A voltmeter is always connect in parallel with the element being measured, and measures the voltage between the points across which its connected. When current carrying conductor placed in a magnetic field, a mechanical force. The range of this meter is v imrm r where the multiplier resistance, r can be r 1 or r 2 or. If we want to use it for measuring ac voltages, then we have to follow these two steps. Permanent magnet moving coil mechanism pmmc mathematical. Jan, 2020 dc voltmeter the basic pmmc instrument can be converted into a dc voltmeter by adding a series resistor known as multiplier, as shown in figure 3. Dc voltmeter the basic pmmc instrument can be converted into a dc voltmeter by adding a series resistor known as multiplier, as shown in figure 3. You can expend the range of a pmmc instrument used as an ammeter or voltmeter using the method explained in the next section. Apr 22, 2015 given a pmmc instrument with a 100 a movement and an internal resistance of 100. Department of applied sciences kct college of engineering. Calculate the ammeter range at each setting of the shunt.
The ammeter a is a low range ammeter and w is a low range and low power factor wattmeter. 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. Ac supply at rated voltage is switched on to the transformer through dpic switch. This instrument uses shelf shielding magnet so it is applicable in aerospace. Basic dc voltmeter the deflection of a pmmc instrument is proportional to the current flowing through the moving coil. Show how it can be used a as an ammeter for the range of 0100 a b as a voltmeter for the range of 0750 v. Dc ammeter and voltmeter is used to measure the value of current in. Based on the movingcoil galvanometer constructed by jacques d arsonval in 1881. How to use pmmc instrument as ammeter and voltmeter. Upon configuring a pmmc permanent magnet moving coil as an ammeter, a shunt resistor. Ammeters and voltmeters are essentially current measuring devices. Find powerpoint presentations and slides using the power of, find free presentations research about ammeter and voltmeter range ppt. An ammeter from ampere meter is a measuring instrument used to measure the current in a circuit.
This permanent magnet moving coil meter movement is the basic movement in most. The other differences between the moving iron and moving coil instrument are shown below in the comparison chart. In a pmmc instrument, if the control springs are eliminated the instrument can be used for measuring the quantity of electricity passed through the coil. When pmmc is used as an ammeter, except for a very small current range, the moving. Ammeter and voltmeter extension of the range of ammeter. Aug 19, 2018 basic ammeter the basic movement of dc ammeter is pmmc darsonval galvanometer. Im full scale deflection current of the movement ifsd rm internal resistance of the movement rs multiplier resistance v full range voltage of the instrument. The instrument may also be made to function as a dc voltmeter by connecting appropriate value resistor in series with the coil. Oct 22, 2020 dc ammeter are mainly pmmc instruments, mi can measure both ac and dc currents, also electrodynamometer type thermal instrument can measure dc and ac, induction meters are not generally used for ammeter construction due to their higher cost, inaccuracy in measurement.
In case of manual instruments, the service of an operator is required. Can be used to indicate the value of dc and ac quantity. Dc ammeterthe dc ammeter is an instrument for measuring the electric current in amperes in a branch of an electric circuit. There are two types of moving coil instruments namely, permanent magnet. In a voltmeter, it is produced by a current that is proportional to the voltage to be measured. Such an instrument design is generally known as a permanentmagnet, moving coil, or pmmc movement.
Measurement of 3 phases reactive power with single phase wattmeter for balanced loading 8. If the meter movement is electrostatic, and thus inherently capacitive in nature, a single multiplier capacitor may be connected in series to give it a greater voltage measuring range, just as a seriesconnected multiplier resistor gives a movingcoil inherently resistive meter movement a greater. Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on youtube. In an ammeter, the torque is produced by the current to be measured or by a definite fraction of it. The range of the meter is now 10 milliamperes and it is possible to read the meter indication of 5 milliamperes with the greatest degree of accuracy. Feb 03, 2017 pmmc instruments, galvanometer, dc voltmeter, dc ammeter 1. The coil winding of a basic movement is small and light, so it can carry only very small currents. The series resistance should be much larger than the. In ammeter designs, external resistors added to extend the usable range of the movement are connected in parallel with the movement rather than in series as is the case for voltmeters. View and download powerpoint presentations on ammeter and voltmeter range ppt. Multirange voltmeter a multirange voltmeter consists of a deflection instrument, several multiplier resistors and a rotary switch. One of the significant difference between the moving iron and moving coil instrument is that in moving iron instrument, the soft iron system uses for measuring mechanism. To increase range of the voltmeter, connect the resistance in series with the pmmc instrument. Basic construction of modern pmmc can be seen in figure 1.
