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220870 vs 220047

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  • 220870 vs 220047

    Both of these Questions are worded almost identically and yet different answers are selected as being correct.
    Can you please review and advise.

    Thanks,
    Myles
    MyAirMyles-Youtube

  • #2
    Hi metallicrazy,

    Not quite the same. First of all they are the actual words used in the exam question bank, so we have a duty to present them as accurately as possible.

    One of them refers to an AC synchronous induction motor, where the output frequency is measured. The second refers to an inductive probe, more usually called a pulse probe and phonic wheel. Hope that clears that up for you?

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    • #3
      Hi, sorry to resurrect this one, but regarding 220870:

      The operating principle of the "induction" type of tachometer is to measure the:

      Frequency of the electric impulse created by a notched wheel rotating in a magnetic field. (Selected answer - wrong) Rotation speed of an asynchronous motor energized by an alternator. (shown as correct answer).


      Can someone give guidance?


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      • #4
        Barry,

        I stand by the earlier response. The first description from you is of a phonic wheel; yes. an induced emf is generated as the ferro-magnetic tooth goes past an induction coil, but the term 'induction tacho' refers to the second type you list. In an induction tacho the induction bit refers to the induction (aka squirrel cage) motor that is part of the set up. Frustrating, innit?

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        • #5
          Ok - thanks Chris!

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