For example, the voltage appearing across an inductor or coil is due to a change in current which causes a change in the magnetic field within the coil, and therefore the self-induced voltage.[1][2] The polarity of the voltage at every moment opposes that of the change in applied voltage, to keep the current constant.[1][3]
The term back electromotive force is also commonly used to refer to the voltage that occurs in electric motors where there is relative motion between the armature and the magnetic field produced by the motor's field coils 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 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.
This voltage is in series with and opposes the original applied voltage and is called "back-electromotive force" (by Lenz's law). With a lower overall voltage across the motor's internal resistance as the motor turns faster, the current flowing into the motor decreases.[4] 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.[5]
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.[6]
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 (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.
Referencesedit
^ abcGraf, "counterelectromotive force", Dictionary of Electronics
^Griffiths, David Jeffery. (2012). Introduction to Electrodynamics (3rd ed.).
^"Self-Inductance," Naval Electrical Engineering Training Series, Module 02: Introduction to Alternating Current and Transformers. 2006-04-20 at the Wayback Machine
^"Nuclear Power Fundamentals Training Manuals". DC Generators, Counter-Electromotive Force 2007-09-29 at the Wayback Machine (CEMF), DC Equipment Terminology, Electrical Science Volume 2.
Counter-electromotive-force in access control applications
April 11, 2024
counter, electromotive, force, counter, cemf, back, electromotive, force, manifesting, voltage, that, opposes, change, current, which, induced, cemf, caused, electromagnetic, induction, details, editfor, example, voltage, appearing, across, inductor, coil, cha. Counter electromotive force counter EMF CEMF back EMF 1 is the electromotive force EMF manifesting as a voltage that opposes the change in current which induced it CEMF is the EMF caused by electromagnetic induction Details editFor example the voltage appearing across an inductor or coil is due to a change in current which causes a change in the magnetic field within the coil and therefore the self induced voltage 1 2 The polarity of the voltage at every moment opposes that of the change in applied voltage to keep the current constant 1 3 The term back electromotive force is also commonly used to refer to the voltage that occurs in electric motors where there is relative motion between the armature and the magnetic field produced by the motor s field coils 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 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 This voltage is in series with and opposes the original applied voltage and is called back electromotive force by Lenz s law With a lower overall voltage across the motor s internal resistance as the motor turns faster the current flowing into the motor decreases 4 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 5 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 6 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 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 References edit a b c Graf counterelectromotive force Dictionary of Electronics Griffiths David Jeffery 2012 Introduction to Electrodynamics 3rd ed Self Inductance Naval Electrical Engineering Training Series Module 02 Introduction to Alternating Current and Transformers Archived 2006 04 20 at the Wayback Machine Nuclear Power Fundamentals Training Manuals DC Generators Counter Electromotive Force Archived 2007 09 29 at the Wayback Machine CEMF DC Equipment Terminology Electrical Science Volume 2 Back EMF Acroname com 2006 08 07 Retrieved 2010 02 07 Back EMF Motion Feedback Back EMF Motion Feedback permanent dead link External links editCounter electromotive force in access control applications Retrieved from https en wikipedia org w index php title Counter electromotive force amp oldid 1163624870, wikipedia, wiki, book, books, library,
