Electrical Engineering ⇒ Topic : Classification of Electrical Measuring Instruments
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Lalan
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Classification of Electrical Measuring Instruments The various electrical measuring instruments can be broadly divided into two classes viz. (i) Absolute instruments (ii) Secondary instruments. (1)Absolute instruments. Those instruments which give the value of the quantity to be measured in terms of the constants of the instrument and its deflection are called absolute instruments. For example, a tangent galvanometer which is used to measure current is an absolute instrument. It is because a tangent galvanometer gives the value of current being measured in terms of the tangent of the angle of deflection, the radius and number of turns of the coil and the horizontal component of earth's magnetic field. No previous calibration or comparison is necessary in case of absolute instruments. They are used only in standard laboratories as standardising instruments. (2)Secondary instruments. Those instruments in which the electrical quantity being measured is given directly by the deflection of the instrument are called secondary instruments. These instruments are provided with a calibrated scale. The calibration is done with the help of an absolute instrument or another calibrated instrument. These are the secondary instruments which are most generally used in everyday work. For example, they are very commonly used in laboratories, power stations, substations, industries etc. | |
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