530 A. Vemuri et al. Averaged RPM estimate skipping 40 pulses Averaged RPM estimate skipping 40 pulses Instantaneous speed (rpm) Instantaneous speed (rpm) 2.45 2.35 2.5 2.55 2.6 2.65 2.7 2.4 15 15.5 16 16.5 17 17.5 18 25 30 20 15 10 5 0 0 0.5 1.5 2.5 2 3 1 Time(sec) Time(sec) x 104 x 104 Amplitude Time a b c Fig. 46.11 (a) Reassigning RPM estimates to a reference time vector, (b) averaged RPM estimate—40 pulses skipped throughout and (c) zoomed image showing smooth averaged curve. Vertical bars denote the time instances to which the RPM has been assigned and the small explosions denote the time instances of zero crossings; Different colors represent different initiating pulses Now, the entire time data can be divided into a number of time blocks and the number of pulses ‘n’ to be skipped in each block can be identified as the integer which provides the time interval between estimates .60 n=R/ that is closest to the desired resolution. The smaller the block, the better will be the estimate. However, if the block size becomes too small, it might not even be possible to skip a certain number of pulses as suggested by the above method. Hence, the user must be careful in choosing the number of blocks to divide the data into.
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