Jan 03, 2020 when pmmc is used as an ammeter, except for a very small current range, the moving coil is connected across a suitable low resistance shunt, so that only small part of the main current flows through the coil. The coil resistance increases with increase in the temperature. How does a pmmc instrument read average value of a dc waveform. We know 21 definitions for pmmc abbreviation or acronym in 4 categories. According to the fundamental law of electromagnetic force, the coil will rotate in the magnetic field when it. All content is posted anonymously by employees working at pmmc. Thus the net effect is to increase the deflection of instrument by 0. Permanent magnet moving coil instrument pmmc working. Pmmc will not be liable for any damages or injury, including but not limited to, special or consequential damages that result from the use of, or the inability to use, the materials in this site, even if there is negligence or pmmc or an authorized pmmc representative has been advised of the possibility of such damages, or both.
The pmmc stands for permanent magnet moving coil and it is also called as darsonval instruments. Aug 18, 20 construction of pmmc instruments the constructional features of this instrument are shown in fig. Extension of instrument range is possible with the help of shunt and series resistances. The magnetic field strength and spring tension decrease with increase in temperature.
Pacific marine mammal center laguna beach, ca pmmc. The swamping resistance is a resistor with zero temperature coefficient, put in series with the meter movement in an ammeter circuit. 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. What will be the value of the shunt resistance required for the instrument to be converted to read a full scale reading of 1 amp. Permanent magnet moving coil instrument or pmmc instrument. The pmmc has efficient damping characteristics and is not affected by stray magnetic field. Measurement and instruments objective questions and answers pdf free download.
Feb 15, 2016 how does a pmmc instrument read average value of a dc waveform. The moving coil is either rectangular or circular in shape. Maximum voltage that can be put across galvanometer is vm i rm 0. Working principle of pmmc instrument is the same as that of the darsonval type of galvanometers, the difference being that direct reading instrument is. The cost of these pmmc instruments is higher than that. Construction of pmmc instruments the constructional features of this instrument are shown in fig. If the instrument is to have a wide range, the instrument should have a.
Torque equation for pmmc the equation for the delevoped torque of the pmmc can be obtained from the basic law of electromagnetic torque. In pmmc meter or d arsonval meter or galvanometer all are the same instrument, a coil of fine wire is. Pmmc is listed in the worlds largest and most authoritative dictionary database of. Contruction construction of pmmc instruments the constructional features of this instrument are shown in fig. Permanent magnet moving coil or pmmc instrument definition. An engineer has a pmmc instrument used as a dc ammeter. The action of these instruments is based on the motoring principle. The permanent magnet moving coil instrument is the most accurate type for dc measurements.
Here are a few fantastic ebooks to get important maritime information in the next couple of minutes. When a current carrying coil is placed in the magnetic field produced by permanent magnet, the coil experiences a force and moves. The resistance can be measured most accurately by a. There are some disadvantages of pmmc permanent magnet moving coil are given below, it has comparatively high cost. Looking for online definition of pmmc or what pmmc stands for. This basic principle is called darsonval principle. Jan 15, 2019 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. Is a pmmc instrument designed to be sensitive to extremely low ppt. The amount of force experienced by the coil is proportional to the current passing through the coil. Permanent magnet moving iron type instruments ppt download. Advantages and disadvantages of pmmc permanent magnet moving.
What is permanent magnet moving coil or pmmc instrument. This website and its content is subject to our terms and conditions. Scale of pmmc instrument is linear as i for a given deflection, tctd or k blind or i k blnd 8. Download licensing forms, media and other resources here.
The simplest galvanometer is a very sensitive instrument with the type of centerzero scale, therefore the pointer can be deflected to either right or left of the zero position. 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. Torque equation for pmmc instrumentation and control. Permanent magnet moving coil instrument pmmc working and. With this setup, we can apply the currentdivider formula. Working principle and construction of pmmc polytechnic hub. Definition moving coil galvanometer is a device which is used to detect small electric current. 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 deflecting torque is given by, td nbai where, td deflecting torque in nm b flux density in air gap, wbm2 n number of turns of the coils. The weight of the instrument is normally counter balanced by the weights situated diametrically opposite and rapidly connected to it. A permanentmagnet moving coiltype instrument works on the principle that when a currentcarrying conductor is placed in a magnetic field, it is acted upon by a force which tends to move it to one side and out of the field. Pmmcthe permanent magnet moving coil instrument is the most accurate type for d. Advantages and disadvantages of pmmc permanent magnet. Measuring instruments ppt video online download 31 pmmc instruments. In permanent magnet moving coil or pmmc instruments, 1c increase in temperature reduces the strength of spring by 0. Why is swamping resistance used in moving coil instruments. When the instrument is used as microammeter or miliammeter, the indication of instrument for a constant current will decrease by 0. 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. Permanent magnet moving coil instrument the permanent magnet moving coil instrument or pmmc type instrument uses two permanent magnets in order to create stationary magnetic field. Download practical maritime ebooks with amazing bonuses. Home permanentmagnet moving coil type pmmc instruments.
