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    Relays and Solenoids

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    Towfiq
    This document discusses solenoids and relays. It explains that a solenoid consists of a coil of wire that creates a magnetic field when current flows through it. This magnetic field can pull a soft iron core or plunger into the center of the coil. Relays use this principle, with the coil operating a switch via an armature. The document notes that relays can be used with both direct and alternating current, but alternating current may cause vibration unless rectified or filtered by a capacitor. It also discusses laminating cores and armatures to prevent eddy currents from forming.

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    Relays and Solenoids

    Uploaded by

    Towfiq
    27 views2 pages
    This document discusses solenoids and relays. It explains that a solenoid consists of a coil of wire that creates a magnetic field when current flows through it. This magnetic field can pull a soft iron core or plunger into the center of the coil. Relays use this principle, with the coil operating a switch via an armature. The document notes that relays can be used with both direct and alternating current, but alternating current may cause vibration unless rectified or filtered by a capacitor. It also discusses laminating cores and armatures to prevent eddy currents from forming.

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    This document discusses solenoids and relays. It explains that a solenoid consists of a coil of wire that creates a magnetic field when current flows through it. This magnetic field can pull a soft iron core or plunger into the center of the coil. Relays use this principle, with the coil operating a switch via an armature. The document notes that relays can be used with both direct and alternating current, but alternating current may cause vibration unless rectified or filtered by a capacitor. It also discusses laminating cores and armatures to prevent eddy currents from forming.

    Copyright:

    © All Rights Reserved
    Download as DOC, PDF, TXT or read online from Scribd
    Download as doc, pdf, or txt
    27 views2 pages

    Relays and Solenoids

    Uploaded by

    Towfiq
    This document discusses solenoids and relays. It explains that a solenoid consists of a coil of wire that creates a magnetic field when current flows through it. This magnetic field can pull a soft iron core or plunger into the center of the coil. Relays use this principle, with the coil operating a switch via an armature. The document notes that relays can be used with both direct and alternating current, but alternating current may cause vibration unless rectified or filtered by a capacitor. It also discusses laminating cores and armatures to prevent eddy currents from forming.

    Copyright:

    © All Rights Reserved
    Download as DOC, PDF, TXT or read online from Scribd
    Download as doc, pdf, or txt
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    Relays and Solenoids

    The wire coil of the electromagnet, without its core of magnetic material is
    called the solenoid. If this solenoid is provided with a movable soft iron core
    and current flows through the turns of the coil , the magnetic field tends to pull
    the plunger in to the centre of the coil. Accordingly the coil with its moving
    centre is called the solenoid.
    The plunger can be used to operate a great many mechanical
    applications. A spring is often fitted above the plunger to positively return it to
    its start position once the current is turned off. The plunger may also be used
    via an non-magnetic extension be used as a pusher, a spring again returning it
    to the start position.
    Either a direct or alternating current may be used to energise the
    solenoid, since either type will produce the magnetic field around the coil.
    There is one precaution however. The core of the electromagnet finds itself in
    the magnetic field of the coil. If a steady direct current flows through the coil ,
    no current will be induced in the core since both the core and field are
    stationary. But if an alternating current flows through the coil, the changing
    magnetic field will cause a current to be induced in the core. This is called the
    eddy current.
    The eddy current is undesirable on two counts. The flow of current
    through the core represents a power loss , which must come from the source.
    Also the flow of current may cause the core to get quite hot. To reduce the
    eddy current, the core is not built solid but is made up of many thick slices,
    called laminations. Each lamination is insulated from its neighbour by a coat of
    varnish or similar material. This offers considerable resistance, and as a result,
    the eddy currents are cut down. In solenoids operating on alternating current,
    the plunger is built up of laminations.
    An alternating current coil will offer a greater resistance to current
    flow than a direct current coil of same ohm resistance due to its inductive
    reactance. Hence, if a coil designed to be operated by an alternating current is
    connected to a source of direct current at the same voltage, the flow of current
    may be great enough to burn out the windings.
    On very common application of an electromagnet is in the
    operation of an electric switch. In this form it is known as an electromagnetic
    relay.
    The sensitivity and current draw of a relay is determined by the
    wire wound on the core. This is determined by size and therefore breaking
    capacity of the contacts.
    The relay coil may be energised by either direct or alternating
    current. Where direct current is employed, there are no special problems.
    Alternating current may be employed since the polarity does not effect the
    attraction of the armature. However, the rapid alternations of the magnetic
    field cause the armature to vibrate, or 'chatter'. Since the contacts are
    controlled by the armature, the controlled circuit too, will be affected..
    One method of remedying the fault is to rectify the alternating
    current before applying it to the relay. Small semi conductor diodes are
    employed. Another method is to connect a fairly large capacitor across the coil.
    Frames are laminated to prevent eddy current losses.
    Overload circuit breaker is a variation on a relay.

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