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The working principle for magnetic card
Jan 15, 2018

The  working principle for magnetic card 

  The residual magnetic flux density Br above the magnetic card plays a decisive role in the working process of the magnetic card. Magnetic card to a certain speed through the work of the coil with the magnetic head, magnetic card external magnetic field lines cutting coil, induced electromotive force in the coil, which transmitted the signal was recorded. Of course, it is also required to record the signal in the magnetic card has a wider frequency response, smaller distortion and higher output level. A very thin metal line can be used as a simple playback device. Metal line and magnetic card close, the direction perpendicular to the magnetic card running direction, magnetic card operation, the metal straight line cutting magnetic lines and produce induced electromotive force, the size of the electromotive force is proportional to the magnetic line cutting. When the running speed of the magnetic card remains unchanged, the induced electromotive force of the metal straight line is proportional to the residual magnetic induction intensity on the surface of the magnetic card, and the induced electromotive force in the conductor can be expressed as follows: e = BrWv where Br - surface residual magnetic induction intensity W - Track width; v - speed of the card during playback. In the case of Br = 2πf / vφrmcos2πft, the relationship between Br and e is integrated to obtain e = 2πfWφrmcos2πft. Of course, with a metal wire for magnetic card work equipment, because the output is small, so it is not practical. The head is made of soft magnetic material with high permeability of the core, winding coil wound above the head in front of a very narrow gap, then into the magnetic head of the magnetic flux, can be seen as two The effective reluctance in parallel, that is, the reluctance of the gap and the reluctance of the head core. Since the effective magnetic resistance of the gap is much larger than the reluctance of the working head iron core, most of the magnetic flux on the magnetic card is input to the head iron core and is interdependent with the coil winding of the working head, thus inducing the electromotive force. In this case , A single metal playback line obtained by the induced electromotive force formula is entirely applicable to the work of magnetic head magnetic card, but only different proportion coefficient

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