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To observe the effect of back-EMF of a motor, one can perform this simple exercise: with an incandescent light on, cause a large motor such as a drill press, saw, air conditioner compressor, or vacuum cleaner to start. The light may dim briefly as the motor starts. When the armature is not turning
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or permanent magnet field, thus also acting as a generator while running as a motor. This effect is not due to the motor's inductance, which generates a voltage in opposition to a changing current via
Faraday's law, but a separate phenomenon. That is, the back-EMF is also due to inductance and
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as the motor turns faster, the current flowing into the motor decreases. One practical application of this phenomenon is to indirectly measure motor speed and position, as the back-EMF is proportional to the rotational speed of the armature.
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In motor control and robotics, back-EMF often refers most specifically to actually using the voltage generated by a spinning motor to infer the speed of the motor's rotation, for use in better controlling the motor in specific ways.
114:(called locked rotor) there is no back-EMF and the motor's current draw is quite high. If the motor's starting current is high enough, it will pull the line voltage down enough to cause noticeable dimming of the light.
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Faraday's law, but occurs even when the motor current is not changing, and arises from the geometric considerations of an armature spinning in a magnetic field.
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This voltage is in series with and opposes the original applied voltage and is called "back-electromotive force" (by
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of the voltage at every moment opposes that of the change in applied voltage, to keep the current constant.
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194:(CEMF), DC Equipment Terminology, Electrical Science Volume 2.
183:"Nuclear Power Fundamentals Training Manuals". DC Generators,
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Graf, "counterelectromotive force", Dictionary of
Electronics
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is also commonly used to refer to the voltage that occurs in
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within the coil, and therefore the self-induced voltage. The
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is due to a change in current which causes a change in the
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Voltage that opposes the change in current which induced it
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Counter-electromotive-force in access control applications
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89:and the magnetic field produced by the motor's
58:For example, the voltage appearing across an
165:Naval Electrical Engineering Training Series
46:which induced it. CEMF is the EMF caused by
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48:electromagnetic induction
226:Back EMF Motion Feedback
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205:"Back-EMF"
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188:Archived
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72:polarity
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