Electrical Engineering ⇒ Topic : Essentials of Indicating Instruments
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Maninder
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Essentials of Indicating Instruments An indicating instrument essentially consists of moving system pivoted in jewel bearings. A pointer is attached to the moving system which indicates on a graduated scale, the value of the electrical quantity being measured. In order to ensure proper operation of indicating instruments, the following three torques are required : (1) Deflecting (or operating) torque (2) Controlling (or restoring) torque (3) Damping torque The deflecting torque is produced by utilising the various effects of electric current or voltage and causes the moving system (and hence the pointer) to move from zero position. The controlling torque is provided by spring or gravity and opposes the deflecting torque. The pointer comes to rest at a position where these two opposing torques are equal. The damping torque is provided by air friction or eddy currents. It ensures that the pointer comes to the final position without oscillations, thus enabling accurate and quick readings to be taken | |
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