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Question 993026 - Turbine Volume Flow Indicator

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  • Question 993026 - Turbine Volume Flow Indicator

    Good afternoon all,

    Hoping you may be able to assist with the explanation for Q993026 that appears in Instruments PT7;

    "A turbine placed in the fuel circuit of a gas turbine engine initially measures...". The correct answer is given as "Best description: Volumetric flow by a tally of the impulses". I assume I'm mistaken in my understanding of this indicator and possibly electrics altogether, but is an AC voltage not being generated by the rotation of a magnet installed into the turbine assembly and this voltage will vary proportionally with the RPM of the turbine? Or is it that the voltage value will remain at a constant whilst the frequency will vary with RPM?

    Assistance greatly appreciated,


  • #2
    Amplitude of the emf (voltage) and frequency both vary in response to rate of flux density change brought about by the changing shaft RPM.
    A signal processing module regulates the voltage after which the power spikes, or more correctly, frequency can be processed into digital pulses and used as the RPM source.
    This digital pulse signal may then be used elsewhere, eg. FADEC


    • #3
      Hi Fraser,

      Thank you for your reply. In that case however, would the answer of "Volumetric flow by measure of a voltage proportional to the rotation speed" also be a valid answer. If the amplitude of the EMF also varies with RPM, I would have thought this would have been directly measured by the sensing device as a change in RPM and thus a torque to calculate volumetric flow?


      • #4
        Hello Binners.

        I'm sure your approach is viable to an agricultural level (think line resistance etc.), however the truth is that the raw AC is converted into square wave digital pulses for monitoring.


        • #5
          Ok thank you Fraser, another one to put down in the 'just remember it bin"