A Wheatstone bridge is used for the accurate measurement of resistance. The Wheatstone bridge works on the principle of null deflection, i.e. the ratio of their resistances are equal, and no current flows through the galvanometer. The general arrangement of the Wheatstone bridge circuit is shown in fig. 1. It is a four arms bridge circuit … Read more
Resistance is classified into three categories as low, medium and high resistance. Medium Resistance ranges from 1Ω to 0.1 MΩ. The different methods used for the measurement of Medium resistance are as follows: Voltmeter-Ammeter method Substitution Method Wheatstone Bridge Method Ohmmeter Method Substitution Method In this section, we will learn about Measurement of Medium Resistance by Substitution Method. In … Read more
Resistance is classified into three categories for the sake of Measurement. Different categories of Resistance are measured by the different techniques. They are classified as Low Resistance: Resistance having value 1Ω or below are kept under this category. Medium Resistance: This category includes Resistance from 1Ω to 0.1 MΩ. High Resistance: Resistance of the order of … Read more
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
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
The phototransistor is a semiconductor light sensor formed from a basic transistor with a transparent cover that provides much better sensitivity than a photodiode. It is basically a 3-layer semiconductor device which has a light-sensitive base region. The base senses the light and converts it into the current which flows between the collector and the … Read more
The measurement of a given quantity is essentially an act or result of comparison between a quantity, whose magnitude (amount) is unknown with a similar quantity whose magnitude (amount) is known, the latter being called standard. Measurement involves the use of the instrument as a physical means of determining quantities or variables. The instruments serve … Read more
An Instrument may be defined as a device or a system which is designed to maintain a functional relationship between prescribed properties of physical variables and must include ways and means of communication to a human observer. Functional Elements of an Instrumentation System Most of the measurement system contains following main functional elements as shown … Read more