. The amount of force experienced by the coil is proportional to the current passing through the coil. Working principle of a pmmc instrument when a current caring conductor is placed in a magnetic field. The pmmc instrument gives the accurate result for dc measurement. The action of most commonly dc meter is based on the fundamental principle of the motor. Let i 1 and i 2 be the instantaneous values of currents in pressure and current coils respectively. The basic moving coil instrument working principle is that when a current carrying conductor is placed in a magnetic field, a mechanical force is exerted on the conductor.
For satisfactory operation electromechanical indicating instrument, three forces are necessary. Q8 principle of operation of a current transformer. Jan 24, 2021 what is a permanent magnet moving coil pmmc. A soft iron core is included between the poles of the magnet so that the coil rotates in the narrow air gap between the poles and the core. When current carrying conductor is placed in a magnetic field, it experiences mechanical force. Pmmc instruments construction and working principle. The coil is suspended so that it can rotate freely in the magnetic field. Mar 26, 2020 for understanding the working principle, first ask yourself what will happen if we connect a pmmc instrument for the measurement of ac quantity. May 12, 2018 permanent magnet moving coil or pmmc instruments are the most accurate type for the measurement of dc current or voltage. A dc input voltage is applied to the input attenuator voltage range selection makes sure a maximum of v applied to gate of nchannel fet. Permanent magnet moving coil mechanism pmmc in pmmc meter or darsonval meter or galvanometer all are the same instrument.
To increase range of the voltmeter, connect the resistance in series with the pmmc instrument. Foxit advanced pdf editor to remove this notice, visit. Ampere is the unit of current so an ammeter is a meter or an instrument which measures current. May 19, 2020 working principle of a pmmc instrument when a current caring conductor is placed in a magnetic field. The pmmc has efficient damping characteristics and is not affected by stray magnetic field. Pmmc instrument working principle permanent magnet moving.
Working principle of pmmc instrument is the same as that of the darsonval type of galvanometers, the difference being that direct reading instrument is provided with a pointer and a scale. Moving iron instruments principle, operation and type. In a pmmc instrument, the damping provided is air damping fluid. 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. It operates on the principle that the torque is exerted on the moving coil placed in the field of the permanent magnet. In the picture above, the meter movement needle is shown pointing somewhere around 35% of fullscale, zero being full to the left of the arc and fullscale being completely to the right of the arc. Sep 06, 2019 construction and working principle of electrodynamometer type wattmeter now let us look at constructional details of electrodynamometer. The magnetic field induces by the electromagnet whose strength depends on the magnitude of the current passes. The current in the wire cause the magnetic field is produces that interacts with the field from the permanent magnet. In the picture above, the meter movement needle is shown pointing somewhere around 35% of fullscale, zero being full to the left of the arc and fullscale being completely to the right of the. Moving coil instrument working principle your electrical.
The damping force can be varied by varying the projection of the magnet over the circular disc. Numerical and objective questions moving iron mi instrument 1. How can it be made to work as i a voltmeter to read 100 v on full scale ii an ammeter. It works on the principle that the iron place near the magnet attracts towards it. Introductionthe permanentmagnet movingcoil pmmc instruments basically consist of a lightweight coil of copper wire suspended in the field of a permanent magnet. Permanent magnet moving coil instrument or pmmc instrument. D c a dc v consists darsonval movement, attenuator and direct coupled amplifier. The basic principle can also be stated that when a field resultant magnetic field produced by the movable current carrying coil tries to come in line with the main field. Produced current is measured by a pmmc instrument the pmmc indicator points labels of voltage value.
Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely a galvanometer works by deflecting a pointer in response to an electric current flowing through a coil in a constant magnetic field. To study the advantage and limitation of pmmc instruments. Based on the rule of fleming left hand, if the thumbnail of the left hand. As the coil is moving and the magnet is permanent, the instrument is called permanent magnet moving coil instrument. Permanent magnet moving coil instrument pmmc working. Measurement and instrumentation unit 1standards and instruments. In pmmc meter or darsonval meter or galvanometer all are the same instrument, a.
A scale of pmmc instrument is linear non linear bi directional logarthm 9. The action of these instruments is based on the motoring principle. And its range can be increased by using a large number of turns in parallel with the instrument. Marks 8 ii discuss briefly how hays bridge can be used for the measurement of inductance. Working principle of pmmc instrument is the same as that of the. In a pmmc instrument the controlling torque is provided by gravity spring cylindrical core no tc 10. Permanent magnet moving coil mechanism pmmc mathematical. Pmmc instrument working principle consider the arrangement shown in figure 1. The motor action is produced by the flow of a small current. Extension of instrument range is possible with the help of shunt and series resistances. Moving iron instruments principle, operation and type, theory.
Bhargav is licensed under a creative commons attribution sharealike 4. So the expression for the torque can be written as. For the example, in dc ammeter and voltmeter are used this system. When a current caring conductor is placed in a magnetic field. To understand the basic construction of movingiron instrument and its principle operation. 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. When a current passes through the galvanometer coil, it. Pmmc instrument such as voltmeter, ammeter, shunt, multiplier, dc voltage source, bread board, connecting wires. When a current is passed through the coil windings, a torque is exerted on the coil by the interaction of the magnets. Discuss the construction and working principle of repulsion type mi instrument. The coils move freely in the field of a permanent magnet. Working principle of pmmc when a current carrying conductor is placed in a magnetic field, it experiences a force and tends to move in the direction as per flemings lefthand rule. The meter having use the transformer principle to detect the current.
