The Moving Coil Meter

Chapter 5.8 The Moving Coil Meter

Fundamental Electrical and Electronic Principles Third Edition Book
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Fundamental Electrical and Electronic Principles Third Edition Book

  • 158Fundamental Electrical and Electronic PrinciplesThis value of force forms the basis for the defi nition of the ampere, namely: that current, which when maintained in each of two infi nitely long parallel conductors situated in vacuo , and separated one metre between centres, produces a force of 2 10 7 newton per metre length on each conductor. Worked Example 5.11 Q Two long parallel conductors are spaced 35 mm between centres. Calculate the force exerted between them when the currents carried are 50 A and 40 A respectively. A d 0.035 m; I 1 50 A; I 2 40 A FdF202050400 035472711111IInewtonso mN ..Ans Worked Example 5.12 Q Calculate the fl ux density at a distance of 2 m from the centre of a conductor carrying a current of 1000 A. If the centre of a second conductor, carrying 300 A, was placed at this same distance, what would be the force exerted? A d 2 m; I 1 1000 A; I 2 300 A BdBFd0teslaso, mT neIII111114000020 62820772.Answwtonso mN 20300000230711FAns 5.8 The Moving Coil Meter Most analogue (pointer-on-scale) instruments rely on three factors for their operation: a defl ecting torque; a restoring torque; and a dampingtorque.Defl ecting Torque Essentially, a moving coil meter is a current measuring device. The current to be measured is passed through a multi-turn coil suspended between the poles of a permanent magnet. The coil is made from fi ne copper wire which is wound on to a light aluminium former . Thus the motor effect, described in section 5.6, is utilised. Since the wire is of small diameter, and the aluminium former