Apparatus and method of monitoring for obstructions in a pipe or channel. The method comprising the steps of: (1) transmitting a wave into a first end of the pipe or channel from a transmitting transducer at a first known location relative to the pipe or c...

A sensor element for use in a backing sensor to monitor a gas turbine shaft. The sensor includes an oscillator circuit (30) having an oscillator and a resonance circuit (42), and a frequency detector (31) for monitoring the frequency of the ossilation circ...