Abstract: A method of zeroing displacement data derived from a rotor having an array of features monitored by an array of stationary timing probes. The method includes steps to calculate the displacement at each probe for each of at least two measured revolutions from time of arrival measurements. Each displacement is defined as a sum of a common term and a unique term. The set of displacements is solved for the common term and the unique terms. A probe offset is calculated from each unique term. The zeroed displacements are determined by subtracting the common term and probe offset from the calculated displacements for each probe.

Abstract: A rotor arrangement and method by which a time reference is provided for a rotor. The rotor includes N time of arrival features. The method includes steps to: provide a plurality of time of arrival probes spaced apart circumferentially outside the periphery of the rotor; for each revolution of the rotor, measure a time of arrival of each feature at each probe; select N time of arrival measurements at each probe; derive a best fit of the measured times of arrival measured at all the probes against angular position; and set the time reference for the next revolution of the rotor equal to the best fit at the end of the current revolution of the rotor.

Abstract: A method of providing a time reference for a rotor, for example a once per revolution time reference. The rotor includes N time of arrival features. The method includes steps for each revolution of the rotor. Provide a plurality of time of arrival probes spaced apart circumferentially outside the periphery of the rotor and measure a time of arrival of each feature at each probe. Select N time of arrival measurements at each probe. Derive a best fit of the measured times of arrival measured at all the probes against angular position. Set the time reference for the next revolution of the rotor equal to the best fit at the end of the current revolution of the rotor. Also a rotor arrangement for the method.

Abstract: A method of zeroing displacement data derived from a rotor having an array of features monitored by an array of stationary timing probes. The method includes steps to calculate the displacement at each probe for each of at least two measured revolutions from time of arrival measurements. Each displacement is defined as a sum of a common term and a unique term. The set of displacements is solved for the common term and the unique terms. A probe offset is calculated from each unique term. The zeroed displacements are determined by subtracting the common term and probe offset from the calculated displacements for each probe.