This approach that only detects the sign of the input signal (zerocrossing sampling) has been extensively studied by the signal processing community beginning with the work of Rice 23 Kedem provides an excellent overview of the work in this area 10 The concept of levelcrossing sampling has been previously studied as a method of samplingThe level crossing is operating correctly after the passage of a train without both the monitor and the Level Crossing equipment operating correctly g) The level crossing monitor shall be designed and tested in such a way as to minimise the risk of providing incorrect information, and of reducing the integrity of the level crossingLevel Crossing counting was adopted in the 1950s by the aircraft industry to count accelerations that exceeded certain levels Although largely replaced by "Rainflow" counting (next section) it is still used today and its features should be understood by engineers 0 The original circuits sent a pulse to electromechanical counters as a signal
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