Sensors and actuators , LE THANH PHUC

Magnetic Reluctance Position Sensor• This sensor consists of a permanent magnet with a coil of wire wound around it.. • The magnetic field in a material is described by a pair of field

SENSORS AND ACTUATORS

Le Thanh Phuc

Faculty of Automotive Engineering

University of Technical Education Ho Chi Minh City

Email: phuclt@hcmute.edu.vn

Magnetic Reluctance Position Sensor

• This sensor consists of a permanent magnet with a coil of wire

wound around it A steel disk that is mounted on the crankshaft

(usually in front of the engine) has tabs that pass between the pole pieces of this magnet

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• The magnetic field in a material is described by a pair of field

quantities that can be compared to the voltage and current of an ordinary electric circuit

• One of these quantities is called the magnetic field intensity vector

H It exerts a force analogous to voltage.

• The response of the magnetic circuit to the magnetic field intensity

is described by the second vector, which is called magnetic flux

density vector B, which is analogous to current In these two

quantities

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Reluctance Method

• The reluctance method begins with Ampere’s law in integral

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where ampere-turns NI are assumed given, and magnetic field intensity H and

magnetic flux density B are to be found The closed-line integral is replaced by a

summation

where the closed path consists of line segments of subscript k, each of which is in the

direction of the field intensity Thus the direction of the field and flux is assumed known

Because flux density B prefers to flow through high-permeability materials, the line

segments (straight or curved) are assumed to follow a path through high-permeability materials such as steel If the steel has a gap made of air, the closed path follows the

shortest part of the airgap.

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SPEED SENSORS BASED ON FARADAY’S LAW

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SOLENOID ACTUATORS

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SOLENOID ACTUATORS

• Solenoid actuators have a solenoidal coil, which is a coil of wire

wound to a shape that is sometimes cylindrical

• All solenoid actuators also have a steel armature, a term for the

moving part

• In solenoid actuators, the armature moves along a straight line, and

thus produces linear motion.

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Clapper Armature

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• Assuming for illustrative purposes that the steel

permeability is infinite and that the two air gaps each have length g and poles of equal area, Ampere’s law gives the following formula for H in both airgaps

H = NI/(2g) and thus the flux density in both airgaps is

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(a) Use the reluctance method, assuming no leakage or fringing fluxes, to find the approximate values of the vectors B and F on

left side of clapper for I = 2 A Find F in newtons per meter

depth of the solenoid into the plane of the page.

(b) Repeat (a) to find the vectors B and F on right side of

clapper.

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Plunger Armature

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Use the reluctance method, assuming no leakage flux, to find the approximate

values of B and F on the end of the plunger.

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