Tham khảo tài liệu 'digital filters part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Digital Filters for Maintenance Management 11 Fig. 6. Set of points and the relevant components sub-units at Abbotswood junction. The supply voltage of the point machine was measured Fig. 7a as well as the current drawn by the electric motor Fig. 7b and the system as a whole Fig. 7d . In addition the force in the drive bar was measured with a load pin introduced into the bolted connection between the drive bar and the drive rod Fig. 7c . Fig. 7 shows the raw measurement signals taken in the fault-free control or as commissioned condition for normal to reverse and reverse to normal operation respectively. Note that the currents and voltages begin and end at zero for both directions of operation but a static force remains following the reverse to normal throw and a different force remains after the normal to reverse throw. It is difficult to compare the measurements taken during induced failure conditions with those from the fault-free condition because of noise in the measurements. 12 Digital Filters Voltage V a 4 3 2 1 Sample Force kN c Currenta A b 0 2000 4000 6000 Sample Sample Currentb A d Sample Fig. 7. As commissioned measured signals for the normal to reverse throw . Filtering the signal One possibility to reduce the noise is by using the SS formulation in 1 as a digital filter capable of reducing observation noise when the measured quantity varies slowly but additive measurement noise covers a broad spectrum 8 9 . In this particular case the signal being measured is modeled as a random walk . it tends to change by small amounts in a short time but can change by larger amounts over longer periods of time. The SS model used for each signal is described by equations 3 . Xt 1 X w zt xt v Q e W R eV 3 Comparing with the general SS equations 1 we have Variables xt zt Q R wt and vt are all scalars. t 1 E 1 w w H 1 Ct 1. The initial value given to X0 is Xo 0. The initial value of P0 is chosen to reflect uncertainty in the initial estimate. Here P0 is .