It is used as a voltmeter ammeter with appropriate resistance. Resistance must add to the pmmc instrument to make the voltage measured value is larger. One thing to be aware of when sizing ammeter shunt resistors is the factor of power dissipation. Construction of dc ammeter how to avoid affecting the current level ammeter must have a resistance much lower than the circuit resistance. High range voltmeter v2 is connected across the secondary of the transformer. Ammeter safety precautions when you use an ammeter. A large voltage can be measured using a voltmeter o f small rating with a multiplier. Moving coil instruments permanent magnet moving coil mechanism. Pmmc instrument working principle permanent magnet moving. Optical bench determination of polar curve, measurement of mhcp of filament lamps 10.
Fullscale calibration is adjusted by the potentiometer marked rcal since fet has high impedance, the sensitivity of this meter is. Pmmc instruments, galvanometer, dc voltmeter, dc ammeter 1. One of the most accurate type of instrument used for d. An ammeter usually has low resistance so that it does not cause a significant voltage drop in the circuit being measured. A permanent magnet moving coil pmmc is one such instrument which is. Since the resistance offered by an ammeter is very small, its introduction in series with load. Ohmmeters can be made from precision resistors, pmmc instruments, and batteries. Ammeter working principle and types of ammeter electrical4u. Example a pmmc instrument has fsd of 100 aand a coil resistance of 1 k. Artha rin adalat ain 2003 bangladesh pdf files, mahesh babu nani movie. The fet is connected as source follower and is directly coupled to npn transistor, an emitter follower.
Electric currents are measured in amperes a, hence the name. The shunt resistance values can be determined to convert a pmmc instrument into an ammeter for measuring virtually any desired level of current. A voltmeter is used for the measurement of voltage potential difference. D c a dc v consists darsonval movement, attenuator and direct coupled amplifier. The voltmeter is connected by touching the meter probes to the two nodes of interest. A pmmc instrument can be used as ammeter and as voltmeter with the help of published on 11 sep 15. You can use an ammeter, voltmeter and stopwatch instead of ppt. Whereas in moving coil instrument the conductor coil is used for dc measurement.
Symbolvoltmeter volt meter is a high resistance galvanometer it is used to measure the potential difference between two points of a circuit in volts a galvanometer can be converted into a volt meter by using a high resistance in series with the galvanometer the value of resistance depends upon the range of the volt meter for voltmeter a high. Working principle of voltmeter and types of voltmeter. Pmmc instruments, galvanometer, dc voltmeter, dc ammeter. Unlike the voltmeter, an ammeter s range resistors have to carry large amounts of current. A meter designed to measure electrical current is popularly called an ammeter because the unit of measurement is amps. The instrument, which is used to measure the ac voltage across any two points of electric circuit is called ac voltmeter. Modern dry cell construction uses a steel can connected to the positive raised contact. Measurement of power by 3 voltmeter and 3 ammeter methods 7. In this video you will learn about range extension of ammeter and voltmeter operating principle of electrical instruments. Pmmc instrument working principle permanent magnet. 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. Questions and answers list eie south central railway.
Basic ammeter the basic movement of dc ammeter is pmmc darsonval galvanometer. Pmmc instrument pmmc instrument, galvanometer, dc ammeter, dc voltmeter, series ohm meter. The npn forms a bridge circuit by use of several resistors with it. It can show false reading due to the above stated reasons cause of errors in permanent magnet moving coil instrument. Application of pmmc ammeter voltmeter ohmmeter 7 dc voltmeter 8 a basic pmmc darsonval meter can be converted into dc voltmeter by adding in a series resistor multiplier where. Dc ammeterthe dc ammeter is an instrument for measuring the electric current in amperes in. An ammeter has a pmmc instrument with a coil resistance of r m. Practically secondary instruments are suitable for measurement.
