Solenoids and hold magnets - TEC AUTOMATISMES - #1

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T=C TËC^AUTOMATISMES 4^ SOLENOIDS : GENERAL TECHNICAL INFORMATION A solenoid is an electromagnetic System made of a magnetic core, a coil and a magnetic frame permitting to guide the magnetic field and to mount the solenoid in the mechanism in which it will be used. 2. COMPONENTS OF A SOLENOID : A. THE COIL: In a solenoid, the coil permits to generate a magnetic field. B. THE CORE: The solenoid's core permits to guide the magnetic field lines created by the electric current of the coil. Usually realised in cut steel, this part of the solenoid is the one used to push or pull (according to the type) the part of the mechanism in which the solenoid is incorporated. The core is located inside the coil which generates the magnetic field. C. THE FRAME : The magnetic frame of a solenoid is the frame in which the coil is incorporated. It has two uses : magnetic and mechani-cal. It permits to close the magnetic field lines created by the coil. For that reason, the frame, as the core, made of a ma­gnetic material. It also permits to fix the solenoid in the me­chanism in which it will be used. 3. OPERATING PRINCIPLE OF A SOLENOID : When powering the solenoid, the coil will create a magnetic field. Guided by the frame and the core, this field will create another magnetic field in the airgap located between the core and the bottom of core, this having for effect to move the core and to plate it at the bottom of the frame. 4. THE FORCE OF A SOLENOID : The force of a solenoid depends of the current intensity passing inside the coil. It is thus possible to increase the force of a solenoid while sending a more important electric intensity in the coil. But this force also depends on two other parameters : the magnetic properties of the material used for the core and the frame and the position of the core in the frame. The force of a solenoid is not constant : it is much more important when the core is plated at the bottom of core. When the core is far from the bottom of core, the force of the solenoid decreases very quickly accordint to the distance to the bottom of core. This can be explained by a phenomenon of dispersion of the magnetic field between the core and the bottom of core. However, it is possible to get an important and precise influence on this decrease of the force according to the position of the core. A solenoid has a reaction time of less than one second. As this reaction time depends on the coil characteristics and the solenoid's dimensions, it is thus can be decreased down to some milliseconds.