Construction and operation of PMMC in Telugu#viralvideo#youtubeshorts#viral#youtube#ele#shortvideo

Working principle and construction of PMMC Technical Editor Technical Editor 6 years ago The PMMC stands for permanent magnet moving coil and it is also called as D’Arsonval instruments. The PMMC works on the electromagnetic effect. A permanent magnet is used to produce magnetic flux and a coil that carries the current to be measured moves in this field. As the pointer is connected to the coil it gets deflected in proportion with the current. Working principle : When a current carrying conductor placed in the magnetic field experiences a force. It is given by the expression is given below, F=BIL Where F=Force in Newton B= Flux density in Tesla I= Current in ampere L= Length of conductor in meter Construction of PMMC : Construction of PMMC Construction of PMMC The basic construction of PMMC is shown in above fig. a light rectangular coil wound on an aluminum frame is pivoted within the air gaps between the two poles of a permanent magnet and a cylindrical soft iron core. This light rectangular coil carries the current to be measured. Soft iron core provides formation of uniform magnetic field. The aluminum frame supports the coil as well as provides eddy current damping. Two phosphor bronze springs coiled in opposite directions serve as leads for the current in the coil. The springs also provide controlling torque. left hand, middle and forefinger are at 90 degrees with each other. After that the magnetic field will be in the forefinger, flow of current will be across the middle finger and finally, the force will be through the thumb finger. Once the current flow within the coil on the aluminum former, the magnetic field can be generated in the coil in proportion to the current flow. The electromagnetic force throughout the fixed magnetic field from the permanent magnet generates the deflection force within the coil. After that the spring generates the force to resist additional deflection; therefore it helps to balance the pointer. So damping force can be generated within the system through the aluminum core movement of the magnetic field. It maintains the pointer stable to a point. Once it attains equilibrium by controlling & deflection torque to provide accuracy in measurement. It is an essential component of the PMMC instrument. The designing of this coil can be done by wounding copper coils to a rectangular block among the magnetic poles. It is made with Aluminum and the rectangular block can be called Aluminum former rotated into the jeweled bearing. So it permits the coil to turn freely. Once the current is supplied throughout these coils, then it gets a deflection within the field, then it is used to find out the voltage or current magnitude. The aluminum is a non-metallic former, used to measure the current whereas the metallic former including high electromagnetic damping is used to calculate the voltage. Magnet System The PMMC instrument includes two high-intensity magnets otherwise a ‘U’ shaped magnet-based design. The designing of these magnets can be done with Alnico & Alcomax for higher superior field intensity & coercive force. In several designs, an extra soft iron cylinder can be arranged among the magnetic poles to create the field identical; while decreasing air reluctance for increasing the strength of the field. Control In the PMMC device, the torque can be controlled due to the springs which are fabricated with phosphorous bronze. These springs are arranged among the two jewel bearings. The spring provides the lane to the lead current to supply in & out of the moving coil. The torque can be controlled mainly due to the delay of the ribbon. Damping Torque Damping torque can be generated within the PMMC instrument using the aluminum core’s movement within the magnetic field. Torque Equation The equation involved in the PMCC instrument is the torque equation. The deflecting torque induces due to the coil’s movement and this can be expressed with the equation shown belowTd = NBLdl Where, ‘N’ is the no. of turns in the coil ‘B’ is the density of flux within the air gap ‘L’ & ’d’ are vertical as well as horizontal lengths of the surface ‘I’ is the flow of current in the coil G = NBLd The restoring torque can be provided to the moving coil can be done with the spring and it can be expressed as Tc = Kθ (‘K’ is the spring constant) Final deflection can be done through the equation Tc = Td Substitute the values of Tc & Td in the above equation, then we can get Kθ = NBLdl We know that G = NBLd Kθ = Gl I = (K/G) θ From the above equation, we can conclude that the deflection torque can be directly proportional to the flow of current in the coil. Advantages of PMMC Instrument The advantages are The scale in the instrument can be divided properly It generates no losses because of hysteresis. It uses less power It is not influenced by the stray magnetic field. High accuracy It is used as a voltmeter/ammeter with appropriate resistance.