Numerical and objective questions moving iron mi instrument 1. Movingiron instruments are generally used to measure alternating voltages. Dc voltmeter is a measuring instrument, which is used to measure the dc voltage across any two points of electric circuit. Ammeter design dc metering circuits electronics textbook.
Since the current indicated is equal to or greater than the next range of the ammeter 5 milliamperes, the meter should not be switched to the next range. A large resistance is connected in series with voltmeter is called multiplier fig. Conversion of voltmeter to ammeter and viceversa niser. To achieve these low resistances, ammeter shunt resistors often have to be custommade from relatively largediameter wire or solid pieces of metal. Figure 1 shows the basic construction of a pmmc instrument. A pmmc instrument gives full scale reading of 25 ma when a potential difference across its terminals is 75 mv. The coil winding of basic movement is small, light and can carry very small currents since the construction of an accurate instrument with a moving coil to carry current greater than 100 ma is impracticable owing to the bulk and weight of coil to be required. Multirange meters are available that combine ammeter, voltmeter, and.
Such a device may be in the form of analog or digital format. Meters for ac voltage or current with moving coil and a rectifier. The resistance in the circuit of the moving coil of a dynamometer wattmeter should be. A low value resistor shunt resistor is used in dc ammeter to measure large current. From the given problem, we can create the equivalent circuit as shown on figure 1. Pmmc, mi, emmc or edm, esv instruments measurement. The bridge balances, or zero current is obtained by adjusting the zero set potentiometer. Analog ammeter and voltmeter designed to measure a. Optical bench determination of polar curve, measurement of. We will connect a red probe wire to the positive terminal on the voltmeter and a black probe wire to the negative terminal on the voltmeter. Introductionthe permanentmagnet movingcoil pmmc instruments basically. In ammeter, external resistance is added in parallel to meter and in voltmeter additional resistance is added in series. When the pmmc instrument is used as an ammeter, its range can be extended with the help of a lowresistance shunt. However maximum pointer deflection is produced by very small current.
Produced current is measured by a pmmc instrument the pmmc indicator points labels of voltage value. Ammeters and voltmeters theory 3 mcqs with answers. Pointer deflection is directly proportional to current flowing in the coil. An ammeter has a current range of 05 a, and its internal resistance is 0.
The pmmc is mostly used as a dc ammeter or voltmeter. In the picture above, the meter movement needle is. Description of different types of ammeters pmmc ammeter. Electrical and electronics measurements and instrumentation kelm.
An ammeter is always connected in series with the load, the current through which is to be measured as shown in fig. Ammeter and voltmeter extension of the range of ammeter and. Describe how pmmc instruments are used as galvanometers, dc ammeters, dc voltmeters, ac ammeters. If we have measured the mass, energy change, and temperature change the. Each lesson consists of an overview, a list of study. In addition to the above eight experiments, at least any two of the experiments from the following list are required to be conducted. Such instruments were useful in their time, but have little place in the modern world exc. The pmmc instrument is essentially a low level dc ammeter. If the ac voltmeter consists of rectifier, then it is said to be rectifier based ac voltmeter. The coil current is directly proportional to the voltage.
The ammeter is usually connected in series with the circuit in which the current is to be measured. Voltmeter measures voltage drop across resistance by putting. Measurement of parameters of choke coils using 3 voltmeter and 3 ammeter methods 9. To determine a number between 0 511 9 bit binary, given, the number to be determined is 301 9 8 7 6 5 4 3 2 1 no. Calculate the required shunt resistance value to convert the instrument into an ammeter with a fsd 100 maand b fsd 1 a. The schematic of a pmmc instrument is shown in fig.
Also find the multiplying factor of shunt and voltage amplification. Measurement of parameters of a choke coil using 3 voltmeter and 3 ammeter methods. The pmmc galvanometer constitutes the basic movement of a dc ammeter. If we place a resistor in series with the permanent magnet moving coil pmmc galvanometer, then the entire combination together acts as dc voltmeter the series resistance, which is used in dc voltmeter is also called series multiplier resistance or simply, multiplier.
348 416 1802 297 1745 587 866 1263 605 1072 1696 635 346 1748 283 1138 252 1455 1707 283 1287 142 1211 1125 525 837 1350 422 553 87 822 129 331 223 313 444 714 1323 1143