PMMC stands for Permanent Magnet Moving Coil. PMMC Instruments are the most accurate type for the measurement of DC current or voltage. Construction of PMMC Instruments Permanent Magnet Moving Coil or PMMC Instruments consists of following components: Moving Coil Magnet System Control Spring Damping Pointer and Scale 1. Moving Coil The moving coil made up … Read more
Construction The construction of a single phase Electrodynamometer Power Factor Meter is shown in fig. 1. It consists of a fixed coil which acts as the current coil. This coil is split up into two parts and carries the current of the circuit under test. Therefore, the magnetic field produced by this coil is proportional to the main current. Two identical pressure coils A … Read more
Classification of Transformer losses A transformer is a static device, hence mechanical losses (like windage or friction losses) are absent in it. There are mainly two types of losses in the transformer. They are 1. Core losses or Iron losses Hysteresis loss Eddy current loss 2. Copper losses Apart from these two types, there are … Read more
The property of a material that opposes the flow of current through it, is called electrical resistance or simply resistance. The symbol of resistance is shown in the fig. 1. Practically, the electrical components that offers certain opposition (resistance) to the flow of current in the circuit is known as resistor. Fig. 1(b) shows some … Read more
In electrical circuits, the classification of circuit elements can be classified as Linear and non-linear element Active and Passive element Unilateral and Bilateral element Time-variant and Time invariant element Linear and non-linear element An element or a system is said to be linear if it obeys the principles of additive and homogeneity properties. For linear elements, … Read more
Functional Block diagram of Digital Frequency Meter Working principle of Digital frequency meter 1. The unknown frequency signal is fed to the Schmitt trigger. The signal may be amplified before being applied to Schmitt trigger. 2. In a Schmitt trigger, the signal is converted into a square wave with very fast rise and fall times, then … Read more
Difference between the construction of PMMC and dynamometer instruments PMMC (Permanent moving magnet coil) Instrument (1) Moving Coil: The moving coil is wound with many turns of enamelled or silk-covered copper wire. The coil is mounted on a rectangular aluminium former which is pivoted on jewelled bearings. The coils move freely in the field of … Read more
Recombination and trapping processes in a semiconductor Recombination is the process where an electron moves from the conduction band into the valence band so that a mobile electron-hole pair disappear. Classical mechanics requires that momentum be conserved in an encounter of two particles. Since the momentum is zero after recombination, this conservation law requires that … Read more
Magnetic bubble memory consists of magnetic bubbles used to store data bits. These bubbles move in thin films of magnetic material. The bubbles are cylindrical magnetic domains having polarization opposite to that of the thin film in which they are embedded. A thin film of magnetic garnet contains wavy strips of magnetic domains when an … Read more
Fuse was patented by Thomas Edison in 1890. Fuse is the simplest & cheapest device used for interrupting an electrical circuit under short circuit or excessive. The fuse element is generally made of materials having low melting point, high conductivity and least deterioration due to oxidation e.g., silver, copper etc. Definition of fuse It is … Read more
