Electromagnetic damping means that when the conductormagnetic fieldThe induced current will make the conductor subject toAmberiThe direction of ampere force always obstructs the movement of conductor.Electromagnetic damping phenomenon originates fromelectromagnetic inductionPrinciple.
The macroscopic phenomenon is that when the closed conductor and the magnetic pole move relative to each other, there will be electromagnetic resistance between them, which will hinder the relative movement.This phenomenon can be explained by Lenz's law: closed conductor and magnetic pole occurCutting magnetic induction lineDue to the change of the magnetic flux penetrated by the closed conductor, the closed conductor will produce induced current, or dynamic current.The magnetic field generated by this current will hinder the relative movement of the two.The resistance is proportional to theMagnetic induction, relative motion speed, etc.
Electromagnetic damping phenomenon is widely used in situations requiring stable friction and braking force, such as watt hour meter, electromagnetic braking machinery, and evenMagnetically Levitated TrainEtc.[1]
In order to increase the stability of the system and suppress the resonance peak of the rotor simply and reliably, a new passive electromagnetic method is proposeddamperIts structure is similar toElectromagnetic bearing. But not requiredclosed-loop control , DC power is used.Through analysis, it is found that electromagneticdamperChange due to rotor whirl in coilmagnetic fieldThe fluctuation caused byelectric currentAnd rotordisplacementThe damping is caused by the phase difference between the two, and the formulas for calculating the fluctuating current and damping coefficient are derived.The experimental results show that thedamperThe damping provided can effectively suppress the resonance amplitude.[1]
(1) SetSensitive galvanometerAfter shaking, the pointer will swing to a greater extent.After the shaking stops, it can be observed that a needle should swing several times, and it can stop after a certain time.[2]
(2) Shake againSensitive galvanometer, so that it has a larger swing.Immediately connect one to both terminalswireway(short route), it can be found that the swing of the pointer decreases rapidly, which is much shorter than the swing time when the short route is not connected.This is because the coil connected to the pointermagnetic fieldIt is generated during the middle swinginduced current, the coil is subject toAmberiFormedresistanceThe effect of the moment makes the swing of the pointer decay rapidly.This can play the role of damping protection.[2]
(3) Shake those connected to the short routeSensitive galvanometerIt can be seen that the pointer swings slightly and stops quickly.The reason is the same as operation (2).[2]
explain
(1) Usually JD409 or JD409-1Sensitive galvanometerThe damping time of is less than 4S, because the moving coil aluminum frame of this galvanometer is closedDamping action。So it is better to use the old-fashionedSensitive galvanometer(The internal dynamic coil aluminum frame is not closed), demonstrating the short circuit damping effect is better.[2]
(2) Experiment descriptionSensitive galvanometerWhen not in use, a short line shall be added to the two terminals to achieve damping protection.Prevent the galvanometer from being vibrated, the pointer from being bent or the shaft tip from falling off due to excessive amplitude during handling or transportation.[2]
Verification method II
Purpose: Demonstrate the short circuit braking method of motor.[2]
Equipment: toy motor, single pole double position switch, dry battery, wire, etc.[2]
(1) Connect toy motor, two dry batteries and single pole double position switch with wires as shown in the figure.[2]
(2) Turn the single pole two position switch to a, and the motor will rotate at high speed.When the power supply is cut off, it can be seen that the motor can still rotate for a long time after the power is cut off.Record the time from power cut to complete shutdown.[2]
(3) Turn the switch to a again. After the motor rotates at high speed, turn the single pole double position switch to b.It is found that the motor will stop rotating quickly.In contrast to operation (2).This is because the motor rotor that has been rotating at a high speed is still in themagnetic fieldWhen rotating at medium and high speedInduced electromotive force。If the external circuit is closed at this time (such as turning the switch to b)induced current, which is equivalent to a generator.haveinduced currentThe rotor coil ofAmberiCouple momentThe brake action of will stop the rotation quickly.Therefore, the short circuit wire outside the motor startsPair rotorElectromagnetic field ofDamping action。[2]
