If the magnetic field moves relative to the conductorinduced current, induced current makes conductor subject toAmberiThe ampere force makes the conductor move, which is called electromagnetic drive.
When the magnetic field moves, it drives the conductor to move together, which is called "electromagnetic driving".WhenmagnetWhen rotating, set the N pole of the magnet at a certain moment at the radius Oa of the metal disk, according toLenz's lawThis will generatevortex, resulting in the formation ofinduced current。The induced current is in a rotating magnetic field and will be subjected to the force of the magnetic field.This force will produce a torque that causes the metal disk to rotate in the direction of magnetic field rotation.At this time, the torque generated by the force of the induced current generated at the pole S of the magnet also causes the metal disk to rotate in the direction of magnetic field rotation.Results The metal disk rotates in the direction of rotation of the magnetic field.
However, if the rotating speed of the disk is the same as that of the magnetic fieldrelative velocityIf it is zero, the induced current will not be generated, and then the electromagnetic driving effect will disappear.Therefore, under the action of electromagnetic drive, the rotating speed of the metal disk is always higher thanmagnetOr the rotating speed of the magnetic field is small, or the rotating speed of the two is always asynchronous.Induction motor（asynchronous motor）It is made according to this principle.
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Electromagnetic drive can be used to make meters for measuring speed, such asTachometerIt is often called magnetic tachometer.In order to ensure the generated AC frequency f=50-1 in the generator, the rotor speed must be controlled.In other cases, in order to give full play to the efficiency of the machine and use the machine correctly, it is often necessary to measure its speed, and then further control and adjust it.
When measuring the speed with a magnetic tachometer, connect the rotating shaft of the tested machine with thePermanent magnetThe permanent magnet is generally composed of one piece filled with four polesMagnetic steelMade, which forms aRotating magnetic field。There is a metal disk above the permanent magnet, which is called the induction plate.There is a small air gap between the induction plate and the permanent magnet, and they do not contact each other.
When the permanent magnetRotating shaftWhen rotating, the sensor will generatevortex。The eddy current will be subjected to the force of the rotating magnetic field, so that the induction plate will be driven and move along the rotating direction of the permanent magnet.The rotation of the sensing plate will drive the spring connected with the sensing plate rotating shaft to tighten it, thus producingElastic recoveryTorque.Finally, when the induction plate rotates over a certain angle, the torque generated by the electromagnetic drive is just offset by the torque of the elastic recovery, and aTemporary balanceStatus.The faster the rotating speed of the permanent magnet driven by the machine, the greater the torque generated by the electromagnetic driving effect on the induction plate, and thus the greater the deflection angle of the pointer.In this way, the rotation speed of the machine can be displayed by the deflection angle of the pointer.
