want to read about : Controls and instrumentation - Engine torque
Engine speed
21. All engines have their rotational speed (r.p.m.) indicated. On a twin or triple-spool engine, the high pressure assembly speed is always indicated; in most instances, additional indicators show the speed of the low pressure and intermediate pressure assemblies.
22. Engine speed indication is electrically ransmitted from a small generator, driven by the engine, to an indicator that shows the actual evolutions per minute (r.p.m.), or a percentage of he maximum engine speed (fig. 12-5).
The engine speed is often used to assess
engine thrust, but it does not give an absolute indication of the
thrust being produced because inlet temperature and pressure
conditions affect the thrust at a given engine speed.
23. The engine speed generator supplies a three- phase alternating current, the frequency of which is dependent upon engine speed. The generator output frequency controls the speed of a synchronous motor in the indicator, and rotation of a magnet assembly housed in a drum or drag cup induces movement of the drum and consequent movement of the indicator pointer,
24. Where there is no provision for driving a generator, a variable-reluctance speed probe, in conjunction with a phonic wheel, may be used to induce an electric current that is amplified and then transmitted to an indicator (fig. 12-6). This method can be used to provide an indication of r.p.m. without the need for a separately driven generator, with its associated drives, thus reducing the number of components and moving parts in the engine.
Engine speed
21. All engines have their rotational speed (r.p.m.) indicated. On a twin or triple-spool engine, the high pressure assembly speed is always indicated; in most instances, additional indicators show the speed of the low pressure and intermediate pressure assemblies.
22. Engine speed indication is electrically ransmitted from a small generator, driven by the engine, to an indicator that shows the actual evolutions per minute (r.p.m.), or a percentage of he maximum engine speed (fig. 12-5).
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23. The engine speed generator supplies a three- phase alternating current, the frequency of which is dependent upon engine speed. The generator output frequency controls the speed of a synchronous motor in the indicator, and rotation of a magnet assembly housed in a drum or drag cup induces movement of the drum and consequent movement of the indicator pointer,
24. Where there is no provision for driving a generator, a variable-reluctance speed probe, in conjunction with a phonic wheel, may be used to induce an electric current that is amplified and then transmitted to an indicator (fig. 12-6). This method can be used to provide an indication of r.p.m. without the need for a separately driven generator, with its associated drives, thus reducing the number of components and moving parts in the engine.