The meter movement is sensitive to changes in temperature, it changes resistance due to this. A permanent magnet is used to produce magnetic flux and a coil that carries the current. Permanent magnet moving coil or pmmc instruments are the most accurate type for the measurement of dc current or voltage. Classification, absolute and secondary instruments, indicating instruments, control, balancing and damping, constructional details, characteristics, errors in measurement, ammeters, voltmeters. For pmmc we have found 21 definitions what does pmmc mean.
The shunt consists of a number of thin plates made up of alloy metal, which is usually magnetic and has a lowtemperature coefficient of. Will it show its average vaue 2vm if yes, i dont understand how. Pmmc with ac measurement rectifier alternating current. The moving coil is wound with many turns of enameled or silk covered copper wire. Pmmc instruments, galvanometer, dc voltmeter, dc ammeter pmmc instrument. A moving coil ammeter has a full scale deflection of 50 amp and a coil resistance of. From the given problem, we can create the equivalent circuit as shown on figure 1. The basic pmmc instrument is sensitive to the temperature. Possible pmmc meaning as an acronym, abbreviation, shorthand or slang term vary from category to category. Therefore, a pmmc instrument connected directly to measure 50hz ac indicates zero. Find powerpoint presentations and slides using the power of, find free presentations research about pmmc ppt. Apr 23, 2018 when the instrument is used as microammeter or miliammeter, the indication of instrument for a constant current will decrease by 0.
Feb 03, 2017 permanent magnet moving coil instrument the permanent magnet moving coil instrument or pmmc type instrument uses two permanent magnets in order to create stationary magnetic field. When pmmc is used as an ammeter, except for a very small current range, the moving coil is connected across a suitable low resistance shunt, so that only small part of the main current flows through the coil. The simplest galvanometer is a very sensitive instrument with the type of. The coil is mounted on rectangular aluminum former, which is pivoted on jeweled bearings. When pmmc is used as an ammeter, except for a very small current range, the moving coil is ppt about 1 results 0. 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. Pmmc instrument on ac at 50hz or higher supply frequencies the damping mechanism of the instrument and the inertia of the meter movement prevent the pointer from following the changing instantaneous levels. Permanent magnet moving coil mechanism pmmc mathematical.
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 construction of an accurate instrument with a moving coil to carry bulk current is. The basic construction of pmmc is shown in above fig. Measuring instruments the device used for comparing the unknown quantity with the unit of measurement or standard quantity is called a measuring instrument. Electrical instruments ppt video online download 18 electrical measuring instruments.
Galvanometer is essentially a pmmc instrument designed to be sensitive to extremely current levels. Permanent magnet moving coil instruments pmmc the permanent magnet moving coil instruments are most accurate type for direct current measurements. In such case a large resistance made of manganin is connected in series with the instrument. We can see that the current i divides into the branches of the pmmc and the shunt resistor. The construction and working of a pmmc instrument article716. View and download powerpoint presentations on pmmc ppt. It operates on the principle that the torque is exerted on the moving coil placed in the field of the permanent magnet. 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 that is free to rotate around its vertical axis. Mar 23, 2011 the weight of the instrument is normally counter balanced by the weights situated diametrically opposite and rapidly connected to it.
Pmmc temperature compensation instrumentation tools. May 12, 2018 permanent magnet moving coil or pmmc instruments are the most accurate type for the measurement of dc current or voltage. Various error in pmmc instrument electrical concepts. Pmmc is listed in the worlds largest and most authoritative dictionary database of abbreviations and acronyms. A free powerpoint ppt presentation displayed as a flash slide show on id. Construction of pmmc instruments the constructional features of this. This light rectangular coil carries the current to be measured. These types of instruments are only used for measuring the dc quan. He wanted to calculate the torque in the coil for a current of 3 milliamperes.
Range extension of pmmc galvanometer free download as powerpoint presentation. Methodological center for vocational training pmmc. I mean what will the meter show if i fed a full wave rectifiers output to it. Electrical measurement and electronic instruments nptel.
The coils move freely in the field of a permanent magnet. Pmmc instruments, galvanometer, dc voltmeter, dc ammeter. 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. Tes global ltd is registered in england company no 02017289 with its registered office at 26 red lion square london wc1r 4hq. When a current is passed through the coil windings, a torque is. Generally, an ebook can be downloaded in five minutes or less.
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