The basic operating principle of a permanent magnet moving coil instrument is the same as that of arsonval galvanometer except that there is slight difference from the. Ammeter means amperemeter which measures ampere value. A permanent magnet moving coil pmmc meter also known as a darsonval meter or galvanometer is an instrument that allows you to. 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. Derive the relation for finding unknown resistance. The pmmc instrument working principle is when the torque is applied to the moving coil that is placed within the permanent magnet field, and then it gives a. The moving coil of the instrument has a series resistor and is connected in parallel with the load. It works on the principle that the iron placed near the magnet attracts towards it. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely.
Electrical measuring instruments and instrumentation list of. Pmmc, mi, emmc or edm, esv instruments measurement. Pmmc the permanent magnet moving coil instrument is the most accurate type for d. Moving coil instrument working principle your electrical guide.
In pmmc meter or darsonval meter or galvanometer all are the same. Working principle and construction of pmmc polytechnic hub. A movingcoil instrument contains principally of a permanent magnet to offer a magnetic field and a small lightweight coil pivoted within the field. The instrument in which the moving iron is used for measuring the flow of current or voltage is known as the moving iron instrument. Based on the rule of fleming left hand, if the thumbnail of the left hand, middle and forefinger are at 90 degrees with each other. Q6 what are the practical difficulties in ac potentiometer. Electrodynamic type instrument construction and working. Ammeter working principle and types of ammeter electrical4u. Pmmc instrument working principle permanent magnet moving coil instrument the permanent magnet moving coil pmmc instrument is an electromechanical meter that can be connected with additional components to function as an ammeter, a voltmeter, or an ohmmeter. Nov 30, 2018 measurements and instrumentation question bank ee8403 pdf free download. As you know, there are three types of torque acting on an instrument.
It is a device or mechanism used to determine the present value of a quantity under observation. Q5 what is the working principle of wattmeter employed in measuring equipment. Construction of pmmc instruments the constructional features of this instrument are shown in fig. Pmmc meter is fitted in ammeter voltmeter multimeter wattmeter 3. Oct 22, 2020 meter is an instrument which can measure a particular quantity. Both are the examples or the permanent magnet moving coil pmmc galvanometer, and use the same fundamental principle as the dc motor. Ee8403 question bank measurements and instrumentation. Hello friends this video provides you all the basic concept of pmmc type instrument pmmc construction and working explained in hindi. Apr 24, 2018 electrodynamic type instrument construction and working principle april 24, 2018 november 5, 2017 by admin electrodynamic type instrument is used for the measurement of ac and dc quantities unlike pmmc instrument which can only be used for the measurement of dc quantity. Dc ammeterthe dc ammeter is an instrument for measuring the electric current in amperes in a branch of an electric circuit.
Moving iron instruments are generally used to measure alternating voltages and currents. Resistance must add to the pmmc instrument to make the voltage measured value is larger. A moving coil instrument having internal resistance of 50. Consequently, current i v through the moving coil is directly proportional to the load voltage. The construction and working of a pmmc instrument article716. The force of attraction depends on the strength of the magnet field. The moving coil is either rectangular or circular in shape. It is generally wound on a non magnetic metallic former. 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. What is permanent magnet moving coil or pmmc instrument. In this instrument, we have a coil suspended in the magnetic field of a permanent magnet. When a currentcarrying conductor is placed in a magnetic field, it experiences a force and tends to move in the direction as per flemings lefthand rule.
Pmmc instrument objective questions electrical instruments. Permanent magnet moving coil or pmmc instruments are the most accurate type for the measurement of dc current or voltage. A permanent magnet is used to produce magnetic flux and a coil that carries the current to be measured moves in this field. A pmmc instrument will read average value rms value both none 7. In this section, you will derive and learn the equation of deflection torque, control torque and damping torque in a pmmc instrument. A pmmc instrument gives full scale reading of 25 ma when a potential difference across its terminals is 75 mv. When the current flows through the coil, a magnetic field is produced by it. The coil is mounted on rectangular aluminum former, which is pivoted on jeweled bearings. Let, b flux density in the air gap wbm 2 i current in the coil a l effective axial length of the coil m. Permanent magnet moving coil instrument pmmc working and. As the pointer is connected to the coil it gets deflected in proportion with the current. In pmmc instruments, a 1oc increase of temperature reduces the strength of springs by about 0.
State the working principle of pmmc analog instrument. The permanent magnet moving coil instrument is the most accurate type for dc measurements. They are a deflecting force b controlling force cdamping force 1. A dc input voltage is applied to the input attenuator voltage range selection makes sure. This basic principle is called darsonval principle. Parts of pmmc permanent magnet controlled springs aluminum. Therefore the polarity should be maintained with pmmc instrument. The moving coil is wound with many turns of enameled or silk covered copper wire. Pmmc instrument explained permanent moving coil instrument.
Advantages and disadvantages of pmmc permanent magnet. In this instrument, we have a coil suspended in the magnetic field of a permanent magnet in the shape of a horseshoe. A permanent magnet is used in this type instrument. This type of instrument gives the total amount of the quantity to be measured over a specified period of time 1.
1286 282 444 730 1235 1673 1499 1386 780 752 1306 384 459 90 271 726 1173 658 355 1692 153 1584 1603 696 942 1389 1500 488 14 1525