46 Estimation of Instantaneous Speed for Rotating Systems: New Processing Techniques 531 Initial RPM estimate - Starting pulse 1 skipping 40 pulses Instantaneous speed (rpm) Time(sec) 2.5 2 3 x 104 1.5 1 X: 9.085 Y: 1.245e+04 X: 16.33 Y: 2.598e+04 X: 16.23 Y: 2.595e+04 X: 8.885 Y: 1.206e+04 X: 3.152 Y: 1944 X: 4.072 Y: 4274 0. 0 0 5 10 15 20 25 30 Fig. 46.12 Instantaneous RPM estimate with constant no. of pulses skipped throughout Averaged adaptive RPM estimate skipping upto 40 pulses No.of pulses skipped as a function of time 2.5 1.5 1 0.5 0 0 5 10 15 20 25 30 0 0 5 10 15 20 25 30 Time(sec) Time(sec) Instantaneous speed (rpm) Pulses skipped 2 3 a b x 10 4 25 20 15 10 5 X: 15.66 Y: 2.538e+04 X: 15.61 Y: 2.53e+04 X: 9.962 Y: 1.428e+04 X: 10.01 Y: 1.439e+04 X: 3.529 Y: 2968 X: 3.488 Y: 2864 Fig. 46.13 (a) Instantaneous RPM estimate from the Adaptive nth Pulse Algorithm and (b) no. of pulses skipped vs time The result from this approach is shown in Fig. 46.13 with consecutive points that are consistently 0.05 s apart throughout the curve which was the user input. The corresponding number of pulses skipped as a function of time is also shown. A whole revolution of the system need not be counted for the instantaneous speed formulation. For a square wave output, a half revolution can also be considered by taking two consecutive zero crossings and not two zero crossings from consecutive pulses. Thus, ‘n’ need not necessarily be a whole number (2.5 pulses or 8.5 pulses can also be skipped). To check whether the estimate is accurate, it is plotted against the raw estimate in Fig. 46.14. It can be seen that the curve is always within bounds of the fluctuating raw estimate.
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