Pmmc instrument pmmc instrument, galvanometer, dc ammeter, dc voltmeter, series ohm meter. Various error in pmmc instrument electrical concepts. If you cannot read the numbers in the above image, reload the page to generate a new one. When the instrument is used as microammeter or miliammeter, the indication of instrument for a constant current will decrease by 0. Pmmc temperature compensation instrumentation tools.
From the given problem, we can create the equivalent circuit as shown on figure 1. A moving coil galvanometer is an instrument used for detection and. Applications of pmmc permanent magnet moving coil instruments are acknowledged to be the best type of all d. The electrical measurements notes pdf em notes pdf book starts with the topics covering control and damping torques, design considerations type of p. Sep 30, 2019 here you can download the free lecture notes of electrical measurements pdf notes em pdf notes materials with multiple file links. Permanent magnet moving coil instrument pmmc working and. Pmmc, mi, emmc or edm, esv instruments measurement. The potential difference across the meter when carrying 20ma is 400mv. Jun 09, 2019 rectifier type instrument measures the alternating voltage and current with the help of rectifying elements and permanent magnet moving coil type of instruments. Here you can download the free lecture notes of electrical measurements pdf notes em pdf notes materials with multiple file links. L6l7 pmmc analyze permanent magnet moving coil l8 tutorial class solve the numerical problems l9 moving iron type instruments explain mi instruments l10 expression for deflecting torque and control torque formulate expression for td and tc l11 errors and compensations define different errors l12 extension of range using shunt and series.
Jul 24, 20 so you are partially correct, pmmc meter movements cannot measure ac directly, but we can use a bridge rectifier to convert the ac into dc humpy dc ac waveform converted to all positive halves and we can. Electrical and electronic measurements kuestion free. Pmmc type instrument uses two permanent magnets in order to create stationary magnetic field. We can see that the current i divides into the branches of the pmmc and the shunt resistor. Nov 09, 2017 in permanent magnet moving coil or pmmc instruments, 1c increase in temperature reduces the strength of spring by 0. Classification, absolute and secondary instruments, indicating instruments, control, balancing and damping, constructional details, characteristics, errors in measurement, ammeters, voltmeters. Sep 21, 2019 electrodynamometer type instruments pdf the electrodynamometer type instrument is a transfer instrument. Maharashtra state board of technical education autonomous. Extension of instrument range is possible with the help of shunt and series resistances. Deflection torque is proportional to the square of the current. The coil resistance increases with increase in the temperature. Measurements and instruments viva short questions and answers pdf. The moving coil is wound with many turns of enameled or silk covered copper wire.
The pmmc has efficient damping characteristics and is not affected by stray magnetic field. The coils move freely in the field of a permanent magnet. Engineering electronics ece electrical eee faqs measurements and instruments unit wise two marks, short, viva, interviews questions and answers pdf download. A permanent magnet moving coil pmmc is one such instrument which is popularly used onboard and has several applications. They are very sensitive and maintain a high degree of accuracy over long periods. 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.
When a current carrying coil is placed in the magnetic field produced by permanent magnet, the coil experiences a force and moves. Aug 22, 2018 electrodynamic type instruments are similar to the pmmctype elements except that the an electrodynamometer for use as a wattmeter is shown in fig. Sep 02, 2018 pmmc instrument pdf 16 mar pmmc stands for permanent magnet moving coil. Permanent magnet moving coil mechanism pmmc mathematical.
Permanentmagnet moving coil type pmmc instruments home permanentmagnet moving coil type pmmc instruments 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. If we use this instrument on ac, whenever the direction of current is reversed during negative half cycle, the direction of torque will also be reversed. 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. Pmmc instruments, galvanometer, dc voltmeter, dc ammeter. Now one question must arises in our mind why we use rectifier type of instruments. The action of these instruments is based on the motoring principle. Instruments, types of instruments, permanent magnet moving. The instrument to be used is 200a for full scale deflection. Feb 03, 2017 pmmc instruments, galvanometer, dc voltmeter, dc ammeter 1. The permanent magnet moving coil instruments are most accurate type for direct current measurements.
Meters, double element and three element dynamometer wattmeter, errors and compensations, measurement of. Permanent magnet moving coil instruments pmmc the permanent magnet moving coil instruments are most accurate type for direct current measurements. However the primary function of rectifier type of instruments work as voltmeter. Range extension of pmmc galvanometer free download as powerpoint presentation. It is one of the simple and most used instrument on board with sophisticated names. Aug 18, 20 construction of pmmc instruments the constructional features of this instrument are shown in fig. A transfer instrument is one which is calibrated with a d.
The constructional features of this instrument are shown in. Classification of instruments electrical instruments may be divided into two categories, that are. Download ebook by learn eee friends is video me ham moving iron instrument ke bare me. The pointer of a moving coil instrument gives full scale deflection of 20ma. Current in one direction through the wire will produce a clockwise torque on the needle mechanism, while current the other direction will produce a counterclockwise torque. Absolute instruments gives the quantity to be measured in term of physical constant of the instrument. Electrical measurements pdf notes em pdf notes smartzworld. What is the difference between movingiron and movingcoil.
There are some disadvantages of pmmc permanent magnet moving coil are given below, it has comparatively high cost. Pdf electrical measurements pdf notes em notes 2019 sw. In the measurement of direct currents and voltage ii. Oct 21, 2016 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. These types of instruments are used only for measurement of the dc quantities. Applications of pmmc permanent magnet moving coil instruments. Old style magnet system consisted of relatively long u shaped permanent magnets. There are two types of moving coil instruments namely, permanent magnet moving coil. The basic pmmc instrument is sensitive to the temperature. 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. Jun 18, 2018 in order to change the range to 025 a. 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. Electrodynamometer type instruments download as powerpoint presentation.
The other popular nomenclature of this instrument is dalvanometer and. Both moving coil and moving iron instruments are used measure the voltage and current of circuits. Advantages and disadvantages of pmmc permanent magnet moving. Advantage and disadvantages the permanentmagnet movingcoil pmmc type instruments have the following advantages and disadvantages. In such case a large resistance made of manganin is connected in series with the instrument. Course file on electrical measurements and instrumentation by.
An ammeter has a pmmc instrument with a coil resistance of r m. The coil is mounted on rectangular aluminum former, which is pivoted on jeweled bearings. The magnetic field strength and spring tension decrease with increase in temperature. Jan 03, 2020 different instruments are used onboard for measuring several electrical parameters to analyze and keep these machines in proper running condition. Sep 05, 2012 instruments essentials of indicating instruments permanent magnet moving coil pmmc types of instruments. Thus the net effect is to increase the deflection of instrument by 0. With this setup, we can apply the currentdivider formula. Rectifier type instrument construction principle of operation. To get the file, download the measurements and instruments viva short questions and answers pdf. But the only thing we can measure directly with a pmmc meter movement is a current up to 1ma.
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